How to control an LED display device

Abstract

How to control an LED display device A method for controlling an LED display device is provided, the method comprising the steps of providing power to a tunable LED and controlling the power supply to vary the peak emission wavelength of the LED within an emission wavelength range. The method for controlling an LED display device provides a way to reproduce a particular light spectrum.

Description

[Technical field]

[0001] The present invention relates to a tunable light emitting diode (LED), a method for controlling a tunable LED, and a method for manufacturing a tunable LED. [Background technology]

[0002] 2. Description of the Related Art In the design of semiconductor devices, III-V semiconductor materials, particularly the group of III-nitride semiconductor materials, have attracted great interest.

[0003] "III-V" semiconductors include binary, ternary, and quaternary alloys of group III elements, such as Ga, Al, and In, with group V elements, such as N, P, As, and Sb, and are of great interest for many applications, including optoelectronics.

[0004] Of particular interest is the class of semiconductor materials known as "III-nitride" materials, which include gallium nitride (GaN), indium nitride (InN), and aluminum nitride (AlN), along with their ternary and quaternary alloys. (Al,In)GaN is a term that encompasses AlGaN, InGaN, and GaN. III-nitride materials have not only achieved commercial success in solid-state light-emitting devices and power electronics, but also offer special advantages in quantum light sources and light-matter interactions.

[0005] Doping GaN semiconductor materials with In is of interest in optoelectronic semiconductor devices because changing the In content of the semiconductor changes the electronic band gap of the material and therefore the wavelength at which the semiconductor emits light. However, changing the In content of the material also affects the in-plane lattice constant of the semiconductor. For example, the in-plane lattice constant of InN is approximately 11% larger than that of GaN, and the lattice dimensions of the intermediate composition vary with indium content. This creates problems in device designs where it is desirable to deposit active semiconductor layers on top of substrate layers with different lattice dimensions, because lattice mismatch at the layer boundaries causes distortions in the lattice, which leads to the formation of defects in the material that act as non-radiative recombination centers. This severely impairs device performance.

[0006] Although there is a huge demand for LEDs that emit at all visible wavelengths, especially longer wavelengths toward the green, yellow, and red, manufacturers have historically faced more problems in producing LEDs that emit at longer wavelengths.

[0007] One of the major challenges faced in growing longer wavelength LEDs, such as green, yellow, and red LEDs, on GaN-based platforms is the need to use high indium (In) content to lower the bandgap of the active region to a level suitable for long wavelength emission. The required InGaN active region has a larger lattice constant than the underlying GaN, and the resulting strain causes defects to form in the material that act as non-radiative recombination centers and degrade device performance.

[0008] High-quality InGaN (high indium content >20%) is difficult to achieve due to the large lattice mismatch between InN and GaN, which also leads to a reduction in the indium composition due to the composition pulling effect.

[0009] Shorter wavelength LEDs are easier to manufacture because they can be made with InGaN light emitting regions that contain a smaller percentage of indium than is required for longer wavelength emission. Summary of the Invention [Problem to be solved by the invention]

[0010] This application relates to a method for controlling an LED display device with tunable light emitting diodes (LEDs).

[0011] The invention is defined in the independent claims referred to hereinafter. Preferred or advantageous features of the invention are defined in the accompanying dependent claims.

[0012] The light emitting diodes or LEDs described in this application are preferably formed from III-V semiconductor materials, and most preferably from III-nitride semiconductor materials.

[0013] "III-V" semiconductors include binary, ternary, and quaternary alloys of group III elements, such as Ga, Al, and In, with group V elements, such as N, P, As, and Sb, and are of great interest for many applications, including optoelectronics.

[0014] Of particular interest is the class of semiconductor materials known as "III-nitride" materials, which includes gallium nitride (GaN), indium nitride (InN), and aluminum nitride (AlN), along with their ternary and quaternary alloys (Al,In)GaN. Different crystal orientations may be used in the present invention, such as polar c-plane orientation, nonpolar orientation, and semipolar orientation. There are two main nonpolar orientations, the a-plane (11-20) and the m-plane (1-100). For semipolar, there is the (11-22) and {2021} family of crystal planes. III-nitride materials have not only achieved commercial success in solid-state light-emitting devices and power electronics, but also offer special advantages in quantum light sources and light-matter interactions.

[0015] While a variety of Group III-nitride materials are of commercial interest, gallium nitride (GaN) is widely regarded as one of the most important emerging semiconductor materials and is of particular interest for many applications.

[0016] It is known that the introduction of pores into bulk III-nitrides such as GaN can significantly affect their material properties (optical, mechanical, electrical, thermal, etc.) Therefore, it is possible to tune the material properties of GaN and III-nitride semiconductors over a wide range by varying their porosity, and porous GaN has attracted great interest in optoelectronic applications.

[0017] Although the invention will be described primarily with reference to GaN and InGaN, it may also be advantageously applicable to combinations of alternative III-nitride materials.

[0018] In the following description, a substrate or template for overgrowth is a semiconductor structure on which further semiconductor layers are grown, resulting in an LED semiconductor device. An exemplary substrate template for overgrowth in the present invention can be a GaN semiconductor structure with multiple layers of doped and undoped GaN.

[0019] Regions or layers of a semiconductor structure can be made porous by electrochemical etching, as shown in International Patent Applications PCT / GB2017 / 052895 (published as WO 2019 / 063957) and PCT / GB2019 / 050213 (published as WO 2019 / 145728).

[0020] (Issues to be resolved) In conventional multicolor (RGB) LED displays, each subpixel is produced from a separate LED wafer and therefore must be combined by mass transfer.

[0021] Red and blue-green LEDs typically need to be made from different semiconductor materials. To provide an RGB LED display, the three color-emitting LEDs need to be grown separately, transferred to a common substrate, and individually re-pitched to form a multicolor display device.

[0022] Current mass transfer processes have the following limitations that must be overcome: Complex COT processes: pick and place with stamps, Unstable yield: Fluid assembly, Higher cost: Laser transfer.

[0023] This becomes particularly challenging as the size of the individual sub-pixels decreases, increasing the resolution requirements of the mass transfer system.

[0024] This is also problematic because high resolution displays require extremely reliable mass transport systems, with millions of individual devices arranged to produce a single working display.

[0025] Additionally, the complexity of mass transport processes increases significantly when combining subpixels fabricated using multiple material systems.

[0026] Most LED display technologies require the use of multiple material systems to produce red, green, and blue emitting subpixels, such as InGaN for the blue and green emitting subpixels and InAlGaP for the red emitting subpixels.

[0027] To realize mass production and commercialization of multi-wavelength LED microdisplays, the present invention uses tunable LEDs with chip-on-wafer (COW) design based on InGaN material, which realizes multiple emission wavelengths from one diode structure, thereby simplifying the manufacturing process of multi-color display devices, improving production efficiency and reducing costs. [Means for solving the problem]

[0028] (Tunable LED) In a first aspect of the present invention, an n-doped portion; A p-doped portion; a light emitting region located between the n-doped portion and the p-doped portion, the light emitting region comprising a light emitting layer that emits light at a peak emission wavelength under an electrical bias applied thereto; A light emitting diode (LED) is provided comprising: the LED configured to receive a power source, and a peak emission wavelength of the LED is continuously controllable over an emission wavelength range by varying or controlling the power source. The peak emission wavelength of the tunable LED is preferably continuously controllable or continuously variable over an emission wavelength range of at least 40 nm by varying or controlling the power source.

[0029] A tunable LED may be described as a tunable LED because the peak emission wavelength of the LED is preferably continuously controllable or continuously variable over the emission wavelength range.

[0030] The tunable LED is configured to receive power or drive current from a power supply or LED driver. As used herein, the term "power supply" refers to the power or current provided to drive the LED in use.

[0031] The peak emission wavelength of the LED is preferably continuously controllable or continuously tunable over a range of emission wavelengths by varying or controlling the magnitude of the drive current supplied to the tunable LED.

[0032] While conventional LED devices produce very small shifts in emission wavelength when the drive current supplied to the LED is changed, the present inventors have found that the wavelength shift can be expanded and controlled to a greater extent than conventional LED materials. Rather than the several nm emission range of prior art devices, the LEDs of the present invention can be controlled to emit over a much wider emission range, for example, over a range of at least 40 nm. Because the LEDs of the present invention can be tuned to emit over a wide wavelength range, they can be referred to as tunable LEDs.

[0033] The LED may be a dynamic color tunable LED, in which the peak emission wavelength of the LED can be adjusted by varying the driving conditions provided to the LED by a power supply.

[0034] The LEDs preferably emit at a single peak emission wavelength in response to a steady power supply, but can be driven to emit at different peak emission wavelengths in response to changes in the power supply. Thus, LEDs can be used to emit a particular color over time, or alternatively, LEDs can be driven to emit a variety of different wavelengths by providing varying drive conditions.

[0035] Preferably, the n-doped portion, the p-doped portion and the light emitting region all comprise or consist of a III-nitride material, preferably GaN, InGaN, AlGaN, or AlInGaN.

[0036] The tunable LED preferably comprises a single epitaxially grown diode structure that includes an n-doped section, a p-doped section, and a light emitting region, such that the LED's variable peak emission wavelengths are all emitted by the same LED diode structure and composition.

[0037] The LED preferably comprises a porous region of III-nitride material. The light emitting region of the LED is preferably formed on the porous region of III-nitride material. In some embodiments, one of the n-doped portion or the p-doped portion may comprise a porous region of III-nitride material. In other embodiments, the n-doped portion, the p-doped portion, and the light emitting region are provided on a substrate comprising a porous region of III-nitride material. During epitaxial growth of the LED, the light emitting region is preferably grown after the porous region is formed.

[0038] The inventors have found that the porous region of III-nitride material allows the same LED to emit light at a range of peak emission wavelengths, rather than just one specific wavelength. The peak emission wavelength of the LED can be varied across a range of emission wavelengths by varying the power supply provided to the LED. Thus, the present invention provides a tunable LED that can be controlled to emit light at any wavelength across a continuous range of emission wavelengths. By varying the driving conditions provided to the LED by the power supply, the LED can emit light at any wavelength within the LED's emission wavelength range, rather than simply emitting light at a discrete peak emission wavelength.

[0039] The inventors have discovered that LED performance emitting at tunable wavelengths over a wide emission range can be imparted by either incorporating a porous region of III-nitride semiconductor material into the LED structure or forming an LED diode structure on a porous region of III-nitride semiconductor material. Benefits provided to the LED by the porous region include strain relief, enlargement of the lattice constant, reduced wafer bow, and beneficial mechanical and thermal effects during growth of the light emitting region at high temperatures.

[0040] The light emitting region of the LED is preferably formed on a porous region of III-nitride material during fabrication, whereby the porous region influences the structure and mechanical properties of the semiconductor layer epitaxially deposited on the porous region. The layer of semiconductor material deposited on the porous region during growth gains benefits such as reduced strain, larger lattice constant, and reduced wafer bow that are imparted to the LED light emitting region and affect its structure and its light emitting behavior.

[0041] Once the LED light emitting (active) region is epitaxially grown on the porous region and the active region is improved in quality by the effect of the porous region, the beneficial effect of the porous region on the light emitting properties is permanently imparted to the LED active region. Thus, the LED diode structure may be retained on the porous region, in which case the tunable LED will comprise a porous region of III-nitride material, or alternatively, the porous region may be removed from the LED structure after epitaxial growth during processing of the LED into a device.

[0042] The width of the emission wavelength range can vary depending on the structure and composition of the LED structure (n-doped portion, light emitting region, and p-doped portion) and the structure and porosity of the porous region, and the width of the emission wavelength range can vary depending on the size and shape of the LED (pixel size and shape).

[0043] The present invention is not limited to a specific LED structure, since the wavelength tunable behavior of the LED can be achieved using a variety of conventional LED structures, preferably provided on a porous template. A wide variety of LED structures are known in the art, and by providing different conventional LED structures on a template with a porous region, LEDs with different emission wavelength ranges can be obtained.

[0044] In a preferred embodiment, the peak emission wavelength is controllable over an emission wavelength range of at least 40 nm, or at least 50 nm, or at least 60 nm, or at least 70 nm, or at least 80 nm by varying the power source. Preferably, the peak emission wavelength is controllable over an emission wavelength range of up to 100 nm, or 110 nm, or 120 nm, or 130 nm, or 140 nm, or 150 nm, or 160 nm, or 170 nm, or 180 nm, or 190 nm, or 200 nm, or 400 nm, or 450 nm. Thus, the magnitude of the emission wavelength range obtainable with the LED of the present invention is much larger than the emission range achievable with conventional LEDs.

[0045] LEDs are advantageously controllable to emit at any peak emission wavelength within their emission wavelength range, and thus by varying the characteristics of the power supply and the size and shape of the LED pixels, LEDs can be controlled to emit at any selected peak emission wavelength within this range.

[0046] The emission wavelength of a tunable LED is preferably continuously variable across its emission wavelength range in response to drive conditions provided by a power supply that is continuously varied across the range of drive conditions.

[0047] The location of the emission wavelength range in the electromagnetic spectrum can also vary depending on the design of the LED structure (n-doped section, light-emitting region, and p-doped section). For example, the wavelengths included in the emission wavelength range can vary depending on the number and composition of light-emitting layers in the LED. Since a wide variety of LED active regions are known in the art for emitting at different wavelengths in the visible spectrum, the light-emitting regions forming the LEDs of the present invention with different light-emitting regions can provide emission wavelength ranges covering different parts of the spectrum.

[0048] The emission wavelength range of the LEDs can be 400 nm to 850 nm, or 400 nm to 800 nm, or 400 nm to 690 nm, or 400 nm to 675 nm. The emission wavelength range can also be a sub-range within the range of 400 nm to 750 nm. The emission wavelength range can be adjusted to cover any part of this range by selecting different LED active areas and controlling the size and shape of the LED pixels.

[0049] Preferably, the emission wavelength range of the LED extends from a lower limit of less than 410 nm, or less than 430 nm, or less than 450 nm, or less than 470 nm, or less than 500 nm, or less than 520 nm, or less than 540 nm, or less than 560 nm, to an upper limit of more than 570 nm, or more than 580 nm, or more than 600 nm, or more than 610 nm, or more than 630 nm, or more than 650 nm, or more than 675 nm. The first and second limits of the emission wavelength range can be adjusted depending on the choice of the LED structure and the shape and size of the LED, as described above.

[0050] For example, in a preferred embodiment, the lower limit of the emission wavelength may be 400 nm to 450 nm (purple), or 450 nm to 500 nm (blue), or 500 nm to 570 nm (green), and the upper limit of the emission wavelength may be 570 nm to 590 nm (yellow), or 590 nm to 610 nm (orange), or 610 to 700 nm (red).

[0051] In a preferred embodiment, the LED's emission wavelength range may extend from a lower limit of less than 500 nm to an upper limit of more than 610 nm, such that the LED's peak emission wavelength can be tuned to emit anywhere from blue (less than 500 nm) to red (more than 610 nm) by varying the power supply. Providing a single LED design that is controllable to emit in blue wavelengths (450-500 nm), green (500-570 nm), and even yellow (570-590 nm), orange (590-610 nm), and red (610-760 nm) would be highly advantageous and could provide significant benefits to LED displays.

[0052] In other preferred embodiments, the emission wavelength range of the LED can be expanded to 520 nm to 660 nm, or 550 nm to 650 nm, by varying the power supply to the LED.

[0053] In a particularly preferred embodiment, the peak emission wavelength is controllable from 540nm to 680nm, or 560nm to 675nm, by varying the power supply. Thus, the same LED may be controllable to emit at any peak emission wavelength from 540nm for green to 680nm for red. Green and red LEDs have historically been more difficult to manufacture than the shorter wavelength blue LEDs due to issues such as the difficulty of incorporating the necessary indium content into the emission region. Thus, providing a single LED design that can be controlled to emit at green wavelengths (500-570nm), as well as yellow (570-590nm), orange (590-610nm), and red (610-760nm) would be highly advantageous and could provide significant benefits to LED displays.

[0054] In another preferred embodiment, the peak emission wavelength is controllable from 520 nm to 675 nm, or from 550 nm to 650 nm, by varying the power supply.

[0055] Although tunable LEDs can emit light over a continuous range of emission wavelengths, in some embodiments it may be desirable to control the LED to function in multiple distinct emission modes, for example in response to a power source having multiple drive modes. For example, by driving the LED in multiple different modes corresponding to distinct emission colors, a simplified color display may be provided in which the distinct emission colors are mixed in a known manner to produce a desired visual effect.

[0056] The LED is preferably controllable to emit light at at least two distinct peak emission wavelengths by varying the drive conditions provided by the power supply between two distinct drive conditions (such as drive currents of two distinct magnitudes). The LED may be controllable to emit light at a first peak emission wavelength in response to a first drive condition provided by the power supply (which may be a drive current having a first magnitude) and to emit light at a second peak emission wavelength in response to a second drive condition provided by the power supply (which may be a drive current having a second magnitude different from the first magnitude).

[0057] The LED is preferably controllable to emit at least three distinct peak emission wavelengths by varying the driving conditions provided by the power supply. Thus, the peak emission wavelength of the tunable LED can be tuned across at least three "colors" in the EM spectrum.

[0058] The LED may be controllable to emit light at a first peak emission wavelength in response to first drive conditions provided by the power supply, to emit light at a second peak emission wavelength in response to second drive conditions provided by the power supply, and to emit light at a third peak emission wavelength in response to third drive conditions provided by the power supply.

[0059] The LED may preferably be controllable to emit a blue peak emission wavelength in response to a first drive condition provided by the power source, a green peak emission wavelength in response to a second drive condition provided by the power source, and a red peak emission wavelength in response to a third drive condition provided by the power source.

[0060] The LED may be controllable to emit a first peak emission wavelength in the range of 400-500 nm in response to first driving conditions supplied by the power source, a second peak emission wavelength in the range of 500-550 nm in response to second driving conditions supplied by the power source, and a third peak emission wavelength above 600 nm in response to third driving conditions supplied by the power source.

[0061] Preferably, the LED is controllable to emit a first peak emission wavelength in the range of 430 to 460 nm in response to first driving conditions supplied by the power supply, emit a second peak emission wavelength in the range of 510 to 560 nm in response to second driving conditions supplied by the power supply, and emit a third peak emission wavelength in the range of 600 to 660 nm in response to third driving conditions supplied by the power supply.

[0062] The first, second, and third drive conditions may be first, second, and third current densities, or the first, second, and third drive conditions may be first, second, and third power densities.

[0063] In a preferred embodiment of the present invention, the tunable emission behavior of the LED structure is made possible by the fact that the LED structure (n-doped portion, light emitting region, and p-doped portion) is grown on a template that includes a porous region. The inventors have found that the presence of a porous region of III-nitride material in the template structure prior to the growth of the LED structure improves the quality of the crystal growth, leading to significant benefits including the possibility to change the emission wavelength of the LED light emitting region. The mechanism by which the porous region enables the tunable emission of the LED is the subject of ongoing research. Benefits that the porous region brings to the LED include strain relief, enlargement of the lattice constant, reduction of wafer bow, and mechanical and thermal effects during high temperature growth of the light emitting region.

[0064] The inventors have recognized that electrochemical porosification of III-nitride materials advantageously leads to reduced distortion of the III-nitride lattice and reduced overall wafer bow or curvature. Without wishing to be bound by theory, it is believed that the porosification process of the porous region of III-nitride materials also etches away structural defects, such as threading dislocations, that were formed during the growth of the layer on the substrate.

[0065] The porosification process removes dislocations from the semiconductor material of the porous region, thereby significantly reducing strain in the porous region, which occurs especially when the lattice dimensions of the porous region do not match those of the underlying substrate material. Thus, when a layer of III-nitride material is deposited over the porous region during epitaxial growth of an LED structure, the porous material is more likely to match the lattice of the overlying non-porous layer. As a result, the layers above the porous region are subjected to significantly less strain than they would be in the absence of the porous region. Because the light emitting region is formed over the porous region, the light emitting region of the LED is formed with reduced semiconductor lattice strain, and the porous region imparts unique properties to the structure and light emitting properties of the light emitting region.

[0066] Because the layers of non-porous semiconductor material formed over the porous regions experience reduced strain, these layers also have fewer structural defects that act as non-radiative recombination centers that impair device performance.

[0067] Compositional tensile effect: Kawaguchi et al. reported the so-called InGaN compositional tensile effect, where the indium fraction is small at the initial growth stage but increases with increasing growth thickness. This observation was to some extent independent of the underlying GaN or AlGaN layers. The authors suggested that this effect is caused by strain due to lattice mismatch at the interface. They found that a larger lattice mismatch between InGaN and the underlying epitaxial layer is accompanied by a larger change in In content.

[0068] Theoretical study of the composition pulling effect in InGaN metalorganic vapor-phase epitaxy growth by Inatomi et al. (Japanese Journal of Applied Physics, Volume 56, Number 7) found that compressive strain suppresses InN incorporation, whereas tensile strain promotes InN incorporation compared to the relaxed bulk growth case.

[0069] The inventors have found that the presence of a porous region in a semiconductor structure during epitaxial growth induces a "strain relaxation" that reduces the strain in the layers of the semiconductor structure, and this can lead to improvements in terms of the compositional tensile effect. Porosification reduces the strain in the III-nitride layers, making the semiconductor structure less strained and thus enabling conditions for more In incorporation. Thus, the present invention can aid in the incorporation of more In into the layers of an LED grown on a porous region, which is highly desirable for longer wavelength emission.

[0070] The n-doped region, the light emitting region, and the p-doped region are preferably formed on the porous region during the fabrication of the LED. The porous region may then be permanently retained in the LED and incorporated into the device, or alternatively, the porous region may be removed after the LED diode structure is formed. Even if the porous region is removed by peeling off the as-grown structure, the mechanical and structural benefits of the porous region for the growth of the light emitting region are retained in the light emitting region.

[0071] The n-doped region, the light emitting region, and the p-doped region are preferably provided above the porous region, in other words, the porous region may be disposed below the n-doped region, the light emitting region, and the p-doped region in the LED structure.

[0072] The light emitting layer may preferably be an indium gallium nitride (InGaN) layer.

[0073] Thus, by providing a porous region of III-nitride material, the n-doped region, the light emitting region, and the p-doped region may be grown over the porous region (possibly with an intervening layer of III-nitride material between the porous region and the LED structure) at a lower strain than would be possible in the absence of the porous region. This reduced strain level in the layered semiconductor structure thus facilitates increased indium incorporation into the light emitting layer of the LED, thereby allowing high quality InGaN light emitting layers to be grown with higher indium contents.

[0074] As noted in the Background section above, there is a huge demand for LEDs emitting in the 400-750 nm, especially 500-750 nm, wavelength range, but the realization of longer wavelength LEDs has been hampered by the technical difficulty of incorporating sufficient indium into the light-emitting layer.

[0075] The inventors have found that growing an LED structure on a porous region of III-nitride material results in a significant shift in the emission wavelength to longer wavelengths compared to the same LED structure grown on a non-porous substrate.

[0076] The inventors have demonstrated that conventional green / yellow (500-570 nm or 570-590 nm emission) InGaN LED structures can be grown on non-porous GaN wafers and shown to emit green / yellow light as predicted. The same "green / yellow" InGaN LED structure was then grown on a template containing porous regions, and when an electrical bias was applied across the LED, the LED emitted light in the red range of 600-750 nm.

[0077] The present invention advantageously allows conventional, easily manufactured LED structures to be shifted to longer wavelength emission and to emit at a variety of different peak emission wavelengths by controlling the power supply to the LED. Although a variety of different emission ranges are possible, in a particularly preferred embodiment, known LED structures previously known as yellow or green LEDs can be made into tunable green-red LEDs.

[0078] The LED light emitting region may be for emitting light at a peak wavelength of 500-600 nm, or 500 nm-550 nm, or 550 nm-600 nm, or 510-570 nm, or 530 nm-560 nm, or 540 nm-600 nm. The LED light emitting region may be for emitting light at a peak wavelength of 500-600 nm, or 510-570 nm, or 530 nm-560 nm, or 540 nm-600 nm, or 590 nm-640 nm, if not grown on a porous III-nitride layer. However, growing the LED light emitting region on a porous region of III-nitride material may shift the emission wavelength of the light emitting region to longer wavelengths (e.g., 600-750 nm) and may also enable the LED to emit light continuously over a range of different emission wavelengths.

[0079] Traditionally, lower growth temperatures have been required during epitaxial deposition of InGaN material to grow InGaN quantum wells with higher indium loadings, which are required for longer wavelength emission. Varying the growth pressure and growth rate have also been attempted as a way to increase indium loading. The drawbacks of lower growth temperatures include more defects in the crystal structure and reduced efficiency of NH3 decomposition.

[0080] However, in the present invention, the presence of porous regions in the LED template during growth reduces strain in the crystal structure, increasing the lattice constant and allowing more In to be incorporated into the active region than previously possible at a given growth temperature. Thus, by incorporating porous regions into the structure, it is no longer necessary to lower the growth temperature of the InGaN to increase In incorporation, since more In can be incorporated at higher temperatures. This allows higher InGaN growth temperatures to be used in the LEDs, leading to higher crystal quality, fewer defects, and improved performance and LED characteristics compared to prior art LEDs.

[0081] The improved crystalline quality of the LED structure grown on the porous region also enables the LED to emit light over a much broader range of emission wavelengths than was previously possible with prior art.

[0082] In some previous attempts to introduce porous materials into LEDs, it was found that the porous materials led to a high degree of spectral broadening, which resulted in an undesirably broad full width at half maximum (FWHM) of the spectral emission peak, which is undesirable in most LED applications, where a narrow emission peak is preferred so that the light emitted by the LED is at or near the desired wavelength.

[0083] Advantageously, the LEDs in the present invention preferably emit with a FWHM of 50 nm or less, or 40 nm or less, or 30 nm or less, and preferably the FWHM of the LED is <20 nm. Thus, although the peak emission wavelength of a tunable LED can be changed by varying the drive conditions supplied to the LED, at any given drive conditions the LED preferably emits with a FWHM of 50 nm or less, or 40 nm or less, or 30 nm or less, or 20 nm or less.

[0084] In a preferred embodiment, the light emitting layer is a light emitting indium gallium nitride layer. The LED preferably also comprises a region of GaN material. Due to the lattice mismatch between GaN and InGaN, the stress relief effect caused by the porous region is particularly advantageous.

[0085] Light emitting diodes are (a) the light emitting region comprises one or two or three or four or five or six or seven or eight quantum wells (or at least one quantum well); or (b) The III-nitride layer is an Al layer having y in the range of 0.1 to 1.0. y Ga (1-y) An aluminum gallium nitride layer having a composition of N; or (c) a UV or blue emitting InGaN / GaN or InGaN / InGaN superlattice or InGaN layer is located between the n-doped portion and the light emitting region; The present invention may have at least one feature selected from the following:

[0086] The n-doped portion, the p-doped portion, and the light emitting region are preferably designed according to conventional LED design known in the art. For example, the thickness, composition, and number of such layers may be selected according to conventional principles of LED design. The LED may include other layers that are common knowledge in the field of LED design and are well understood by those skilled in the art. For example, the LED may include a III-nitride layer located on the light emitting layer, and a III-nitride barrier layer located on the III-nitride layer. Such structural features are known and may be used in the LED of the present invention.

[0087] (Power supply control) The peak emission wavelength of a tunable LED is controlled by controlling the power supply to the LED.

[0088] To achieve the tunable characteristics of the present invention, the power supply can be controlled in a variety of ways, for example, either voltage or current driving schemes can be used in either continuous wave (CW) or pulsed modes.

[0089] In a preferred embodiment, the power source may be a pulsed power source. Alternatively, the power source may be a continuous wave (CW) or quasi-continuous wave power source.

[0090] The power supply may be a constant voltage power supply or, alternatively, a constant current power supply.

[0091] The parameters that are varied to control the power supply may vary depending on the driving scheme used to drive the LED. For example, the LED may be controlled by varying the power, power density, current, current density, or voltage of the power supply to the LED. Control of these parameters is well understood by those skilled in the art since power, current, and voltage are related by P=IV.

[0092] The peak emission wavelength emitted by a tunable LED during use is determined by the current density (alternatively expressed as power density) passing through the LED diode structure during use. The current density (units: A / cm2) experienced by a tunable LED is 2 ) is the magnitude of the current (unit: amperes) supplied by the power source and the cross-sectional area (unit: cm) of the LED diode structure through which the current passes. 2 When a tunable LED is fabricated, the cross-sectional area (in cm) of the LED diode structure through which the current passes is determined by 2 ) is fixed, so by varying the amount of current supplied to the LED during use, the current density through the LED is varied.

[0093] For a given LED of fixed size, it is possible to consider the drive conditions in terms of the magnitude of the drive current, but since LEDs can be manufactured in a wide variety of shapes and sizes, it may be more appropriate to define general drive conditions in terms of current density or power density.

[0094] Since the emission wavelength range is a continuous range of wavelengths, the LED can advantageously emit at any wavelength within that range by varying the power supply.

[0095] The power supply can be variable over a power range that corresponds to the emission wavelength range of the LED. For example, the power range can be expressed in terms of power (in watts) or power density (in W / cm 2 ), defined by a lower power at which the LED emits at the long wavelength end of its emission wavelength range, and a higher power at which the LED emits at the short wavelength end of its emission wavelength range. Alternatively, the power range can be defined in terms of current (in amperes) or current density (in A / cm 2 ) or upper and lower limits of voltage.

[0096] The power supply to the LED is preferably regulated or controlled by an LED driver. The light emitting diode may be configured or connected to an LED driver configured to supply power to the LED. The LED driver is preferably configured to supply a variable power supply to the LED. For example, the LED driver is preferably capable of varying the magnitude of the drive current supplied to the LED by continuously varying the magnitude of the drive current over a range or by providing a number of distinct drive current modes having different fixed magnitudes.

[0097] A variety of conventional LED drivers can be used to regulate the power supply to the LEDs. The LED driver can be an integrated circuit (IC), for example, the LED driver can be a CMOS driver or a TFT driver. The driver can be a backplane IC driver or a discrete component such as an on-chip IC driver made from the same GaN epiwafer.

[0098] The duty cycle of each drive condition may be at least 0.001%, 0.01%, 0.1%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

[0099] (Power Control) The peak emission wavelength of the LED may advantageously be controllable by varying the power or power density supplied to the LED.

[0100] The peak emission wavelength can be decreased in response to an increase in power supplied to the LED from the power supply, and the peak emission wavelength can be increased in response to a decrease in power supplied from the power supply.

[0101] For example, an LED can emit light at a first peak emission wavelength when the power source supplies a first power to the LED, and the LED can emit light at a second peak emission wavelength longer than the first emission wavelength when the power source supplies a second power lower than the first power.

[0102] In a particularly preferred embodiment, the first peak emission wavelength is less than 570 nm and the second peak emission wavelength is greater than 610 nm, such that the LED emits green light in response to a first power and red light in response to a second power. Thus, the LED can be controlled to emit light at any wavelength between green and red by controlling the power supplied to the LED.

[0103] The LED preferably emits at a third peak emission wavelength when the power supply provides a third power density different from the first and second powers.

[0104] The peak emission wavelength of the LED of the present invention advantageously varies with the power or power density of the power source in a consistent manner that can be scaled to a display device that includes the LED. In a preferred embodiment, the peak emission wavelength of the LED of the present invention can vary in a scaleable relationship with the logarithm of the power or power density of the power source. This is highly advantageous in device design, since a predictable relationship between the power source and the peak emission wavelength allows the emission of the LED to be precisely controlled. The power source can be scaled easily, so that if a particular emission wavelength is desired, it is simple to calculate and supply the exact power required to produce that emission wavelength.

[0105] (Current control) The peak emission wavelength of the LED may advantageously be controllable by varying the current or current density of the power supply supplied to the LED.

[0106] The shift in the peak emission wavelength of the tunable LED as a function of the driving current density may preferably be greater than 10 nm / decade, or greater than 20 nm / decade.

[0107] The peak emission wavelength can be decreased in response to an increase in the current density supplied to the LED from the power supply, and the peak emission wavelength can be increased in response to a decrease in the current density supplied from the power supply.

[0108] For example, an LED can emit light at a first peak emission wavelength when the power source supplies a first current density to the LED, and the LED can emit light at a second peak emission wavelength longer than the first emission wavelength when the power source supplies a second current density lower than the first current density.

[0109] The LED preferably emits at a third peak emission wavelength when the power supply provides a third current density different from the first and second current densities.

[0110] In a particularly preferred embodiment, the first peak emission wavelength is less than 570 nm and the second peak emission wavelength is greater than 610 nm, such that the LED emits green light in response to a first current density and red light in response to a second current density. Thus, the LED can be controlled to emit light at any wavelength between green and red by controlling the current density supplied to the LED.

[0111] The peak emission wavelength of the LED of the present invention advantageously varies with the current or current density of the power supply in a consistent manner that can be scaled to a display device. In a preferred embodiment, the peak emission wavelength of the LED of the present invention can have a convertible relationship to the logarithm of the current or current density of the power supply. This is highly advantageous in device design, since a predictable relationship between the power supply characteristics and the peak emission wavelength allows for precise control of the LED's emission. The power supply can be easily scaled, so that if a particular emission wavelength is desired, it is simple to calculate and supply the exact current density required to produce that emission wavelength.

[0112] LED is 0.001A / cm 2 ~1000A / cm 2 , or 0.01A / cm 2 ~500A / cm 2 , or 0.1A / cm 2 ~250A / cm 2 may be drivable by a current density of

[0113] In a preferred embodiment of the present invention, the LEDs are 2 or more than 7A / cm 2 or more than 9A / cm 2 More than or equal to 10A / cm 2 Over 11A / cm 2 The same LED emits green light at wavelengths below 570 nm in response to current densities above 4 A / cm. 2 Less than or equal to 3A / cm 2 Less than or equal to 2A / cm 2 In response to current densities below 610 nm, it emits red light at wavelengths greater than 610 nm.

[0114] In a preferred embodiment, the LEDs are rated at 19 A / cm 2 or more than 20A / cm 2 or more than 21A / cm 2 In response to current densities of 430 nm to 500 nm, it emits light at wavelengths of 430 nm to 500 nm.

[0115] (Porous template) The n-type region, the light emitting region, and the p-type region (sometimes referred to as an LED structure or LED diode structure) are preferably grown on a semiconductor template that includes a porous region. The semiconductor template may also include multiple layers of semiconductor material arranged to provide a suitable substrate for the growth of the LED structure. However, once the n-type region, the light emitting region, and the p-type region are grown on the template, the LED structure and the template together form part of the LED.

[0116] The porous region and template may be removed from the LED structure during subsequent chip processing, if desired.

[0117] The porous region may have a thickness of at least 1 nm, preferably at least 10 nm, particularly preferably at least 50 nm, for example, the porous region may have a thickness of 1 nm to 10,000 nm.

[0118] The porous region may have a porosity of 1% to 99%, or a porosity of 10% to 80%, or a porosity of 20% to 70%, or a porosity of 30% to 60%. The porosity of a porous region may be measured as the volume of all pores relative to the volume of the entire porous region.

[0119] The degree of porosity has been found to have an effect on the magnitude of the wavelength shift induced by the porous region: generally, the higher the % porosity, the greater the wavelength shift of the LED compared to the same LED structure on a non-porous template.

[0120] The porous region is preferably formed from one of GaN, InGaN, AlGaN, AlInGaN, or AlN.

[0121] The porous region may be below or beneath the n-type, light-emitting, and p-type regions of the LED. Preferably, the n-type, light-emitting, and p-type regions (LED structure) are disposed above or above the porous region, as determined by the growth order of the layers in the LED. The LED structure is preferably grown above the porous region, so that the LED structure benefits from strain relaxation in the porous III-nitride layer.

[0122] (LED layer) The LED may include a connection layer of III-nitride material disposed between the n-doped portion and the porous region. Preferably, the connection layer has a thickness of at least 100 nm, although smaller or larger thicknesses may be used. The connection layer may preferably be one of GaN, InGaN, AlGaN, AlInGaN, or AlN.

[0123] The LED preferably comprises a non-porous intermediate layer of a III-nitride material porous region between the porous region and the light emitting region. The porous region is preferably formed by electrochemical porosification through the non-porous layer of III-nitride material using the methods of PCT / GB2017 / 052895 (published as WO2019 / 063957) and PCT / GB2019 / 050213 (published as WO2019 / 145728), so that the non-porous layer of III-nitride material typically forms a non-porous intermediate layer that remains above the porous region. The non-porous intermediate layer advantageously provides a smooth surface for growing further layers during the course of manufacture.

[0124] Preferably, the LED comprises a non-porous intermediate layer of III-nitride material disposed between the porous region and the connection layer, which may preferably be a non-porous layer through which electrochemical etching of the porous region takes place.

[0125] The non-porous intermediate layer may preferably be one of GaN, InGaN, AlGaN, AlInGaN, or AlN.

[0126] The porous region is a porous layer, and the light emitting diode comprises a porous layer of III-nitride material. Preferably, the porous region is a porous layer that is continuously porous, for example formed from a continuous layer of porous III-nitride material.

[0127] The porous region may comprise multiple porous layers, and optionally multiple non-porous layers. In a preferred embodiment of the invention, the porous region is a stack of alternating porous and non-porous layers, with a top surface of the stack defining a top of the porous region and a bottom surface of the stack defining a bottom of the porous region. A light emitting region may be formed on the porous region comprising a stack of porous layers of III-nitride materials.

[0128] In some embodiments, the light emitting region is disposed on a stack of multiple porous layers of III-nitride material. Thus, the porous region may be a stack of III-nitride material layers, at least some of which are porous, rather than a single porous layer of III-nitride material. The stack of porous layers may preferably be a stack of alternating porous and non-porous layers.

[0129] Alternatively, the porous region may be a layer of III-nitride material that includes one or more porous regions, for example, one or more porous regions in an otherwise non-porous layer of III-nitride material, In other words, the porous region need not be a continuous layer of porous material.

[0130] In a preferred embodiment, the porous region or layer may have a lateral dimension (width or length) comparable to the substrate on which it is grown. For example, a conventional substrate wafer size is 1 cm 2 The porous layers or regions may have a variety of sizes, such as 1 / 10 of a pixel (e.g., 0.1 μm) or 2, 4, 6, 8, 12, or 16 inches in diameter. However, smaller porous regions that do not span the entire substrate may be formed by patterning one or more layers and / or by depositing regions of different charge carrier concentrations within the same layer. Thus, the lateral dimensions of the porous layers or regions may vary from approximately 1 / 10 of a pixel (e.g., 0.1 μm) to the lateral dimensions of the substrate itself.

[0131] The n-doped portion preferably comprises an n-doped Group III-nitride layer.

[0132] Preferably, the n-doped portion and / or the n-doped layer comprises n-GaN, or n-InGaN, or a stack of alternating layers of n-GaN / n-InGaN, or a stack of alternating layers of n-InGaN / n-InGaN with different concentrations of indium.

[0133] The n-doped portion may comprise a monocrystalline n-doped III-nitride portion, in which case preferably the n-doped portion comprises a monocrystalline n-doped III-nitride layer having a flat upper surface.

[0134] The porous region and each layer between the porous region and the single crystal n-doped III-nitride layer may be a planar layer having a respective top surface and a respective bottom surface that are parallel to the planar top surface of the single crystal n-doped III-nitride layer.

[0135] The light emitting layer preferably comprises one or more InGaN quantum wells, preferably 1 to 10 quantum wells.

[0136] The light emitting layer may be a nanostructured layer of InGaN with quantum structures such as quantum dots, fragmented quantum wells, or discontinuous quantum wells.

[0137] The light-emitting layer and / or the quantum well preferably comprises an InN layer having a structure in which 0.07≦x≦0.40, preferably 0.12≦x≦0.30 or 0.22≦x≦0.30 or 0.30≦x≦0.40, particularly preferably 0.22≦x≦0.27 and 0.27≦x≦0.40. x Ga 1-x It has a composition of N.

[0138] The LED preferably comprises a III-nitride layer overlying the light emitting layer, and a III-nitride barrier layer overlying the III-nitride layer.

[0139] The III-nitride layer on the light-emitting layer may be referred to as a "capping layer," which is used 1) to increase the quantum confined Stark effect to achieve longer wavelength emission by band bending and thus red shifting, and 2) to protect the high In% of InGaN to ensure that sufficient In% is incorporated to achieve the long wavelength and also provide a larger barrier.

[0140] The LED preferably comprises a capping layer of III-nitride material between the quantum wells and the p-doped region, which may be GaN, InGaN, AlGaN, or AlN.

[0141] The LED preferably comprises a barrier layer of a III-nitride material between the quantum well and the p-doped region, which may be GaN, InGaN, AlGaN, or AlN.

[0142] The p-doped region comprises a p-doped III-nitride layer and a p-doped aluminum gallium nitride layer and is disposed between the p-doped III-nitride layer and the light emitting region. The p-doped aluminum nitride layer is preferably an electron blocking layer (EBL) disposed between the cap layer and the p-type layer, the electron blocking layer comprising 5-25 atomic % aluminum and preferably having a thickness of 10-50 nm.

[0143] In preferred embodiments, the porous region is not part of a distributed Bragg reflector (DBR), but in other embodiments the porous region may form and act as an optical reflector or mirror or filter with a unique reflectance / transmittance band over a range of wavelengths.

[0144] The morphology of the quantum wells (QWs) in the active light emitting region can be varied. For example, the light emitting region can contain uniform QWs with well-defined interfaces, or fragmented QWs with less well-defined interfaces, fragments, or QW wells with varying widths / compositions, or quantum dots such as localized centers. Controlling the QW morphology in this way can determine the range of tunable emission wavelengths that can be controlled and manipulated.

[0145] The light emitting region preferably comprises a plurality of quantum wells (QWs). The quantum wells may be continuous. The quantum wells may be segmented or discontinuous.

[0146] (Current limiting layer) The LED may include a current limiting or confining layer, which is a dielectric layer configured to limit the lateral area of ​​the LED through which current is conducted. The use of a current limiting layer may advantageously allow for further control of the current density in order to better control the peak emission wavelength of the LED.

[0147] The current limiting layer advantageously allows for manipulation of the power density supplied to the tunable LED in order to control the peak emission wavelength.

[0148] The current limiting layer is preferably a dielectric material layer, for example, the current limiting layer can be any dielectric material, such as SiO2, SiN, or SiNx.

[0149] The current limiting layer may be disposed in various locations within the LED so long as it limits the lateral area of ​​the LED through which current is conducted. The current limiting layer may be disposed between the electrical n-contact and the electrical p-contact within the LED.

[0150] The current limiting layer may be disposed adjacent to either the n-doped or p-doped portion of the LED. For example, the current limiting layer may be disposed between the n-doped portion and the light emitting region. Alternatively, the current limiting layer may be disposed between the light emitting region and the p-doped portion. The current limiting layer may be disposed between the electrical contacts and the LED structure (the n-doped portion, the p-doped portion, and the light emitting region).

[0151] The current limiting layer preferably includes an opening extending through the current limiting layer, or one or more openings extending through the current limiting layer. The opening may preferably be located at the center of the current limiting layer. For example, the current limiting layer may include a circular opening in the center of the LED structure.

[0152] The LED may be configured such that the electrical contacts contact the LED structure through openings in the current-limiting layer, such that the area of ​​the openings defines the contact area where the contacts contact the LED structure.

[0153] The lateral dimensions of the or each of the openings are preferably much smaller than the lateral dimensions of the LED. By providing openings through the dielectric current limiting layer, high local current densities can be achieved, which can advantageously allow improved control of the power through the LED.

[0154] For example, the lateral width (or diameter) of the opening can be 50% or less of the lateral width of the LED structure (LED mesa). The width of the opening can be 45% or less, or 40% or less, or 35% or less, or 30% or less, or 25% or less, or 20% or less of the width of the LED structure.

[0155] The relative area of ​​the openings compared to the total area of ​​the current-limiting layer (blocked region) may be varied to modify the local current density.

[0156] (Pixel size) The light emitting region and / or LED may have lateral dimensions (width and length when viewed from above) that are greater than 50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or greater than 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or greater than 100 μm or 200 μm, 300 μm, and less than 1000 μm.

[0157] The light emitting area and / or LED may have lateral dimensions (width and length) greater than 100 μm and less than 300 μm. In this case, the LED may be referred to as a "mini-LED". In a preferred embodiment, the mini-LED may be square or circular or square with round corners and may have dimensions of 300 μm×300 μm, 200 μm×200 μm, 100 μm×100 μm, etc.

[0158] The light emitting area and / or the LED may alternatively have lateral dimensions (width and length) of less than 100 μm. In this case, the LED may be referred to as a "micro-LED". The micro-LED may preferably have lateral dimensions of less than 80 μm, or less than 70 μm, or less than 60 μm, or less than 50 μm, or less than 30 μm, or less than 25 μm, or less than 20 μm, or less than 15 μm, or less than 10 μm, or less than 5 μm, or less than 3 μm, or less than 1 μm, or less than 500 nm, or less than 200 nm, or less than 100 nm, or less than 50 nm.

[0159] In a preferred embodiment, the micro LEDs may be square or circular or square with round corners and may have dimensions such as 75 μm×75 μm, 50 μm×50 μm, 40 μm×40 μm, 30 μm×30 μm, 25 μm×25 μm, 20 μm×20 μm, or 10 μm×10 μm, or 5 μm×5 μm, or 2 μm×2 μm, or 1 μm×1 μm, or 500 nm×500 nm, or less.

[0160] The LEDs may be circular, triangular, rectangular, square, oval, diamond, hexagonal, pentagonal, and any combination of these shapes. For irregularly shaped pixel designs, at least one dimension should fall within the dimensions defined above in order for the LED to be classified as a mini LED or micro LED. For example, the width or diameter of the LED is preferably less than 100 μm, in which case the LED will be classified as a micro LED.

[0161] (Light emitting area) The light emitting region preferably comprises a plurality of quantum wells (QWs) or multiple quantum wells (MQWs) including quantum dots, quantum wires, or other quantum nanostructures.

[0162] In some embodiments, the light emitting region comprises multiple quantum wells (QWs), and the quantum wells are contiguous.

[0163] The inventors have found that non-uniformity in the light-emitting region has a significant effect in expanding the range of emission wavelengths that the light-emitting region can emit in response to changes in power supplied to the LED. In the prior art, non-uniformity in the light-emitting region is typically considered a defect, which is undesirable and should be avoided as much as possible, since high quality, low defect semiconductor wafers are typically the goal. The inventors have rejected this prejudice in the art and found that intentionally creating non-uniformity in the light-emitting region can advantageously result in a tunable LED that can expand the emission wavelength range and emit over a much wider wavelength range than was previously possible in the prior art.

[0164] In alternative embodiments of the invention, the light emitting region is non-uniform, fragmented, or discontinuous. The light emitting region may be purposely introduced with multiple QW regions with different indium compositions and well widths and quantum barriers, non-uniform or fragmented or intermittent or gapped or discontinuous quantum wells resulting in well width fluctuations, InGaN quantum dots or nanostructures, quantum wells formed on polar, semi-polar, or non-polar facets, etc., to realize the effect of carrier localization centers in InGaN quantum wells.

[0165] In a preferred embodiment, the light emitting region comprises a plurality of quantum wells (QWs), the quantum wells being non-uniform, fragmented or discontinuous.

[0166] The QWs may have well width variations. For example, the well widths of the QWs may vary by at least 2%, 5%, 10%, 20%, 25%, or 50%, or 75%. The well width variations may be between quantum wells (vertical) or even within a quantum well (lateral).

[0167] The QWs can have alloy composition variations, for example the indium composition of the QWs can vary by at least 2%, 5%, 10%, 20%, 25%, or 50%, or 75% across the light emitting area.

[0168] We have found that perturbations in well width and / or alloy composition can result in carrier localization centers at either the top or bottom interface of the QWs. Either carrier localization center will result in tunable wavelength in our tunable LED. The greater the density of these carrier localization centers, the wider the tunable wavelength range can be achieved.

[0169] The LED may comprise a V-shaped pit extending or propagating through the light-emitting active area. Preferably, the LED comprises a plurality of V-shaped pits extending through the light-emitting area.

[0170] Preferably, the LEDs are at least 1×10 7 / cm 2 , e.g. at least 5 × 10 7 / cm 2 Or at least 1 × 10 8 / cm 2 of V-shaped pit density (measured looking down on the LED structure), e.g. 1×10 7 / cm 2 ~5×10 9 / cm 2 The V-shaped pit density may be

[0171] LEDs are 5 x 10 9 / cm 2 V-shaped pit density of less than 1×10 9 / cm 2 Less than or 5 x 10 8 / cm 2 The V-shaped pit density may be less than 100 nm.

[0172] V-pits are a known phenomenon in the art of epitaxial semiconductor growth, and methods for growing V-pits in semiconductor structures are known in the art. For example, V-pits and their growth are described in the prior art document The effect of nanometre-scale V-pits on electronic and optical properties and efficiency droop of GaN-based green light-emitting Diodes; Zhou et al; Scientific Reports | (2018) 8:11053 | DOI:10.1038 / s41598-018-29440-4.

[0173] These V-shaped pits, although V-shaped when viewed in cross section, actually form as cone- or funnel-shaped voids in semiconductor structures grown bottom-up using conventional epitaxial growth techniques. Although the pits are V-shaped in cross section, when viewed from above, the pits are typically hexagonal. The tip of the V-shaped pit always points downward toward earlier deposited layers of the semiconductor structure because the pit widens as subsequent epitaxially grown layers are deposited on top of the structure.

[0174] Although V-shaped pits are known in the art, they are typically considered problematic defects in semiconductor structures and are undesirable since the typical goal is high quality, low defect semiconductor wafers.

[0175] In the rare circumstances in which V-shaped pits have been incorporated into semiconductor structures in the past, they have been used as a screening mechanism to create a higher bandgap region that prevents current carriers from traveling down threading dislocations as a leakage path.

[0176] However, in preferred embodiments of the present invention, the V-pit is purposefully incorporated into the LED structure. The V-pit extends far enough down into the semiconductor structure to terminate at a layer below the active light emitting region. This means that the V-pit must extend through the thickness of the active light emitting region.

[0177] The inventors have discovered that V-shaped pits extending completely through the light emitting region of an LED structure can advantageously broaden the range of emission wavelengths that a tunable LED can emit.

[0178] Because the V-shaped pit extends through the active region of the LED, during bottom-up epitaxial growth, quantum well (QW) layers that are flat over the rest of the structure are grown on the sloped sidewalls of the V-shaped pit. The QWs deposited on the sidewalls of the pit are distorted and elongated around the sides of the pit, resulting in a different thickness and composition compared to the flat QWs over the bulk of the structure.

[0179] Around the V-pit, the QW layer of semiconductor material is grown as a flat, planar layer. Thus, the light-emitting active region is flat around the V-pit. However, at the location of the V-pit, the active layer is distorted and stretched downward along the sidewalls into the V-pit. This stretching effect changes the thickness of the QWs on the sidewalls of the pit, resulting in a different thickness for the QWs on the sidewalls compared to the flat QW layer formed throughout the rest of the LED structure.

[0180] The inventors have found that the V-pits can provide localized strain relaxation, and that the MQWs deposited on the sidewalls of these V-pits have a different thickness and composition compared to the rest of the MQWs, so that the MQWs in the region of the V-pits generate different emission wavelengths.

[0181] The quantum wells grown on the sidewalls of the V-shaped pit are thinner than most of the flat QWs elsewhere in the structure, which may affect the bandgap of the QWs and allow the QWs in this region to emit at a different wavelength than the flat QWs elsewhere in the structure. In addition, the QWs on the pit sidewalls end up having a higher indium (In) content than the surrounding flat QWs. Because the sidewalls expose the semipolar facets of the QWs, which take up more indium during epitaxial growth, the QWs in the region of the V-shaped pit may have a higher indium content than the flat QWs surrounding the pit. Higher indium incorporation typically results in a longer peak emission wavelength. Both the thickness and indium content of the QWs affect the emission wavelength generated in the light-emitting region. Thus, the presence of a V-shaped pit in an LED structure may advantageously modify the composition and thickness of the QWs in the light-emitting region to expand the range of emission wavelengths over which the LED can be driven to emit light.

[0182] V-shaped pits typically grow from threading dislocations in a semiconductor structure. The threading dislocations perpetuate themselves upwards through the structure as additional layers are grown on top of the layer containing the threading dislocation, and at some point the dislocations expand to become V-shaped pits. Typically, those skilled in the art aim to keep the threading dislocation concentration low in order to produce "high quality", low defect wafers.

[0183] Alternatively, the V-shaped pits can be grown using a three-dimensional epitaxial growth mode. Three-dimensional epitaxial deposition techniques are known in the art and are typically used to grow "islands" or "pyramids" of semiconductor material on a template. By controlling the deposition of the LED structure using 3D epitaxial deposition techniques, the V-shaped pits can be artificially grown at the desired location without the need for threading dislocations to be present to "seed" the V-shaped pit formation. Using this deposition control, the bottom (lowest part) of the pit can be created at the desired location in the structure, i.e., both at the desired lateral position and at the desired height in the structure, for example in a specific layer of the semiconductor structure below the active light emitting region.

[0184] The bottom of the V-shaped pit can be located in a connection layer of the semiconductor structure. The connection layer can be disposed between the porous region and the n-doped portion.

[0185] The bottom of the V-shaped pit may be located in a pre-strain layer of the semiconductor structure, which may be disposed above the n-doped portion and below the light emitting region.

[0186] Preferably, the LED comprises a plurality of V-shaped pits extending through the active light emitting area.

[0187] Preferably, the LEDs are at least 1×10 7 / cm 2 , e.g. at least 5 × 10 7 / cm 2 Or at least 1 × 10 8 / cm 2 The LED has a V-shaped pit density (measured looking down on the LED structure) of 5×10 9 / cm 2 V-shaped pit density of less than 1×10 9 / cm 2 Less than or 5 x 10 8 / cm 2 The V-shaped pit density may be less than 100 nm.

[0188] For example, 1×10 7 / cm 2 ~5×10 9 / cm 2 , or 5 × 10 7 / cm 2 ~5×10 9 / cm 2 , or 1 × 10 8 / cm 2 ~5×10 8 / cm 2 is the V-shaped pit density.

[0189] The LED may have more than 0.1 V-pits per square micrometer, or more than 1 V-pit per square micrometer, or more than 2 V-pits per square micrometer.

[0190] The concentration of V-pits in an LED is preferably controlled, since too many V-pits can adversely affect the light emission of the LED by impeding radiative recombination, For example, an LED may comprise less than 10 V-pits per square micrometer, or less than 8 V-pits per square micrometer, or less than 6 V-pits per square micrometer.

[0191] In a preferred embodiment, the LED structure has a density of 10 9 Preferably, the semiconductor structure below the active light emitting region (typically the substrate, the porous region, and the connecting layers) has a density of less than 10 per square centimeter. 9 The threading dislocation density is preferably limited to this level so that further epitaxial growth does not result in excessive V-shaped pits in the light emitting region.

[0192] Both the density and size (depth) of the V-shaped pits can be controlled. The size of the V-pits can be controlled by the position of the pits initiated in the pre-strained layer and the low-temperature nGaN layer and the growth conditions.

[0193] The morphology of the quantum wells (QWs) in the active light-emitting region can vary. For example, the light-emitting region can contain uniform QWs with well-defined interfaces, or fragmented QWs with less well-defined interfaces, fragments, or QW well width / composition fluctuations, or quantum-dot-like localized centers. Controlling the QW morphology in this way can determine the range of tunable emission wavelengths that can be controlled and manipulated.

[0194] The light emitting region preferably comprises a plurality of quantum wells (QWs). The quantum wells may be continuous. The quantum wells may be segmented or discontinuous.

[0195] If the QWs are continuous and highly uniform in thickness and composition, the recombination of charge carriers can only occur in a regular and well-defined manner, whereas if the QWs are fragmented or discontinuous, many nanostructures are formed, which in turn give rise to different bandgaps that result in emission at different colors.

[0196] (Control method of wavelength tunable LED) In another aspect of the present invention, there is provided a method of controlling a tunable LED, the method comprising: providing power to a tunable LED according to the first aspect of the present invention; and controlling the power supply to vary the peak emission wavelength of the tunable LED across a range of emission wavelengths; The method may include varying the power source to vary the peak emission wavelength of the tunable LED within the emission wavelength range.

[0197] The method may include dynamically tuning a power supply to an LED during a single display frame.

[0198] A power source or power supply may be provided to the tunable LED from a power supply, via an LED driver as desired.

[0199] The method can include providing a drive current to a tunable LED and varying a magnitude of the drive current to vary a peak emission wavelength of the tunable LED within an emission wavelength range.

[0200] Preferably, the peak emission wavelength of a tunable LED is varied by varying the drive current supplied to the LED during operation.

[0201] An LED can be controlled to emit at a number of distinct peak emission wavelengths by varying the drive current supplied to its subpixel between a number of distinct non-zero values, which can advantageously provide a tunable monochromatic display.

[0202] An LED can be controlled to emit at multiple distinct peak emission wavelengths during a display frame by varying the drive current supplied to its subpixel between multiple distinct non-zero values, thereby allowing dynamic pixel tuning and advantageously tuning the color emitted by an individual LED during a display frame.

[0203] The power source may be controlled to vary the peak emission wavelength over an emission wavelength range of at least 40 nm, or at least 50 nm, or at least 60 nm, or at least 70 nm, or at least 80 nm, preferably up to a range of 100 nm, or 110 nm, or 120 nm, or 140 nm, or 160 nm, or 180 nm, or 200 nm.

[0204] In particularly preferred embodiments, the power supply can be controlled to vary the peak emission wavelength from 400 nm to 680 nm, 430 nm to 670 nm, 450 nm to 650 nm, 500 nm to 680 nm, or 520 nm to 675 nm.

[0205] The power source may be a pulsed power source, or the power source may be a continuous wave (CW) or quasi-continuous wave power source.

[0206] The control of the power supply may be current control or voltage control.

[0207] The power supply may be a constant voltage or constant current power supply. AC or DC power supplies may also be used.

[0208] The power supply can be operated in a pulse width modulation (PWM) mode, or a pulse amplitude modulation (PAM) mode, or both.

[0209] The magnitude or amplitude of the power source may be varied between at least two non-zero values ​​during one display frame.

[0210] The magnitude or amplitude of the power source may be varied between multiple distinct non-zero values ​​in one display frame, for example, between three non-zero values ​​in one display frame.

[0211] The power supply is 0.001A / cm 2 ~1000A / cm 2 , or 0.01A / cm 2 ~500A / cm 2 , or 0.1A / cm 2 ~250A / cm 2 can be controlled to provide a current density of 100 .mu.m to the LED.

[0212] The power supply can be controlled to provide a drive current to the LED with a duty cycle of at least 0.001%, 0.01%, 0.1%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0213] The method may include providing a first drive current such that the LED emits light at a first peak emission wavelength, and providing a second drive current having a different magnitude or amplitude than the first drive current such that the LED emits light at a second peak emission wavelength.

[0214] A first drive current may be provided to the LEDs at a first duty cycle and a second drive current may be provided to the LEDs at a second duty cycle. The method may include controlling a duration of the first duty cycle and / or the second duty cycle to control the observed luminance and / or chromaticity produced by the display device.

[0215] The method can include providing a third drive current having a different magnitude or amplitude than the first drive current and the second drive current such that the LED emits light at a third peak emission wavelength.

[0216] The method may include supplying a third drive current to the LEDs at a third duty cycle, and preferably controlling the duration of the third duty cycle, to control the observed luminance and / or chromaticity produced by the display device.

[0217] The drive current supplied to the LEDs can be varied between the first drive current, the second drive current, and / or the third drive current to control the observed chromaticity produced by the display device.

[0218] The or each of the LEDs may be operated in a plurality of modes in response to a plurality of different drive current magnitudes or amplitudes, the LED being configured to emit light at a distinct peak emission wavelength in each of the plurality of modes. In each mode, the sub-pixel is driven with a current density of a different amplitude, thereby causing the sub-pixel to emit light at a different peak wavelength in the different amplitude modes. The amplitude of the drive current supplied to the tunable LED may be varied during operation of the display device, preferably within a single display frame.

[0219] (Power Control) The power supply is the power (unit: watts) or power density (unit: watts / cm2) delivered to the LED. 2 ) can be controlled to vary the peak emission wavelength of the LED.

[0220] To shorten the peak emission wavelength, the power provided by the power supply may be increased, or to lengthen the peak emission wavelength, the power provided by the power supply may be decreased.

[0221] The power supply may be controlled to supply a first power such that the LED emits light at a first peak emission wavelength, and the power supply may be controlled to supply a second power lower than the first power such that the LED emits light at a second peak emission wavelength that is longer than the first emission wavelength.

[0222] In a particularly preferred embodiment of a green-red LED, the first peak emission wavelength may be less than 570 nm and the second peak emission wavelength may be greater than 610 nm, such that the LED emits green light in response to a first power and red light in response to a second power. The LED may also emit in a continuous spectrum of wavelengths from the first peak emission wavelength to the second peak emission wavelength by varying the power between the first and second powers.

[0223] (Current control) The power supply is the current (unit: amperes) or current density (unit: A / cm 2 ) can be controlled to vary the peak emission wavelength of the LED.

[0224] Similar to power, the current density supplied by the power source may be increased to shorten the peak emission wavelength, or decreased to lengthen the peak emission wavelength.

[0225] The power supply may be controlled to supply a first current density at which the LED emits light at a first peak emission wavelength, and may be controlled to supply a second current density, lower than the first current density, at which the LED emits light at a second peak emission wavelength that is longer than the first emission wavelength.

[0226] In a particularly preferred embodiment of a green-red LED, the first peak emission wavelength may be less than 570 nm and the second peak emission wavelength may be greater than 610 nm, such that the LED emits green light in response to a first current density and red light in response to a second current density.

[0227] (Voltage Control) The power supply can be controlled to vary the peak emission wavelength of the LED by varying the voltage supplied to the LED.

[0228] To shorten the peak emission wavelength, the voltage supplied by the power supply may be increased, or to lengthen the peak emission wavelength, the voltage supplied by the power supply may be decreased.

[0229] The power supply may be controlled to supply a first voltage at which the LED emits light at a first peak emission wavelength, and the power supply may be controlled to supply a second voltage lower than the first voltage so that the LED emits light at a second peak emission wavelength that is longer than the first emission wavelength.

[0230] In a particularly preferred embodiment of a green-red LED, the first peak emission wavelength may be less than 570 nm and the second peak emission wavelength may be greater than 610 nm, such that the LED emits green light in response to a first voltage and emits red light in response to a second voltage. The LED may also emit in a continuous spectrum of wavelengths from the first peak emission wavelength to the second peak emission wavelength by varying the voltage between the first and second voltages.

[0231] (Manufacturing method of wavelength tunable LED) In a further aspect, a method for manufacturing a tunable LED is provided, the method comprising: an n-doped portion; A p-doped portion; a light emitting region located between the n-doped portion and the p-doped portion, the light emitting region comprising a light emitting layer that emits light at a peak emission wavelength under an electrical bias applied thereto; The method includes a step of growing the

[0232] The method can include growing an n-doped portion, a p-doped portion, and a light emitting region on a porous region of III-nitride material.

[0233] The method may include forming a porous region of III-nitride material in at least one of the n-doped portion or the p-doped portion, and forming a light emitting region over the porous region of III-nitride material.

[0234] The method may optionally include removing the porous region from the LED structure (the n-doped portion, the p-doped portion, and the light emitting region) after the n-doped portion, the p-doped portion, and the light emitting region have been formed.

[0235] The light-emitting layer may emit light at a peak emission wavelength of 400 to 800 nm, or 450 to 800 nm, or 500 to 800 nm, or 550 to 800 nm, or 610 to 800 nm, under an electrical bias applied thereto.

[0236] The method can include connecting the LED to a variable power supply.

[0237] The method may include connecting the LED to an LED driver configured to provide a variable power supply to the LED. The LED driver may be configured to control the power or current or voltage of the power supply to the LED. The LED driver may be configured to provide a pulsed power supply, or a CW power supply, or a quasi-CW power supply to the LED.

[0238] An LED structure including the n-doped portion, the p-doped portion, and the light emitting region can be an LED structure for emitting light at a wavelength shorter than the peak emission wavelength of the LED because the porous region of III-nitride material red-shifts the emission wavelength of the light emitting region to the peak emission wavelength.

[0239] The n-doped portion, the p-doped portion and the light emitting region are preferably formed from III-nitride semiconductor materials.

[0240] In a preferred embodiment, the light emitting region may comprise a light emitting indium gallium nitride layer for emitting light at a peak wavelength of 500 nm to 550 nm or 550 nm to 600 nm; In this case, growth on a porous region of III-nitride material shifts the emission wavelength of the light emitting region to a peak wavelength of 600-750 nm under electrical bias.

[0241] The light emitting region may comprise a light emitting indium gallium nitride layer emitting at a peak wavelength of 500-550 nm, or 500-580 nm, or 510-570 nm, or 530 nm-560 nm, or 550 nm-600 nm. The light emitting indium gallium nitride layer may be one or more layers known to emit at these wavelengths in conventional LEDs, for example when grown on a non-porous GaN substrate. However, the inventors have found that by growing a conventional yellow or green LED structure on a porous III-nitride layer, an LED emitting at a peak wavelength of 600-750 nm under electrical bias can be obtained.

[0242] The method may include growing a yellow or green LED structure on a porous region of III-nitride material.

[0243] In a preferred embodiment, the light emitting layer is a light emitting indium gallium nitride layer. The LED preferably also comprises a region of GaN material. Due to the lattice mismatch between GaN and InGaN, the stress relief effect provided by the porous region is particularly advantageous.

[0244] The method includes forming a light emitting active region having carrier localization centers in quantum wells (preferably InGaN QWs), such as multiple types of QW regions with different indium compositions and well widths and quantum barriers, non-uniform or fragmented or interrupted or gapped or discontinuous quantum wells resulting in well width fluctuations, InGaN quantum dots or nanostructures, quantum wells formed on polar, semi-polar, or non-polar facets, etc.

[0245] The method may include forming a plurality of quantum wells (QWs), where the quantum wells are non-uniform, fragmented, or discontinuous.

[0246] The multiple QWs may have variations in indium composition and / or well width.

[0247] The method may include forming one or more V-shaped pits in an LED structure such that the V-shaped pits extend through the thickness of the light emitting region. Preferably, the method includes forming at least 0.1 V-shaped pits per square micrometer, or at least 1 V-shaped pit per square micrometer, or at least 2 V-shaped pits per square micrometer. Preferably, the method includes forming at least 1×10 7 / cm 2 , e.g. at least 5 × 10 7 / cm 2 Or at least 1 × 10 8 / cm 2 The V-shaped pit density is, for example, 1×10 7 / cm 2 ~5×10 9 / cm 2 Preferably, the method includes forming a V-shaped pit density of 5×10 9 / cm 2 V-shaped pit density of less than 1×10 9 / cm 2 Less than or 5 x 10 8 / cm 2 forming a V-shaped pit density in the light emitting area of ​​less than 100 nm.

[0248] V-pits are a known phenomenon in the art of epitaxial semiconductor growth, and methods for growing V-pits in semiconductor structures are known in the art. For example, V-pits and their growth are described in the prior art document The effect of nanometre-scale V-pits on electronic and optical properties and efficiency droop of GaN-based green light-emitting Diodes; Zhou et al; Scientific Reports | (2018) 8:11053 | DOI:10.1038 / s41598-018-29440-4.

[0249] The V-shaped pit may be grown in the semiconductor structure such that it terminates in a layer below the active light emitting region, which means that the V-shaped pit must extend through the thickness of the active light emitting region.

[0250] A V-shaped pit can be grown from a threading dislocation in a semiconductor structure by controlling the growth conditions during epitaxial deposition of a layer on top of the layer containing the threading dislocation. The threading dislocation perpetuates itself upwards through the structure as additional layers are grown on top of the layer containing the threading dislocation, and by controlling the growth conditions, the dislocation is enlarged into a V-shaped pit.

[0251] Alternatively, the V-shaped pits can be grown using a three-dimensional epitaxial growth mode. Three-dimensional epitaxial deposition techniques are known in the art and are typically used to grow "islands" or "pyramids" of semiconductor material on a template. By controlling the deposition of the LED structure using 3D epitaxial deposition techniques, the V-shaped pits can be artificially grown at the desired location without the need for threading dislocations to be present to "seed" the V-shaped pit formation. Using this deposition control, the bottom (lowest part) of the pit can be created at the desired location in the structure, i.e., both at the desired lateral position and at the desired height in the structure, for example in a specific layer of the semiconductor structure below the active light emitting region.

[0252] The bottom of the V-shaped pit can be located in a connection layer of the semiconductor structure. The connection layer can be disposed between the porous region and the n-doped portion.

[0253] The bottom of the V-shaped pit may be located in a pre-strained layer of the semiconductor structure, which may be disposed above the n-doped portion and below the light emitting region.

[0254] Preferably, the LED comprises a plurality of V-shaped pits extending through the active light emitting area.

[0255] Both the density and size (depth) of the V-shaped pits can be controlled. The size of the V-pits can be controlled by the position of the pits initiated in the pre-strained layer and the low-temperature nGaN layer and the growth conditions.

[0256] The quantum wells (QWs) in the active light emitting region may be deposited such that the quantum wells are continuous and / or of uniform thickness. Alternatively, the quantum wells (QWs) in the active light emitting region may be deposited such that the quantum wells are segmented or discontinuous.

[0257] (manufacturing process) The n-type region, light emitting region, and p-type region (sometimes referred to as the LED structure) are preferably grown on a semiconductor template that includes a porous region. The semiconductor template may also include multiple layers of semiconductor material arranged to provide a suitable substrate for the growth of the LED structure.

[0258] The method may include a first step of electrochemically porosifying a layer of III-nitride material to form a porous region of III-nitride material. This may be achieved using a wafer-scale porosification process such as those set out in International Patent Applications PCT / GB2017 / 052895 (published as WO 2019 / 063957) and PCT / GB2019 / 050213 (published as WO 2019 / 145728).

[0259] The method may preferably include forming a porous region of III-nitride material by electrochemical porosification through a non-porous layer of III-nitride material, such that the non-porous layer of III-nitride material forms a non-porous intermediate layer, which may advantageously provide a smooth surface for the growth of further layers, such as one or more connection layers of III-nitride material.

[0260] The porous region may be formed by porosifying one or more layers or regions of III-nitride material on a substrate. The substrate may be silicon, sapphire, SiC, β-Ga2O3. The crystal orientation of the substrate may be polar, semi-polar, or non-polar. The thickness of the substrate may vary, typically from 100 μm to 1500 μm.

[0261] The porous region may be a porous layer, in which case the method includes growing the n-doped portion, the p-doped portion, and the LED light emitting region on a porous layer of III-nitride material. Preferably, the porous region may be a continuously porous porous layer, for example formed from a continuous layer of porous III-nitride material.

[0262] The porous region may comprise multiple porous layers, and optionally multiple non-porous layers. In a preferred embodiment of the invention, the porous region is a stack of alternating porous and non-porous layers, with the top surface of the stack defining the top of the porous region and the bottom surface of the stack defining the bottom of the porous region.

[0263] Alternatively, the porous region may be a layer of III-nitride material that includes one or more porous regions, such as one or more porous regions in an otherwise non-porous layer of III-nitride material.

[0264] In a preferred embodiment, the porous region or layer may have a lateral dimension (width or length) comparable to the substrate on which it is grown. For example, a conventional substrate wafer size is 1 cm 2 , or 2 inches, 4 inches, 6 inches, 8 inches, 12 inches, or 16 inches in diameter. However, smaller porous regions that do not span the entire substrate may be formed by patterning one or more layers and / or depositing regions of different charge carrier concentrations within the same layer. Thus, the lateral dimensions of the porous layer or region may vary from approximately 1 / 10 of a pixel (e.g., 0.1 μm) to the lateral dimensions of the substrate itself.

[0265] Prior to the porosification step, a doped region of n-doped III-nitride semiconductor material, preferably comprising a layer or stack of layers, may be deposited on the substrate. The III-nitride layer may comprise one or a combination of these elements, Al, Ga, In (three components of a quaternary layer). The thickness of the III-nitride stack is preferably between 10 and 4000 nm. The III-nitride region may have a thickness of 1×10 17 cm -3 ~5×10 20 cm -3 The doping concentration may be 0.1 to 1000 .mu.m.

[0266] Preferably, before being porosified, an intermediate layer of undoped III-nitride material is deposited on the doped material. The thickness of the intermediate layer is preferably between 1 nm and 3000 nm, more preferably between 5 nm and 2000 nm. Being undoped, the intermediate layer remains non-porous after the porosification step, which advantageously provides a good surface for epitaxial growth of further layers of semiconductor.

[0267] In a preferred embodiment, the doped region consists of an alternating stack of doped and undoped layers. In a preferred embodiment, the stack includes 5-50 pairs of layers. The thickness of each highly doped layer may vary from 10 nm to 200 nm, and the lightly doped or undoped layers may have a thickness of 5-180 nm.

[0268] As is known in the art, electrochemical porosification removes material from n-type doped regions of III-nitride materials, creating empty pores in the semiconductor material.

[0269] In a preferred embodiment, the LED structure is formed on a stack of multiple porous layers of III-nitride material. Thus, the porous region may be a stack of III-nitride material layers, at least some of which are porous, rather than a single porous layer of III-nitride material. The stack of porous layers may preferably be a stack of alternating porous and non-porous layers.

[0270] The method may preferably include depositing one or more connecting layers of III-nitride material on a surface of the intermediate layer of III-nitride material, and then growing the n-doped region, the LED light emitting region, and the p-doped region on the connecting layers.

[0271] Alternatively, if there is no non-porous intermediate layer on the porous region, the method may include depositing a connecting layer of III-nitride material on a surface of the porous region of III-nitride material.

[0272] The method may include the further steps of growing an n-doped region, an LED light emitting region, and a p-doped region on the connecting layer.

[0273] The LED produced by this manufacturing method is preferably a tunable LED according to the first aspect of the present invention.

[0274] (Display Device) A first aspect of the present invention provides a tunable LED, the peak emission wavelength of which depends on the drive current density or drive power density supplied to the LED in use.

[0275] This tunable LED can be incorporated into a display device in a variety of ways to provide a variety of desirable device characteristics.

[0276] According to a second aspect of the invention, there may be provided a display device comprising a tunable LED according to the first aspect of the invention, the LED being configured to receive a power supply.

[0277] The display device may include a tunable light emitting diode (LED), the tunable LED comprising: an n-doped portion; A p-doped portion; a light emitting region located between the n-doped portion and the p-doped portion, the light emitting region comprising a light emitting layer that emits light at a peak emission wavelength under an electrical bias applied thereto; the LED is configured to receive a power source, and a peak emission wavelength of the LED is continuously controllable over an emission wavelength range of at least 40 nm by varying the power source.

[0278] The display device preferably comprises a plurality of tunable LEDs according to the first aspect of the invention, each tunable LED configured to receive its own power supply, and each of the plurality of tunable LEDs is controllable such that the peak emission wavelength of each tunable LED is controllable by varying the power supply to that LED.

[0279] The display device preferably comprises a plurality of LED pixels, each of which may comprise a single tunable LED or a plurality of LED sub-pixels, some or all of which may be tunable LEDs as described above.

[0280] Various embodiments of a display device are described and illustrated with reference to the figures.

[0281] In a display device according to the invention, the display device preferably comprises a plurality of LED pixels, preferably each device pixel comprises at least one tunable LED according to the first aspect of the invention. Preferably at least one sub-pixel of each pixel is a tunable LED according to the first aspect of the invention. The display device may comprise a plurality of LED pixels, each device pixel may comprise 1, 2, 3 or 4 tunable LEDs according to the first aspect of the invention.

[0282] In a preferred embodiment of the invention, some or all of the tunable LEDs are preferably configured to receive a variable magnitude of drive current from a power supply such that the magnitude of the drive current to each tunable LED is variable. By varying the magnitude of the drive current to a tunable LED, the peak emission wavelength of that LED can be varied as the display device is used. The drive current supplied to each tunable LED may be individually controllable, whereby the peak emission wavelength of each tunable LED in the display can be individually controlled and varied. Alternatively, the device may be configured such that the same drive conditions are supplied simultaneously to a group of tunable LEDs, whereby all of the tunable LEDs in that group emit light at the same peak emission wavelength when the drive current is on, and the peak emission wavelength of the entire group can be varied by varying the magnitude of the drive current.

[0283] In an alternative embodiment, some or all of the tunable LEDs of a display device may be configured to receive a drive current of a fixed magnitude (i.e., non-variable) that is either on or off. When the fixed drive current is on, these tunable LEDs behave as conventional LEDs and emit light at a single peak emission wavelength determined by the drive conditions supplied to the LEDs. Thus, tunable LEDs configured to receive a drive current of a fixed magnitude may be used as fixed emission wavelength LEDs in a display device.

[0284] Preferably, at least one subpixel of each pixel is a tunable LED according to the first aspect of the invention. Other subpixels may be incorporated into the display device. For example, each pixel of the display device may comprise one or more fixed emission wavelength LED subpixels. The fixed emission wavelength LED subpixels are preferably configured to receive a drive current of a fixed magnitude.

[0285] The device is configured to separately control a drive current provided to each of the plurality of LEDs such that each of the plurality of LEDs is individually drivable.The device is configured to provide a plurality of different drive currents to the plurality of LEDs such that different LEDs are drivable to emit light at different peak emission wavelengths in response to the different drive currents.

[0286] Alternatively, the device is configured to separately control two or more groups of LEDs such that each LED in a group emits at the same peak emission wavelength, and the display device is configured to provide different drive currents to the LEDs in the different groups, such that the LEDs in the different groups are drivable to emit at different peak emission wavelengths in response to the different drive currents.

[0287] The display device preferably comprises a power supply arranged to provide a drive current to the plurality of LEDs. The display device may comprise a power supply unit or may be connectable to a power supply unit.

[0288] The power supply may be a pulsed power supply. The power supply may be configured to operate in a pulse width modulation (PWM) mode or a pulse amplitude modulation (PAM) mode. Preferably, the power supply is configured to operate in a pulse amplitude modulation (PAM mode) and a pulse width modulation (PWM) mode.

[0289] The power supply may be a continuous wave (CW) power supply or a quasi-continuous wave power supply. The power supply may be a constant voltage power supply or a constant current power supply.

[0290] Each light emitting diode is preferably connected to an LED driver configured to provide power to the LED.

[0291] The power supply to the LEDs is preferably regulated or controlled by an LED driver. The LED driver is preferably configured to provide variable magnitude power to the tunable LEDs of the display device. For example, the LED driver can preferably vary the magnitude of the drive current provided to each tunable LED by continuously varying the magnitude of the drive current over a range, or by providing a number of distinct drive current modes having different fixed magnitudes.

[0292] A variety of conventional LED drivers can be used to regulate the power supply to the LEDs. The LED driver can be an integrated circuit (IC), for example, the LED driver can be a CMOS driver or a TFT driver. The driver can be a separate component, such as a backplane IC driver or an on-chip IC driver made from the same GaN epiwafer.

[0293] The LED driver can be connected to a power supply, for example an external power supply (mains power) or a battery.

[0294] A display device may include a controller configured to control power to the LEDs of the device. The controller may be programmed to control the power or drive current provided to the LEDs by the LED drivers. For example, the controller may be programmed or programmable to control the magnitude, duration, and phase of the power provided to each LED of the display.

[0295] The controller may be programmable to control the device in different control modes, for example the controller may be responsive to user input whereby the controller controls the LEDs of the device to operate in a selected mode in response to the user input.

[0296] The controller may be programmable to control the LEDs of the display device in a fixed wavelength emission mode by providing a drive current of a fixed magnitude to the LEDs, the magnitude of the fixed drive current corresponding to the wavelength to be emitted, and / or the controller may be programmable to control the LEDs of the display device in a dynamic wavelength tunable emission mode by providing a drive current of a variable magnitude to the LEDs, the magnitude of the fixed drive current varying corresponding to the wavelength to be emitted at a given time.

[0297] The display device may comprise an array of LED pixels, each pixel comprising two or more sub-pixels, and at least one of the sub-pixels of each pixel being a tunable LED.

[0298] A display device may comprise an array of LEDs, each having the same diode structure and each LED being tunable to emit light at a peak wavelength across the same emission wavelength range.

[0299] The display device may be an augmented reality (AR), mixed reality (MR), or virtual reality (VR) device, or the device may be a smart wearable device, a smart display, or a direct-view display.

[0300] The LED or at least one of the LEDs is preferably a dynamic color tunable LED.

[0301] The display device preferably comprises a porous region of a semiconductor material, preferably a III-nitride semiconductor material, the first and / or second sub-pixels being preferably formed on the porous region as described above in relation to the first aspect.

[0302] Throughout this document, the term "display device" may be interchangeably used with "LED device."

[0303] In the prior art, an array of red, green, and blue (RGB) LED pixels are placed close together so that activating these pixels alone or in combination produces the effect of emitting various secondary colors to a viewer. However, the present invention provides a better alternative, providing a single LED pixel that can be controlled to emit light at a continuous range of different wavelengths. The LED is controlled to emit "true" colors at a variety of different wavelengths, without the need to superimpose the different emission wavelengths of separate LEDs (such as RGB pixels) to arrive at a composite emission wavelength.

[0304] The display device may be a single full color display.

[0305] A display device is provided comprising an array containing a plurality of identical tunable LEDs according to the invention, each LED of the array can be controlled to emit light at the same wavelength or at a different wavelength within the emission wavelength range, the array can also be controlled to turn individual pixels on or off to control the intensity of the light emitted.

[0306] The display device of the present invention may comprise both the tunable LEDs described herein and additional LEDs, either additional tunable LEDs with different emission wavelength ranges or additional conventional single wavelength LEDs. In a preferred embodiment, the tunable LEDs of the present invention may be provided as an array with additional LEDs configured to emit at additional peak emission wavelengths outside the emission wavelength range of the tunable LED. If the additional peak emission wavelengths are outside the emission wavelength range, these wavelengths cannot be obtained using the tunable LEDs. Thus, similar to a conventional RGB array, the tunable LEDs and additional LEDs may be used in combination to obtain an even wider range of possible emission wavelengths.

[0307] A display device of the present invention may comprise an LED array comprising a plurality of LED subpixels according to any of the above aspects of the present invention. Depending on the size of the LED pixels, the array may be an array of mini-LEDs or micro-LEDs.

[0308] In another aspect, an LED display device can be provided with multiple tunable LEDs (or mini-LEDs or micro-LEDs) acting as sub-pixels as described above. In an LED display, each of the multiple LEDs is preferably separately controllable such that the peak emission wavelength of each LED is controllable by varying the power supply to each LED individually. By separately controlling the emission wavelength of each LED, a color display can be provided. However, because each tunable LED can emit over a range of wavelengths rather than a standard single wavelength, a wide range of possible colors can be provided using fewer LEDs than is required for conventional RGB multi-color displays in the prior art.

[0309] In an LED display, a group of multiple tunable LEDs may be configured to receive the same driving conditions from a power supply, such that the peak emission wavelengths of all the tunable LEDs in a group can be controlled simultaneously by varying the power supply to the group.

[0310] The LED display may comprise a first tunable LED having a peak emission wavelength controllable over a first emission wavelength range and a second tunable LED having a peak emission wavelength controllable over either the first emission wavelength range or a second emission wavelength range. The second emission wavelength range may be a separate wavelength range or it may overlap with the first emission wavelength range. Thus, the first and second tunable LEDs may be controlled to emit at separate peak emission wavelengths. For example, a pixel of the LED display device may comprise a first tunable LED subpixel having a peak emission wavelength controllable over the first emission wavelength range and a second tunable LED subpixel having a peak emission wavelength controllable over either the first emission wavelength range or the second emission wavelength range.

[0311] In another preferred embodiment, an LED display may comprise a plurality of tunable LEDs controllable over a first emission wavelength range and at least one further LED configured to emit at a peak emission wavelength outside the first emission wavelength range. For example, the further LED may be configured to emit at a wavelength outside the wavelength range of the tunable LEDs to extend the range of colors obtainable from the display. For example, a pixel of an LED display device may comprise a plurality of tunable LED subpixels controllable over a first emission wavelength range and at least one further LED subpixel configured to emit at a peak emission wavelength outside the first emission wavelength range.

[0312] The multiple tunable LEDs are preferably operable at different peak emission wavelengths within a first emission wavelength range. For example, one of the multiple tunable LEDs may emit at a first wavelength within that range, while another of the multiple tunable LEDs emits at a second wavelength within the first emission wavelength range. In this manner, a wide variety of secondary and complementary colors may be realized.

[0313] In a preferred embodiment, some or all of the multiple tunable LEDs can be operated at the same peak emission wavelength to provide a desired emission intensity at that wavelength. The emission intensity of the LEDs at longer wavelengths is lower than the emission intensity at shorter wavelengths because the longer wavelengths are achieved by reducing the amount of power supplied to the LEDs. Providing multiple tunable LEDs may advantageously enable the display to compensate for this intensity difference by controlling the number of LEDs emitting at the desired wavelength. For example, two or more LEDs may be controlled to emit red wavelengths to increase the brightness of the emitted red light to a level suitable for the display.

[0314] In a preferred embodiment, the LED display comprises a plurality of tunable LEDs controllable to emit light with a peak emission wavelength between 500 nm and 680 nm, or between 520 nm and 675 nm, and the LEDs comprise at least one further LED configured to emit light with a peak emission wavelength less than 560 nm, preferably less than 500 nm. The tunable LEDs are thus controllable to emit light in a range of colours from green through yellow and orange to red, whilst the further LED is configured to emit blue light. These LEDs thus enable the display to emit light over a wide range of wavelengths across the blue to red spectrum.

[0315] In a particularly preferred embodiment, the LED display comprises a plurality of tunable LEDs controllable to emit at a peak emission wavelength between 560 nm and 680 nm, or between 570 nm and 675 nm, and the LEDs comprise at least one further LED configured to emit at a peak emission wavelength below 560 nm, preferably below 500 nm. Thus, the tunable LEDs are controllable to emit in colours ranging from green through yellow and orange to red, whilst the further LED is configured to emit blue light.

[0316] In another preferred embodiment, the LED display comprises a plurality of tunable LEDs controllable to emit light at a peak emission wavelength between 400 nm and 680 nm, or between 450 nm and 630 nm, or between 470 and 610 nm. The tunable LEDs are thus controllable to emit light in a range of colours from purple or blue through green, yellow and orange to red.

[0317] In a further aspect, a display device can be provided that includes a tunable LED configured to receive a drive current and emit light in response to the drive current, where a peak emission wavelength of the tunable LED depends on the amplitude of the drive current supplied to the tunable LED, and where the amplitude of the drive current for the tunable LED is variable between at least two non-zero values ​​during a display frame.

[0318] The tunable LED is preferably a tunable LED according to the first aspect of the invention described above, the LED being configured to receive a power supply, and therefore any of the features of the tunable LED described above are applicable to the display device of the invention.

[0319] The tunable LED is preferably a pixel of a display device, and the peak emission wavelength of the pixel is preferably tunable by varying the drive current supplied to that pixel during operation.

[0320] The tunable LED is preferably controllable to emit a desired spectral output in response to analog drive current pulses, the amplitude of which varies between non-zero values ​​during a single display frame.

[0321] The tunable LED is preferably controllable to emit light at multiple distinct peak emission wavelengths by varying the drive current supplied to the tunable LED among multiple distinct non-zero values ​​during a display frame. For example, the tunable LED may be controllable to emit light at multiple distinct peak emission wavelengths by varying the drive current supplied to the tunable LED among at least three, or at least four, or at least five, or at least six, or at least seven distinct non-zero values ​​during a display frame. Each distinct drive current applied to the tunable LED causes the LED to emit light at a corresponding distinct peak emission wavelength. By applying three drive current pulses with distinct current magnitudes, the tunable LED thus emits light at three distinct peak emission wavelengths, each emission wavelength corresponding to a different input drive current.

[0322] The tunable LED is controllable to emit a desired spectral output during a single display frame in response to a drive current that includes a series of distinct current pulses, the distinct current pulses having a plurality of different amplitudes, the series of distinct current pulses preferably including at least three, or at least five, or at least seven current pulses having different amplitudes.

[0323] The amplitude of the drive current of the tunable LED is preferably variable between at least three, or at least four, or at least five, or at least six, or at least seven non-zero values ​​during one display frame.

[0324] The perceived spectral output of a tunable LED during a display frame is the temporal combination of two or more peak emission wavelengths emitted by the tunable LED in response to two or more non-zero drive currents supplied to the LED during the display frame.

[0325] The duration of each successive drive current pulse determines the brightness of the peak emission wavelength corresponding to that drive current, and therefore the sum of the emission wavelengths that make up the emission spectrum perceived by a detector, e.g., the human eye, viewing a display device.

[0326] By selecting which of the available distinct drive currents to supply to the tunable LEDs during a display frame, the time-averaged emission spectrum perceived by the observer can be varied over a wide color gamut.

[0327] The duration of the display frame may be 50 ms or less, or 45 ms or less, or 40 ms or less. The duration of the display frame is preferably less than or equal to the response time of the detector. The duration of the display frame is preferably equal to or less than the response time of the human eye as the detector, which is about 50 ms.

[0328] Each tunable LED in a multi-LED display device is preferably controllable to reproduce a predetermined spectral output, which corresponds to a temporal combination of multiple peak emission wavelengths emitted during a display frame.

[0329] The display device may comprise an array of tunable LEDs, where each tunable LED is controllable to reproduce a predetermined spectral output corresponding to a temporal combination of multiple peak emission wavelengths emitted during a display frame.

[0330] Preferably, the multiple tunable LED sub-pixels are individually tunable across the display area of ​​the display device.

[0331] The display device may be a large area luminaire for reproducing a programmed illumination light spectrum or a series of illumination light spectra.

[0332] The display device can be configured to generate an emission spectrum whose shape is controllable by application of multiple fixed drive currents.

[0333] The display device may be configured to generate an emission spectrum whose shape is controllable by applying a continuous drive current, in other words, rather than driving a tunable LED by applying one of a number of available discrete drive current levels, the drive current may be provided in the form of a continuous pulse, e.g., an analog-like signal of drive current whose magnitude varies during a display frame.

[0334] The display device may comprise a pulsed current source configured to generate drive current pulses that vary among a number of non-zero values ​​during a display frame. For example, the pulsed current source may be configured to generate drive current pulses that vary among at least two, or at least three, or at least four, or at least five, or at least six, or at least seven non-zero values ​​during a display frame.

[0335] The display device may comprise a pulsed current source configured to generate analog drive current pulses that vary in amplitude during a display frame.

[0336] The display device may include a multiplexer configured to provide separate drive currents to the multiple LEDs.

[0337] The device may be an illumination device, such as a hyperspectral light source.

[0338] A plurality of tunable LEDs ("tunable" LEDs) may be provided in an array to form a display device. Each tunable LED is preferably arranged to form a pixel (or sub-pixel) of the display device. The pixels of the display device may each be configured to receive its own drive current from a pulsed current source configured to generate current pulses (either a series of digital pulses having distinct amplitudes, or analog pulses of varying amplitude). The drive current supplied to each pixel is preferably controllable independently of the current applied to other pixels. The pulsed current source may be configured to supply pulses of drive current to a multiplexer connected to each individual pixel of the display device.

[0339] Current pulses can be designed for two main applications: To accurately represent the spectrum of the image reproduced by a display device, or Adjusting the current pulse for each LED pixel or subpixel so that they all emit the same emission wavelength and intensity across the entire display, compensating for non-uniformities in LED performance due to the manufacturing process. In this case, the tuned display is driven with the adjusted current pulses to combine the emission from two or more subpixels to produce the perceived color of each pixel.

[0340] Aspects of the invention can provide a display device formed from light emitting diodes preferably comprising porous semiconductor material, wherein each pixel is composed of a number of sub-pixels, the peak emission wavelength of each sub-pixel being dependent on the drive current density, and wherein the peak emission wavelength of at least one of the sub-pixels is not intentionally fixed during operation.

[0341] The peak emission wavelength of at least one sub-pixel that has a peak emission that is not fixed in operation is preferably controllable by varying the drive current density supplied to that sub-pixel in operation.

[0342] A display device can be provided formed from light emitting diodes comprising a porous semiconductor material, each pixel being composed of a number of sub-pixels, Each sub-pixel has the same diode structure, the display device is configured to supply a drive current density to each sub-pixel separately, and the peak emission wavelength of each sub-pixel is independently controllable by varying the drive current density supplied to the sub-pixel.

[0343] Each subpixel may consist of an LED formed on a porous region of a semiconductor material.

[0344] Each LED subpixel is configured to receive a power source, and at least one subpixel is a tunable subpixel whose peak emission wavelength is controllable over a range of emission wavelengths by varying the power source.

[0345] The peak emission wavelength of the tunable sub-pixel is preferably controllable over a range of emission wavelengths by varying the current density of the power supply or by varying the power density of the power supply.

[0346] The peak emission wavelength of the tunable subpixel is preferably controllable over an emission wavelength range of at least 40 nm, or at least 50 nm, or at least 60 nm, or at least 70 nm, or at least 80 nm, and preferably up to 100 nm, or 110 nm, or 120 nm, or 140 nm, or 160 nm, or 180 nm, or 200 nm, by varying the power source.

[0347] In a preferred embodiment, each subpixel preferably has the same diode structure, and the drive current density alone is used to control the peak wavelength of emission from each subpixel.

[0348] Preferably, at least one of the sub-pixels is operable in a plurality of modes, the sub-pixel being configured to emit at a distinct peak emission wavelength in each of the plurality of modes. Preferably, the sub-pixel is driven with a different current density in each mode, thereby causing the sub-pixel to emit at different peak wavelengths in the different modes.

[0349] The mode of the sub-pixel is preferably dynamically changeable during operation of the display device.

[0350] Each sub-pixel of the display device is preferably a tunable sub-pixel.

[0351] The display device may be configured to vary the emission peak wavelength of the or each of the tunable subpixels at regular time intervals. For example, the display device may be configured to alternate or swap the emission wavelengths of the subpixels at regular time intervals to distribute heating of the subpixels caused by high current density emission wavelengths. The time interval may be a display frame or shorter.

[0352] Display devices may be configured to vary the emission wavelength of a sub-pixel by varying the drive current applied to the sub-pixel at regular intervals.

[0353] The display device may comprise a plurality of sub-pixels configured to emit light at peak wavelengths within the same color, where the sub-pixels are configured to emit light at different peak wavelengths within the color. In a preferred embodiment, the device may comprise four sub-pixels, two of which are pixels configured to emit light at peak wavelengths within the same color. The sub-pixels configured to emit light at peak wavelengths within the same color preferably have identical diode structures, and the device is configured to drive them with different current densities to produce different peak emission wavelengths.

[0354] The display device may comprise a plurality of tunable sub-pixels configured to emit light at different peak emission wavelengths in response to different applied current densities.

[0355] Preferably, at least one sub-pixel is controllable to emit at a peak wavelength ranging from 450 nm to 530 nm. Preferably, the peak emission wavelength of the tunable sub-pixel is controllable from 450 nm to 630 nm or greater.

[0356] Optionally, at least one subpixel is configured to be driven with a single current density and therefore emit light at a single peak wavelength, and preferably may be configured to emit red light at a single peak wavelength.

[0357] The display device preferably comprises a plurality of tunable sub-pixels configured to emit light at different peak emission wavelengths in response to different applied current densities, where each of the plurality of tunable sub-pixels is controllable to emit light at a peak wavelength spanning a range of wavelengths.

[0358] Each tunable subpixel may preferably have a peak emission wavelength controllable over a range from 450 nm to 630 nm or greater. The display device may be configured to vary the current density supplied to each of the tunable subpixels such that by varying the current density over a continuous current density range, the peak emission wavelength varies over a continuous wavelength range from 450 nm to 630 nm or greater.

[0359] Each tunable subpixel can be configured to emit over a range of wavelengths above or below a central wavelength of the subpixel, preferably over a range of wavelengths 20 nm or more below or above the central wavelength. Each tunable subpixel within a pixel of a display device can have a different central wavelength, as desired.

[0360] The display device may comprise a first subpixel configured to emit light at a peak emission wavelength between 430 nm and 480 nm, and / or a second subpixel configured to emit light at a peak emission wavelength between 500 nm and 540 nm, and / or a third subpixel configured to emit light at a peak emission wavelength between 580 nm and 620 nm.

[0361] By incorporating tunable LEDs into a display device, the available color gamut of the display can be advantageously expanded beyond what is achievable by operating each sub-pixel at a fixed peak emission wavelength.

[0362] The number of sub-pixels in a pixel of the display device may be less than 3, preferably less than 2. One or more of the sub-pixels may have a fixed peak emission wavelength.

[0363] The shift in peak emission wavelength of the tunable subpixel as a function of drive current density is preferably greater than 20 nm / decade.

[0364] The peak emission wavelength used to display a particular color point may be selected to maximize the overall operation of the display.

[0365] Preferably, each sub-pixel has the same diode structure, and the peak emission wavelength of the sub-pixels is controlled by providing different current densities to the different sub-pixels.

[0366] (Contact pad ratio) The tunable LED of the first embodiment allows the same LED diode structure to emit light at a range of different peak emission wavelengths under different current densities. The main advantage of this is that a single tunable LED can be controlled to emit light at a variety of different emission wavelengths. The inventors have realized that the present invention can also be utilized to provide a variety of fixed emission wavelength LEDs using the same semiconductor material and diode structure. Thus, instead of varying the current density supplied to the LED by varying the drive current during use, the current density experienced by a given LED can be set by fixing the magnitude of the drive current to that LED and controlling the area of ​​that LED that receives the drive current.

[0367] Thus, some or all of the tunable LEDs of the display device may be configured to receive a fixed magnitude (i.e., non-variable) drive current that is either on or off. When the fixed drive current is on, these tunable LEDs behave as conventional LEDs and emit light at a single peak emission wavelength that is determined by the current density resulting from the fixed drive current and the area of ​​the LED receiving the drive current. Thus, tunable LEDs may be used as fixed emission wavelength LEDs in the display device. The drive current provided to some or all of the subpixels may be the same, with only differences in the LED area and electrical contact area resulting in different drive current densities experienced by different subpixels. By providing separate LEDs that receive different current densities, multiple LEDs having the same diode structure may be used to emit light at different peak emission wavelengths. This may advantageously eliminate the need to combine separate semiconductor material systems to achieve different emission colors, significantly simplifying the manufacturing process of the display device.

[0368] The display device may comprise a plurality of tunable LED subpixels configured to emit light at different peak emission wavelengths. The device may comprise a first subpixel comprising a first light-emitting layer having a first light-emitting area A1, and a first electrical contact contacting the first subpixel over a first contact area and configured to apply a drive current to the first subpixel. The first subpixel may have a first contact ratio defined by the ratio of the first contact area: the first light-emitting area A1. The device may further comprise a second subpixel comprising a second light-emitting layer having a second light-emitting area A2, and a second electrical contact contacting the second subpixel over a second contact area and configured to apply a drive current to the second subpixel. The second subpixel may have a second contact ratio defined by the ratio of the second contact area: the second light-emitting area A2. The first contact ratio is preferably different from the second contact ratio, such that the two subpixels are configured to emit light at different peak wavelengths in response to the same drive current.

[0369] Each tunable LED is a tunable LED as described above in relation to the first aspect of the invention.

[0370] The display device preferably comprises a porous region of a semiconductor material, preferably a III-nitride semiconductor material, The first and / or second sub-pixels are preferably formed on the porous region.

[0371] The display device may comprise a plurality of pixels, each pixel of the display device comprising a first sub-pixel and a second sub-pixel as defined above.

[0372] A preferred embodiment may provide a display device comprising at least two LED subpixels, each subpixel having a light-emitting layer with a light-emitting area, and electrical contacts contacting the subpixels over a contact area, Each subpixel has a contact ratio determined by the ratio of contact area to light-emitting area for that subpixel, and at least two subpixels do not have the same contact ratio.

[0373] At least two sub-pixels having different contact ratios are preferably configured to emit at different peak emission wavelengths under the same drive current.

[0374] Subpixel Emission Area A i is the active light-emitting area of ​​the subpixel when viewed from above. This is sometimes referred to as the mesa area of ​​the subpixel because LED subpixels are typically formed as mesas with vertical sidewalls, as is known in the art. The light-emitting area is the area of ​​the light-emitting layer that is electrically activated when a drive current is applied to the subpixel.

[0375] Conventional LED devices experience minimal shifts in the wavelength of the emission light produced by the LED device in response to changes in drive current, however, the inventors have discovered that by providing an LED on a porous III-nitride template, the wavelength shift can be amplified and controlled to a greater extent than conventional LED materials, as will be discussed in more detail in connection with the first aspect of the invention.

[0376] This allows multiple subpixels to be combined together on the same wafer, reducing the number of mass transfer operations required to fabricate a display. In particular, multiple subpixels may be formed by etching a single LED diode structure into separate subpixel mesas. When this is done, the separate mesas each have the same diode structure. However, by processing the LED subpixel mesas into a display device using the present invention, the subpixel mesas may be made to emit at different peak emission wavelengths, despite being formed from the same semiconductor material and the same diode structure.

[0377] Because the drive current density experienced by a given LED or LED subpixel is determined by both the absolute drive current (magnitude of the drive current) and the area of ​​the LED through which the current flows, the inventors have discovered that by controlling the contact area through which the electrical contacts supply drive current to the diode structure of the LED, it is possible to manipulate the drive current density experienced by the LED.

[0378] In particular, the inventors have found that by controlling the "contact ratio," i.e., the ratio of contact area to emissive area of ​​a given subpixel, the peak emission wavelength of a subpixel in response to a given drive current can be varied.

[0379] By varying the contact ratio, different LED subpixels having different areas but otherwise identical diode structures (the same layered LED structure with n-type, active, and p-type layers formed from the same materials) will therefore emit different peak emission wavelengths in response to the same absolute drive current.

[0380] The contact ratio of each subpixel determines the peak emission wavelength emitted in response to a drive current, so if the contact ratios of the first and second subpixels are different, this means that the first and second subpixels are configured to emit light at different peak emission wavelengths in response to the same drive current.

[0381] The first subpixel may be configured to emit light at a first peak emission wavelength in response to a drive current having a first magnitude, and the second subpixel may be configured to emit light at a second peak emission wavelength different from the first peak emission wavelength in response to a drive current having the first magnitude, the difference in emission wavelength being attributable solely to a difference in the first and second contact ratios.

[0382] The first LED subpixel has a diode structure and preferably the second LED subpixel also has the same diode structure.

[0383] Luminous area A i is the area of ​​the light emitting region when viewed from above. The light emitting area is preferably arranged to extend or span the entire subpixel diode structure, so that the light emitting area is the same as the subpixel area when viewed from above.

[0384] The first and second subpixels are preferably formed from the same semiconductor material. Particularly preferably, the first and second subpixels are formed from the same LED structure, for example by etching the LED structure to form the first and second subpixel mesas. In such a case, the layer structure and materials of the different subpixels are the same, so that any difference in emission wavelength is determined only by differences in the drive current and / or contact ratio between the electrical contacts and the corresponding subpixels.

[0385] Both sub-pixels preferably both comprise light emitting regions that comprise InGaN semiconductor material.

[0386] The first and second contact areas are the surface areas that the first and second contacts contact with the first and second subpixels, respectively.

[0387] In some preferred embodiments, the first light-emitting area A1 is the same size as the second light-emitting area A2. The first contact area is different from the second contact area because the first and second subpixels have different contact ratios.

[0388] In alternative embodiments, the first light-emitting area A1 is a different size than the second light-emitting area A2. The first contact area may be the same size as the second contact area, or alternatively the contact areas may be different. As long as the first and second contact ratios are not the same, the two subpixels will emit light at different peak wavelengths in response to the same drive current.

[0389] The different first and second contact areas are configured to convert drive currents having the same magnitude into different current densities at the first and second subpixels.

[0390] The first subpixel can receive a first current density through the first contact area in response to a drive current having a first magnitude, while the second subpixel receives a second current density through the second contact area in response to the drive current having the first magnitude. If the first and second contact areas are different, the second current density will be different from the first current density.

[0391] The contact ratio is defined as the ratio of the contact area to the light-emitting area (contact area / light-emitting area).

[0392] The lower the contact ratio (smaller contact area compared to the light emitting area), the shorter the peak emission wavelength of that subpixel in response to a given drive current.

[0393] The higher the contact ratio (larger contact area compared to the light emitting area), the longer the peak emission wavelength of that subpixel in response to a given drive current.

[0394] In some embodiments, the first contact area is smaller than the second contact area, such that a drive current having a first magnitude applied to the first subpixel via the first electrical contact is passed through a smaller contact area than the same drive current applied to the second subpixel via the second electrical contact, such that the first subpixel experiences a first current density that is higher than a second current density experienced by the second subpixel.

[0395] The first subpixel may be configured to emit light at a first peak emission wavelength that is shorter than a second peak emission wavelength emitted by the second subpixel in response to a drive current having a first magnitude, such that although the absolute same drive current may be applied to both subpixels, the two subpixels will emit light at different peak wavelengths due to the different contact ratios of the two subpixels.

[0396] The contact area of ​​the electrical contact on the subpixel can be controlled by varying the size of the electrical contact. Alternatively, a masking (passivation) layer can be provided on the subpixel, the masking layer comprising an opening through which the electrical contact contacts the subpixel. The size of the opening in the masking layer can thus determine the contact area between the electrical contact and the subpixel. The masking layer advantageously acts as a current limiting layer to limit the current density.

[0397] The first subpixel may include a first masking layer, the first masking layer including a first opening through which the first electrical contact contacts the first subpixel, whereby the first opening defines a first contact area.

[0398] The second subpixel may include a second masking layer having a second opening through which the second electrical contact contacts the second subpixel, whereby the second opening defines a second contact area.

[0399] The first and / or second electrical contacts may be p-type electrical contacts or n-type electrical contacts.

[0400] In some embodiments, the first electrical contact contacts a p-doped portion of the first subpixel diode structure and the second electrical contact contacts a p-doped portion of the second subpixel diode structure.

[0401] In another embodiment, the first electrical contact contacts an n-doped portion of the first subpixel diode structure and the second electrical contact contacts an n-doped portion of the second subpixel diode structure.

[0402] The present invention is not limited to only two sub-pixels: a display device may comprise multiple sub-pixels, each having a different contact ratio.

[0403] The display device may comprise a plurality of subpixels having a first contact ratio, a plurality of subpixels having a second contact ratio, and optionally a plurality of subpixels having a third contact ratio, such that in response to a standard drive current having a set magnitude, the different contact ratios of the subpixels may cause the subpixels to emit light at different wavelengths corresponding to their contact ratios.

[0404] the display device comprises a third subpixel comprising a third light-emitting layer having a third light-emitting area A1; a third electrical contact contacting the third subpixel over a third contact area and configured to apply a drive current to the third subpixel; and the third subpixel has a third contact ratio defined by a ratio of the third contact area:the third light-emitting area A1. The third contact ratio is preferably different from the first and second contact ratios.

[0405] Thus, in response to the same drive current, the third sub-pixel may emit light at a third peak emission wavelength different from the first and second peak wavelengths in response to a drive current having the first magnitude.

[0406] In a particularly preferred embodiment, the first, second and third subpixels are configured to emit light at red, green and blue wavelengths in response to the same drive current, and the display device may thus be a red-green-blue (RGB) display device.

[0407] A display device may comprise a plurality of pixels, each of which may comprise two or more sub-pixels, preferably three or more sub-pixels.

[0408] The first subpixel and the second subpixel may be disposed on a common n-type conductive layer of semiconductor material.

[0409] The display device may comprise a driver circuit configured to control a drive current supplied to each sub-pixel of the display device.

[0410] The first and second light emitting areas are preferably the footprints of the first and second light emitting layers over the porous region. In a preferred embodiment, the first and second subpixels may be formed entirely over the porous region of the display device.

[0411] The first and / or second and / or third electrical contacts may comprise titanium, platinum, chromium, aluminum, nickel, gold, or indium tin oxide (ITO), or any other material known in the art to provide suitable electrical contacts on a semiconductor device.

[0412] (Contact ratio between different subpixel colors) Depending on the size (area) of the subpixel compared to the contact area, the inventors have found that the distance that the current spreads outward from the electrical contact depends more on the contact area than on the total area of ​​the LED mesa. For example, for LEDs where the contact area is much smaller than the area of ​​the LED, further increasing the mesa area will not affect the peak emission wavelength because the current spreading may be limited to a relatively small area around the electrical contact, regardless of the overall size of the LED mesa. Thus, the inventors have realized that the difference in applied current density may be better defined by reference to the ratio of the contact areas between different LEDs or different LED subpixels.

[0413] In accordance with an aspect of the present invention, a display device can be provided that includes a plurality of LED subpixels configured to emit light at different peak emission wavelengths. The device includes: a first subpixel and a first electrical contact in contact with the first subpixel over a first contact area AC1 and configured to apply a drive current to the first subpixel; a second subpixel and a second electrical contact contacting the second subpixel over a second contact area AC2 and configured to apply a drive current to the second subpixel; It may comprise:

[0414] The LED sub-pixels configured to emit at different peak emission wavelengths are preferably tunable LEDs according to the first aspect above.

[0415] The first contact area AC1 may be a different size than the second contact area AC2. The device may have a color contact ratio defined by the ratio of the first contact area AC1 to the second contact area AC2.

[0416] If the same drive current I is supplied to both subpixels, the color contact ratio determines the relationship between the different current densities J experienced by the two subpixels: the subpixel with the smaller contact area will experience a higher current density J from the same drive current I than the subpixel with the larger contact area.

[0417] The current density experienced by a subpixel is determined by the following formula: J=I / AC(contact area).

[0418] Thus, if a fixed drive current I is supplied to two subpixels through two electrical contacts with different contact areas AC1 and AC2, the difference in the contact areas is ΔAC=AC1-AC2, and the difference in current densities experienced by the two subpixels is ΔJ=I / ΔAC.

[0419] The current density required for a subpixel to emit at a desired peak emission wavelength is either known or can be readily determined by conventional conversion techniques.

[0420] To provide two subpixels emitting at the two desired peak emission wavelengths, the two required current densities J are thus known and ΔJ can be calculated, from which ΔAC between the first and second contact areas can be determined.

[0421] The ratio of the contact areas required to obtain different colors is also fixed.

[0422] In a preferred embodiment, the display device comprises a first subpixel and a first electrical contact contacting the first subpixel over a first contact area AC1 and configured to apply a drive current to the first subpixel; a second subpixel and a second electrical contact configured to contact the second subpixel over a second contact area AC2 and apply a drive current to the second subpixel. The first contact area AC1 is a different size than the second contact area AC2. The size of the first contact area AC1 is selected such that the first subpixel emits red light when a drive current I is applied through the first contact. The size of the second contact area AC2 is selected such that the second subpixel emits green light when a drive current I is applied through the second contact.

[0423] The ratio of the two contact areas is R red / green =AC1(red) / AC2(green).

[0424] Since the current density and the contact area are inversely proportional to each other by J=I / AC, the ratio R red / green =AC1(red) / AC2(green)=J2(green) / J1(red).

[0425] If I is fixed, the peak wavelength is W peak ≒J≒1 / AC.

[0426] Since J has a particular range within which the desired visible wavelengths are emitted by the subpixel, the range of the contact area AC is also limited. [Table 1]

[0427] However, since I cannot be constrained, the emitted wavelength is not determined by AC alone.

[0428] To control J within a particular range, AC will vary proportionally to the drive current I.

[0429] In order to reduce the I portion, the color relationship between different sub-pixels can be fixed by using the ratio of contact area between different colors under the same I. R=Red. Y=Yellow. G=Green. [Table 2]

[0430] In a preferred embodiment, a display device is provided that includes a plurality of LED subpixels configured to emit light at different peak emission wavelengths. a first subpixel and a first electrical contact in contact with the first subpixel over a first contact area AC1 and configured to apply a drive current to the first subpixel; a second subpixel and a second electrical contact contacting the second subpixel over a second contact area AC2 and configured to apply a drive current to the second subpixel; and a third subpixel and a third electrical contact contacting the third subpixel over a third contact area AC3 and configured to apply a drive current to the third subpixel; It may comprise:

[0431] The first contact area AC1 may be a different size than the second contact area AC2 and the third contact area AC3. The second contact area AC2 may be a different size than the first contact area AC1 and the third contact area AC3. The device may have a color contact ratio defined by the ratio of the first contact area AC1 to the second contact area AC2 and the ratio of the first contact area AC1 to the third contact area AC3.

[0432] The first subpixel is preferably a red subpixel. The second subpixel is preferably a green subpixel. The third subpixel is preferably a blue subpixel. The device may have a red / green color ratio determined by the ratio of the first contact area AC1 to the second contact area AC2, and a red / blue color ratio determined by the ratio of the first contact area AC1 to the third contact area AC3.

[0433] Alternatively, the first subpixel may be a red subpixel, the second subpixel may be a yellow subpixel, and the third subpixel may be a green subpixel. The device may have a red / yellow color ratio determined by the ratio of the first contact area AC1 to the second contact area AC2, and a red / green color ratio determined by the ratio of the first contact area AC1 to the third contact area AC3. The red / yellow color ratio is preferably between 1.5:1 and 7:1. The red / green color ratio is preferably at least 10:1. / / J=I / AC→R 1 / 2 =AC1 / AC2=J2 / J1 (when the same current is injected)

[0434] In use, the display device is preferably controlled by supplying a fixed drive current I to all sub-pixels of the display device. Since all sub-pixels receive the same magnitude of drive current, the drive current densities experienced by different sub-pixels will differ based primarily on their respective contact areas. When the same drive current I is supplied to both sub-pixels, the color contact ratio determines the relationship between the different current densities J experienced by the two sub-pixels.

[0435] The method of manufacturing the display may include forming a first electrical contact on the first subpixel over a first contact area AC1 and contacting the first subpixel, and forming a second electrical contact on the second subpixel over a second contact area AC2. The first contact area AC1 is preferably a different size than the second contact area AC2.

[0436] The method may include forming first and second tunable LED subpixels according to the first aspect described above.

[0437] The ratio of the first contact area AC1 to the second contact area AC2 defines the color contact ratio of the device.

[0438] The current density required for a subpixel to emit at a desired peak emission wavelength is either known or can be readily determined by conventional conversion techniques.

[0439] To provide two subpixels emitting at the two desired peak emission wavelengths, the two required current densities J are thus known and the required ΔJ between the two subpixels can be calculated, from which ΔAC between the first and second contact areas can be determined.

[0440] To fix the color relationship between the different sub-pixels, the ratio of the contact areas required to obtain the different colors is also fixed: R=Red, Y=Yellow, G=Green.

[0441] As discussed above, the contact area of ​​the red pixels is formed to be at least 10 times larger than the contact area of ​​the green pixels, and the contact area of ​​the red pixels is formed to be approximately 1.5 to 7 times larger than the contact area of ​​the yellow pixels.

[0442] In a preferred embodiment, the first contact area AC1 is formed to a different size than the second contact area AC2. The size of the first contact area AC1 is selected such that the first subpixel emits red light when a drive current I is applied through the first contact. The size of the second contact area AC2 is selected such that the second subpixel emits green light when a drive current I is applied through the second contact. In this embodiment, AC1 is formed to be at least 10 times the area of ​​AC2.

[0443] The ratio of the two contact areas is R red / green =AC1(red) / AC2(green).

[0444] In a preferred embodiment, a method for manufacturing a display device comprises the steps of: a first subpixel and a first electrical contact in contact with the first subpixel over a first contact area AC1 and configured to apply a drive current to the first subpixel; a second subpixel and a second electrical contact contacting the second subpixel over a second contact area AC2 and configured to apply a drive current to the second subpixel; and a third subpixel and a third electrical contact contacting the third subpixel over a third contact area AC3 and configured to apply a drive current to the third subpixel; The method includes forming a

[0445] All subpixels of the device are preferably formed with the same LED diode structure.

[0446] The first contact area AC1 is preferably a different size than the second contact area AC2 and the third contact area AC3. The second contact area AC2 is preferably a different size than the first contact area AC1 and the third contact area AC3. The device may have a color contact ratio defined by the ratio of the first contact area AC1 to the second contact area AC2 and the ratio of the first contact area AC1 to the third contact area AC3. If the three contact areas are different sizes and the subpixels have the same tunable LED diode structure, the three subpixels will emit different peak wavelengths in response to the same magnitude of drive current.

[0447] The first subpixel is preferably a red subpixel. The second subpixel is preferably a green subpixel. The third subpixel is preferably a blue subpixel. The device may have a red / green color ratio determined by the ratio of the first contact area AC1 to the second contact area AC2, and a red / blue color ratio determined by the ratio of the first contact area AC1 to the third contact area AC3.

[0448] Alternatively, the first subpixel may be a red subpixel, the second subpixel may be a yellow subpixel, and the third subpixel may be a green subpixel. The device may have a red / yellow color ratio determined by the ratio of the first contact area AC1 to the second contact area AC2, and a red / green color ratio determined by the ratio of the first contact area AC1 to the third contact area AC3. The red / yellow color ratio is preferably between 1.5:1 and 7:1. The red / green color ratio is preferably at least 10:1.

[0449] (Pixel size and shape) In an aspect of the invention, there is provided a display device comprising a light emitting diode (LED), preferably comprising a porous semiconductor material. The device may comprise a pixel comprising a plurality of sub-pixels, each having a light emitting layer. The first subpixel has a first light-emitting layer having a first area A1, and the second subpixel has a second light-emitting layer having a second area A2 different from the first area A1. The first sub-pixel is configured to emit light at a first peak wavelength and the second sub-pixel is configured to emit light at a second peak wavelength that is different from the first peak wavelength.

[0450] Throughout this document, the term "display device" may be interchangeably used with "LED device."

[0451] The area A of a subpixel is the active light-emitting area of ​​the subpixel when viewed from above. This is referred to as the mesa area of ​​the subpixel because LED subpixels are formed as mesas with vertical sidewalls, as is known in the art. This area is the area of ​​the light-emitting layer that is electrically activated when a drive current is applied to the subpixel.

[0452] Thus, in the present invention, a display device may comprise multiple LED sub-pixels having different relative areas that emit light at different emission wavelengths in response to the same drive current.

[0453] The invention may relate to displays in which the emission colour of a sub-pixel is controlled by the total area of ​​the sub-pixel.

[0454] Conventional LED devices experience a minimal shift in the wavelength of the emission light produced by the LED device in response to changes in drive current; however, the inventors have discovered that by providing an LED on a porous III-nitride template, the wavelength shift can be expanded and controlled to a greater extent than conventional LED materials.

[0455] This allows multiple sub-pixels to be combined together, reducing the number of mass transfer operations required to manufacture a display.

[0456] The LED configuration can be selected to achieve a number of different results, such as a specified peak wavelength of multiple LEDs at a given current, a specified emission intensity at a given wavelength, a specified brightness at a given wavelength, etc.

[0457] By providing the LED on a porous template of III-nitride material, as described above, a tunable LED can be provided that has a continuous correlation between peak emission wavelength and drive current.

[0458] Because the drive current density experienced by a given LED or LED subpixel is determined by both the absolute drive current and the area of ​​the LED through which the current flows, it is possible to manipulate the drive current density experienced by the LED by controlling the area or size of the LED.

[0459] Different LEDs having different areas but otherwise identical diode structures (the same layered LED structure of n-type layers, active layers, and p-type layers) will therefore emit different peak emission wavelengths in response to the same magnitude of drive current.

[0460] In a display device of the present invention, at least one subpixel may be a tunable subpixel, and the display device may be configured to supply a variable drive current to the tunable subpixel such that the tunable subpixel emits light at different peak emission wavelengths in response to different drive currents.

[0461] In a preferred embodiment, the first subpixel is a tunable subpixel configured to emit light at a first peak emission wavelength in response to a first drive current applied to the first subpixel, and to emit light at a third peak emission wavelength in response to a third drive current applied to the first subpixel.

[0462] Similarly, the second subpixel may be a tunable subpixel configured to emit light at a second peak emission wavelength in response to a second drive current applied to the second subpixel, and to emit light at a fourth peak emission wavelength in response to a fourth drive current applied to the second subpixel.

[0463] The inventors have found that by growing the n-doped, light emitting, and p-doped portions of an LED on a porous region of III-nitride material, the same LED can advantageously be made to emit light at a range of peak emission wavelengths, rather than one particular wavelength. The peak emission wavelength of the LED can be varied across the emission wavelength range by varying the power supply supplied to the LED. Thus, the present invention can include tunable LEDs that can be controlled to emit light at any wavelength across a continuous emission wavelength range.

[0464] Individual tunable LED subpixels may be provided as part of a pixel that includes multiple subpixels, which are equivalent to independent LED devices since each subpixel can be separately controlled.

[0465] The structure and properties of the tunable LED subpixel are described above in relation to the first embodiment.

[0466] The display device may be configured to supply the same fixed drive current I to both the first and second sub-pixels.

[0467] The display device may be configured to supply a first drive current I1 to the first sub-pixel and a second drive current I2 to the second sub-pixel, the second drive current having a different magnitude than the first drive current.

[0468] The first subpixel may have a first form or shape and the second subpixel may have a second form or shape. The first form or shape may be different from the second form or shape, or alternatively, the first and second forms or shapes may be the same.

[0469] In one preferred embodiment, the first sub-pixel is circular in shape and the second sub-pixel is formed as a ring concentrically disposed around the circular first sub-pixel.

[0470] Preferably, the first subpixel and the second subpixel have the same diode structure, so that the emission characteristics of the subpixels can vary as a result of differences in the shapes and sizes of the subpixels and differences in the drive currents applied to the subpixels, rather than as a result of the structure of the diode layer.

[0471] A display device may comprise a plurality of pixels, each of which may comprise two or more sub-pixels, preferably three or more sub-pixels.

[0472] The first subpixel and the second subpixel may be disposed on a common n-type conductive layer of semiconductor material.

[0473] The display device may comprise a driver circuit configured to control a drive current supplied to each sub-pixel of the display device.

[0474] The first subpixel may be configured to emit light at a first peak wavelength with a first luminous intensity in response to a first drive current applied to the first subpixel, and / or the second subpixel may be configured to emit light at a second peak wavelength with a second luminous intensity in response to a second drive current applied to the second subpixel.

[0475] The first subpixel may be configured to emit light at a first peak wavelength and a first brightness in response to a first drive current applied to the first subpixel, and / or the second subpixel may be configured to emit light at a second peak wavelength and a second brightness in response to a second drive current applied to the second subpixel.

[0476] The first area A1 of the first light-emitting layer may be larger than the second area A2 of the second light-emitting area, or the first area A1 of the first light-emitting layer may be smaller than the second area A2 of the second light-emitting area.

[0477] The first area A1 of the first light-emitting layer can have a different shape than the second area A2 of the second light-emitting layer.

[0478] The first area and the second area are preferably the footprints of the first and second light-emitting layers on the porous region. In a preferred embodiment, the first and second sub-pixels may be formed entirely over the porous region of the display device.

[0479] (How to control an LED display device) In a further aspect, a method for controlling an LED display device is provided.

[0480] The method includes separately controlling power to each of a plurality of LEDs (which may be LED subpixels) in an LED display, such that the peak emission wavelength of each LED is controlled to emit at a desired peak emission wavelength within its emission wavelength range.

[0481] Each LED or LED subpixel in the display may preferably be controlled as described above in relation to the previous embodiment.

[0482] The method may include providing first drive conditions to a first group of LEDs such that the first group of LEDs all emit at a first wavelength, and providing second drive conditions to a second group of LEDs such that the second group of LEDs all emit at a second wavelength.

[0483] The method may include controlling a power supply to a first tunable LED (e.g., an LED subpixel) such that the first tunable LED emits light at a first peak emission wavelength within a first emission wavelength range, and controlling a power supply to a second tunable LED such that the second tunable LED emits light at a second peak emission wavelength, which may be a wavelength within the first emission wavelength range or the second emission wavelength range.

[0484] The method may include controlling power to a first plurality of tunable LEDs in an LED display such that the first plurality of LEDs emit light at a peak emission wavelength within a first emission wavelength range, and controlling power to at least one further LED such that the first plurality of LEDs emit light at a peak emission wavelength outside the first emission wavelength range. For example, the plurality of tunable LEDs may be green-red LEDs capable of emitting light from green to red wavelengths, and the further LED may be a blue LED for emitting blue light not achievable by the tunable LED alone.

[0485] The method can include providing different power sources to the multiple tunable LEDs such that the multiple tunable LEDs emit light at different peak emission wavelengths within the first emission wavelength range.

[0486] The method may include powering some or all of the first plurality of tunable LEDs to emit light at a first peak emission wavelength to provide a desired light emission intensity at the first peak emission wavelength. Since the intensity of the emitted light depends on the power supplied to the LEDs, longer wavelengths will be emitted at a lower intensity than shorter wavelengths. By operating some or all of the plurality of LEDs at the same wavelength, the overall intensity of the emitted light may be controlled.

[0487] In a particularly preferred embodiment, the method may include powering a plurality of tunable LEDs such that they emit at a peak emission wavelength of from 560 nm to 680 nm, or from 570 nm to 675 nm, and powering at least one further LED such that it emits at a peak emission wavelength less than 560 nm, preferably less than 500 nm.

[0488] The method may include varying the emission wavelength of the LED by varying a drive current applied to the LED at regular intervals.

[0489] The method may include alternating or swapping the emission wavelengths of the LEDs or LED sub-pixels at regular time intervals to distribute heating of the sub-pixels caused by emission wavelengths of high current density.

[0490] In a further aspect of the present invention there is provided a method of controlling a display device comprising a tunable LED, the method comprising: The method includes providing a drive current to a tunable LED and varying an amplitude of the drive current among multiple non-zero values ​​during a single display frame such that the tunable LED generates multiple peak emission wavelengths during the single display frame.

[0491] By varying the amplitude of the drive current among multiple non-zero values ​​during a single display frame, multiple peak emission wavelengths are generated from the tunable LED within the duration of the display frame, such that the temporal combination of the multiple peak emission wavelengths reproduces an optical spectrum.

[0492] This advantageously allows the observer to perceive a particular light spectrum being emitted by an LED or by multiple LEDs, which light spectrum is not normally emitted by LEDs. For example, the temporal combination of multiple peak emission wavelengths can produce light of a particular color that does not correspond to the emission band gap of known semiconductor materials. Thus, using this method, the range of colors that can be perceived as emitted by an LED is significantly expanded.

[0493] The duration of a display frame may be 50 ms or less, or 45 ms or less, or 40 ms or less. The duration of a display frame is preferably less than or equal to the response time of the detector. The duration of a display frame is preferably less than or equal to the response time of the human eye as the detector, which is about 50 ms.

[0494] The method may include providing a first drive current to a tunable LED and varying an amplitude of the first drive current between multiple non-zero values ​​during a single display frame such that the tunable LED generates multiple peak emission wavelengths during the single display frame; and providing a second drive current to a second tunable LED and varying an amplitude of the second drive current between multiple non-zero values ​​during the single display frame such that the second tunable LED generates multiple peak emission wavelengths during the single display frame.

[0495] The display device may comprise a plurality of tunable LEDs, and the method may preferably include providing a separate drive current to each LED, the drive currents provided to the different LEDs may be of different magnitudes and durations, such that the different LEDs emit different emission spectra during the same display frame.

[0496] Each tunable LED in a multi-LED display device is preferably controllable to reproduce a predetermined spectral output, which corresponds to a temporal combination of multiple peak emission wavelengths emitted during a display frame.

[0497] The tunable LED is preferably a tunable LED as described above in accordance with the foregoing aspect of the invention.

[0498] The method may include varying the amplitude of the drive current during a single display frame by providing separate drive current pulses at separate amplitudes. The method may include varying the drive current between at least two, or at least three, or at least four, or at least five, or at least six, or at least seven non-zero amplitudes during a display frame. The method may include step-controlling the brightness of each emitted peak emission wavelength by controlling the duration of each drive current pulse. The method may include repeating the series of drive current pulses in subsequent display frames.

[0499] The method may include generating a series of drive current pulses having distinct magnitudes and durations and supplying the series of drive current pulses to a tunable LED of a display device.

[0500] Alternatively, the method may include varying the amplitude of the drive current over a succession of amplitudes during a single display frame.

[0501] The method may include generating an analog drive current pulse having a magnitude that varies within the duration of a display frame and supplying the drive current pulse to a tunable LED of a display device.

[0502] The method may include controlling a plurality of tunable LEDs of a display device to recreate a light spectrum.

[0503] According to a further aspect of the invention, a method of controlling a display device comprising first and second tunable LED subpixels configured to emit light at different peak emission wavelengths is provided. As mentioned above, the device may comprise a first subpixel comprising a first light-emitting layer having a first light-emitting area A1, and a first electrical contact contacting the first subpixel over a first contact area and configured to apply a drive current to the first subpixel. The first subpixel may have a first contact ratio defined by the ratio of the first contact area: the first light-emitting area A1. The device may further comprise a second subpixel comprising a second light-emitting layer having a second light-emitting area A2, and a second electrical contact contacting the second subpixel over a second contact area and configured to apply a drive current to the second subpixel. The second subpixel may have a second contact ratio defined by the ratio of the second contact area: the second light-emitting area A2. The first contact ratio is preferably different from the second contact ratio such that the two sub-pixels are configured to emit light at different peak wavelengths in response to the same drive current.

[0504] A method for controlling such a display device includes: providing a first drive current I1 to a first subpixel; and providing a second drive current I2 to a second subpixel; Includes.

[0505] The magnitude of the first drive current I1 may be the same as the magnitude of the second drive current I2, in which case the first and second contact ratios are different to provide different current densities to the first and second subpixels, J=I / ΔAC.

[0506] The method may include providing a third drive current I3 to a third subpixel having a third contact ratio different from the first and second contact ratios. The magnitude of the third drive current I3 may be the same as the magnitudes of the first and second drive currents. Thus, the different first, second and third contact ratios may provide different current densities to the first, second and third subpixels.

[0507] The device can be controlled using variable current injection. The current density J can be controlled as follows: 1. J = ΔI / A 2. J = I / ΔA 3. J = ΔI / ΔA

[0508] Therefore, no specific contact area is required.

[0509] According to a further aspect of the invention, there is provided a method of controlling a display device comprising a pixel consisting of a plurality of sub-pixels each having an emissive layer, namely a first sub-pixel having a first emissive layer having a first area A1 and a second sub-pixel having a second emissive layer having a second area A2 different from the first area A1, wherein the first sub-pixel is configured to emit light at a first peak wavelength and the second sub-pixel is configured to emit light at a second peak wavelength different from the first peak wavelength.

[0510] The method is: providing a first drive current I1 to a first subpixel; and providing a second drive current I2 to a second subpixel; may include.

[0511] The magnitude of the first drive current I1 may be the same as the magnitude of the second drive current I2. Alternatively, the magnitude of the first drive current I1 may be different from the magnitude of the second drive current I2.

[0512] Preferably, the first and second drive currents are fixed in magnitude (i.e. do not vary) during use of the display device. In that case, the peak emission wavelengths of the first and second subpixels will also be fixed during use. The peak emission wavelengths emitted by the first and second subpixels will be determined by the current density experienced by the subpixels, which in turn depends on the magnitude of the respective drive currents and the size of the subpixel mesa and / or the size of the electrical contacts through which current is supplied to the subpixels.

[0513] All steps of controlling an LED or a display device comprising one or more LEDs may be performed by a controller configured to control power to the LEDs in the device.

[0514] The controller may control power to the LEDs in the device in response to user input. In response to user input, the controller may control the LEDs in the device to operate in a selected mode. For example, the controller may control one or more LEDs in the display device to operate in a fixed wavelength emission mode by providing a drive current of a fixed magnitude to the LEDs, the magnitude of the fixed drive current corresponding to the wavelength to be emitted. And / or the controller may control one or more LEDs in the display device to operate in a dynamically tunable emission mode by providing a drive current of a variable magnitude to the LEDs, the magnitude of the fixed drive current varying corresponding to the wavelength to be emitted at a given time.

[0515] (Display device manufacturing method) In a further aspect of the present disclosure, there is provided a method for manufacturing a display device, the method comprising: forming an LED diode structure into a plurality of separate LED mesas; and connecting the LED mesas to a power source configured to provide a variable power supply to at least a portion of the plurality of separate LED mesas; Includes.

[0516] Preferably, the LED diode structure is a tunable LED manufactured according to the method of the previous embodiment described above.

[0517] The tunable LED diode structure may be fabricated, for example, on a wafer scale and then separated into a number of separate LED mesas, which may then form individual LED subpixels of a display device.

[0518] This allows multiple subpixels to be combined together on the same wafer, reducing the number of mass transfer operations required to fabricate a display. In particular, multiple subpixels may be formed by etching a single LED diode structure into separate subpixel mesas. When this is done, the separate mesas each have the same diode structure. However, by processing the LED subpixel mesas into a display device using the present invention, the subpixel mesas may be configured to emit light at different peak emission wavelengths, despite being formed from the same semiconductor material and the same diode structure.

[0519] The method can include forming separate LED mesas having different surface areas.

[0520] The method may be a method for manufacturing a display device comprising a plurality of LED subpixels configured to emit light at different peak emission wavelengths. The method includes depositing a first electrical contact on a first LED subpixel comprising a first light-emitting layer having a first light-emitting area A1, the first electrical contact contacting the first subpixel over a first contact area, such that the first subpixel has a first contact ratio defined by a ratio of the first contact area:the first light-emitting area A1. The method includes a further step of depositing a second electrical contact on a second LED subpixel comprising a second light-emitting layer having a second light-emitting area A2, the second electrical contact contacting the second subpixel over a second contact area, such that the second subpixel has a second contact ratio defined by a ratio of the second contact area:the second light-emitting area A2. The first contact ratio may be different from the second contact ratio.

[0521] The method may include depositing a first masking layer over the first subpixel, forming a first opening in the first masking layer, and depositing the first electrical contact such that it contacts the first subpixel through the first opening, and / or depositing a second masking layer over the second subpixel, forming a second opening in the second masking layer, and depositing the second electrical contact such that it contacts the second subpixel through the second opening, before depositing the first electrical contact. In this embodiment, the area of ​​the first opening is the first contact area and / or the area of ​​the second opening is the second contact area.

[0522] The method may include etching an LED structure having a diode structure with a light emitting layer prior to depositing the electrical contacts to form a first subpixel mesa having a first light emitting layer with a first area A1 and a second subpixel mesa having a second light emitting layer with a second area A2, the first subpixel and the second subpixel having the diode structure of the LED structure, and thus the first and second subpixels may have the same diode structure and composition since both are formed from the same starting LED structure.

[0523] The LED structure may comprise an n-type conductive layer and a porous region beneath the diode structure, and the etching step preferably does not etch through the n-type conductive layer.

[0524] In some embodiments, the area of ​​the first subpixel mesa is the same as the area of ​​the second subpixel mesa, while in other embodiments, the area of ​​the first subpixel mesa is not the same as the area of ​​the second subpixel mesa.

[0525] In a further aspect, there is provided a method of manufacturing an LED display device, the method comprising: etching an LED structure having a diode structure with a light emitting layer to form a first subpixel mesa having a first light emitting layer with a first area A1 and a second subpixel mesa having a second light emitting layer with a second area A2, the first subpixel and the second subpixel having a diode structure of the LED structure, and because the first and second subpixels are etched from the same LED structure, both resulting subpixels have the same diode structure and the same composition.

[0526] The LED structure preferably comprises an n-type conductive layer and a porous region beneath the diode structure. The etching step preferably does not etch through the n-type conductive layer.

[0527] The first area is preferably selected such that a first current density is generated in the first light-emitting layer when a first drive current I1 is applied to the first subpixel, and the second area is preferably selected such that a second current density is generated in the second light-emitting layer when a second drive current I2 is applied to the second subpixel.

[0528] The first area may be selected such that when a first drive current I1 is applied to the first subpixel, the first subpixel emits light with a first emission intensity, and the second area may be selected such that when a second drive current I2 is applied to the second subpixel, the second subpixel emits light with a second emission intensity.

[0529] The first area may be selected such that when a first drive current I1 is applied to the first subpixel, the first subpixel emits light at a first brightness, and the second area may be selected such that when a second drive current I2 is applied to the second subpixel, the second subpixel emits light at a second brightness.

[0530] The method may include coupling the first and second sub-pixels to a driver circuit configured to control a drive current supplied to each sub-pixel of the display device.

[0531] The method may include the additional step of applying a first electrical contact to the first subpixel, the first electrical contact contacting the first subpixel over a first contact area. The method may include the additional step of applying a second electrical contact to the second subpixel, the second electrical contact contacting the second subpixel over a second contact area. As noted above, a masking layer may be used to control the size of the first and / or second contact areas.

[0532] (How to reproduce the light spectrum) In many applications it is desirable to be able to reproduce a particular spectrum of light.

[0533] In the prior art, this is achieved by: Modulating the intensity of one or more illumination sources with a fixed broadband emission spectrum: this is subtractive and therefore inherently inefficient. Combining the emission from multiple narrowband emission sources, which has limited tunability due to the fixed number of emission sources. Using filters to modify light from a high-power broadband spectrum source, which has the drawbacks of inherent inefficiency and limited tunability due to the fixed number of tuning elements.

[0534] In a further aspect of the invention, there is provided a method of reproducing a light spectrum using a tunable LED, the method comprising the steps of supplying a drive current to the tunable LED and varying an amplitude of the drive current between a plurality of non-zero values ​​during a single display frame, wherein varying the amplitude of the drive current between a plurality of non-zero values ​​during a single display frame generates a plurality of peak emission wavelengths, whereby a temporal combination of the plurality of peak emission wavelengths reproduces a light spectrum.

[0535] This can advantageously allow an observer to perceive a particular light spectrum being emitted by an LED or by multiple LEDs, which light spectrum is not normally emitted by LEDs. For example, the temporal combination of multiple peak emission wavelengths can produce light of a particular color that does not correspond to the emission band gap of known semiconductor materials. Thus, using this method, the range of colors that can be perceived as emitted by an LED is greatly expanded.

[0536] The duration of the display frame may be 50 ms or less, or 45 ms or less, or 40 ms or less. The duration of the display frame is preferably equal to or less than the response time of the detector. The duration of the display frame is preferably equal to or less than the response time of the human eye as the detector, which is about 50 ms.

[0537] Each tunable LED in a multi-LED display device is preferably controllable to reproduce a pre-set spectral output corresponding to a temporal combination of multiple peak emission wavelengths emitted during a display frame.

[0538] The tunable LED is preferably a tunable LED as described above according to the preceding aspect of the invention.

[0539] The method may include varying the amplitude of the drive current during a single display frame by providing a series of distinct drive current pulses having distinct amplitudes. The method may include varying the drive current between at least two, or at least three, or at least four, or at least five, or at least six, or at least seven non-zero amplitudes during a display frame. The method may include step-controlling the brightness of each emitted peak emission wavelength by controlling the duration of each drive current pulse. The method may include repeating the series of drive current pulses in a subsequent display frame.

[0540] The method can include generating a series of drive current pulses having distinct magnitudes and durations and providing the series of drive current pulses to a tunable LED.

[0541] Alternatively, the method may include varying the amplitude of the drive current over a succession of amplitudes during a single display frame.

[0542] The method may include generating an analog drive current pulse having a magnitude that varies within the duration of a display frame and providing the drive current pulse to a tunable LED.

[0543] The method may include controlling a plurality of tunable LEDs of a display device to recreate a light spectrum.

[0544] Features described herein in relation to one aspect of the invention are equally applicable to all other aspects of the invention.

[0545] Next, an embodiment of the present invention will be described with reference to the drawings. [Brief description of the drawings]

[0546] [Figure 1] FIG. 1 shows a porous template suitable for an LED according to the present invention. [Diagram 2] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Diagram 3] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 4] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Diagram 5] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 6] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 7] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 8] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 9] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 10] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 11] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 12] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 13] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 14] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 15] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 16] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 17] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 18] 2 to 18 show a process for manufacturing an LED according to a preferred embodiment of the present invention. [Figure 19] FIG. 19 is a graph of normalized electroluminescence (EL) intensity versus wavelength for an InGaN LED on a porous region. [Figure 20] FIG. 20 is a graph of normalized electroluminescence (EL) intensity versus wavelength at different current injection for an InGaN LED on a non-porous substrate. [Figure 21] FIG. 21 is a graph of normalized electroluminescence (EL) intensity versus wavelength at different current injection for the same InGaN LED as FIG. 20 grown on a porous region. [Figure 22] FIG. 22 shows the IV curves measured for InGaN microLEDs with different pixel sizes on non-porous substrates, with the inset image showing yellow emission. [Figure 23] FIG. 23 shows the IV curves measured for InGaN microLEDs with different pixel sizes on porous substrates, with the inset image showing the red emission. [Figure 24] FIG. 24 shows the IV curves measured on InGaN microLEDs of different pixel sizes on templates with subsurface porous regions. [Diagram 25] FIG. 25 shows low current IV curves measured on InGaN microLEDs of different pixel sizes on templates with subsurface porous regions. [Figure 26]FIG. 26 is a series of five EL images of the same microLED pixel driven at different currents in continuous wave mode (CW), showing five different color emissions. [Figure 27A] FIG. 27A is a plot of emission wavelength versus current density for a 25 μm×25 μm 100×100 tunable LED pixel array driven in pulsed mode with 100 μs pulses and 1% duty cycle. [Figure 27B] FIG. 27B is a plot of emission wavelength versus current density for a 30 μm×30 μm 100×100 tunable LED pixel array driven in pulsed mode with 100 μs pulses and 1% duty cycle. [Figure 28] FIG. 28 is a plot of intensity versus wavelength for a single tunable LED driven at different currents in pulsed drive mode with 100 μs pulses and 1% duty cycle. [Figure 29A] FIG. 29A is a schematic diagram of an LED structure with a current limiting layer according to a preferred embodiment of the present invention. [Figure 29B] FIG. 29B is a schematic diagram of an LED structure with a current limiting layer according to another preferred embodiment of the present invention. [Diagram 30] FIG. 30 is a schematic cross-sectional view of an LED according to a preferred embodiment of the present invention. [Diagram 31] 31-34 are schematic cross-sectional views of the LED of FIG. 30 including two V-shaped pits. [Diagram 32] 31-34 are schematic cross-sectional views of the LED of FIG. 30 including two V-shaped pits. [Diagram 33] 31-34 are schematic cross-sectional views of the LED of FIG. 30 including two V-shaped pits. [Diagram 34] 31-34 are schematic cross-sectional views of the LED of FIG. 30 including two V-shaped pits. [Diagram 35] FIG. 35 is a TEM image of a cross section of an LED having a V-shaped pit according to a preferred embodiment of the present invention. [Diagram 36]FIG. 36 is a graph of normalized intensity versus peak emission wavelength for a tunable LED in accordance with the present invention. [Figure 37] FIG. 37 is a graph of peak emission wavelength versus drive current for a tunable LED in accordance with the present invention. [Figure 38] FIG. 38 is a graph of peak emission wavelength for tunable LEDs of different pixel sizes. [Figure 39] FIG. 39 is a schematic cross-sectional side view of a tunable LED structure according to a preferred embodiment of the present invention. [Diagram 40] FIG. 40 is a schematic cross-sectional side view of a tunable LED structure according to another preferred embodiment of the present invention. [Diagram 41] FIG. 41 is a schematic diagram of the contact area between the contact layer and the semiconductor layer in an LED diode. [Diagram 42] FIG. 42 is a schematic plan view of electrical contacts disposed on the LED subpixel mesas. [Figure 43A] FIG. 43A is a schematic diagram of three subpixel mesas having the same subpixel mesa area but different contact areas and therefore different contact ratios. [Figure 43B] FIG. 43B is a schematic diagram of three subpixel mesas having the same subpixel mesa area and the same contact pad size, but different contact areas and therefore different contact ratios. [Figure 43C] FIG. 43C is a schematic diagram of three subpixel mesas having different subpixel mesa areas, different contact areas, and different contact ratios. [Diagram 44] FIG. 44 is a schematic cross-sectional side view of three sub-pixels on a common semiconductor template having different contact areas and therefore different contact ratios. [Diagram 45] FIG. 45 is a schematic cross-sectional side view of three sub-pixels on a common semiconductor template having different contact areas and therefore different contact ratios. [Figure 46A]46A-46G show alternative embodiments of non-uniform, fragmented, or discontinuous light emitting regions of tunable LEDs according to the present invention. [Figure 46B] 46A-46G show alternative embodiments of non-uniform, fragmented, or discontinuous light emitting regions of tunable LEDs according to the present invention. [Figure 46C] 46A-46G show alternative embodiments of non-uniform, fragmented, or discontinuous light emitting regions of tunable LEDs according to the present invention. [Figure 46D] 46A-46G show alternative embodiments of non-uniform, fragmented, or discontinuous light emitting regions of tunable LEDs according to the present invention. [Figure 46E] 46A-46G show alternative embodiments of non-uniform, fragmented, or discontinuous light emitting regions of tunable LEDs according to the present invention. [Figure 46F] 46A-46G show alternative embodiments of non-uniform, fragmented, or discontinuous light emitting regions of tunable LEDs according to the present invention. [Figure 46G] 46A-46G show alternative embodiments of non-uniform, fragmented, or discontinuous light emitting regions of tunable LEDs according to the present invention. [Figure 47A] FIG. 47A is a TEM image of a cross section of a conventional non-tunable LED. [Figure 47B] FIG. 47B is a TEM image of the light-emitting area of ​​a tunable LED with V-shaped pits according to an embodiment of the present invention. [Figure 47C] FIG. 47C is a TEM image of the tunable LED of FIG. 47B showing a porous region and a light emitting region with a plurality of V-shaped pits according to a preferred embodiment of the present invention. [Figure 48A] FIG. 48A is a graph of peak emission wavelength versus drive current density for a conventional non-tunable LED. [Figure 48B] FIG. 48B is a graph of peak emission wavelength versus drive current density for a tunable LED in accordance with an embodiment of the present invention. [Figure 48C] FIG. 48C is a graph of peak emission wavelength versus drive current density for a tunable LED according to another embodiment of the present invention. [Figure 49A] FIG. 49A is a graph of peak emission wavelength versus drive current density for another tunable LED in accordance with the present invention. [Figure 49B] 49B-49D are photographs of the tunable LED of FIG. 49A with insets the emission spectra showing different peak emission wavelengths at different drive current densities. [Figure 49C] 49B-49D are photographs of the tunable LED of FIG. 49A with insets the emission spectra showing different peak emission wavelengths at different drive current densities. [Figure 49D] 49B-49D are photographs of the tunable LED of FIG. 49A with insets the emission spectra showing different peak emission wavelengths at different drive current densities. [Figure 50A] FIG. 50A is a schematic diagram of the spatial arrangement of monochromatic subpixels in a conventional display pixel. [Figure 50B] 50B-50G are schematic diagrams of pixels of an LED display device including at least one tunable LED according to the present invention. [Figure 50C] 50B-50G are schematic diagrams of pixels of an LED display device including at least one tunable LED according to the present invention. [Figure 50D] 50B-50G are schematic diagrams of pixels of an LED display device including at least one tunable LED according to the present invention. [Figure 50E] 50B-50G are schematic diagrams of pixels of an LED display device including at least one tunable LED according to the present invention. [Figure 50F] 50B-50G are schematic diagrams of pixels of an LED display device including at least one tunable LED according to the present invention. [Figure 50G]50B-50G are schematic diagrams of pixels of an LED display device including at least one tunable LED according to the present invention. [Figure 51A] 51A-51C show the color gamut obtainable with a prior art display and with a device of the present invention. [Figure 51B] 51A-51C show the color gamut obtainable with a prior art display and with a device of the present invention. [Figure 51C] 51A-51C show the color gamut obtainable with a prior art display and with a device of the present invention. [Figure 52A] 52A-52D show a display pixel and the color gamut obtainable with that pixel according to an embodiment of the invention. [Figure 52B] 52A-52D show a display pixel and the color gamut obtainable with that pixel according to an embodiment of the invention. [Figure 52C] 52A-52D show a display pixel and the color gamut obtainable with that pixel according to an embodiment of the invention. [Fig. 52D] 52A-52D show a display pixel and the color gamut obtainable with that pixel according to an embodiment of the invention. [Figure 53] FIG. 53 illustrates a method of controlling a display pixel containing a tunable LED according to the present invention. [Figure 54A] 54A and 54B show a display pixel and the color gamut obtainable with that pixel according to an embodiment of the invention. [Figure 54B] 54A and 54B show a display pixel and the color gamut obtainable with that pixel according to an embodiment of the invention. [Figure 55A] 55A-55D show a display pixel and the color gamut obtainable with that pixel according to another embodiment of the invention. [Figure 55B] 55A-55D show a display pixel and the color gamut obtainable with that pixel according to another embodiment of the invention. [Figure 55C] 55A-55D show a display pixel and the color gamut obtainable with that pixel according to another embodiment of the invention. [Fig. 55D] 55A-55D show a display pixel and the color gamut obtainable with that pixel according to another embodiment of the invention. [Figure 56] FIG. 56 shows a display pixel according to another embodiment of the invention and the color gamut obtainable with that pixel. [Figure 57] FIG. 57 shows a display pixel according to another embodiment of the invention and the color gamut obtainable with that pixel. [Figure 58] FIG. 58 shows a display pixel according to another embodiment of the invention and the color gamut obtainable with that pixel. [Figure 59A] FIG. 59A shows a tunable display pixel according to an embodiment of the present invention. [Figure 59B] 59B-60D show driving schemes for controlling the pixel of FIG. 59A. [Figure 59C] 59B-60D show driving schemes for controlling the pixel of FIG. 59A. [Figure 60A] 59B-60D show driving schemes for controlling the pixel of FIG. 59A. [Figure 60B] 59B-60D show driving schemes for controlling the pixel of FIG. 59A. [Figure 60C] 59B-60D show driving schemes for controlling the pixel of FIG. 59A. [Figure 60D] 59B-60D show driving schemes for controlling the pixel of FIG. 59A. [Figure 61A] FIG. 61A shows a display pixel according to an embodiment of the present invention. [Figure 61B] 61B-61C show a driving scheme for controlling the pixel of FIG. 61A. [Figure 61C]61B-61C show a driving scheme for controlling the pixel of FIG. 61A. [Figure 62] Figure 62 shows a display pixel according to an embodiment of the invention, and a driving scheme for controlling the pixel. [Figure 63] Figure 63 shows a display pixel according to an embodiment of the invention, and a driving scheme for controlling the pixel. [Fig. 64A] FIG. 64A is a schematic diagram of drive current conditions for a tunable LED in accordance with the present invention. [Fig. 64B] FIG. 64B shows the peak emission wavelengths emitted by a tunable LED according to the present invention in response to different drive currents. [Figure 65] FIG. 65 is a schematic diagram of drive current conditions for a tunable LED according to the first embodiment of the present invention. [Figure 66] FIG. 66 is a schematic diagram of drive current conditions for a tunable LED according to embodiment 2 of the present invention. [Figure 67] FIG. 67 is a schematic diagram of drive current conditions for a tunable LED according to embodiment 3 of the present invention. [Figure 68] FIG. 68 is a schematic diagram of drive current conditions for a tunable LED according to embodiment 4 of the present invention. [Figure 69] FIG. 69 is a schematic diagram of drive current conditions for a tunable LED according to the fifth embodiment of the present invention. [Figure 70] FIG. 70 shows the peak emission wavelength emitted by a tunable LED according to the present invention, with five different drive currents superimposed. [Figure 71] FIG. 71 shows five different drive current digital pulse patterns. [Figure 72] FIG. 72 shows the emission spectrum obtained from the tunable LED in response to the pulse pattern of FIG. [Figure 73A] 73A-73D show spectral reconstruction using multiple digital pulses of drive current according to embodiment A of the present invention. [Figure 73B]73A-73D show spectral reconstruction using multiple digital pulses of drive current according to embodiment A of the present invention. [Figure 73C] 73A-73D show spectral reconstruction using multiple digital pulses of drive current according to embodiment A of the present invention. [Fig. 73D] 73A-73D show spectral reconstruction using multiple digital pulses of drive current according to embodiment A of the present invention. [Figure 74] FIG. 74 shows an exemplary target emission spectrum. [Figure 75] FIG. 75 shows the peak emission wavelengths emitted by a tunable LED according to the present invention in response to different drive currents. [Figure 76] FIG. 76 shows an exemplary analog drive current pulse that can be used in embodiment B of the present invention. [Figure 77] FIG. 77 shows the perceived output spectrum produced by the tunable LED in response to the analog current pulse of FIG. [Figure 78] FIG. 78 shows a large area spectrally tunable illumination source according to preferred embodiment C of the present invention. [Figure 79] FIG. 79 shows a spectrally corrected display device with a spectrally tunable pixel according to a preferred embodiment D of the present invention. [Figure 80A] FIG. 80A is a schematic plan view of a display pixel having two tunable subpixels with the same diode structure but different emitting areas. [Figure 80B] FIG. 80B shows an array of red-green (RG) pixel packages of FIG. 80A implemented on a backplane driver integrated circuit along with an array of blue LED subpixels. [Figure 81] FIG. 81 is a graph of drive current density versus emission wavelength for a tunable LED subpixel in accordance with an embodiment of the present invention. [Figure 82A] 82A and 82B show an example device pixel with two subpixels having the same diode structure but different areas. [Fig. 82B] 82A and 82B show an example device pixel with two subpixels having the same diode structure but different areas. [Figure 83] FIG. 83 illustrates the luminous efficiency versus emission wavelength for an exemplary tunable LED subpixel according to an embodiment of the present invention. [Figure 84] FIG. 84 shows the photopic luminosity function for emission at different wavelengths in an exemplary tunable LED subpixel according to an embodiment of the present invention. [Fig. 85A] FIG. 85A is a schematic plan view of a two-subpixel device pixel according to a preferred embodiment of the present invention. [Fig. 85B] FIG. 85B is a schematic cross-sectional side view of the pixel of FIG. 85A taken along line AA. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0547] FIG. 1 shows a porous template suitable for an LED according to the present invention.

[0548] The porous template comprises a porous region of III-nitride material on a substrate with a non-porous layer of III-nitride material disposed on an upper surface of the porous region, and if desired, there may be an additional layer of III-nitride material between the substrate and the porous region.

[0549] As described in more detail below, the porous region may be provided by epitaxially growing an n-doped region of III-nitride material followed by an undoped layer of III-nitride material and rendering the n-doped region porous using the porosification processes described in International Patent Applications PCT / GB2017 / 052895 (published as WO 2019 / 063957) and PCT / GB2019 / 050213 (published as WO 2019 / 145728).

[0550] As mentioned above, this porosification results in strain relaxation in the crystal lattice, which means that subsequent growth of further semiconductor layers benefits from a reduction in the compressive strain of their lattices.

[0551] The porous region may comprise one or more layers of one or more III-nitride materials and may have a variety of thicknesses while still providing the benefit of strain relaxation that shifts the wavelength of an InGaN light emitting layer grown on the porous region. In preferred embodiments, the porous region may include, for example, GaN and / or InGaN.

[0552] A variety of LED structures can be grown on the template shown in FIG.

[0553] In particular, LED structures including InGaN light emitting layers known in the art for producing yellow or green LEDs can be grown on the porous template using standard LED manufacturing processes, but when grown on the porous template, the LED structure that normally emits at a first wavelength will emit at a longer wavelength that is red-shifted.

[0554] Thus, by using porous regions of III-nitride material as a template or pseudo-substrate for growing known InGaN LED structures, longer wavelength LEDs can be fabricated in a facile manner.

[0555] In a preferred embodiment, an LED according to the invention comprises the following layers and can be manufactured using the step-by-step process described below.

[0556] The following description of the LED structure is in terms of a top-emitting structure, referred to as bottom-up, although the invention is equally applicable to bottom-emitting structures.

[0557] (Figure 2 - Substrate and III-nitride layer for porosity) A suitable substrate is used as the starting surface for epitaxial growth. The substrate may be silicon, sapphire, SiC, β-Ga2O3, GaN, glass, or metal. The crystal orientation of the substrate may be polar, semi-polar, or non-polar. The size of the substrate is 1 cm 2 From 2 inch, 4 inch, 6 inch, 8 inch, 12 inch, 16 inch diameter and more, the thickness of the substrate can be greater than 1 μm, for example, from 1 μm to 15000 μm.

[0558] A layer or stack of layers of III-nitride material is epitaxially grown on the substrate. The III-nitride layers may include one or a combination of these elements, Al, Ga, In (binary, ternary, or quaternary layers).

[0559] The thickness T of the III-nitride stack is preferably at least 10 nm, or at least 50 nm, or at least 100 nm, for example between 10 and 10000 nm.

[0560] The III-nitride layer is 1×10 17 cm -3 ~5×10 20 cm -3 The III-nitride layer may also include an undoped "cap" layer of III-nitride material over the doped region.

[0561] The boundary of the doped region may be the exposed top surface of the III-nitride layer, in which case the surface of the layer is rendered porous during electrochemical etching.

[0562] Alternatively, the doped region of III-nitride material may be covered by an undoped "cap" layer of III-nitride material, thereby rendering the doped region below the surface of the semiconductor structure. The starting depth (d) of the doped region below the surface may be, for example, 1 to 2000 nm.

[0563] (Figure 3 - Porosification of porous regions) After a III-nitride layer (or stack of layers) has been deposited on a substrate, it is made porous using a wafer-scale porosification process such as that shown in International Patent Applications PCT / GB2017 / 052895 (published as WO 2019 / 063957) and PCT / GB2019 / 050213 (published as WO 2019 / 145728). During this process, doped regions of the III-nitride material are made porous, but none of the undoped regions of the III-nitride material are made porous.

[0564] After the porosification step, the structure thus includes porous regions that remain where previously the n-doped III-nitride material was, and optionally a non-porous intermediate layer overlying the porous regions.

[0565] The porosity of the porous region is controlled by the electrochemical etching process and may be between 1% and 99% porosity, preferably between 20% and 90% porosity, or between 30% and 80%, although lesser or greater porosities may be used.

[0566] The thickness of the porous region after porosification is preferably greater than 1 nm, more preferably greater than 10 nm, and most preferably at least 40 nm or 50 nm or 100 nm, but the material thickness required to obtain the benefit of the strain relief provided by the porous region may vary depending on the type of III-nitride material from which the porous region is made.

[0567] The porous region created by the porosification process may be a bulk layer of III-nitride material with uniform composition and uniform porosity throughout the layer. Alternatively, the porous region may comprise multiple layers of porous materials with different compositions and / or different porosities, forming a porous stack of III-nitride materials. For example, the porous region may be a continuous layer of porous GaN, or a continuous layer of porous InGaN, or a stack comprising one or more layers of porous GaN and / or one or more layers of porous InGaN. The inventors have found that the benefits of strain relaxation of the porous region for growth can be obtained over a wide variety of porous regions with different thicknesses, compositions, and layered stacks.

[0568] In the illustrated embodiment, the porous region is a single porous layer.

[0569] If there is an undoped cap layer of III-nitride material on the doped region, the undoped region remains non-porous after through-surface porosification of the underlying doped region. The thickness D of this non-porous cap layer may preferably be at least 2 nm, or at least 5 nm, or at least 10 nm, preferably 5-3000 nm. Providing an undoped cap layer on the doped region advantageously results in a non-porous layer of III-nitride material covering the porous region after porosification. This non-porous cap layer may advantageously allow for better growth of further material on the porous region.

[0570] The porosification methods of PCT / GB2017 / 052895 (published as WO 2019 / 063957) and PCT / GB2019 / 050213 (published as WO 2019 / 145728) can be performed on the entire semiconductor wafer and no processing / patterning / treatment is required to prepare a template for porosification.

[0571] (Figure 4-Connection layer) After formation of the porous layer, III-nitride LED epitaxy structures can be grown on the porous template / pseudo-substrate provided by the porous layer and the non-porous cap layer.

[0572] The first layer for growing an LED structure on a template may be referred to as connection layer 1.

[0573] Although it is possible to grow the LED epitaxial structure directly on the non-porous cap layer, it is preferred that a connection layer 1 is provided on the cap layer before growing the LED structure. The inventors have found that by using a III-nitride connection layer 1 between the porous region and the LED epitaxy structure, a good epitaxial relationship between the LED and the porous template / substrate can be advantageously ensured. The growth of this layer ensures that the subsequent growth on top of the connection layer is smooth, epitaxial and of suitable high quality.

[0574] The connection layer 1 is formed from a III-nitride material and may contain one or a combination of these elements, Al, Ga, In (binary, ternary or quaternary layers).

[0575] The connection layer may be a doped or undoped layer. The connection layer may be doped with a suitable n-type dopant material, as desired, for example, Si, Ge, C, O. The III-nitride layer may be doped with a suitable n-type dopant material, for example, Si, Ge, C, O. 17 cm -3 ~5×10 20 cm -3 The doping concentration may be 0.1 to 1000 .mu.m.

[0576] The thickness of this connection layer is preferably at least 100 nm, and may be, for example, between 100 and 10,000 nm.

[0577] (Figure 5-N doped region) After growth of the connection layer, the bulk n-doped III-nitride region 2 is grown.

[0578] The n-doped region 2 may comprise or consist of a grown III-nitride layer containing indium, or a stack of thin III-nitride layers with or without indium, or a bulk layer or stack of III-nitride layers with varying atomic percentage of indium throughout the layer or stack. For example, the n-doped region may be a layer of n-GaN or a layer of n-InGaN, or alternatively, the n-doped region may be a stack of alternating layers of n-GaN / n-InGaN, or a stack of alternating layers of n-InGaN / n-InGaN with different amounts of indium in the alternating layers.

[0579] Preferably, the n-doped region 2 contains indium, so that the crystal lattice of the n-doped region has lattice parameters similar to the lattice of the InGaN light emitting layer of the LED. The atomic percentage of indium in the n-doped region may vary, for example, from 0.1 to 25%.

[0580] In preferred embodiments, the indium content of the n-doped region is within 20 atomic %, or within 15 atomic %, or within 10 atomic %, or within 5 atomic % of the indium content of the InGaN light emitting layer, which may advantageously ensure that the lattice constant of the n-doped region is sufficiently close to that of the InGaN light emitting layer to avoid excessive strain between these layers.

[0581] The total thickness of the n-doped region may be at least 2 nm, or at least 5 nm, or at least 10 nm, or at least 20 nm. The thickness of the n-doped region may vary, for example, from 2 nm to 5000 nm, or may be even thicker. If the n-doped region comprises a stack of layers, the thickness of the individual layers in the stack is preferably from 1 to 40 nm.

[0582] The n-doped region is preferably 1×10 17 cm -3 ~5×10 20 cm -3 , preferably 1 x 10 18 cm -3 ~5×10 20cm -3 , particularly preferably 1×10 18 cm -3 It has an n-type doping concentration of .

[0583] (Figure 6-Light-emitting area) After growth of the n-doped region 2, an underlayer or pre-layer or pre-well (not shown in FIG. 6) may be grown to relieve strain in the light emitting layer. The underlayer may be a single layer or stack / multilayer of GaN, InGaN, or GaN / InGaN, or InGaN / InGaN. Alternatively, the underlayer may have a structure similar to an InGaN QW / GaN quantum barrier but with a lower indium percentage. For example, prior to depositing the light emitting layer having a relatively high percentage of indium, an underlayer consisting of a layer of bulk InGaN with a lower indium percentage than the light emitting layer may be grown. Alternatively, the underlayer may take the form of an InGaN "dummy" QW with a lower indium percentage than the light emitting layer and one or more GaN quantum barriers.

[0584] After growth of the n-doped region 2 and any optional underlayers, a light emitting region 3 comprising an InGaN light emitting layer is grown.

[0585] The light emitting region 3 may include at least one InGaN light emitting layer. Each InGaN light emitting layer may be an InGaN quantum well (QW). Preferably, the light emitting region comprises 1 to 7 quantum wells. Adjacent quantum wells are separated by barrier layers of III-nitride material having a different composition than the quantum wells.

[0586] The light emitting layer, sometimes referred to as a "quantum well" throughout this document, can take a variety of forms. For example, the light emitting layer can be a continuous layer of InGaN, or the layer can be continuous, fragmented, discontinuous, gapped, or nanostructured, such that the quantum well effectively comprises a plurality of 3D nanostructures that behave as quantum dots.

[0587] The quantum wells and barriers are grown at temperatures in the range of 600-800°C.

[0588] Each quantum well is made of an InGaN layer with an atomic indium content of 15-40%. Preferably, the light emitting indium gallium nitride layer and / or the quantum well is made of InGaN with 0.05≦x≦0.40, preferably 0.12≦x≦0.35 or 0.22≦x≦0.30, particularly preferably 0.22≦x≦0.27. x Ga 1-x It has a composition of N.

[0589] The thickness of each quantum well layer may be 1.5-8 nm, preferably 1.5-6 nm, or 1.5-4 nm. The quantum wells may be capped with a thin (0.5-3 nm) III-nitride QW capping layer, which may contain one or a combination of these elements, Al, Ga, In (the three components of the quaternary layer).

[0590] The QW capping layer is a layer added immediately after QW growth and can be AlN, AlGaN with any Al % between 0.01 and 99.9%, GaN, InGaN with any In % between 0.01 and 30%.

[0591] The III-nitride QW barriers separating the light emitting layers (quantum wells) may comprise one or a combination of these elements, Al, Ga, In (the three components of the quaternary layer). The QW barrier layers may be AlN, AlGaN with any Al% between 0.01 and 99.9%, GaN, and InGaN with any In% between 0.01 and 15%. Preferably, the QW barrier layers comprise AlN and / or AlGaN.

[0592] The QW capping layers and the QW barriers are not shown with individual reference numbers in the figure since these layers form part of the light emitting region 3 .

[0593] A QW capping layer may be grown after each QW growth but before the barrier growth, for example, if an LED includes three QWs, each of these QWs may be grown with a QW capping layer followed by the growth of a QW barrier layer, such that the light emitting region includes three such QW capping layers and three such QW barrier layers.

[0594] 1. The cap can be grown under the same conditions as the QW. 2. The cap can be grown at elevated temperature without being grown to high temperature (effectively this is an annealing step), in which case the temperature increase may be done in a different gas mixture. 3. During the temperature rise process, temperature rise and growth can occur.

[0595] The design of the light-emitting region can be varied according to conventional LED design parameters as understood in the art. For example, the composition, thickness, and number of light-emitting and barrier layers can be varied depending on the desired EL emission wavelength of the LED. As previously described in this application, the indium content of the InGaN light-emitting layer can be increased if longer wavelength emission is desired.

[0596] As mentioned above, the present invention can be provided by growing a known LED structure, known to emit light at a first wavelength under an electrical bias, on a template containing a porous region. The strain relaxation caused by the porous region beneath the LED structure allows more indium to be incorporated into the light emitting layer under the same growth conditions, which results in a red shift in the wavelength of the resulting LED compared to the same LED structure grown under the same conditions on a non-porous substrate. Thus, using the present invention, a wider variety of emission wavelengths can be achieved than was possible with the prior art, particularly longer wavelengths at higher InGaN growth temperatures. This results in a higher quality crystal structure in the LED, and therefore a higher performance LED.

[0597] When making longer wavelength LEDs, the capping layer is important because there is a lot of indium in the light emitting layer, because previous attempts to make longer wavelength yellow, orange, or red LEDs have not been successful due to not incorporating enough indium, so capping is very important to ensure that enough indium is trapped within the light emitting region.

[0598] (Figure 7-Cap layer) After growth of the light emitting layer, an undoped cap layer 4 is grown. The undoped cap layer 4 is referred to as the light emitting region cap layer because it is formed after growth of the complete light emitting region, e.g., after growth of the stack of QWs, QW capping layer, and QW barrier layer.

[0599] The capping layer (light emitting region capping layer) 4 is a very well known standard layer in growth schemes for III-nitride LEDs.

[0600] The thickness of the capping layer may be from 5 to 30 nm, preferably from 5 to 25 nm or from 5 to 20 nm.

[0601] The purpose of the light emitting region capping layer 4 is to protect the indium in the light emitting region (QW stack) and prevent it from desorbing / evaporating during subsequent processing. Since InGaN QWs are usually grown at lower temperatures that are unfavorable for GaN / AlGaN, a temperature ramp-up step is typically required before further layers can be grown on top of the light emitting region. The capping layer is used to ensure that the InGaN light emitting layer is properly capped and protected, thereby providing an opportunity and time window to change the growth conditions of the p-doped layers for better material quality. The light emitting region capping layer 4 also ensures that the Mg dopant does not creep into the QW region during the growth of the p-type layers.

[0602] (Electron Blocking Layer (EBL)) After growth of the quantum wells, capping layer, and barrier layer, an aluminum-containing electron-blocking III-nitride layer (EBL) 5 is grown. The Al% can be, for example, 5-25%, although higher Al contents are possible.

[0603] The EBL is doped with a suitable p-type doping material. The p-type doping concentration of the EBL is preferably 5×10 18 cm -3 ~8×10 20 cm -3 It is.

[0604] The thickness of the EBL may be from 10 to 50 nm, preferably 20 nm.

[0605] (Figure 8-P doped layer) On top of the electron blocking layer (EBL) 5 a p-doped layer 6 is grown.

[0606] The p-type region is preferably doped with Mg, and the p-type doping concentration of the p-type layer is preferably 5×10 18 cm -3 ~8×10 20 cm -3 It is.

[0607] The p-doped III-nitride layer may include In and Ga.

[0608] The thickness of the doped layer is preferably 20-200 nm, particularly preferably 50-100 nm. The doping concentration may vary throughout the p-type layer, with a steep rise in doping level in the last 10-30 nm of the layer towards the LED surface to allow for better p-contact.

[0609] To activate the Mg acceptors in the p-doped layers, the structure can be annealed inside an MOCVD reactor or in an annealing oven. The annealing temperature can be in the range of 700-850° C. in a N2 or N2 / O2 environment.

[0610] Because both the EBL and the p-doped layer are p-type doped, these layers may be referred to as p-doped regions.

[0611] (Figure 9 - Transparent conductive layer) The stack of active semiconductor layers is covered with a transparent conductive layer 7. The transparent conductive layer can be made of Ni / Au, indium tin oxide, indium zinc oxide, graphene, Pd, Rh, silver, ZnO, etc. or a combination of these materials.

[0612] The transparent conductive layer may have a thickness of 10 to 250 nm.

[0613] Transparent conductive layers are known in the art and any suitable material and thickness may be used.

[0614] An annealing step may be necessary to make the p-contact ohmic.

[0615] (Figure 10) Depending on the LED structure being fabricated, the semiconductor structure may be processed into an LED, mini-LED, or micro-LED device.

[0616] Regular LEDs are typically larger than 200 μm (the lateral dimensions of the width and length of the LED structure). Mini LEDs are typically 100-200 μm in lateral size, and micro LEDs are typically less than 100 μm in size.

[0617] Figures 10 onwards show the semiconductor structure after layers 2-7 of the semiconductor structure have been etched into multiple separate LED stacks or mesas, each having the same structure.

[0618] The steps of manufacturing LEDs are conventional and well known to those skilled in the art. The sequence of the manufacturing steps below is not specific to the present invention, and those skilled in the art will appreciate that LED devices within the scope of the present invention may be manufactured using alternative manufacturing steps other than those illustrated below. However, for purposes of example only, one preferred manufacturing route for manufacturing LEDs according to the present invention is described below.

[0619] In the next step, the transparent conductive layer 7 is structured to cover only the top surface of the active light emitting element. The structuring can be done using standard semiconductor processing methods including resist coating and photolithography. The transparent conductive layer is etched by using wet chemistry or by using a sputter etching process with argon. This step is followed by wet or dry etching of the III-nitride structure. Mesas are created in the III-nitride layer using inductively coupled plasma reactive ion etching, reactive ion etching only or neutral beam etching. The dry etching process can include one or more of Cl, Ar, BCl3, SiCl4 gases.

[0620] The purpose of this step is to separate the individual light emitting devices and to access the buried n-doped layer of the pn junction.

[0621] After the dry etching process, a wet etching process is performed to remove the dry etching damage from the mesa sidewalls. This wet chemistry can involve KOH (1-20%), TMAH, or other basic chemicals.

[0622] (Fig.11-Passivation treatment) The next step is to deposit a passivation layer 8 or a combination of passivation layers. The starting passivation layer can be Al2O3 (10-100 nm) (deposited by atomic layer deposition) followed by sputtered or plasma enhanced chemical vapor deposition of SiO2, SiN, or SiON (50-300 nm).

[0623] Al2O3 can be deposited at 50-150°C.

[0624] SiO2, SiN, and SiON can be deposited at 250-350°C.

[0625] The sputtering process may be carried out at room temperature.

[0626] Figures 12 to 13 The next step is to create an opening in the oxide passivation layer 8 to expose the top of the LED structure. This can be done via wet or dry etching or a combination of both.

[0627] Wet etching may use buffered oxide etchants, dilute hydrofluoric acid, phosphoric acid, or mixtures thereof.

[0628] Channels are also etched through the connection layer 1 between the LED structures, followed by depositing a dielectric mask material 8 in the channels to electrically isolate the LED structures from each other, thereby allowing the LEDs to operate independently of each other.

[0629] The next step in the device fabrication is to coat the transparent conductive layer 7 on the p-doped layer 6 with a metal layer which acts as the electrical p-contact 9. This coating may be done in a single step or in multiple steps. The metal may completely or partially cover the pixel. In this example a single step is used to simplify details.

[0630] The metal contacts 9 may include Ti, Pt, Pd, Rh, Ni, Au. The thickness of the complete metal stack may be 200-2000 nm.

[0631] (Figure 14 - Exposed connection layer) Using standard photolithography techniques, openings can be created in the second mask layer 8 to expose areas of the connection layer 1. The size of the openings can vary from 200 nm to 50000 nm. The distance between the openings can be from 500 nm to 30000 nm. The openings are created only in areas of the wafer that are not occupied by LED structures.

[0632] To etch the second mask layer 8, dry etching using a fluorine-based gas is preferably used.

[0633] (Fig.15-N contact) The next step in the device fabrication is to cover the opening in the oxide 8 with a metal contact 10 to access the connection layer 1 which is in electrical contact with the n-doped layer of the LED structure. This coverage may be done in a single step or in multiple steps. The metal may cover the pixel completely or partially. In this example a single step is used to simplify the details.

[0634] The metals may include Ti, Pt, Pd, Rh, Ni, Au. The thickness of the complete metal stack may be between 200 and 2000 nm.

[0635] (Fig. 16 to 18) After this processing, the substrate may be thinned and / or the porous regions may be removed so that the connection layer 1 is exposed.

[0636] Surface structuring or texturing may be performed on the substrate in the porous region or layer 1 to enhance light output, control emission angle, and other optical treatments and designs.

[0637] Finally, the wafer / device may be flipped over and bonded to another carrier substrate, which may be silicon / sapphire or any type for passive devices, or alternatively the device may be bonded to a CMOS silicon backplane for an active matrix micro LED display panel.

[0638] As shown in FIG. 16, the top side of the device can be bonded to another carrier wafer / substrate / backplane 11 or to a microdriver circuit board to form an array of pixels.

[0639] The substrate may then be removed from the device and the bottom side of the device may be bonded to a cover glass or transparent material 12, as shown in FIG.

[0640] The substrate and the porous and non-porous regions can be removed from the device, as shown in Figure 18. The top side of the device can be bonded to another carrier wafer / substrate / backplane 11 or to a microdriver circuit board to form an array of pixels. The bottom side of the device can be bonded to a cover glass or transparent material 12.

[0641] Those skilled in the art will appreciate that the emission wavelength of an individual LED structure may be controlled by varying the composition and layer structure of the LED structure in accordance with known principles of LED construction. Thus, the present invention may be used to provide a variety of tunable LED devices that emit over different emission wavelength ranges, providing color combinations other than green to red.

[0642] (Fig. 19 to 23) FIG. 19 shows an example of an InGaN LED on a porous layer, which emits light at a peak wavelength of about 625 nm due to the red-shift in wavelength caused by the porous region.

[0643] Figures 20 and 21 compare the emission characteristics of an InGaN LED on a non-porous substrate (Figure 20) and the same InGaN LED grown on a template with a porous layer of III-nitride material. Comparing these two graphs shows the shift to longer emission wavelengths caused by the porous underlayer, with the emission of the LED on the porous template being consistently 21 nm to 45 nm longer than the emission of the same LED on a non-porous template.

[0644] Figures 22 and 23 compare the IV characteristics of a yellow InGaN microLED on a non-porous substrate (Figure 22) with the same InGaN microLED grown on a template containing a porous layer. On the porous template, the InGaN microLED emits red light, as shown in the inset image.

[0645] Figure 24 shows the IV curves measured on InGaN microLEDs with different pixel sizes (10 μm×10 μm, 20 μm×20 μm, 30 μm×30 μm, 50 μm×50 μm) on a porous substrate. Figure 25 shows the IV characteristics of the same pixel, with a 1×10 -6 The axes have been modified to focus on low currents, from μA to just over 100 μA.

[0646] Figure 26 is a series of five EL images of the same tunable microLED InGaN pixel driven at different currents in continuous wave mode (CW), showing five different color emissions. In the left image, the microLED emission color appears red at a drive current of 50 μA. In the second image from the left, the microLED emission color appears red-orange at a drive current of 100 μA. In the third image from the left, the microLED emission color appears orange at a drive current of 1 mA. In the fourth image from the left, the microLED emission color appears yellow-green at a drive current of 10 mA. In the right image, the microLED emission color appears green at a drive current of 20 mA.

[0647] Thus, by varying the drive current from 50 μA to 20 mA, the same micro LED can emit light in the red to green wavelength range. The spectral width of this emission wavelength range is on the order of 90 nm (from about 570 nm to about 660 nm), a much wider range of emission wavelengths than was previously achievable with a single LED in the prior art.

[0648] Figure 27A is a plot of emission wavelength vs. current density for a 25 μm×25 μm InGaN LED pixel array (100×100 array, containing 10,000 pixels) driven in pulsed mode with 100 μs pulses at a 1% duty cycle. Figure 27B is a plot of emission wavelength vs. current density for a 30 μm×30 μm InGaN LED pixel array (100×100 array, containing 10,000 pixels) driven in pulsed mode with 100 μs pulses at a 1% duty cycle.

[0649] Both of these plots show the possibility of controlling the peak emission wavelength by a pulsed power supply. In particular, the wavelength is linearly dependent on the current density (when plotted on a logarithmic scale). This linearity can be replicated when driven by a pulsed voltage power supply. Thus, the tunable emission wavelength of the LED can be controlled by either voltage or current driving schemes in CW or pulsed mode, which are all standard methods for display driver ICs.

[0650] This linear relationship between the driving current intensity and the resulting emission wavelength is highly advantageous for LED display design purposes, allowing precise control of the emission wavelength by varying the current density of the power supply.

[0651] Figure 28 is a plot of intensity versus wavelength for a tunable InGaN LED driven with different DC currents. The power supply is operated in a pulsed mode with 100 μs pulses at a duty cycle of 1%.

[0652] Figure 28 also reflects the gradual and continuous shift of the LED's peak emission wavelength as the power supply current is changed. At a drive current of 200 mA, the peak emission wavelength is about 575 nm and the intensity is about 10 μW / nm. However, when the drive current is decreased, the peak emission wavelength gradually shifts to longer wavelengths and lower emission intensity. When the drive current reaches 7 mA, the peak emission wavelength is about 675 nm and the emission intensity is about 0.1 μW / nm.

[0653] 29A is a schematic diagram of an LED structure on a porous template with a porous region of III-nitride material. The LED includes a current limiting layer 100 disposed between an n-doped portion of the LED (labeled n-GaN in this example) and a light emitting region, labeled as the MQW (multiple quantum well) region of the LED. Although a SiN current limiting layer 100 is shown in the figure, the current limiting layer 100 (alternatively referred to as a current constraining layer) may be formed from another dielectric material.

[0654] A circular opening 110 is provided through the center of the dielectric current-limiting layer 100. The opening extends through the thickness of the current-limiting layer and provides a conductive path between the n-doped and light-emitting regions of the LED. In the illustrated embodiment, the diameter of the opening is approximately 33% of the lateral width of the LED structure, although the width of the opening can be varied to modify the local current density through the opening.

[0655] 29B is a schematic diagram of an LED structure with a current confining layer 100 located in another location, between the p-doped portion of the LED (labeled p-GaN in this example) and the light emitting region (MQW region). An opening 110 extends through the thickness of the current confining layer 100 to provide a conductive path between the p-doped and light emitting regions of the LED.

[0656] (Fig. 30 to 35) 30 to 34 are schematic cross-sectional views of LED structures formed on porous templates according to preferred embodiments of the present invention.

[0657] The LED structure comprises a substrate, which may be silicon, sapphire, SiC, β-Ga2O3, GaN as described above. The size of the substrate may be as small as 1×1 cm-2, 50 mm, 100 mm, 150 mm, 200 mm, 300 mm or more in diameter.

[0658] A porous region is formed on a substrate, and a contact layer (layer 1) of (Al,In)GaN is formed on the porous region. An n-type layer (layer 2) of n(Al,In)GaN is disposed on the contact layer to form the n-type portion of the LED device. A pre-strained layer (layer 3) is formed on the n-type layer, and an active region (layer 4) including multiple quantum wells (MQWs) is disposed on top of the pre-strained layer and below a p-type layer (layer 5) of p-(Al,In)GaN.

[0659] This is a typical LED structure formed on a porous semiconductor template. The porous region may be a uniform porous layer or region, or it may be a partially patterned porous region.

[0660] The porous region can be any of the porous regions described above and various thicknesses, compositions, and configurations are possible within the scope of the present invention.

[0661] In a preferred embodiment of the present invention, as shown diagrammatically in Figure 31, two V-shaped pits are formed in the LED structure, which have a V-shaped cross section and penetrate the top portion of the LED structure to create a V-shaped void.

[0662] As shown, a first V-shaped pit 311 extends from the connection layer (layer 1) to the top surface of the LED device, which is formed by the outer surface of the p-type layer (layer 5). The narrow tip of the V-shaped pit is located in the connection layer, and the width of the pit increases with each layer epitaxially grown on top of the connection layer, reaching its widest point at the surface of the p-type layer.

[0663] A second V-shaped pit 312 extends from the pre-strained layer (layer 3) to the top surface of the LED device, which is formed by the outer surface of the p-type layer (layer 5).

[0664] As shown in Figure 32, first and second V-shaped pits 311, 312 extend through the active region MQW of the LED structure. As such, the V-shaped pits create gaps or voids in the semiconductor structure. The V-shaped pits may be generated in either layer 1 or layer 3, but must extend through the fourth layer, which is the MQW region.

[0665] The active light emitting multiple quantum wells (MQWs) and quantum barriers (QBs) may be made of (Al,In)GaN and (Al,In)GaN, respectively, and may be of virtually any combination of materials, compositions, and thicknesses. The MQWs may have any period from 1×QW, 2×QW, 3×QW, 4×QW, 5×QW, up to 10×QW or more.

[0666] In some preferred embodiments, the QWs are continuous. In some preferred embodiments, the QWs are fragmented.

[0667] The V-shaped pits may originate or result from the presence of threading dislocations. Alternatively, the V-shaped pits may be formed by a different growth mode in the epitaxy process, namely by three-dimensional growth.

[0668] The growth of V-pits is described, for example, in The effect of nanometre-scale V-pits on electronic and optical properties and efficiency droop of GaN-based green light-emitting Diodes; Zhou et al; Scientific Reports | (2018) 8:11053 | DOI:10.1038 / s41598-018-29440-4.

[0669] As shown in Figure 33, a second V-shaped pit 312 originates from a threading dislocation 330. The threading dislocation originates in the porous region or connecting layer (layer 1) and extends upward through the successively deposited layers of semiconductor material (layers 1 and 2). In the pre-strained layer (layer 3), the threading dislocation 330 begins to widen into a V-shaped pit 312, which becomes wider as more semiconductor layers are epitaxially grown on layer 3.

[0670] As the V-pit advances through the MQW active region during epitaxial growth, MQWs will also grow on the sidewalls 340 of the V-pit. The deposited MQWs will be of a different thickness and composition compared to a planar MQW in the absence of such a pit.

[0671] Because the formation of the V-shaped pit begins before the active region containing the MQWs is deposited, the semiconductor material that is epitaxially deposited on the underlying layers is deposited into the V-shaped pit. In the V-shaped pit, the layers of material that form the MQWs are thus distorted as they are stretched downward along the sidewalls 340 of the V-shaped pit. This is shown in the transmission electron microscope (TEM) image of FIG.

[0672] As shown in Figure 35, on either side of the V-shaped pit 312, the layers of the semiconductor structure are grown as flat planar layers. Thus, the active MQW region is flat around the periphery of the V-shaped pit (on either side as shown in the cross-section). However, at the location of the V-shaped pit, the MQW layers are distorted and stretched downward into the V-shaped pit along the sidewalls 340. This stretching effect changes the thickness of the QWs on the sidewalls 340 of the pit, which results in a different thickness of QWs on the sidewalls compared to the flat QW layer formed throughout the rest of the LED structure. The inventors have found that the V-pits can create localized strain relaxation, and the MQWs deposited on the sidewalls of these V-pits have different thickness and composition compared to the rest of the MQWs, causing the MQWs in the region of the V-pits to generate different emission wavelengths.

[0673] (Fig. 36 and Fig. 37) Figure 36 is a graph of normalized intensity versus peak emission wavelength for a tunable LED including the V-shaped pits shown in connection with Figures 31-35. As the driving conditions applied to the LED are changed, the LED emits light at different peak emission wavelengths. As shown in Figure 36, the peak emission wavelength of the LED can be varied over a continuous wavelength range from about 530 nm to about 640 nm.

[0674] Figure 37 is a graph of peak emission wavelength versus drive current for a tunable LED in accordance with the present invention. Figure 37 shows that as the drive current applied to the LED is increased, the peak emission wavelength changes smoothly from about 550 nm to about 635 nm, with higher drive currents causing the LED to emit at shorter wavelengths, while lower drive currents cause the LED to emit at lower wavelengths. The change in peak emission wavelength is continuous and consistent as the drive current is changed, making scaling of the LED device simple.

[0675] (Fig.38) Figure 38 is a graph of the peak emission wavelength for tunable LEDs with different pixel sizes. As shown in Figure 38, varying the size of the LED pixel affects the peak emission wavelength at which the pixel emits. Under the same driving conditions, pixels of different sizes (which are identical except for the size) will emit at different peak wavelengths.

[0676] (Fig. 39 and Fig. 40) 39 and 40 are schematic cross-sectional side views of tunable LED structures according to two alternative embodiments.

[0677] In the following examples, the LEDs and LED subpixels are preferably tunable LEDs as described above.

[0678] The LED structure of Figures 39 and 40 shows a simplified diode structure in which a light emitting region comprising a multiple quantum well (MQW) is disposed between first and second semiconductor layers. The LED structure is provided on a substrate which preferably comprises a porous region of semiconductor material.

[0679] 39 and 40 show alternative arrangements of electrical contacts attached to an LED. In both embodiments, a first electrical contact is shown disposed on a first semiconductor layer. An electrically insulating masking layer 390 (sometimes referred to as a passivation layer) is partially disposed between the first semiconductor layer and the first contact layer, such that the first contact layer contacts the first semiconductor layer only through the openings in the masking layer 390. The size of the openings determines the contact area where the first semiconductor layer and the first contact layer contact each other. When a drive current is applied through the electrical contacts, this contact area limits the area through which the drive current can flow to the LED structure. The size of the contact area and the magnitude of the drive current determine the current density experienced by the LED structure, which in turn determines the peak emission wavelength of the light emitted by the MQWs.

[0680] In FIG. 39 and FIG. 40, the second contact layer is arranged differently.

[0681] In Figure 39, the second contact layer is positioned to contact the second semiconductor layer through an opening in masking layer 390. As with the first contact layer, the size of the opening determines the contact area shared by the second contact layer and the second semiconductor layer.

[0682] In FIG. 40, the second contact layer is disposed on the substrate rather than on the first semiconductor layer.

[0683] The LED structures of Figures 39 and 40 may be formed as described above in connection with Figures 1-18, with the first and second semiconductor layers acting as p-type and n-type layers such that the MQW emits light at a peak wavelength when a drive current is applied between the two electrical contacts.

[0684] The first semiconductor layer may include, but is not limited to, p-Gan and n-Gan.

[0685] The first contact layer may include, but is not limited to, titanium, platinum, chromium, aluminum, nickel, gold, and several compounds such as ITO (indium tin oxide).

[0686] Since the emission wavelength blue-shifts with increasing injection current density, there are different contact areas to control the current density, as shown in FIG.

[0687] FIG. 41 shows three different contact areas between the contact layer and the semiconductor layer in an LED diode. A first electrical contact layer is shown disposed on the first semiconductor layer. An electrically insulating masking layer 390 is partially disposed between the first semiconductor layer and the first contact layer such that the first contact layer contacts the first semiconductor layer only through the opening in the masking layer 390. The size of the opening determines the contact area where the first semiconductor layer and the first contact layer contact each other. When a drive current is applied through the electrical contact, this contact area limits the area through which the drive current can flow to the LED structure. The size of the contact area and the magnitude of the drive current determine the current density experienced by the LED structure. The current density experienced by the LED structure, in turn, determines the peak emission wavelength of the light emitted by the MQW.

[0688] FIG. 42 is a plan view of electrical contacts placed on the LED subpixel mesas. The maximum contact possible is with the entire area of ​​the LED subpixel mesa, resulting in a contact ratio of 1:1, so the contact area A contact is the area of ​​the subpixel mesa A mesawill necessarily be smaller than

[0689] 43A-43C show three alternative ways to obtain RGB sub-pixels using three sub-pixels with the same diode structure.

[0690] In Figure 43A, the three subpixel mesas have the same subpixel mesa area, but different sizes of electrical contact pads. Different sizes of electrical contact pads mean that each of the three subpixels has a different contact area, and therefore each of the subpixels has a different contact ratio (ratio of contact area:light emitting area, which is the same as ratio of contact area:subpixel mesa area, since the light emitting area spans the entire subpixel mesa). The left subpixel has the largest contact area and therefore the largest contact ratio. The right subpixel has the smallest contact area and therefore the smallest contact ratio. The middle subpixel has a contact area and contact ratio between the other two.

[0691] The smaller the contact ratio, the smaller the contact area through which the drive current passes to supply the subpixel, and therefore the higher the current density experienced by the subpixel. As shown in Figures 27A and 27B, a higher current density results in a shorter peak emission wavelength, so that of the three subpixels in Figure 43A, the left subpixel emits light with the longest peak wavelength and the right subpixel emits light with the shortest peak wavelength.

[0692] In a particularly preferred embodiment, the contact ratios and drive currents of the three subpixels are selected such that the three subpixels emit red (left subpixel), green (centre subpixel), and blue (right subpixel) in response to a single drive current.

[0693] FIG. 43B shows an alternative way to arrive at the same three contact ratios as FIG. 43A. In FIG. 43B, the three subpixels still have the same mesa area, and therefore the same light-emitting area. In FIG. 43B, the three electrical contact pads also have the same area when viewed from above. However, a masking layer 390 is placed between the subpixels and the electrical contact layer, and the masking layer on the three subpixels has openings of different sizes. The size of the opening controls the contact area, since the contact layer can only contact the subpixel diode structure through the opening. The left subpixel has the largest opening in the masking layer, and therefore the largest contact area, which results in the largest contact ratio. The right subpixel has the smallest opening through the masking layer, and therefore the smallest contact area and contact ratio. The center subpixel has a masking layer opening that is a size between the other two subpixels, which results in the contact area and contact ratio between the other two subpixels.

[0694] The size of the openings in the masking layer are selected to create the same contact area as the subpixels of Figure 43 A. Thus, in response to the same drive current, the three subpixels of Figures 43A and 43B will emit at three corresponding peak emission wavelengths, preferably RGB wavelengths.

[0695] FIG. 43C shows a third method for making three subpixels with the same contact ratio as shown in FIGS. 43A and 43B.

[0696] In Figure 43C, the three subpixel mesas each have a different subpixel mesa area and each have a different sized electrical contact, creating different contact areas on the three subpixels. However, in Figure 43C, the relative sizes of the subpixels and contact areas are the same as those shown in Figures 43A and 43B. Thus, the red subpixel shown on the left in Figure 43C has the same contact ratio as the left red subpixel in Figures 43A and 43B, the green subpixel shown in the top right of Figure 43C has the same contact ratio as the center green subpixel in Figures 43A and 43B, and the blue subpixel shown in the bottom right of Figure 43C has the same contact ratio as the right blue subpixel in Figures 43A and 43B. Because the peak emission wavelength at a given drive current is determined by the contact ratio (the ratio of contact area:light-emitting area, which is the same as the ratio of contact area:subpixel mesa area because the light-emitting area spans the entire subpixel mesa), all of the subpixels in Figures 43A-43C will emit at the same three wavelengths in response to the same drive current.

[0697] Figures 44 and 45 show three LED subpixels formed from a single LED structure, similar to the embodiment shown in Figure 13. However, in the embodiment shown in Figures 44 and 45, instead of each LED subpixel having a uniform metal contact layer 9, the three subpixels each have different sized electrical contacts 9A, 9B, 9C, which creates different contact areas between the contacts and the three subpixel diode structures.

[0698] The embodiment of FIG. 44 corresponds to the example of FIG. 43A, where all three subpixels have the same mesa size and therefore the same light-emitting area, but the three electrical contacts are formed in openings of different sizes in the electrically insulating masking layer 8. The left subpixel has the largest electrical contact 9A and therefore the largest contact area and the largest contact ratio. The right subpixel has the smallest electrical contact 9C and therefore the smallest contact area and the smallest contact ratio. The middle subpixel has an electrical contact 9B with a size between the sizes of the other contacts 9A, 9C and therefore the middle subpixel has a contact area and contact ratio between the other two subpixels. These three subpixels will emit light at three different peak wavelengths in response to the same drive current. The left subpixel will emit light at the longest wavelength because it has the highest contact ratio, and the right subpixel will emit light at the shortest wavelength because it has the lowest contact ratio.

[0699] Figure 45 is a similar view to Figure 43B, in which the electrical contacts 9A, 9B, 9C have the same size when viewed from above, but the contact areas of the electrical contacts with the three subpixels are controlled by the size of the openings through the masking layer 8. Because the contact areas of the electrical contacts 9A, 9B, 9C with the three subpixels are the same as in Figure 44, the three subpixels will emit light at corresponding wavelengths in response to the same drive current.

[0700] 46A-46G show alternative embodiments of the light emitting area of ​​a tunable LED according to the present invention.

[0701] MQW example: 1. Continuous MQW 2. V Pit 3. Intermittent QW, gapped QW, and fragmented QW 4.QD 5. Fluctuations in well width 6.Alloy composition 7. Different combinations of MQW and underlayer

[0702] These structural features can be identified and examined by standard materials characterization techniques such as cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX or EDS), and three-dimensional atom probe (3DAP).

[0703] FIG. 46A shows a continuous MQW light emitting region of an LED, with three identical QWs spaced between four identical quantum barriers (QBs).

[0704] Figure 46B shows the continuous MQW of Figure 46B with a V-shaped pit propagating through the light-emitting region. The V-shaped pit terminates in a threading dislocation and has a QW on its semipolar facet.

[0705] FIG. 46C illustrates an MQW where the QW layer comprises a discontinuity or gap in the semiconductor material.

[0706] Figure 46D shows an MQW in which quantum dots (QDs) create inhomogeneities in the MQW. The QDs can be located on or in the QB layer or the QW layer, for example in gaps in the QW structure.

[0707] Figure 46E shows an MQW with well width fluctuations, where the thickness of the QW layers is not uniform across the light-emitting region. The QWs may have different widths from one another and may vary in width within a single QW.

[0708] Figure 46F shows an MQW with fluctuations in alloy composition in the light-emitting region. The QB and QW compositions vary from layer to layer. In particular, the In% composition of indium varies within the same QW, i.e., for QW2, the In% varies from 10-12%, or 10-15%, or 10-25%, or 10-35%.

[0709] FIG. 46G shows MQWs with different combinations of MQWs and underlayers. The In% composition is different across different QWs. For example, QW1 has 15% In%, QW2 has 25% In%, and QW3 has 30% In%. In an embodiment of the invention, the lower In% QWs are preferably located at the bottom of the MQWs due to their strain and thermal effects, while the high In% QWs are preferably at the top. In a preferred embodiment, for example, QW1 is a blue-emitting QW, QW2 is a green-emitting QW, and QW3 is a red-emitting QW.

[0710] Figure 47A is a cross-sectional TEM image of a conventional non-tunable LED. The non-tunable LED-MQW has uniform and smooth top and bottom interfaces (here five MQWs are clearly visible).

[0711] Figures 47B and 47C are TEM images of a tunable LED with V-shaped pits according to an embodiment of the invention. The tunable LED-MQWs are non-uniform, which can be induced by a variety of methods, one example being V-pits and semipolar facets, which incorporate more indium and thinner QWs. Another example, also evident in Figure 47B, is that the MQWs are not uniform in the sense of intermittent QWs, discontinuous QWs, fragmented QWs, QWs with fluctuations in well width or In composition.

[0712] FIG. 47C shows a cross section of the tunable LED of FIG. 47B, illustrating a porous region and a light emitting region with a plurality of V-shaped pits, in accordance with a preferred embodiment of the present invention.

[0713] In this structure, the light emitting region contains multiple intentionally induced emission wavelength regions, such as multiple types of QW regions with V-shaped pits extending through the light emitting region.

[0714] V-shaped pits (V-pits) are actually hexagonal pits when viewed from above, the V-shape being in cross-section. V-pits can be initiated at the sites of dislocations during the growth of the InGaN, GaN, InGaN / InGaN superlattice, or InGaN / GaN superlattice structures underlying the MQWs under special epitaxy growth conditions, such as low growth temperatures (e.g., <1000°C, or <900°C, or <800°C, or <700°C) and nitrogen atmosphere.

[0715] 48A is a graph of peak emission wavelength versus drive current density for a conventional non-tunable LED. By varying the drive current density applied to the LED, the emission wavelength can be shifted slightly over an emission wavelength range of about 15 nm.

[0716] FIG. 48B is a graph of peak emission wavelength versus drive current density for a tunable LED according to an embodiment of the present invention. In a tunable LED, changing the current density of the drive power supply produces a much larger change in the peak emission wavelength (WLP) emitted from the LED. In this embodiment, the drive current density is set to approximately 0.1-100 A / cm. 2 When the wavelength is changed, the peak emission wavelength changes from about 635 nm to about 550 nm, i.e., an emission wavelength range of about 85 nm.

[0717] 48C is a graph of peak emission wavelength versus drive current density for a tunable LED according to another embodiment of the invention, in which the peak emission wavelength varies from about 720 nm to about 580 nm, or an emission wavelength range of about 140 nm, as the drive current density is varied.

[0718] 49A is a graph of peak emission wavelength versus drive current density for another tunable LED according to the present invention. In this embodiment, the drive current density is set to approximately 0.1-200 A / cm 2As the λ / 2 is varied, the peak emission wavelength changes from 615 nm to 508 nm, or an emission wavelength range of about 100 nm. The data in this graph only goes up to 514.5 nm due to limitations in testing capabilities; therefore, the current density at 508 nm is an estimate. However, the range of obtainable emission wavelengths can be significantly expanded in either direction.

[0719] 49B-49D are photographs of the tunable LED of FIG. 49A showing the same tunable LED emitting at four different wavelengths across its emission wavelength range. The inset emission spectra show different peak emission wavelengths at different drive current densities. This shows that the same tunable LED emits at peak emission wavelengths of orange (615 nm), yellow (556 nm), green (534 nm), and blue (508 nm) in response to different drive current densities.

[0720] (Display Device) Traditionally, a pixel in a color display is composed of multiple monochrome subpixels: a blue subpixel, a green subpixel, and a red subpixel. The observed chromaticity of the pixel is the spatial combination of the light emitted by the three subpixels, as shown in Figure 50B.

[0721] In the tunable LED of the present invention, individual LED sub-pixels can display colors over a wide spectral range, for example from blue to red. This allows different colors to be achieved using a single LED chip and different driving time frames. The observed generated pixel color is a temporal combination of the light emitted by the LED sub-pixels.

[0722] A variety of display device pixels can be configured to incorporate one or more tunable LEDs in accordance with the present invention. In all of the pixel embodiments below, the overall emitted color perceived by a viewer is the spatial and temporal combination of light emitted by the sub-pixels in any given device pixel.

[0723] Figure 51B shows a device pixel consisting of a single tunable LED. By varying the drive conditions supplied to the LED, the peak emission wavelength from this pixel can be varied over a range of emission wavelengths, the width and absolute wavelength of which are determined by the drive conditions and the size and structure of the LED diode.

[0724] Figure 50C shows a device pixel with two subpixels, both of which are tunable wavelength LEDs in accordance with the present invention. The two subpixels are separately controlled by separately controlling the drive current supplied to each subpixel, and thus can be controlled to emit at different wavelengths.

[0725] Figure 50D shows a device pixel with three tunable LED subpixels. By controlling the drive current supplied to the three separate subpixels, the peak emission wavelength of each subpixel can be individually varied.

[0726] FIG. 50E shows a device pixel with one tunable subpixel and one fixed emission wavelength subpixel.

[0727] FIG. 50F shows a device pixel with one tunable subpixel and two fixed emission wavelength subpixels.

[0728] Figure 50G illustrates a device pixel with two fixed emission wavelength blue and red subpixels, and two fixed emission wavelength green subpixels configured to emit at different peak wavelengths in the green range of the spectrum, where the green subpixels are tunable subpixels and are configured to receive two different fixed drive current densities corresponding to different peak emission wavelengths in the green range.

[0729] (Extended color gamut display devices) Conventional LED displays typically display color by combining light from sub-pixels of different primary colors, as shown in Figure 50 A. A conventional pixel includes red, green, and blue sub-pixels.

[0730] The combination of light from the three primary color sub-pixels makes it possible to display any color within the triangle (defined by the primary colors) shown in Figure 51 A. The triangle shown in Figure 51 A defines the color gamut that can be achieved with such a display. Color space outside the triangle cannot be accessed by a conventional three sub-pixel pixel, limiting the color gamut that can be achieved by the pixel.

[0731] Solutions for expanding the color gamut: Including additional sub-pixels of different colors, where the color gamut is defined by a quadrilateral as shown in Figure 51B. This requires additional cost and complexity. Further expansion to 4 or more subpixels would further expand the color gamut but would increase complexity and cost.

[0732] Incorporation of the tunable LED of the present invention into an LED display device preferably provides a chromaticity controllable display device having an emission spectrum that is strongly dependent on drive current density, a peak emission wavelength shift of more than 20 nm / decade, and an LED structure with a peak emission wavelength that is controllable from 450 nm to 630 nm or wider.

[0733] The display comprises sub-pixels formed from LED devices with controllable chromaticity (tunable emission wavelength).

[0734] Preferably, the sub-pixels have the same diode structure, and the peak emission wavelength from any given sub-pixel is controlled solely by the current density supplied to that sub-pixel during use.

[0735] The subpixels may have a constant chromaticity (e.g., in response to a fixed drive current) or may vary in chromaticity (in response to a varying drive current) such that a larger gamut of colors can be achieved, the achievable gamut being equal to or larger than the gamut defined by the sRGB primaries.

[0736] In some embodiments, all of the sub-pixels may dynamically change chromaticity every frame, while in other embodiments, only some of the sub-pixels may dynamically change chromaticity every frame.

[0737] Thus, one or more tunable LEDs according to the present invention may be incorporated into a display device to achieve a wide color gamut.

[0738] FIG. 51C shows the expanded color gamut achievable with a wavelength-enabled LED device when the peak emission wavelength is controlled between 450 nm and 620 nm.

[0739] (Embodiment 1 (FIGS. 52A to 52D)) Figure 52A shows a display pixel with three subpixels, each of which can be an LED device with controllable peak wavelength of light emitted.

[0740] When viewed from a distance, the observed emission chromaticity is a spatial and temporal combination of the sub-pixel emissions.

[0741] The blue (B) and red (R) sub-pixels are operated with a fixed emission corresponding to a fixed observed chromaticity. The peak emission wavelengths of the B and R sub-pixels are fixed by supplying drive currents having fixed magnitudes, which correspond to the current densities required for emission at the desired blue and red wavelengths.

[0742] The green (G) subpixel can be operated in two modes with different peak wavelengths by providing two separate drive current modes with different magnitudes corresponding to the current densities required for emission at the two desired green wavelengths. The green subpixel can be operated in either green mode by switching to the desired drive current mode.

[0743] Combined with the B and R sub-pixels, each of the two G sub-modes is capable of displaying a different color gamut.

[0744] The effective color gamut of a display is the color gamut that can be realized by the G subpixel in each mode.

[0745] Along these lines, if tunable LEDs are used for the R or B subpixels, these subpixels can also be switched between two or more modes. Switching every pixel between two or more modes allows the color gamut to be set once or dynamically controlled during normal operation.

[0746] In an alternative embodiment, conventional blue and red LEDs may be incorporated into the pixel to act as the blue and red subpixels, with a tunable LED forming the green subpixel.

[0747] (Embodiment 2 (FIG. 53)) A display formed such that each display pixel comprises three sub-pixels, each of which is preferably a tunable LED device, as described above, that emits light with a controllable peak wavelength.

[0748] During operation of the display device, the subpixels are switched from emitting one peak wavelength to emitting a different peak wavelength within a unit of time, as shown in Figure 53. The peak emission wavelength of any given subpixel is changed by varying the magnitude of the drive current supplied to that subpixel. The unit of time may be one display frame, or may be shorter such that there are several unit times during a single display frame.

[0749] Emission of peak wavelengths requiring high current densities can cause significant localized heating, affecting the performance and reliability of the entire device and display.

[0750] The advantage of this method of controlling the sub-pixels is that the heating of the sub-pixels is more evenly distributed and shared across the display pixel, avoiding hot spots on any particular sub-pixel.

[0751] Although the B and R subpixels are shown swapped in the four time units shown in Figure 53, the G subpixel can also switch emission wavelength if it is a tunable LED. Any combination can be switched in the present invention by simply varying the drive current supplied to the different subpixels.

[0752] (Embodiment 3 (FIGS. 54A and 54B)) Figure 54A shows a schematic of a display device formed with a pixel comprising four sub-pixels, each of which is preferably a tunable LED device with controllable peak wavelength of light emitted as described above, although in the embodiment shown the B and R sub-pixels could alternatively be provided by conventional blue and red LEDs.

[0753] The display comprises multiple sub-pixels of the same color (e.g., red, green, or blue, because each of these "colors" is commonly accepted as spanning the entire wavelength range of the visible spectrum) that are configured to emit at different peak wavelengths within that color.

[0754] For example, in a preferred embodiment, a pixel "color" may be 400 nm to 450 nm (purple), 450 nm to 500 nm (blue), 500 nm to 570 nm (green), 570 nm to 590 nm (yellow), 590 nm to 610 nm (orange), or 610 to 700 nm (red). If there are multiple subpixels within a given "color," then all of the subpixels may be configured to emit at any wavelength within one of these ranges.

[0755] In a preferred embodiment shown in Figure 54A, a display pixel comprises two green sub-pixels having different peak wavelengths.

[0756] The advantage of this pixel design is that the color gamut of the display is expanded without the need to switch a single LED subpixel between G subpixel operation modes (as required in Figures 52A-52D).

[0757] In the embodiment shown in Figures 54A and 54B, the peak emission wavelength of the green (G) subpixel G1 is different from the peak emission wavelength of the green subpixel G2.

[0758] By extension, there may (in addition or alternatively) be two R pixels or two B pixels with different peak wavelengths. For example, a pixel may include two red sub-pixels R1 and R2 with different peak emission wavelengths in the red, and / or a pixel may include two blue sub-pixels B1 and B2 with different peak emission wavelengths in the blue.

[0759] In either case, the LED devices may preferably have the same diode structure (N, active area, P), and only the drive current density is used to control the emission peak wavelength. This can be applied to all embodiments. Thus, for example, two green subpixels G1 and G2 may be identical in structure to each other, but driven with different drive current densities. Due to the difference in drive current density, G1 will emit light at a different peak emission wavelength than G2.

[0760] (Embodiment 4 (FIGS. 55A to 55D)) FIG. 55A shows a schematic of a pixel of a display device with two sub-pixels, each of which is a tunable LED device whose peak wavelength of light it emits is controllable.

[0761] When viewed from a distance, the observed emission chromaticity is a spatial and temporal combination of the sub-pixel emissions.

[0762] Every sub-pixel is actuated with a controllable emission that corresponds to a particular observed chromaticity.

[0763] Any of the sub-pixels may preferably be controllable to emit with a peak emission wavelength between 450 nm and 630 nm by varying the drive current supplied to the sub-pixel. Figure 55B shows the chromaticity that the pixel can achieve when the peak emission wavelength of the two tunable sub-pixels is varied from 450 nm to 620 nm.

[0764] As shown in FIG. 55C, for any observed set of chromaticity points that can be displayed by two sub-pixels, all chromaticities that lie on a straight line between the points can be displayed.

[0765] The effective color gamut of the display is shown in FIG. 55D and is defined by a line corresponding to the chromaticity of the LED device when the peak emission wavelength is controlled to 450 nm to 630 nm, and a straight line connecting the maximum and minimum peak emission wavelengths.

[0766] (Embodiment 5 (FIG. 56)) Figure 56 shows a pixel of a display formed with two sub-pixels, each of which is preferably a tunable LED device with controllable peak wavelength as described above, although in the embodiment shown the R sub-pixel could alternatively be provided by a conventional red LED.

[0767] In Figure 56, one subpixel has a controllable emission in the wavelength range, for example, 450nm to 530nm (B to G). The other subpixel is operated at a fixed emission wavelength corresponding to a fixed observed chromaticity, for example, 630nm (R). Even though the R subpixel is a tunable LED, the peak emission wavelength of the R subpixel can be fixed by providing a drive current of a fixed magnitude corresponding to the current density required to emit light at the desired red wavelength.

[0768] This is particularly advantageous because, although a higher drive current is required to achieve blue emission, resulting in increased radiant flux, the human eye's lack of sensitivity to blue light results in a smaller than expected change in luminous flux from a green-blue pixel as the peak wavelength shifts between about 530 nm and about 450 nm, thereby reducing control complexity and enabling more efficient displays.

[0769] (Embodiment 6 (FIG. 57)) FIG. 57 shows a pixel of a display formed from a pixel with three sub-pixels, each of which is a tunable LED device whose peak wavelength of light it emits is controllable.

[0770] When viewed from a distance, the observed emission chromaticity is a spatial and temporal combination of the sub-pixel emissions.

[0771] Subpixel SP1 is configured to emit light at a wavelength between 440 nm and 480 nm by varying the magnitude of the drive current supplied to SP1 in use. Subpixel SP2 is configured to emit light at a wavelength between 500 nm and 540 nm by varying the magnitude of the drive current supplied to SP2 in use. Subpixel SP3 is configured to emit light at a wavelength between 580 nm and 620 nm by varying the magnitude of the drive current supplied to SP3 in use. SP1, SP2 and SP3 thus operate as blue (B), green (G) and red (R) subpixels respectively, and by varying the magnitude of the drive current to each subpixel, the peak emission wavelength of each subpixel can be varied over an emission wavelength range of 40 nm.

[0772] Each of R, G, and B can operate in multiple modes with peak wavelengths that are switchable 20 nm above and below the central wavelength.

[0773] When combined, each mode allows a different color gamut to be displayed.

[0774] As shown in Figure 57, the effective color gamut of the display is wider than what is achievable with R, G, and B sub-pixels having fixed emission wavelengths.

[0775] (Generalization of embodiment 6 (FIG. 58)) FIG. 58 shows a pixel of a display formed from a pixel with three sub-pixels, each of which is a tunable LED device whose peak wavelength of the light it emits is controllable.

[0776] When viewed from a distance, the observed emission chromaticity is a spatial and temporal combination of the sub-pixel emissions.

[0777] Each tunable subpixel is controllable to emit light over a wide emission wavelength range such that each subpixel can be operated as a red, green, or blue subpixel depending on the drive current supplied to the subpixel. The subpixels are controllable to operate in multiple modes having different peak wavelengths.

[0778] When combined, each mode allows a different color gamut to be displayed.

[0779] As shown in Figure 58, the effective color gamut of a display is the color gamut that is achievable by the R, G, and B sub-pixels in any mode.

[0780] For each chromaticity in the possible color space, there exists a continuous range of primary color combinations that make it possible to display this chromaticity.

[0781] The choice of which combination to select when controlling a display device is preferably made by calculating the efficiency of each combination and selecting the most efficient one.

[0782] The efficiency calculation may advantageously be made taking into account: - the luminous efficiency from each subpixel at a particular peak emission wavelength; - the amount of light emission required for each sub-pixel to achieve a selected chromaticity and luminance; - the light extraction efficiency from the active area of ​​the LED device to the observer, - Efficiency of power delivery from the display device driver to the LED device.

[0783] (Temporal Color Control) In a typical display, different colors cannot be displayed at the same location. Therefore, each emitting area (pixel) is divided into single-color regions (subpixels) that can be addressed separately. When viewed from a distance, the color seen is a spatial combination of the colors of the subpixels. A subpixel emits a fixed chromaticity that is different from the other subpixels.

[0784] By adjusting the proportional amount of light emitted from each subpixel, the observed chromaticity of the pixel is set, as shown in Figure 50A.

[0785] Typically, three or more sub-pixels are required for a display to be able to display a wide range of colors (wide color gamut). Reducing the number of sub-pixels is advantageous for reducing cost and complexity, but doing so will affect the achievable color gamut.

[0786] In some prior art display technologies, it is not possible to create all color subpixels from the same material, which requires significant cost and complexity to combine and arrange subpixels made from different semiconductor materials and form the pixels into a display.

[0787] Sub-pixels with different emission characteristics have different efficiencies, resulting in locally non-uniform heating.

[0788] More efficient subpixels require shorter drive times ("on times") to achieve a particular observed chromaticity than less efficient subpixels. It is inefficient to have a system in which large numbers of subpixels are not emitting light for a significant percentage of the time.

[0789] Incorporating the tunable LEDs of the present invention into a display device provides a display in which each pixel is capable of emitting a wide range of colors.

[0790] Each pixel comprises multiple subpixels, however, in some embodiments, a single wavelength capable LED may be used to form a pixel having only one subpixel, as shown in Figure 59A.

[0791] The peak wavelength, and therefore the chromaticity, of the light emitted from a subpixel depends on the drive current: by selecting drive signals that cause the drive current to be varied during a display frame, the observed chromaticity of the pixel is determined by the temporal combination of colors emitted in sequence from one or more subpixels.

[0792] Greyscale control at each chromaticity is achieved using varying the duty cycle of the sub-pixels.

[0793] The present invention can advantageously provide displays with fewer than three sub-pixels that are capable of displaying a wide color gamut, which has significant advantages over prior art displays.

[0794] Benefits and all advantages of the present invention compared to existing solutions: - Reducing the number of sub-pixels reduces complexity and cost. - Pixels can be constantly illuminated, increasing system efficiency and therefore observed brightness. - The pixel heats up when operated at high currents, but operation at a low drive current allows the pixel to cool.

[0795] (Embodiment 7) Figure 59A shows a preferred embodiment in which a pixel of a display device consists of a single tunable LED. By varying the drive current supplied to the pixel, the peak emission wavelength of the LED can be varied over a wide emission wavelength range, as discussed above, such that colors from blue to red can be emitted by the device pixel.

[0796] In the case of a single pixel, duty cycle control is used to access different greyscale levels: the duration that a current pulse is applied to the pixel can be varied to control the observed pixel brightness.

[0797] In a preferred embodiment shown in Figures 59B and 59C, the display device is configured to provide three separate drive current modes to the LED pixels. blue , I green , or I red The LED may be operated to supply one of the following:

[0798] The color of a pixel seen by a viewer is the temporal combination of the light that the pixel emits during a display frame. In Figure 59B, each of the three drive modes is applied for 1 / 3 of the display frame, so that the observed color of the pixel is an equal mix of blue, green, and red wavelengths.

[0799] Figure 59C shows an alternative control mode in which each of the three drive currents is supplied for 1 / 6 of the display frame. Because the duty cycles of each drive current are still equal to each other, the observed pixel color will be an equal mix of blue, green, and red wavelengths, just like in Figure 59B. However, in Figure 59C, the overall on-time of the subpixels is shorter, so the pixel brightness will be lower than with the control mode of Figure 59B.

[0800] Figures 60A to 60D show three drive current modes I blue , I green , or I red Figure 60 shows the case where LEDs are supplied with the same overall duty cycle, but in a different order. For a single pixel, the four drive scheme variations shown in Figures 60A-60D will yield equivalent results, since the viewer experiences the time average.

[0801] (Embodiment 8) In some preferred embodiments, a pixel may comprise multiple tunable subpixels that are configurable to emit at different peak emission wavelengths in response to different drive currents, for example a single subpixel may be drivable to emit at wavelengths ranging from blue to red in response to changes in the drive current supplied to that subpixel.

[0802] FIG. 61A shows a display device pixel that includes two sub-pixels, each of which is a tunable LED with an emission wavelength range encompassing blue to red wavelengths.

[0803] Drive Scheme A in Figure 61B shows a drive scheme for the upper sub-pixel and a different drive scheme for the lower sub-pixel. Both the upper and lower sub-pixels are driven in a blue drive mode for 1 / 4 of the display frame, in a green drive mode for 1 / 4 of the display frame, and in a red drive mode for 1 / 2 of the display frame. The color of a pixel seen by a viewer is a temporal combination of the light emitted by the pixel during a display frame, so that both the upper and lower sub-pixels appear to emit light of the same color.

[0804] Driving Scheme B in Figure 61C shows an alternative driving scheme that uses shorter current pulses to achieve the same result as Driving Scheme A. Despite the shorter current pulses, the upper and lower sub-pixels are still driven in blue, green, and red modes with the same total duty cycle, so the observed color will be the same.

[0805] In all of these driving schemes, the produced pixel color is a spatial and temporal combination of the emitted colors.

[0806] (Embodiment 9) In some preferred embodiments, a pixel may comprise a plurality of subpixels, at least one of which is a tunable subpixel configurable to emit light at different peak emission wavelengths in response to different drive currents, for example, a single subpixel may be drivable to emit light at wavelengths ranging from blue to red in response to changes in the drive current supplied to that subpixel.

[0807] In some particularly preferred embodiments, each pixel may comprise two sub-pixels, in which case: One subpixel is activated with a fixed color, One subpixel changes color.

[0808] The advantage of this arrangement is that the less efficient sub-pixels can have a longer "on time".

[0809] Figure 62 shows a display device pixel that includes two subpixels. The top subpixel is a tunable LED with an emission wavelength range encompassing wavelengths from blue to green, while the bottom subpixel is a red subpixel. The red subpixel may be a conventional red LED subpixel incorporated into a display device, but preferably the red subpixel is a tunable LED with an emission wavelength range encompassing red wavelengths.

[0810] FIG. 62 shows that the upper subpixels are in blue mode I during a display frame. blue and Green Mode I green while the lower red subpixel can be driven by applying pulses of drive current in red drive mode I red It is shown that the LTC3411 can be driven by applying a continuous drive current of

[0811] This arrangement may advantageously provide a simplified RGB pixel.

[0812] The emission colors shown are merely examples, as subpixels having fixed emission wavelengths of colors other than red may be provided as well, and subpixels having controllable emission wavelengths over ranges other than blue to green may be provided.

[0813] (Embodiment 10) In some preferred embodiments, a pixel may comprise a plurality of sub-pixels that are tunable sub-pixels that are configurable to emit light at different peak emission wavelengths in response to different drive currents.

[0814] In the embodiment shown in Figure 63, for example, a single top subpixel can be driven to emit light in wavelengths ranging from blue to red in response to changes in the drive current supplied to that subpixel, and a separate bottom subpixel can be driven to emit light in wavelengths ranging from green to red in response to changes in the drive current supplied to that subpixel.

[0815] In some particularly preferred embodiments, each pixel may comprise two subpixels, where a first tunable subpixel is drivable to emit light over a first range of wavelengths in response to changes in the drive current supplied to that subpixel (e.g., the drive current is controlled over a first drive current range) and a second tunable subpixel is drivable to emit light over a second range of wavelengths in response to changes in the drive current supplied to that subpixel (e.g., the drive current is controlled over a second drive current range). Preferably, the first wavelength range covers a different range of wavelengths than the second wavelength range, although the first wavelength range may overlap with the second wavelength range.

[0816] In this embodiment, both sub-pixels change color.

[0817] The advantage of this arrangement is that a higher drive current that causes significant localized heating is followed by a lower drive current that does not, thereby allowing the sub-pixels to maintain a more stable temperature.

[0818] Figure 64A is a schematic diagram of the drive current conditions for a tunable LED according to the present invention. During a single display frame, the drive current is activated in three different non-zero modes. The duty cycle (duration of the drive current pulse relative to the display frame) of each mode is different and individually controllable.

[0819] The current gain of the drive current determines the wavelength produced by the tunable sub-pixel, while the duty cycle of the drive current determines the grayscale level produced by the sub-pixel.

[0820] The length of the display frame may be varied to accommodate any desired frame rate, and may be controlled by controlling the LED drive conditions provided by the power supply.

[0821] When a pixel is formed by a single LED, duty cycle control is used to access different grey scale levels.

[0822] The following embodiments illustrate various possible driving conditions that can be used to control a display device comprising one or more tunable LED subpixels according to the present invention.

[0823] These control methods advantageously allow dynamic pixel adjustment of the LEDs of a display device.

[0824] (Embodiment 11 (Figure 65)) A single pixel may be one or more sub-pixels, and each sub-pixel can change color according to image information (the sub-pixels can display colors ranging from blue to red). Each pixel can determine its own color by modulating the signal to generate image information. The color and brightness of a pixel is a combination of the duty cycle and amplitude of the signal pulse.

[0825] (Embodiment 12 (Figure 66)) A single pixel may have three or more sub-pixels (capable of displaying colors ranging from blue to red). The sub-pixel size will be the same. Each sub-pixel can determine its own color by modulating a signal, and the image information for each pixel can be determined by combining multiple sub-pixels. The color and brightness of a pixel is a combination of the duty cycle and amplitude of the signal pulse. For a single pixel, these drive scheme changes are equivalent since the viewer experiences the time average.

[0826] (Embodiment 13 (Figure 67)) A single pixel may have three or more sub-pixels (capable of displaying colors ranging from blue to red). The tip size is varied to adjust the current magnitude and pulse width. Each sub-pixel can determine its own color by modulating a signal, and the image information for each pixel can be determined by combining multiple sub-pixels. The color and brightness of a pixel is a combination of the duty cycle and amplitude of the signal pulse.

[0827] (Embodiment 14 (Figure 68)) A single pixel may have three or more sub-pixels (capable of displaying colors ranging from blue to red). The chip size is optimized to achieve the same driving mode for each sub-pixel. Each sub-pixel can determine its own color by modulating a signal, and the image information for each pixel can be determined by combining multiple sub-pixels. The color and brightness of a pixel is a combination of the duty cycle and amplitude of the signal pulse.

[0828] (Embodiment 15 (Figure 69)) Some sub-pixels may be focused on generating specific colors through signal modulation, while other sub-pixels may change color (capable of displaying colors ranging from blue to red) as required by the image information. The sub-pixel sizes may be the same or different. Each sub-pixel can determine its own color by modulating a signal, and the image information for each pixel can be determined by combining multiple sub-pixels. The color and brightness of a pixel is a combination of the duty cycle and amplitude of the signal pulse.

[0829] (Spectral reconstruction) In many applications it is desirable to be able to reproduce a particular spectrum of light.

[0830] In the prior art, this is achieved by: Modulating the intensity of one or more illumination sources with a fixed broadband emission spectrum: this is subtractive and therefore inherently inefficient. Combining the emission from multiple narrowband emission sources, which has limited scalability due to the fixed number of emission sources. Using filters to modify light from a high power broadband spectrum source, which has the disadvantages of inherent inefficiency and limited tunability due to a fixed number of tuning elements.

[0831] As shown in Figures 70-79, an embodiment of the present invention relates to the use of a tunable LED light source, where the emission wavelength is continuously tunable through control of the applied current.

[0832] The tunable LED light source may be driven in turn with multiple different current pulses. The different current pulses may have different magnitudes or amplitudes. The time at which a particular current pulse is applied may differ from the time at which other current pulses are applied to the tunable LED.

[0833] The emission wavelength emitted by a tunable LED is a function of the drive conditions applied to the LED at any one time, so that each applied current pulse of different amplitude will produce a different peak emission wavelength.

[0834] In a preferred embodiment, the total length of the pulses applied at different current amplitudes is shorter than the response time of the detector (approximately 50 ms for the human eye as the detector), and the emission spectrum perceived by the detector (preferably the human eye) is then the time average of the spectrum emitted by the tunable LED, which is the time average of the emission spectrum produced by each current pulse.

[0835] Current control can be achieved using either analog or digital pulse forms.

[0836] 70-72 show examples of "digital pulses" that include a series of separate current pulses.

[0837] 70 shows the emission spectrum of a tunable LED according to a preferred embodiment of the present invention, with overlaid lines representing five separate drive currents I1-I5. Each of the drive currents I1-I5 has a different magnitude from the other drive currents. The intersections of the overlaid lines I1-I5 with the emission spectrum of the LED indicate the peak emission wavelengths emitted by the tunable LED in response to each of the separate drive currents I1-I5.

[0838] FIG. 71 shows an exemplary series of current pulses applied to a tunable LED. Each of I1-I5 has its own distinct magnitude (amplitude) and therefore generates its own distinct peak emission wavelength when applied to the tunable LED. Thus, the order in which the pulses are applied to the LED, as well as the temporal duration of each current pulse, will determine the overall emission spectrum generated by the LED in time for a given display frame. By controlling the order and duration of the current pulses, a wide variety of different perceived emission spectra can be achieved.

[0839] Figure 72 shows a combination of five separate emission spectra with different peak emission wavelengths, which correspond to the five spectra generated by the five current pulses in Figure 70. The overall output spectrum perceived by an observer, as shown by the "output" line in Figure 72, is a combination of these five separate spectra.

[0840] (Embodiment A) 73A-73D show spectral reconfiguration using multiple current set points (digital pulsing) using the tunable LED described above.

[0841] A number n of current set points (n=5 in the illustrated example of FIG. 73A) are selected across the tuning range of the LED (the range of peak emission wavelengths the tunable LED is capable of emitting).

[0842] The target spectrum (shown in FIG. 73B) is reconstructed as a linear combination of the emission spectra of the LEDs at the selected current set points (shown in FIG. 73C). The intensity of each component peak wavelength is converted to time (pulse duration) at each of the n current settings to account for the emission brightness of the LEDs at each current setting, to arrive at a pattern of digital pulses that is completed within the duration of a display frame (shown in FIG. 73D). In use, the pulse pattern is repeated for the length of time that the target emission spectrum is to be displayed, until a change in the output spectrum is desired. At this time, the LEDs may be driven with different pulse patterns to produce different perceived spectra.

[0843] (Embodiment B (Figures 74 to 77)) For a large number of current set points (→∞), spectral reconstruction using analog current pulses can be considered.

[0844] To recreate a particular desired emission spectrum, all current pulses can be calculated such that the sum of the light emitted at each wavelength within the tuning range of the tunable LED matches the desired target emission spectrum.

[0845] An exemplary target emission spectrum is shown in FIG.

[0846] A tunable LED having the emission characteristics shown in Figure 75 can be driven with analog current pulses, where the amplitude of the current pulse varies over time, to produce the target emission spectrum of Figure 74. Figure 76 illustrates an example of an "analog pulse" of drive current having an amplitude that varies during a display frame. When such an analog pulse is used to drive a tunable LED, the LED will produce different peak emission wavelengths as the amplitude of the drive current pulse varies during a display frame, resulting in an output spectrum as shown in Figure 77.

[0847] Similar to the digital pulse described above in embodiment A, the target spectrum shown in FIG. 74 is reconstructed as a temporal combination of the LED's emission spectra, and the analog drive pulse behaves like a drive current with a very large number of (n→∞) constituent components.

[0848] (Embodiment C (Figure 78)) One or more tunable LEDs can provide a large area spectrally tunable illumination source for use as a hyperspectral light source or for general illumination purposes, which can be realized using the concepts of embodiments A and B above.

[0849] The spectrum generated can be either a narrow or a broad spectrum, depending on the driving conditions applied to the LED(s).

[0850] The illumination spectrum may be fixed between illumination frames (by maintaining the same drive conditions or repeating the same drive pulses during each display frame) or may be varied between frames (by varying the pulse pattern / sequence or pulse shape between frames), with the illumination frames being of a duration shorter than the response time of the detector used.

[0851] This can be particularly useful in applications requiring a specific, controlled spectrum, including medical imaging, phototherapy, specialty lighting, and agritech.

[0852] (Embodiment D (Figure 79)) In aspects of the invention, one or more spectrally tunable pixels for a spectrally accurate display can be provided, with each individual pixel (or each individual sub-pixel) behaving as described above in embodiment A or B.

[0853] As shown in FIG. 79, a plurality of tunable LEDs ("tunable" LEDs) may...

Claims

1. 1. A method for controlling an LED display device with tunable LEDs, comprising: providing a power source that provides drive current pulses to the tunable LED; and controlling the power supply to vary the peak emission wavelength of the LED over an emission wavelength range of at least 40 nm; and controlling the duration of each drive current pulse to control the brightness of each emitted peak emission wavelength; A control method comprising:

2. 2. The method of claim 1, wherein the emission wavelength range is at least 50 nm, or at least 60 nm, or at least 70 nm, or at least 80 nm, and preferably extends up to 100 nm, or 110 nm, or 120 nm, or 140 nm, or 160 nm, or 180 nm, or 200 nm.

3. 3. The method of claim 1 or 2, wherein the power supply is controlled to vary the peak emission wavelength from 400 nm to 800 nm, preferably from 520 nm to 660 nm, or from 550 nm to 650 nm, or from 560 nm to 680 nm, by varying the power supply.

4. 4. The method of claim 1, wherein the power supply is controlled to vary the peak emission wavelength of the tunable LED by varying the current density supplied to the tunable LED.

5. 5. The method of claim 4, wherein the power supply is controlled to supply a first current density at which the tunable LED emits light at a first peak emission wavelength, and wherein the power supply is controlled to supply a second current density less than the first current density so that the tunable LED emits light at a second peak emission wavelength that is longer than the first emission wavelength.

6. 6. The method of claim 5, wherein the first peak emission wavelength is less than 570 nm and the second peak emission wavelength is greater than 610 nm, whereby the tunable LED emits green light in response to the first current density and red light in response to the second current density.

7. The method according to any one of claims 1 to 6, wherein the power supply is operated in pulse width modulation (PWM) mode and / or pulse amplitude modulation (PAM) mode.

8. The method according to any one of claims 1 to 6, wherein the power supply is a constant voltage power supply or the power supply is a constant current power supply.

9. A method according to any one of the preceding claims, wherein the amplitude of the power supply is varied between at least two non-zero values during one display frame.

10. 10. The method of claim 1, comprising providing a drive current to the tunable LED and varying the amplitude of the drive current between a plurality of non-zero values during a single display frame, whereby the tunable LED generates a plurality of peak emission wavelengths during a single display frame.

11. 11. The method of claim 10, comprising varying the amplitude of the drive current during a single display frame by supplying a series of distinct drive current pulses at distinct amplitudes.

12. 12. The method of claim 11, comprising varying the drive current between at least two, or at least three, or at least four, or at least five, or at least six, or at least seven non-zero amplitudes during the display frame.

13. 13. The method of any one of claims 1 to 12, wherein the power supply is controlled to provide a drive current to the LED with a duty cycle of at least 0.001%, 0.01%, 0.1%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

14. providing a first drive current to the LED so that the LED emits light at a first peak emission wavelength; and providing a second drive current having an amplitude different from that of the first drive current so that the LED emits light at a second peak emission wavelength; the first drive current is supplied to the LED at a first duty cycle and the second drive current is supplied to the LED at a second duty cycle; controlling the duration of the first duty cycle and / or the second duty cycle to control the observed luminance and / or chromaticity produced by the display device. The method according to any one of claims 1 to 13.

15. A pixel of a display device comprising a plurality of LED subpixels; The method includes providing a power source to each LED subpixel; 10. The method of claim 1, comprising providing a fixed magnitude power supply to at least one LED subpixel and providing a variable magnitude power supply to the at least one tunable LED subpixel.

16. The method of claim 1 , wherein the display device comprises a plurality of tunable sub-pixels, preferably each of the sub-pixels being a tunable sub-pixel.

17. 17. The method of claim 16, comprising varying the peak emission wavelength of the or each tunable sub-pixel at regular time intervals.

18. 18. A method according to claim 16 or 17, comprising alternating or swapping the emission wavelengths of the sub-pixels at regular time intervals to distribute heating of the sub-pixels caused by emission wavelengths of high current densities.

19. 19. The method of claim 16, 17 or 18, comprising varying the emission wavelength of the sub-pixels by varying the drive current applied to the sub-pixels at regular intervals.

20. 20. A method for controlling a display device according to any one of claims 1 to 19, comprising the steps of: supplying a first drive current having a first magnitude to a first LED subpixel; and supplying a second drive current having a second magnitude different from the first magnitude to a second LED subpixel having the same diode structure as the first LED subpixel.

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