Anti-glare high-efficiency micro-display light source

Abstract

The invention discloses an anti-glare high-efficiency micro-display light source based on a resonant cavity light-emitting diode, and belongs to the field of semiconductor photoelectrons. The laser comprises black silicon (100), an upper electrode (200), an isolation layer (300), a current expansion layer (400), an upper Bragg reflector (500), an oxidation limiting layer (600), a resonant cavity (700), a lower Bragg reflector (800), a substrate (900) and a lower electrode (1000) from top to bottom. Wherein the upper Bragg reflector and the lower Bragg reflector are formed by periodically and alternately arranging high-refractive-index materials and low-refractive-index materials. The logarithm of the lower Bragg reflectors (800) is larger than the logarithm of the upper Bragg reflectors (500). The structure of the resonant cavity (700) comprises a limiting layer (701) and an active region (702). The surface of the chip is covered with black silicon, glare interference is eliminated, the light extraction efficiency is improved in combination with the resonant cavity structure in the vertical direction, the single-pixel working current is reduced through the AlAs oxidation limiting layer inside, and the anti-glare and high-efficiency light source suitable for micro display can be achieved.

Description

Technical Field

[0001] This invention relates to an anti-glare, high-efficiency micro-display light source based on a resonant cavity light-emitting diode, belonging to the field of semiconductor optoelectronics. Background Technology

[0002] With the rapid development of micro-display technologies such as AR / VR near-eye displays, micro-projections, and wearable devices, LEDs, widely used in the display field due to their advantages of small size, long lifespan, and low energy consumption, are facing new requirements. Micro-displays have pixel sizes of only 5-50μm and pixel pitches of less than 10μm, requiring light sources with extremely high emission directionality (to suppress pixel crosstalk) and extremely low stray light (to avoid glare interference) to ensure high contrast and clarity of the image. On the other hand, due to their miniaturization and high brightness requirements, micro-displays require LEDs to maintain ultra-high light extraction efficiency under high current density while simultaneously meeting low power consumption and long lifespan requirements. Developing a light source that combines high efficiency, anti-glare, and suitability for micro-sized displays is key to overcoming the bottlenecks in micro-display technology. The luminous intensity of an LED is determined by its luminous efficiency, which is determined by its internal quantum efficiency and external quantum extraction efficiency. While the internal quantum efficiency has been improved to 90% or even close to 100% due to advancements in epitaxial and control technologies, the external quantum efficiency remains relatively low due to the influence of electrode absorption and internal total internal reflection. Furthermore, modern display light sources not only require light itself, but also a comfortable and user-friendly lighting environment. Traditional LED structures are susceptible to glare interference, meaning there are unsuitable brightness ranges within the field of view, with extreme brightness contrasts in space or time, causing discomfort or reduced visibility. For example, outdoor LED displays are difficult to see in sunlight because ambient light reflection overwhelms the contrast of the self-emitted light, and reflected light may be misinterpreted as signals. Therefore, it is necessary to suppress reflected noise at its source.

[0003] To achieve micro-displays, the structure of traditional LEDs is as follows: Figure 1As shown, from top to bottom, the structure includes: an upper electrode (100), a current blocking layer (200), a P-type upper confinement layer (300), an active layer (400), an N-type lower confinement layer (500), a substrate (600), and a lower electrode (700). Holes are injected from the upper electrode (100) through the P-type confinement layer (300) into the active layer (400), and electrons are injected from the lower electrode (700) through the N-type confinement layer (500) into the active layer (400). Then, electrons and holes undergo spontaneous recombination within the active layer (400), emitting light of the desired wavelength. Because the upper electrode (100) is opaque, the electrode portion of the upper electrode (100) with the light emission aperture must be etched away to obtain light emission. Furthermore, to inject as much current as possible into the active region (400) below the light emission aperture, a current blocking layer (200) needs to be deposited before fabricating the electrode. A closer analysis of this structure reveals the following problems:

[0004] (1) Lateral current propagation reduces light extraction efficiency. Hole current injection is provided by the electrodes around the light-emitting aperture that are in contact with the upper confinement layer. Through lateral current propagation, holes are injected into the active region below the light-emitting aperture. However, at the same time, the hole current also propagates into the active region outside the light-emitting aperture. Due to the obstruction by the opaque electrodes, the light radiated in the active region outside the light-emitting aperture is difficult to escape outside the device. Moreover, due to the small size of the light-emitting aperture, the effect of lateral current propagation on reducing light extraction efficiency is particularly significant.

[0005] (2) Isotropic spontaneous emission limits light extraction efficiency. Electrons and holes injected into the active region recombine to emit light in the form of spontaneous emission. The intensity distribution of spontaneous emission is the same in all directions of space. Considering the small aperture and the critical angle of the emitted light, only light within a limited angle range can be emitted outside the device. Even the light radiation located in the active region below the aperture can only be extracted outside the device by a small portion, thus limiting the light extraction efficiency of the LED. Furthermore, when LEDs are applied in the field of micro-displays, the various effects brought about by size reduction will further reduce the light extraction efficiency.

[0006] (3) Surface light reflection and sidewall light leakage cause glare interference. For micro-display light sources, the area ratio of metal electrodes in tiny pixels exceeds 50%. Their strong reflected light interferes with the light emitted from the active area to form a halo, generating crosstalk glare in the dense pixel array of the micro-display. After being amplified by the near-eye optical system, it becomes the main factor causing dizziness in users. Moreover, the pixel size of the micro-display is only tens of micrometers, the pixel pitch is small, and the isotropic spatial distribution characteristics of LED radiation light result in a large angle of light extraction, leading to the generation of a large amount of lateral stray light, which reduces the contrast and clarity of the picture.

[0007] Therefore, developing a light source that can simultaneously solve the problems of glare interference and efficiency bottlenecks in micro-display scenarios has become the key to breaking through the performance limits of micro-display technology. Summary of the Invention

[0008] The purpose of this invention is to propose an anti-glare high-efficiency micro-display light source. It not only utilizes a resonant cavity structure to significantly improve the chip light extraction efficiency, but also covers the chip surface with an anti-glare black silicon microstructure. This solves the problems of low efficiency of ordinary LED structures and glare generation of ordinary RCLEDs, and achieves an anti-glare high-efficiency micro-display light source with higher efficiency and stronger anti-interference capability in the field of micro-display applications.

[0009] See Figure 2 The device structure, from top to bottom, is as follows: black silicon microstructure (100), upper electrode (200), isolation layer (300), current spreading layer (400), upper Bragg mirror (500), oxide confinement layer (600), resonant cavity (700), lower Bragg mirror (800), substrate (900), and lower electrode (1000). The uppermost black silicon layer (100) exposes the light-emitting aperture and the electrodes (200) on both sides of the aperture. The upper Bragg mirror (500) is composed of a periodically alternating arrangement of relatively high refractive index material (501) and relatively low refractive index material (502), and the lower Bragg mirror (800) is also composed of a periodically alternating arrangement of relatively high refractive index material (801) and relatively low refractive index material (802). The number of pairs of lower Bragg mirrors (800) is greater than that of upper Bragg mirrors (500). The resonant cavity (700) structure includes a confinement layer (701) and an active region (702).

[0010] During operation, the lower electrode (1000) is grounded, and the upper electrode (100) is connected to a positive potential. Holes are injected into the active region (702) through the upper electrode (100) and the upper DBR (500), while electrons are injected into the active region (702) through the lower electrode (1000) and the lower DBR (800). Subsequently, electrons and holes undergo spontaneous recombination in the active region (702), emitting light of the desired wavelength, which is then radiated to the outside of the chip through the light exit aperture. Because the resonant cavity (700) changes the spatial distribution of the spontaneous emission intensity in the active region (702), the spatial distribution of the light radiation intensity is no longer isotropic, but rather preferably in the vertical direction perpendicular to the horizontal direction. A larger portion of the light enters within the radiation solid angle, enabling it to have better beam directionality and spot symmetry than a cavity-less structure, thereby improving the device extraction efficiency.

[0011] Compared with ordinary LED micro-display light sources, the present invention has the following advantages:

[0012] (1) High luminous efficiency. The present invention adopts a resonant cavity design, which effectively overcomes the limitation of total internal reflection by utilizing its directional output characteristics, and greatly improves the light extraction efficiency; at the same time, it utilizes the Purcell effect to accelerate the spontaneous emission rate, suppress non-radiative recombination, and improve the potential of internal quantum efficiency, so that RCLED can achieve an external quantum efficiency much higher than that of ordinary LEDs in specific wavelengths and directions, and achieve high brightness under low current.

[0013] (2) Anti-glare interference. This invention performs a "blackening" treatment on the chip surface, that is, covering it with a layer of black silicon (100), exposing only the light-emitting aperture for light emission and a small portion of electrodes for applying a positive potential. The anti-glare interference effect of black silicon (100) has two aspects:

[0014] On the one hand, it provides anti-reflection protection against ambient light, which occurs on the surface of the device. Black silicon (100) covers the metal electrode (200). When incident light first comes into contact with the silicon material surface, due to the special angle of the black silicon microstructure (100), part of the light is absorbed, and although part of the light is reflected, it is reflected to the adjacent black silicon (100) microstructure, and the phenomenon of part of the light being absorbed and part of the light being reflected continues. This light transmission mode of multiple reflections and multiple absorptions will theoretically repeat indefinitely until all the incident light is absorbed by the black silicon (100), which greatly reduces the light reflection on the device surface.

[0015] On the other hand, there is the trapping effect of internal leakage light, which occurs inside the device. Light rays propagating at a large angle within the resonant cavity (700), after being reflected by the lower DBR (800), may bypass the upper DBR (500) and the resonant cavity (700) and strike the outer region of the non-reflective mesa at an undesigned angle. This portion of leakage light undergoes total internal reflection when refracted at a large angle from the high-refractive-index optically dense material black silicon (100) to the low-refractive-index optically sparse material. The complex microstructure on the back of black silicon (100) increases the probability of total internal reflection. The outgoing light propagates multiple times within the microstructure, increasing the optical path. Even if the light propagates into the air, it will still encounter adjacent microstructures and be absorbed by the materials again, which greatly reduces the light emission from inside the device.

[0016] (3) High-efficiency oxide pore-confined microdisplay. Figure 2In this process, the oxide confinement layer (600) is made of AlGaAs material with a high Al content. Non-conductive aluminum oxide is formed through a lateral oxidation process, resulting in an oxide hole that is only conductive in the middle. When current is injected from the outside, the current can only pass through the oxide hole. Since the oxide hole is close to the active region (702), it effectively restricts the lateral expansion of the current when it reaches the active region (702). By reasonably matching the size ratio of the oxide hole and the electrode light-emitting hole, it can be ensured that the injected carriers are concentrated in the active region (702) below the light-emitting hole, and then spontaneously recombine and are emitted from the light-emitting hole. Therefore, by controlling the size of the oxide hole to the micrometer level, not only can micro-displays be realized, but the utilization rate of the injected current is also high, thereby improving the electro-optical conversion efficiency of the device.

[0017] (4) Low single-pixel operating current. For micro-display applications, the single-pixel current should be as small as possible to reduce the total power. The oxide confinement aperture can be made very small, so that a high current density can be obtained even at a low injection current, that is, to achieve high-concentration carrier injection in the active region (702) at low current. For the mobile display field, a micro-current on the order of microamperes can meet the requirements for light output brightness, and theoretically, by further shrinking the oxide confinement aperture, low current and high injection can be achieved, and the device can eventually output light below nA. Attached Figure Description

[0018] Figure 1 Schematic diagram of traditional LED structure

[0019] Figure 2 Schematic diagram of anti-glare high-efficiency micro-display light source

[0020] Figure 1 In the middle, the structure of the device from top to bottom is: upper electrode (100), current blocking layer (200), P-type upper confinement layer (300), active region (400), N-type lower confinement layer (500), substrate (600), and lower electrode (700).

[0021] Figure 2 In the diagram, the device structure from top to bottom is as follows: black silicon (100), upper electrode (200), isolation layer (300), current spreading layer (400), upper Bragg mirror (500), oxide confinement layer (600), resonant cavity (700), lower Bragg mirror (800), substrate (900), and lower electrode (1000). The upper Bragg mirror (500) is composed of alternating layers of relatively high refractive index material (501) and relatively low refractive index material (502), and the lower Bragg mirror (800) is also composed of alternating layers of relatively high refractive index material (801) and relatively low refractive index material (802). The number of pairs of lower Bragg mirrors (800) is greater than that of upper Bragg mirrors (500). The resonant cavity (700) structure includes a confinement layer (701) and an active region (702). Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to examples, but the present invention is not limited to the following embodiments.

[0023] The specific steps are as follows:

[0024] I. Growth epitaxial membrane

[0025] Thirty pairs of N-doped Bragg mirrors with a doping concentration of 10 were sequentially epitaxially grown on an N-type GaAs substrate using metal-organic chemical vapor deposition (MOCVD). 18 cm -3 The high-refractive-index material and the low-refractive-index material are Al with a thickness of 46.6 nm and a refractive index of approximately 3.477, respectively. 0.5 Ga 0.5 As and Al with a thickness of 50.1 nm and a refractive index of approximately 3.112. 0.95 Ga 0.05 As. Next, an undoped resonant cavity and active region are grown, using three Ga... 0.5 In 0.5 P / (Al 0.5 Ga 0.5 In 0.5 The p-type quantum wells serve as the light-emitting active region, with both the well and barrier thicknesses being 5 nm. Following this is a p-type AlAs layer used for lateral oxidation, with a doping concentration of 10⁻⁶. 18 cm -3 The thickness is 50.1 nm; finally, there are 6 pairs of P-doped Super-Bragg mirrors with a doping concentration of 10. 18 cm -3 The high-refractive-index material and the low-refractive-index material are Al with a thickness of 46.6 nm and a refractive index of approximately 3.477, respectively. 0.5 Ga 0.5 As and Al with a thickness of 50.1 nm and a refractive index of approximately 3.112. 0.95 Ga 0.05 Thus, the epitaxial wafer for a 650nm red resonant cavity light-emitting diode is obtained.

[0026] II. Photolithography stage layer

[0027] Clean the epitaxial wafer: Boil twice each with acetone and ethanol, then rinse 30 times with water and dry with nitrogen.

[0028] Photolithography mesa: negative resist photolithography, 300nm long SiO2, resist removal, etching micro-unit mesa, each micro-unit mesa has a horizontal dimension of 45×45μm. 2 The etching depth reaches the point where the oxide layer is exposed.

[0029] The SiO2 is etched to perform lateral oxidation, thus preparing a lateral oxide layer.

[0030] III. Photolithographic isolation layer

[0031] Positive photoresist lithography, etching SiO2, and removing the resist.

[0032] IV. Photolithography Electrode Layer

[0033] Negative photolithography

[0034] Sputtering 300nm Ti / Au

[0035] peeling

[0036] V. Photolithography of Black Silicon Layer

[0037] Negative photolithography

[0038] Growing black silicon

[0039] peeling

[0040] VI. Thinning of grinding discs

[0041] Backside wafer thinned to 150nm, 300nm AuGeNi back electrode sputtered

[0042] VII. Annealing

[0043] Alloy annealing. Anneal at 430℃ for 40s to achieve good ohmic contact.

[0044] 8. Dicing and Packaging

[0045] After dicing, the small chip is placed on the socket, and the electrodes and bonding pads are connected to complete the fabrication of the anti-glare high-efficiency micro-display light source.

Claims

1. A high-efficiency, anti-glare micro-display light source, characterized in that: Viewed along the vertical cross-section of the device, the device structure includes black silicon (100), upper electrode (200), isolation layer (300), current spreading layer (400), upper Bragg mirror (500), oxide confinement layer (600), resonant cavity (700), lower Bragg mirror (800), substrate (900), and lower electrode (1000); black silicon (100) covers the device surface and sidewalls; The upper Bragg reflector (500) is composed of alternating layers of a first relatively high refractive index material (501) and a first relatively low refractive index material (502), and the lower Bragg reflector (800) is composed of alternating layers of a second relatively high refractive index material (801) and a second relatively low refractive index material (802). The number of pairs of the lower Bragg reflector (800) is greater than that of the upper Bragg reflector (500). The structure of the resonant cavity (700) includes a confinement layer (701) and an active region (702).

2. The anti-glare high-efficiency micro-display light source according to claim 1, characterized in that: The center reflection wavelength of the upper Bragg reflector (500), the center reflection wavelength of the lower Bragg reflector (800), the resonant wavelength of the resonant cavity (700), and the radiation peak wavelength of the active region (702) are the same.

3. The anti-glare high-efficiency micro-display light source according to claim 1, characterized in that: The oxide confinement layer (600) is made of AlGaAs.

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