Light emitting diode integrated with an aluminum-containing layer and related methods

Abstract

A light emitting diode structure includes an active region having at least one aluminum containing quantum well stack that emits light from the light emitting diode structure when activated. The light emitting diode structure exhibits an improved internal quantum efficiency value that is higher than an internal quantum efficiency value of a light emitting diode structure that does not include aluminum within the quantum well stack. The light emitting diode structure also exhibits an improved peak wavelength that is longer than an unimproved peak wavelength of an unimproved light emitting diode structure.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Patent Application Serial No. 63 / 019,765, filed May 4, 2020, entitled “Additional Layers Below QuantumWells in LED Structures for Enhanced Performance and Directionality”, and U.S. Patent Application Serial No. 63 / 135,288, filed January 8, 2021, entitled “Light Emitting Diodes with Aluminum-Containing Layers Integrated Therein and Associated Methods,” both of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure generally relates to light-emitting diodes with integrated aluminum layers and related methods. Background Technology

[0004] The aspects of this disclosure generally relate to light-emitting elements, such as those used in various types of displays, and more specifically, to the incorporation of improved active elements in the active layer of the light-emitting element.

[0005] While there is a growing need to increase the number of light emitters (e.g., pixels) in displays to provide a better user experience and enable new applications, increasing the number of light emitters in display formats has become a challenge. To achieve increasingly smaller light emitters and increase both the count and density of light emitters, the potential use of miniature light-emitting diodes (LEDs), such as microLED structures or nano-emitters, is attractive. However, currently available technologies for manufacturing large quantities of high-density microLED structures capable of producing different colors (e.g., red, green, blue) are cumbersome, time-consuming, expensive, or result in LED structures with performance limitations.

[0006] Advanced LED structures, such as high-efficiency LEDs based on indium gallium nitride (InGaN) quantum well (QW) structures, require the precise fabrication of various material layers designed to cooperate in order to produce light emission with desired emission characteristics.

[0007] Figure 1An epitaxial LED structure 100, typically implemented in the prior art, is illustrated. The LED structure 100 includes a semiconductor template 110, also referred to as a semiconductor substrate, for supporting one or more bulk or preparation layers 120. Active multiple quantum well (MQW) regions 130 are formed on the bulk or preparation layer 120. The bulk or preparation layer 120 is, for example, a thick layer or a structure of two or more materials configured to provide reduction effects for lattice mismatch and / or thermal expansion coefficient mismatch and / or defect filtering from the semiconductor template 110 to the active MQW region 130. The material composition of the bulk or preparation layer 120 is adjusted to gain greater flexibility in the material selection for the active MQW region 130, thereby enabling the formation of active regions with desired light emission characteristics. Finally, one or more p-layers 140 are deposited on the active QW to form a pn diode providing electronic connectivity to the LED structure 100. The p-layer 140 includes a p-doped layer and / or a contact layer. The LED structure 100 is then etched or otherwise shaped to form the desired microLED shape factor for a specific application. Summary of the Invention

[0008] While existing LED structures 100 provide a framework for designing microLEDs, a range of material choices, specific epitaxial deposition conditions, and combinations thereof are possible. For example, including certain material layers within a microLED structure is known to provide advantageous optical and electrical properties, such as reduced defects leading to higher radiative efficiency and reduced emission wavelength shift. However, to date, microLEDs with high efficiency and luminescence in the red wavelength, particularly those based on indium gallium nitride (InGaN) or indium gallium phosphide (InGaP), have been difficult to manufacture.

[0009] The following is a simplified summary of one or more aspects to provide a basic understanding of such aspects. This invention is not a broad overview of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to characterize the scope of any or all aspects. Its purpose is to present some ideas of one or more aspects in a simplified form as a prelude to a more detailed description that follows.

[0010] This disclosure provides techniques and structures for improving the performance of light-emitting elements.

[0011] In some embodiments, a light-emitting diode (LED) structure includes: a bulk or preparation layer formed on a semiconductor template; an active region formed on the bulk or preparation layer and including: a first barrier layer formed on the bulk or preparation layer; at least one aluminum-containing active quantum well (QW) stack formed on the first barrier layer; a second barrier layer formed on the active QW stack; and at least one p layer formed on the active region; wherein, when the at least one active QW stack is driven by an injected current, the active region emits light from the LED structure.

[0012] In other embodiments, a light-emitting diode (LED) structure includes: a semiconductor template; a first preparation layer formed on the semiconductor template; a second preparation layer formed on the first preparation layer; at least one active quantum well (QW) layer formed over the second preparation layer; and at least one p layer formed on the active QW layer; wherein the active QW layer emits light from the LED structure when activated.

[0013] In other embodiments, a method for forming a light-emitting diode (LED) structure on a semiconductor substrate. The method includes: depositing at least one preparatory layer on the semiconductor substrate; forming an active multiple quantum well (MQW) region on the at least one preparatory layer; and depositing a p-layer on the active MQW region; wherein forming the active MQW region includes: depositing a first barrier material, depositing an active QW material, and depositing a second barrier material; wherein forming the active MQW region optionally includes: depositing an underlayer between the first barrier material and the active QW material, depositing an intermediate layer between the underlayer and the active QW material, and depositing a capping layer between the active QW material and the second barrier material; wherein at least one of depositing the active QW material, depositing the underlayer, depositing the intermediate layer, and depositing the capping layer includes incorporating aluminum. Attached Figure Description

[0014] The attached figures only illustrate some implementation methods and should therefore not be considered as limiting the scope.

[0015] Figure 1 The diagram illustrates a typical existing microLED structure.

[0016] Figure 2 The illustration shows a top view of a portion of an example LED array having multiple microLED structures supported by a single substrate for use in a display.

[0017] Figure 3 The illustration shows a schematic cross-section of an example microLED structure with a first preparation layer and a second preparation layer, exhibiting improved morphology and strain characteristics in an embodiment.

[0018] Figure 4 The illustration shows a schematic cross-section of an example LED structure with an active QW layer and an AlGaN layer, exhibiting improved morphology and strain characteristics in the embodiment.

[0019] Figure 5 The illustration shows a schematic cross-section of an example LED structure with improved directionality in an embodiment.

[0020] Figure 6 The illustration shows a schematic cross-section of an example LED structure that exhibits improved performance by reducing hole leakage in the embodiment.

[0021] Figure 7 The illustration shows a schematic cross-section of an example microLED structure comprising aluminum within an active multiple quantum well (MQW) region, as shown in the embodiment.

[0022] Figure 8A and Figure 8B The illustration shows a schematic cross-section of an example microLED structure including an aluminum-containing substrate within the active MQW region, as shown in the embodiment.

[0023] Figure 9 The illustration shows a schematic cross-section of an example microLED structure including an aluminum capping layer positioned above the active QW within the active MQW region.

[0024] Figure 10 The illustration shows a schematic cross-section of an example microLED structure comprising aluminum incorporated within at least one active QW layer in an embodiment.

[0025] Figure 11 The illustrations in the embodiments are similar to Figure 10 The microLED structure and further includes a schematic cross-section of an example microLED structure containing an aluminum substrate.

[0026] Figure 12 The illustrations in the embodiments are similar to Figure 10 The microLED structure and further includes a schematic cross-section of an example microLED structure containing an aluminum capping layer.

[0027] Figure 13 The illustrations in the embodiments are similar to Figure 12 The microLED structure and further includes a schematic cross-section of an example microLED structure containing an aluminum substrate.

[0028] Figure 14 This is a flowchart illustrating an example process for fabricating a microLED structure in an embodiment. Detailed Implementation

[0029] The detailed descriptions below of the accompanying drawings or illustrations are intended as descriptions of various configurations and not as representations of the only configuration in which the concepts described herein can be practiced. The detailed descriptions include specific details used to provide a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts can be implemented without these specific details. In some instances, well-known components are shown in block diagram form to avoid confusing such concepts.

[0030] For certain applications, microLED structures operating at red, green, and blue (RGB) wavelengths are combined in low-duty-factor, low-density displays for low-cost, low-power applications such as smartwatches, smartphones, and televisions. In such low-density displays, for example, the microLED structures for each color are fabricated separately, then transferred and combined on separate display backplanes of low-duty-factor RGB pixels to provide full color equivalent to existing liquid crystal displays or OLED displays with lower power consumption advantages.

[0031] In another application, microLED structures (e.g., LEDs with shape factors on the order of tens of micrometers or smaller) can be used to form high-density arrays of light emitters, enabling a new class of display applications, such as compact light field displays for augmented reality (AR) or virtual reality (VR) imaging. One way to achieve such high-density arrays of microLED structures is to monolithically integrate micrometer-scale emitters on a single substrate. However, monolithic integration of microLED structures emitting at different wavelengths is inherently problematic due to the differences in structure and material composition between microLED structures designed to emit light in different ranges of wavelengths (such as red, green, and blue), and the difficulty in achieving the necessary precision to transfer separately formed microLED structures onto a high-density configuration backplane. For example, while it is possible to use compatible materials to operate blue and green microLED structures with high luminous efficiency and effectiveness, achieving red (or even long-wavelength green, amber, or red-orange) microLED structures with comparable luminous efficiency and effectiveness has proven difficult. For example, while microLED structures in the blue and green visible light wavelength range have been demonstrated to be highly efficient, microLED structures in the red visible light wavelength range have been more difficult to manufacture.

[0032] The paper by Tanner et al., dated January 28, 2020, entitled “Polar InGaN / GaN quantum wells: Revisiting the impact of carrier localization on the green gap problem,” discusses the internal quantum efficiency (IQE) of InGaN-based red LEDs (e.g., at 620 nm and above) as being known to be very low (e.g., see Tanner et al.). Figure 1 (IQE is shown as essentially zero). The embodiments described herein disclose the inclusion of aluminum within the various layers of an LED structure, and IQE values ​​of 12% and greater have been achieved at a wavelength of 635 nm. Example QW structure layer compositions include one or more of the following: GaN, AlGaN, GaN, InxGa1-xN, and AlGaN. The improved LED structure may also include one or more additional intermediate layers comprising aluminum.

[0033] One aspect of current embodiments includes the understanding that, to meet the needs of display devices, the number and density of light-emitting structures forming display elements (e.g., pixels) should increase, thus requiring a reduction in the size of the light-emitting structures while maintaining light emission efficiency and quality. It is attractive to implement increasingly smaller light-emitting structures using miniature LEDs (e.g., micro-LED structures or nanoemitters), but the few techniques available for manufacturing large quantities of high-density miniature LEDs capable of producing different colors (e.g., red, green, blue) are cumbersome, time-consuming, expensive, or result in structures with performance limitations. More complex display architectures, such as those for light field displays, can benefit from the use of miniature LED structures, but the requirements of such displays make the implementation of miniature LEDs difficult. Current embodiments address this problem by providing a new technique that allows monolithic integration of large quantities of miniature light-emitting structures generating different colors of light on the same substrate (e.g., a single integrated semiconductor device).

[0034] Certain semiconductor processing techniques used to fabricate light-emitting structures, such as epitaxial growth and dry etching or selective region growth (SAG), offer promising pathways for monolithically integrating large numbers of micro-LEDs on a single integrated semiconductor device. The quality of one or more materials grown on the template used to fabricate the light-emitting structure has a significant impact on the performance characteristics of the LED.

[0035] For this purpose, there is a need for structural configurations that enable the formation of small light-emitting structures with high-quality active (e.g., emitting) regions. For example, for QW-based LEDs, strategic additions that may introduce complexity into the fabrication process include providing functionality to improve or enhance the morphology and / or orientation of the light-emitting structure.

[0036] One approach disclosed herein involves incorporating high bandgap materials or layers into LED structures. High bandgap layers are typically not included in conventional semiconductor devices unless they are required for device operation or to enhance device performance in some way. However, the embodiments described herein achieve the growth or integration of aluminum-containing layers before (e.g., below or beneath) the active region of a light-emitting multiple quantum well (MQW) into the MQW active region itself. These aluminum-containing layers improve the quality of the active quantum well and provide better directionality to the light generated by the active quantum well. These embodiments provide multiple high-brightness microLED structures in a monolithic structure with dimensions on the order of tens of micrometers or smaller and operating across a wavelength range across the electromagnetic spectrum, enabling a wide variety of new applications that were previously impossible.

[0037] While the following discussion focuses on improvements to microLED structures operating in the red wavelength range, it should be noted that the techniques and structures described herein can also be applied to other miniature or larger LEDs, as well as other semiconductor-based light emitters operating at other wavelengths, such as visible (including long-wavelength green, amber, and red-orange), infrared, or ultraviolet wavelengths. A first example of the red wavelength range is between 0.59 μm and 0.76 μm. A second, narrower example of the red wavelength range is between 0.61 μm and 0.76 μm.

[0038] Figure 2 This is a top view illustrating a portion of an example LED array 200 having multiple microLED structures 210, 220, and 230 supported by a single substrate 240, which can be used in a display. The microLED structures 210, 220, and 230 can emit light at red, green, and blue wavelengths, respectively. Although a portion of the LED array 200 is shown with sixteen microLED structures, the LED array 200 can be a much larger array of microLED structures 210, 220, and 230 that can be used in displays where, for example, the microLED structures 210, 220, and 230 can be arranged as pixels (e.g., groups or subarrays of microLED structures 210, 220, and 230). In such cases, the arrangement of the pixels, their shape, their number, their size, and their corresponding wavelength emission are configurable during manufacturing to tailor the LED array 200 for a specific application. In some embodiments, the LED array 200 is used in high-resolution, high-density displays such as those used in light field applications. In other embodiments, the LED array 200 may be incorporated into a compact display for augmented reality (AR) or virtual reality (VR) applications.

[0039] Specifically, to achieve high-density emitters, it is desirable to use mutually compatible processes to form microLED structures 210, 220, and 230 on substrate 240 in a monolithic integrated manner. That is, instead of forming each type of microLED structure on separate substrates (e.g., forming one or more red-emitting microLED structures on a first substrate, one or more green-emitting microLED structures on a second substrate, and one or more blue-emitting microLED structures on a third substrate), and then transferring each microLED structure to a fourth substrate to form a microLED array for use in a display, an array of all three types of microLED structures 210, 220, and 230 is formed directly on substrate 240. In particular, by forming all three types of microLED structures 210, 220, and 230 as an array directly onto substrate 240 (e.g., a single substrate), a higher density LED array can be formed. In other words, instead of forming microLED structures 210, 220, and 230 of each color on separate wafers and transferring each LED to another substrate to form an LED array for a display, the LED array 200 achieves a higher density because the microLED structures 210, 220, and 230 are formed directly onto the substrate 240.

[0040] However, existing literature documents the extreme difficulty of forming microLED structures to produce full-color displays (e.g., red-green-blue (RGB) displays) using processes and materials compatible with efficient light emission across the necessary wavelength range. While highly efficient, large-scale (e.g., hundreds of micrometers in size) nitride-based blue LEDs (such as those based on indium gallium nitride (InGaN) QW) and highly efficient, large-scale phosphide-based red LEDs (such as those based on aluminum gallium indium phosphide (AlGaInP)) have been available, a “green gap” resulting from the lack of green LEDs operating with similarly high efficiency has been recognized for decades. The conventional approach to forming each type of LED within its respective emission range (e.g., red, blue, green) uses its own optimized process, then transfers the resulting LED structure onto separate display substrates to form an LED array. This approach has limitations related to the minimum LED size required to enable the transfer of independently formed microLED structures to separate display substrates and the alignment fidelity necessary for precisely aligning the microLED structures to form high-density microLED arrays. One aspect of the current embodiments includes the understanding that it is very difficult to form an array of microLED structures (e.g., microLED structures emitting red, green, and blue) on a single substrate and to facilitate full-color images with similar levels of luminous efficiency and efficiency.

[0041] Current embodiments address this problem by using a microLED structure design and fabrication process that controls the inclusion of active elements within a quantum well (QW) to achieve high-efficiency microLED structures at longer wavelengths while using materials and fabrication processes compatible with monolithic integration of microLED structures of multiple colors. More specifically, current embodiments disclose device structures and fabrication processes that enable the formation of high-efficiency microLED structures at longer wavelengths (e.g., red) using materials compatible with the fabrication of high-efficiency microLED structures at shorter wavelengths (e.g., blue and green), thereby enabling monolithic integrated arrays of microLED structures emitting different colors. However, it should be emphasized that the techniques disclosed herein are applicable to epitaxially formed LEDs of all sizes and configurations, including, for example, red-only microLED structures.

[0042] As mentioned above, highly efficient, large-scale nitride-based blue LEDs and phosphide-based red LEDs are known to be fabricated separately. When forming nitride-based light-emitting QW structures for longer wavelength LEDs (e.g., red), it is difficult to increase the percentage composition of the necessary active material (e.g., indium (In) in the QW) to achieve longer wavelength emission while maintaining layer uniformity and controlling defects. In particular, especially under high reactant vapor pressures, it is difficult to obtain the required high percentage of In with good uniformity within the QW. A reduced indium percentage results in shorter wavelength emission from the QW structure than the nominal design of the LED. Additionally, defects such as In aggregation, phase separation, and pitting are commonly seen within the QW structure. Limited adjustments are available via growth condition parameters (e.g., temperature, time, vapor pressure) before improvements in indium composition reach the limits of conventional gallium nitride (GaN) / InGaN / GaN QW materials and growth techniques while maintaining suitable material quality.

[0043] Including a thin layer of aluminum (Al) as an underlayer before depositing the active InGaN QW layer in the MQW structure has been shown to achieve improved blue LED performance due to the increased hole concentration in the QW caused by the additional polarization charge at the AlGaN / InGaN interface and the potentially slightly reduced point defects. This technique has been used to produce blue LEDs on silicon substrates using a stack of 1 nm AlGaN layers, 3.5 nm thick InGaN QW layers, followed by a 5 nm GaN layer as a barrier layer (“High-efficiency blue LEDs with thin AlGaN interlayers in InGaN / GaN MQWs grown on Si(111)substrates,” S. Kimura et al., Proc. of SPIE, Vol. 9748, 97481U). Including a material such as Al as an underlayer appears to contribute to the carrier distribution and potential reduction of defects within the active region.

[0044] However, while including Al within the InGaN QW may be feasible for blue LEDs, conventional knowledge would indicate that including Al in red LEDs would be unsuitable. Specifically, since Al is a wider bandgap material compared to In, including Al within the QW structure would create a wider overall bandgap for the QW, potentially resulting in a blue shift (i.e., a shift towards shorter wavelengths) in the emitter wavelength. While this blue shift can be easily compensated for in blue LEDs, the typical goal for red LEDs is to achieve light emission with longer wavelengths, making the inclusion of Al within the QW structure of red LEDs appear to have the opposite effect.

[0045] Previously, using thin layers of AlGaN (e.g., 1 to 2 nm thick) to cover QW structures has been an attempt to extend the emission wavelengths of nitride-based blue LEDs to green and even slightly reddish-orange wavelengths. For example, a 1 nm thick AlGaN layer was deposited directly on top of each 3 nm thick InGaN QW layer as a capping layer, and then covered in an MQW structure by a 10 nm thick InGaN barrier layer to achieve light emission in green-yellow, yellow, and amber wavelengths with an external quantum efficiency (EQE) value in the range of 11%–20% (Hashimoto, “Addressing the green gap with a novel active region,” www.compoundsemiconductor.net, March 2014, p. 44). Hashimoto’s paper speculates that the AlGaN capping layer is used to deflect the wavefunction of electrons toward the interior of the wells, thereby increasing electron-hole overlap and radiative recombination, and to create a barrier for electron overflow from each well while restoring the surface smoothness after the InGaN wells. As yet another example, the same technique, which incorporates a 1 nm thick AlGaN layer as a capping layer for each QW layer (i.e., a 3 nm thick active layer of indium gallium nitride (InGaN) followed by a 1 nm AlGaN layer, both grown at 755 °C, capped by a 10 nm InGaN layer grown at 855 °C as a barrier layer), has shown to produce LEDs operating at a wavelength of 629 nm, which lies on the shorter side of the red wavelength range, even at a low EQE value of 2.9% (JIHwang et al., “Development of InGaN-based red LED grown on (0001) polar surface,” Applied Physics Express 7, 071003 (2014)). However, the AlGaN capping layer does not appear to prevent defects involving In within the QW structure itself, a common cause of the light emission shift to shorter wavelengths and low EQE values ​​in red LEDs. In fact, Hwang et al. specifically point out that no red shift in the emission wavelength is present when the injection current is increased to drive the resulting LED. Furthermore, in all the experimental results reported above, each LED device is a large-area device, with dimensions on the order of several hundred micrometers on each side.

[0046] As an unexpected result, discussed in more detail below, contrary to this conventional wisdom, it has been found that uniformly incorporating Al within or at one or more locations within an MQW structure does indeed produce improved performance in red LEDs, including highly efficient generation of longer wavelength emission. In particular, the prudent incorporation of aluminum in the bottom layer, capping layer, and even in the active quantum well itself and its combinations has unexpectedly produced improved red LED performance, even for microLED devices with side dimensions as small as one micrometer, with high efficiency and in the red range of the visible spectrum (e.g., longer than 625 nm).

[0047] Figure 3 This is a schematic cross-section illustrating an example microLED structure 300 with improved morphology and strain characteristics, having a first preparation layer 320 and a second preparation layer 330. The LED structure 300 is formed on the surface of a semiconductor template 310 (e.g., a support layer). The LED structure 300 includes: a first preparation layer 320 (preparation layer 1) formed, grown (e.g., epitaxially grown), or deposited over the semiconductor template 310; a second preparation layer 330 (preparation layer 2) formed, grown, or deposited over the first preparation layer 320; an active QW region 340 formed, grown, or deposited over the second preparation layer 330; and a p-layer 350 including a contact layer (e.g., a p-doped layer) formed, grown, or deposited over the active QW region 340. In some implementations, techniques such as epitaxial growth and dry etching or selective region growth can be used to define the location, shape, and size of the LED structure 300 on the semiconductor template 310.

[0048] The first preparation layer 320 and the second preparation layer 330 are configured to prepare the surface for forming the active QW region 340 with appropriate morphology and strain, such that the active QW region 340 has improved material properties and light emission performance. For this purpose, the first preparation layer 320, the second preparation layer 330, or both comprise a high bandgap material, such as an aluminum-containing layer. For example, the aluminum-containing layer comprises an AlInGaN alloy with an Al composition ranging from 5% to 100%. Each of the first preparation layer 320 and the second preparation layer 330 may have a thickness of 0.3 nm to 250 nm.

[0049] The active QW region 340 is configured to emit light during the operation of the LED structure 300.

[0050] In one example, the first preparation layer 320 is an aluminum-containing layer and includes a superlattice. For example, the superlattice may be formed from alternating layers of AlInGaN and AlGaN. As an example, the superlattice may be formed from alternating layers of AlInGaN and AlGaN with different Al and In compositions. In another example, the first preparation layer 120 is a bulk layer. The bulk layer may be an aluminum-containing layer. Unlike the active QW region 340, the first preparation layer 320 and the second preparation layer 330 are not configured to emit light in the same visible wavelengths as the active QW region 340. For example, if the active QW region 340 is intended to emit light in red wavelengths, the superlattice included in the first or second preparation layer may be associated with wavelengths in green, blue, or even ultraviolet wavelengths so as not to interfere with the intended function of the active QW region 340.

[0051] As an example, the second preparation layer 330 may be an aluminum-containing layer as indicated above. In one example, the second preparation layer 330 may include a superlattice, a bulk layer, or one or more QW structures not configured to emit light at the same wavelength as the active QW region 340 during operation of the LED structure 300. Furthermore, in those instances where the second preparation layer 330 comprises a single quantum well or multiple quantum wells, the second preparation layer 330 may additionally include a high-bandgap intermediate layer, such as an AlGaN layer, formed below or above the single or multiple quantum wells. Including the first preparation layer 320 and the second preparation layer 330, for example, incorporating a high-bandgap material such as an Al-containing layer, improves the luminescence properties of the active QW region 340. For example, by providing beneficial effects such as increased tolerance to higher temperature processing, trapping migrating impurities, improved strain characteristics, and optimized stoichiometry of the active QW region 340, luminescence performance such as emission wavelength specification, narrowing of emission wavelength peak, and emission intensity of the active QW can be improved.

[0052] Figure 4 This is a schematic cross-section of an example LED structure 400 with improved morphology and strain characteristics. The LED structure 400 is similar to... Figure 3An LED structure 300 is formed on the surface of a semiconductor template 310, which may be a GaN template or a support layer. The LED structure 400 includes an active QW layer 410, an AlGaN layer 420, an active QW region 340, and a p-layer 350. Although only a single combination of the active QW layer 410 and the AlGaN layer 420 is illustrated, the LED structure 400 may include multiple or repeated combinations of the active QW layer 410 and the AlGaN layer 420. The active QW layer 410 may be associated with a wavelength shorter than the emission wavelength of the active QW region 340. For example, if the active QW region 340 is configured to produce light emission in red wavelengths, the active QW layer 410 may be associated with wavelengths in green, blue, or ultraviolet wavelengths. The AlGaN layer 420 may be made of an AlInGaN alloy comprising AlGaN with a composition ranging from 5% to 100% of In.

[0053] and Figure 3 Compared to LED structure 300, LED structure 400 includes at least one active QW in a non-active QW layer 410 over which an AlGaN layer 420 is formed. For example, the non-active QW layer 410, which may include one or more non-active QWs, corresponds to a first preparation layer 320, while the AlGaN layer 420 corresponds to a second preparation layer 330. Although Figure 4 The diagram shows only a single pair of non-active QW layer 410 and AlGaN layer 420, but without departing from this scope, LED structure 400 may include multiple layered pairs of non-active QW layer 410 and AlGaN layer 420.

[0054] Figure 5 This is a schematic cross-section of an example LED structure 500 with improved directionality. The LED structure 500 is similar to... Figure 3 An LED structure 300 is formed on the surface of a semiconductor template 310. The LED structure 500 includes a first preparation layer 320, a reflective layer 510, an active QW region 340, and a p-layer 350. The reflective layer 510 may be an AlInN / GaN bottom mirror or an AlInGaN / InGaN bottom mirror, and may be formed prior to the active QW region 340. In another example, the reflective layer 510 may include AlInGaN / AlInGaN with different Al and In compositions. Therefore, the reflective layer 510 may include at least one aluminum-containing layer forming a reflective stack. In the case where the reflective layer 510 is an AlInN / GaN bottom mirror, the AlInN layer has an Al content of about 82% relative to In, which can be matched with the GaN lattice, thereby avoiding strain-related problems in subsequent active layers while maintaining a high refractive index contrast of 7% comparable to an AlGaN / GaN system with an Al content of about 50% relative to In.

[0055] Furthermore, the reflective layer 510 can be, or can be configured, to function as a distributed Bragg reflector (DBR), which allows for customization of the radiation pattern generated by the active QW region 340 for specific applications, thereby improving the directivity of the emission from the active QW 340. For example, when the reflective layer 510 is, or can be configured, to operate as a DBR, the LED structure 500 can be configured to operate as a cavity LED or a vertical-cavity surface-emitting laser (VCSEL). That is, the p-layer 350 and the reflective layer 510 form a resonant cavity containing the active QW 340, such that the LED structure 500 can operate as a cavity LED or a VCSEL depending on the thickness of the active QW 340 relative to a predetermined emission wavelength of the light from the active QW 340.

[0056] Each of the aforementioned LED structures 300, 400, and 500 can be fabricated using techniques such as epitaxial growth and dry etching or selective region growth to have a diameter or feature size of up to 1 micrometer suitable for high-density applications. In some embodiments, the diameter is larger than one micrometer, such as between one and ten micrometers.

[0057] The use of aluminum-containing layers offers additional benefits beyond the morphological, strain, and directionality advantages provided by LED structures 300, 400, and 500 for the manufacture of small LEDs and the monolithic integration of such small LEDs. These aluminum-containing layers can act as traps for impurities, thus reducing impurities in the active region (e.g., active QW region 340) by positioning them in the passive region of the LED structure. Furthermore, the movement of the captured or positioned impurities is prevented even when high temperatures are applied during subsequent process operations. Figure 4 In the example, the AlGaN layer 420 grown on the non-active QW layer 410 can be used to trap impurities (e.g., oxygen), which reduces the incorporation of impurities (e.g., oxygen) into the active QW region 340. Figure 5 In the example, the AlInN layer used to form the reflective layer 510 can also be used as an oxygen trapping layer.

[0058] Figure 6 This is a schematic cross-section of an example LED structure 600 that exhibits improved performance by reducing hole leakage. The LED structure 600 is similar to... Figure 3An LED structure 300 is formed on the surface of a semiconductor template 310. The LED structure 600 includes a first preparation layer 320, a hole blocking layer 610, an active QW region 340, and a p-layer 350. The hole blocking layer 610 prevents holes from overflowing from the semiconductor template 310 and the first preparation layer 320 into the active QW region 340, and also prevents holes from overflowing from the active QW region 340 into the first preparation layer 320 and the semiconductor template 310. In some embodiments, the hole blocking layer 610 may include n-AlGaN. In other embodiments, the hole blocking layer 610 is a superlattice formed of an AlGaN / GaN or InAlN / GaN layer that improves the emission efficiency of the active QW region 340. However, the hole blocking layer 610 may use other suitable materials, including n-AlGaN, n-doped AlGaN / GaN superlattices, and n-doped InAlN / GaN superlattices.

[0059] Figure 7 This is a schematic cross-section illustrating an example microLED structure 700 in which aluminum is introduced into an active MQW region 730. The microLED structure 700 includes a semiconductor template 710 (also referred to as a semiconductor substrate for supporting one or more bulk or preparation layers 720), an active MQW region 730, and at least one p-layer 740. The active MQW region 730 may be formed on the bulk or preparation layer 720 and includes at least one active QW stack 732 with aluminum inclusions having adjacent barrier layers 734 (e.g., GaN or InGaN barrier layers). Each active QW stack 732 may include a single layer of aluminum-containing material, or may include two or more layers of different materials, wherein at least one of these layers contains aluminum. Figure 7 The example shows an active MQW region 730 with four active QW stacks 732, each active QW stack 732 having an adjacent barrier layer 734; however, depending on the desired light emission performance of the microLED structure 700, fewer or more active QW stacks 732 and corresponding barrier layers 734 may be included.

[0060] As mentioned above, the inclusion of Al, being a wider bandgap material than In, would seem to favor shorter wavelength light emission from the resulting microLED structure. However, counterintuitively, the inclusion of Al produces microLED structures with higher efficiency and photoluminescence performance compared to those without Al inclusions. More specifically, as discussed above, the inclusion of Al causes a shift in the wavelength emitted from the microLED structure towards shorter wavelengths (e.g., a blue shift) as the current density across the LED structure increases, thus requiring adjustments to the overall microLED structure to compensate for the blue shift. Various methods of incorporating Al into the active QW stack 732, such as incorporating specific layers in and around the active QW region, are disclosed and described in further detail below.

[0061] Figure 8A and Figure 8B The illustration shows schematic cross-sections of example microLED structures 800A and 800B, including an aluminum-containing substrate within the active MQW regions 830A and 830B, respectively. MicroLED structures 800A and 800B are similar to... Figure 7 The microLED structure 700. Active MQW regions 830A and 830B are formed on the bulk or preparation layer 720. Figure 8A The active MQW region 830A of a microLED structure 800A comprising a stack of four active QW layers 832 is shown, collectively referred to as the QW stack. Each QW layer 832 is deposited on a corresponding AlGa(In)N underlayer 836 (hereinafter referred to as Al underlayer 836) to form paired layers separated by a barrier layer 734. The thickness of the Al underlayer 836 can range from a few atomic layers to a few nanometers. Beyond such thicknesses, the Al underlayer 836 may cause an undesirable blue shift in the microLED structure due to an increased bandgap. The active QW layers 832 can be formed of InGaN. The Al underlayer 836 is an aluminum alloy, such as AlGaN, AlInN, and InAlGaN, compatible with the fabrication process of nitride-based microLED structures like microLED structure 800A. The Al underlayer 836 can be referred to as the intermediate layer.

[0062] In QW-based LED structures, including an AlGaN underlayer beneath the active QW layer has been demonstrated in the blue wavelength range, which becomes conceptually meaningful because the blue shift in the emission wavelength caused by the introduction of Al is compatible with blue LEDs. However, while the additional inclusion of the Al underlayer 836 would appear to further widen the effective bandgap of the active MQW region 830A, the Al inclusions within the Al underlayer 836 produce improved material quality and uniformity within the active QW layer 832 due to the high In content. It appears that the inclusion of the AlGaN or AlInN underlayer modifies the crystal surface morphology on which the active QW layer is grown, thereby reducing defects and improving the stability of the material during high-temperature processing, such as during the growth of the barrier layer 734. Therefore, any blue shift caused by the wider effective bandgap of the active MQW region 830A appears to be overcome by the improved growth pattern and the reduction of defects within the active QW layer 832. Thus, compared to LEDs without... Figure 8A Compared to other microLED structures, the combination of features shown in the microLED structure unexpectedly produces superior efficiency and longer wavelength emission. For example, the microLED structure 800A has been demonstrated to exhibit a similar peak IQE value with a blue shift of 10 nm or less in wavelength as the applied current density increases, compared to a prior art LED structure 100 having a similar material structure.

[0063] Figure 8B Showing something similar to Figure 8A The microLED structure 800A includes an intermediate layer 838 located between an Al bottom layer 836 and an active QW layer 832 in the active MQW region 830B. The intermediate layer 838 can be formed from conventional barrier layer materials such as GaN or other materials such as AlGaN, InGaN, and AlInGaN materials with various compositions compatible with nitride-based microLED fabrication. The combination of the Al bottom layer 836 and the intermediate layer 838 further improves the adhesion and uniformity of the active QW layer 832, reduces defects at the interface and within the active QW layer 832, and increases In retention within each active QW layer 832. Therefore, compared to microLED structures without the Al bottom layer 836, the light emission of the microLED structure 800B shifts towards red wavelengths, and the quantum efficiency performance of the microLED structure 800B is improved.

[0064] Figure 9 The diagram is similar to Figure 7The microLED structure 700 further includes an aluminum capping layer 932 (hereinafter referred to as Al capping layer 932) positioned above the active QW layer 832 within the active MQW region 930 formed on the bulk or preparation layer 720. For example, an AlGaN layer with a thickness on the order of one nanometer or less can be used as capping layer 932. Al capping layer 932 can be referred to as another intermediate layer. Although the inclusion of Al capping layer 932 may appear to produce a wider effective bandgap for the active MQW region 930, Al capping layer 932 offers several advantages, such as balancing the strain between the active QW layer 832 and the barrier layer 734, as in the Al underlayer 836 of microLED structures 800A and 800B. This allows for customized morphology before and after the growth of the active QW layer 832, retention of In within the active QW layer 832, and / or providing band alignment favorable for long-wavelength emission while minimizing blue shift. Therefore, the active QW layer 832 exhibits better In retention and uniformity compared to the non-active QW layer. Figure 9 The combination of features shown produces superior efficiency and longer wavelength emission compared to microLEDs.

[0065] The Al capping layer 932 can serve as a barrier against the migration of point defects, including those from any electron-blocking layer and from the p-layer, which can be incorporated into the overall structure. However, this paper recognizes that the Al capping layer 932 may not always help prevent defects within the active QW layer 832 itself, thus potentially requiring additional measures, such as... Figure 8A and Figure 8B The illustrated Al layer 836 includes...

[0066] Figure 10This is a schematic cross-section illustrating an example microLED structure 1000 comprising aluminum within at least one active QW layer 1032 of an active MQW region 1030 formed on a bulk or preparation layer 720. Although four active QW layers 1032 are shown, collectively referred to as a QW stack, the active MQW region 1030 may include more or fewer active QW layers 1032 without departing from its scope. In some embodiments, for example, during the deposition of the active QW layers 1032, an Al-containing gas is introduced at a specific concentration to incorporate Al into the alloy composition of the active QW layers 1032 at a concentration between 0.01% and 5%. In some embodiments, this process is performed for all active QW layers 1032 within the active MQW region 1030 to include Al. In other embodiments, a similar process is used to vary the amount of Al included in each active QW layer 1032 of the active MQW region 1030. For example, Al inclusions within a specific QW layer can take the form of pseudo-alloys, digital alloys, or short-period superlattices. Within the active MQW region 1030, the active QW layer 1032 is separated by a barrier layer 734 formed of a suitable material such as GaN.

[0067] Including Al within the active QW layer 1032 improves the uniformity of In distribution and prevents In desorption from the active QW layer 1032 during subsequent high-temperature processing, such as during the growth of the barrier layer 734, which typically requires temperatures approximately 100°C higher than those during the deposition of the active QW layer 1032. The inclusion of Al appears to compensate for QW strain, thereby modifying the polarization-induced electric field. In other words, including Al during the deposition of the active QW layer 1032 appears to improve In containment and In retention, reducing defects associated with high-In-content InGaN materials and / or enhancing the stability of InGaN within the active QW layer 1032, thereby overcoming the potential negative impacts of including wider bandgap materials such as Al. Furthermore, Al can be used as a dopant within the active MQW region 1030 to obtain various wavelengths of light-emitting structures, including both conventional LEDs (with dimensions on the order of one hundred micrometers or larger) and microLED structures configured to operate in the infrared, visible, and ultraviolet wavelengths. Al is advantageous because it is a standard precursor that is readily available in systems commonly used to produce QW structures, such as in metal-organic chemical vapor deposition (MOCVD) systems.

[0068] The incorporation of Al into the active QW layer 1032 varies depending on the growth conditions of the active QW material (e.g., temperature, pressure, time), thus the amount of Al inclusions in the active QW layer 1032 can be adjusted to provide the desired properties of the active QW layer 1032. Although the active MQW region 1030 is shown with four active QW layers 1032, it can include more or fewer active QW layers 1032 and corresponding barrier layers 734 to achieve the desired light emission and operating characteristics of the microLED structure 1000.

[0069] Figure 11 The diagram is similar to Figure 10 The microLED structure 1000 further includes an aluminum-containing substrate, such as Figure 8A and Figure 8B A schematic cross-section of an example microLED structure 1100 is shown, illustrating the Al underlayer 836 of microLED structures 800A and 800B. An active MQW region 1130 is formed on a bulk or preparation layer 720 and comprises a combination of an Al underlayer 836 and an active QW layer 1032 (both having Al inclusions). The Al underlayer 836 appears to promote deposition uniformity and adhesion of the active QW layer 1032 therein, and the Al inclusions within the active QW layer 1032 promote In retention within the QW, thereby improving adhesion to structures without Al inclusions. Figure 11 The improved quantum efficiency in the red wavelength compared to the characteristic microLED structure results in an improved quantum efficiency in the red wavelength. In some embodiments, an intermediate layer 838 (such as...) may be included between the Al bottom layer 836 and the active QW layer 1032. Figure 8B (As shown).

[0070] Figure 12 The diagram is similar to Figure 10 The microLED structure 1000 and further includes a microLED structure 900. Figure 9 A schematic cross-section of an example microLED structure 1200 with an Al capping layer 932. The active MQW region 1230 of the microLED structure 1200 is formed on a bulk or preparation layer 720 and includes an Al capping layer 932 together with an active QW layer 1032 that also includes Al. The combination of the active QW layer 1032 covered by the Al capping layer 932 promotes In retention within the active QW layer 1032, resulting in improved quantum efficiency at red wavelengths compared to the quantum efficiency of a microLED structure without the active MQW region 1230.

[0071] Figure 13 The diagram is similar to Figure 12 The microLED structure 1200 and further includes Figure 8BA schematic cross-section of an example microLED structure 1300 with an Al underlayer 836. The microLED structure 1300 has active MQW regions 1330 formed on a bulk or preparation layer 720, which for each active QW layer 1032 include an Al underlayer 836 and an Al capping layer 932, and further include a barrier layer 734 adjacent to the Al underlayer 836 and the Al capping layer 932. Optionally, as... Figure 13 As shown, when the Al bottom layer 836 is, for example, AlGa(In)N, the intermediate layer 838 can be disposed between the Al bottom layer 836 and the active QW layer 1032. Including Al within the active MQW region 1330 improves the uniformity of In distribution within each active QW layer 1032, promotes In retention within the active MQW region 1330, and reduces In desorption from the active QW layer 1032 during the growth of the barrier layer 734. The MicroLED structure 1300 is thus combined... Figure 8B , Figure 9 and Figure 10 The beneficial effects of the MicroLED structure shown.

[0072] Figure 14 This is a flowchart illustrating an example process 1400 for fabricating a microLED structure. Process 1400 can be performed, for example, in an MOCVD system or other systems suitable for microLED fabrication. In block 1410 of process 1400, one or more bulk or preparation layers are deposited on a substrate. In one example of block 1410, a first preparation layer 320 and a second preparation layer 330 are deposited onto a semiconductor template 310. In another example of block 1410, a bulk or preparation layer 720 is deposited onto the semiconductor template 710. Block 1412 is optional. When included, in block 1412, process 1400 deposits one or more barrier materials. In one example of block 1412, a barrier layer 734 is deposited onto the bulk or preparation layer 720. Note that in some embodiments, instead of depositing the barrier materials separately in block 1412, the first barrier material may be incorporated into one or more bulk or preparation layers 720 deposited in block 1410.

[0073] Box 1420 is a decision box. When it is determined at box 1420 that an Al-containing underlayer is to be added, process 1400 proceeds to box 1422; otherwise, process 1400 proceeds to box 1424. In box 1422, process 1400 deposits an Al-containing underlayer. In one example of box 1422, an Al underlayer 836 is deposited on a previously deposited layer.

[0074] Box 1424 is a decision box. If it is determined at box 1424 that an intermediate layer needs to be added, then process 1400 proceeds to box 1426; otherwise, process 1400 proceeds to box 1430. In box 1426, process 1400 deposits the intermediate layer onto the previously deposited layer. In one example of box 1426, the intermediate layer 838 is deposited onto the Al underlayer 836.

[0075] Box 1430 is a decision box. If it is determined at box 1430 that Al is included in the active QW layer, process 1400 proceeds to box 1432; otherwise, process 1400 proceeds to box 1440. In box 1432, process 1400 deposits the active QW material incorporating Al. In one example of box 1432, Al is added as the active QW layer 1032 is deposited onto the barrier layer 734. In another example of box 1432, Al is added as the active QW layer 1032 is deposited onto the Al underlayer 836. In yet another example of box 1432, Al is added as the active QW layer 1032 is deposited onto the intermediate layer 838. Process 1400 then proceeds to box 1450. In box 1440, process 1400 deposits the active QW material without adding Al. In one example of box 1440, the active QW region 340 is deposited onto the second preparation layer 330. In another example of box 1440, the active QW layer 832 is deposited on the Al underlayer 836. In another example of box 1440, the active QW layer 832 is deposited on the intermediate layer 838. In another example of box 1440, the active QW layer 832 is deposited on the barrier layer 734.

[0076] Box 1450 is a decision box. When a decision is made at box 1450 to include the Al capping layer, process 1400 proceeds to box 1452; otherwise, process 1400 proceeds to box 1470. In box 1452, process 1400 deposits the Al capping layer. In one example of box 1452, the Al capping layer 932 is deposited onto the active QW layer 832. In another example of box 1542, the Al capping layer 932 is deposited onto the active QW layer 1032.

[0077] Box 1470 is the decision box. If it is determined at box 1470 that an additional QW layer needs to be deposited, process 1400 proceeds to box 1412; otherwise, process 1400 proceeds to box 1480. Therefore, boxes 1412 through 1470 are repeated for each additional QW layer to be added.

[0078] In box 1480, process 1400 deposits barrier material. In one example of box 1480, barrier layer 734 is deposited onto active QW stack 732. In another example of box 1480, barrier layer 734 is deposited onto active QW layer 832. In yet another example of box 1480, barrier layer 734 is deposited onto Al capping layer 932. In box 1482, process 1400 deposits one or more p-layers. In one example of box 1482, one or more p-layers 350 are deposited onto active QW region 340. In yet another example of box 1482, p-layer 740 is deposited onto barrier layer 734. Process 1400 can then terminate.

[0079] This disclosure describes various embodiments using techniques and structures to improve the performance of light emitted from a microLED structure at red wavelengths. While the above discussion focuses on microLED structures emitting at red wavelengths, the techniques and structures of the described embodiments can also be used to tailor the performance of LEDs operating in other wavelength ranges, including shorter visible wavelengths and infrared wavelengths. Furthermore, while the disclosed embodiments primarily illustrate nitride-based microLED structures, similar material and layered structure modifications for bandgap and defect engineering are applicable to other light-emitting structures, such as phosphide-based LED structures. Further, although the disclosed embodiments involve including Al as a standard precursor readily available in MOCVD systems typically used to produce QW structures within the MQW region of the microLED structure, the inclusion of other materials is contemplated to further design the desired light emission from the microLED structure. Additionally, additional intermediate layers, such as those in… Figure 9 In between the active QW layer 832 and the Al capping layer 932, and / or in Figure 12 and 13 It is located between the active QW layer 1032 and the Al capping layer 932.

[0080] The LED structure may include an active region having at least one quantum well, wherein the active region is configured to provide relevant light emission from the LED structure. A certain amount of aluminum is incorporated within the at least one quantum well. The active region of the LED structure may further include at least one aluminum-containing layer incorporating an amount of aluminum greater than the amount incorporated within the at least one quantum well. The amount of aluminum incorporated within the at least one quantum well is 0.01% to 5% of the at least one quantum well. This LED structure exhibits an improved internal quantum efficiency value, which is higher than the unimproved internal quantum efficiency value exhibited by an unimproved LED structure without aluminum incorporated within the at least one quantum well. This LED structure operates at an improved peak wavelength, which is longer than the unimproved peak wavelength of an unimproved LED structure without aluminum incorporated within the at least one quantum well. The diameter of the LED structure is less than ten micrometers.

[0081] An LED structure includes an active region configured to provide light emission associated with the LED structure, wherein the active region includes a barrier layer and an active quantum well (QW) layer, the active QW layer being substantially composed of a primary active QW material, and wherein the active QW layer further includes a quantity of secondary material incorporated within the active QW layer, the secondary material exhibiting a wider bandgap than the primary active QW material. The active region may further include at least one intermediate layer, the at least one intermediate layer incorporating a larger quantity of secondary material than the amount of secondary material incorporated within the active quantum well layer. The at least one intermediate layer is disposed between the barrier layer and the active quantum well layer. The at least one intermediate layer may be a bottom layer. The at least one intermediate layer may be a capping layer. The secondary material is aluminum. The LED structure exhibits an improved internal quantum efficiency value, which is higher than the unimproved internal quantum efficiency value exhibited by an unimproved LED structure that does not have a quantity of secondary material distributed throughout the at least one quantum well. This LED structure operates at a modified peak wavelength, which is longer than the unmodified peak wavelength of an unmodified LED structure that does not have a certain amount of secondary material distributed throughout at least one quantum well. The diameter of this LED structure is less than ten micrometers.

[0082] A method for forming a light-emitting diode (LED) structure includes at least one quantum well region comprising a barrier layer and an active quantum well layer. When forming the at least one quantum well region, a primary active quantum well material is deposited together with a quantitative amount of secondary material exhibiting a wider bandgap than the primary active quantum well material. The amount of secondary material is 0.01% to 5% of the primary active quantum well material. Depositing the primary active quantum well material together with a quantitative amount of secondary material involves forming a pseudo-alloy of the primary active material and the secondary material.

[0083] Combination of features

[0084] Specifically, the following embodiments are envisioned, as well as any combination of such embodiments that are compatible with each other.

[0085] (A) A light-emitting diode (LED) structure includes: a bulk or preparation layer formed on a semiconductor template; an active region formed on the bulk or preparation layer; and at least one p-layer formed on the active region. The active region includes: a first barrier layer formed on the bulk or preparation layer; at least one aluminum-containing active quantum well (QW) stack formed on the first barrier layer; and a second barrier layer formed on the active QW stack. When the at least one active QW stack is driven by an injected current, the active region emits light from the LED structure.

[0086] (B) In the LED structure represented as (A), the active region is configured to emit light from the LED structure at a red wavelength.

[0087] (C) In either of the LED structures represented as (A) and (B), at least one active QW stack includes (a) an aluminum-containing underlayer formed on a first barrier layer and (b) an active QW layer formed on the aluminum-containing underlayer.

[0088] (D) In ​​any of the LED structures represented as (A)-(C), the aluminum-containing substrate comprises an alloy selected from the group consisting of AlGa(In)N, AlGaN, AlInN and InAlGaN.

[0089] (E) In any of the LED structures represented as (A)-(D), at least one active QW stack further includes (c) an aluminum capping layer formed on the active QW layer.

[0090] (F) In any of the LED structures represented as (A)-(E), the aluminum capping layer comprises 1 nm thick AlGaN material.

[0091] (G) In any of the LED structures represented as (A)-(F), at least one active QW stack includes (a) an aluminum-containing underlayer formed on a first barrier layer, (b) an intermediate layer formed on the aluminum-containing underlayer, and (c) an active QW layer formed on the intermediate layer.

[0092] (H) In any of the LED structures denoted as (A)-(G), the intermediate layer comprises a material selected from the group consisting of GaN, AlGaN, InGaN and AlInGaN.

[0093] (I) In any of the LED structures denoted as (A)-(H), at least one active QW stack includes an aluminum-containing QW layer formed on a first barrier layer.

[0094] (J) In any LED structure denoted as (A)-(I), the aluminum-containing QW layer includes one of pseudo-alloy, digital alloy, and short-period superlattice.

[0095] (K) In any of the LED structures denoted as (A)-(J), at least one active QW stack includes (a) an aluminum-containing substrate formed on a first barrier layer and (b) an aluminum-containing active QW layer formed on the aluminum-containing substrate.

[0096] (L) In any of the LED structures denoted as (A)-(K), at least one active QW stack includes (a) an aluminum-containing active QW layer formed on a first barrier layer; and (b) an aluminum-containing capping layer formed on the active QW layer.

[0097] (M) In any of the LED structures denoted as (A)-(L), at least one active QW stack includes (a) an aluminum-containing underlayer formed on a first barrier layer, (b) an aluminum-containing active QW layer formed on the aluminum-containing underlayer, and (c) an aluminum-containing capping layer formed on the aluminum-containing active QW layer.

[0098] (N) In any of the LED structures represented as (A)-(M), a plurality of microLED structures are monolithically formed on a substrate template as an array, the array including each of a blue microLED structure emitting light at a blue wavelength, a green microLED structure emitting light at a green wavelength, and a red microLED structure emitting light at a red wavelength.

[0099] (O) A light-emitting diode (LED) structure includes: a semiconductor template; a first preparation layer formed on the semiconductor template; a second preparation layer formed on the first preparation layer; at least one active quantum well (QW) layer formed over the second preparation layer; and at least one p layer formed on the active QW layer; wherein the active QW layer emits light from the LED structure when activated.

[0100] (P) In the LED structure denoted as (O), the first preparation layer includes an active QW and the second preparation layer includes an aluminum-containing underlayer.

[0101] (Q) In either of the LED structures represented as (O) or (P), the second preparation layer includes a reflective layer.

[0102] (R) In any of the LED structures represented as (O)-(Q), the second preparation layer includes a hole blocking layer.

[0103] (S) A method for forming a light-emitting diode (LED) structure on a semiconductor substrate. The method includes: depositing at least one preparatory layer on the semiconductor substrate; forming an active multiple quantum well (MQW) region on the at least one preparatory layer; and depositing a p-layer on the active MQW region. Forming the active MQW region includes: depositing a first barrier material; depositing an active QW material; and depositing a second barrier material. Forming the active MQW region optionally includes: depositing an underlayer between the first barrier material and the active QW material; depositing an intermediate layer between the underlayer and the active QW material; and depositing a capping layer between the active QW material and the second barrier material. At least one of depositing the active QW material, depositing the underlayer, depositing the intermediate layer, and depositing the capping layer includes incorporating aluminum.

[0104] Therefore, although this disclosure has been provided in accordance with the illustrated implementation, those skilled in the art will readily recognize that variations in embodiments are possible and that such variations will be within the scope of this disclosure. Consequently, many modifications can be made by those skilled in the art without departing from the scope of the appended claims. Changes can be made to the above methods and systems without departing from their scope. Therefore, it should be noted that matters contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not restrictive. The following claims are intended to cover all general and specific features described herein and all statements regarding the scope of the methods and systems, which, as a matter of language, may be said to fall within the scope of the methods and systems.

Claims

1. A light-emitting diode structure, comprising: Semiconductor template; An active region, the active region being formed on the semiconductor template and comprising: A first barrier layer is formed on the semiconductor template; An aluminum-containing underlayer formed on the first barrier layer; A nitride-based quantum well formed on the underlying layer and comprising indium and aluminum; An aluminum-containing capping layer formed on the nitride-based quantum well; and A second barrier layer formed on the capping layer; and p-layer, the p-layer being formed on the active region; When the light-emitting diode structure is driven by injected current, the nitride-based quantum well is configured to emit red light with a wavelength between 0.59 µm and 0.76 µm.

2. The light-emitting diode structure according to claim 1, further comprising a preparation layer, the preparation layer comprising a thick layer of material or a structure of two or more materials, wherein the preparation layer is formed on the semiconductor template and the active region is formed on the preparation layer.

3. The light-emitting diode structure according to claim 2, wherein, The preparation layer is configured to filter out defects from the semiconductor template.

4. The light-emitting diode structure according to claim 2, wherein, The preparation layer comprises a material with a band gap, such that the preparation layer is configured to emit light at blue or ultraviolet wavelengths.

5. The light-emitting diode structure according to claim 1, wherein, The Al composition of the nitride-based quantum well ranges from 0.01% to 5%.

6. The light-emitting diode structure according to claim 1, wherein, The capping layer is an AlGaN capping layer.

7. The light-emitting diode structure according to claim 1, wherein, The underlying layer is an AlGaN layer.

8. The light-emitting diode structure according to claim 7, further comprising a GaN intermediate layer disposed between the AlGaN bottom layer and the nitride-based quantum well.

9. The light-emitting diode structure according to claim 1, wherein, The active region is comprised of a miniature light-emitting diode with a lateral dimension between 1 µm and 10 µm.

10. The light-emitting diode structure according to claim 1, wherein, The Al composition of the nitride-based quantum well is uniform within the nitride-based quantum well.

11. The light-emitting diode structure according to claim 1, wherein, Multiple micro-light-emitting diode structures are monolithically formed on the semiconductor template as an array, the array including each of a blue micro-light-emitting diode structure that emits light at a blue wavelength, a green micro-light-emitting diode structure that emits light at a green wavelength, and a red micro-light-emitting diode structure that includes an active region that emits the red light.

12. A monolithic red, green, and blue LED, comprising: Semiconductor substrate; The first group of LEDs is grown on the semiconductor substrate and emits red light; The second group of LEDs is grown on the semiconductor substrate and emits green light; A third group of LEDs, which are grown on the semiconductor substrate and emit blue light; The first group of LEDs emitting red light includes an active region, which includes: First barrier layer; An aluminum-containing underlayer formed on the first barrier layer; A nitride-based quantum well formed on the underlying layer and comprising indium, gallium, and aluminum; An aluminum-containing capping layer formed on the nitride-based quantum well; and A second barrier layer formed on the capping layer; and p-layer, which is formed on the second barrier layer.

13. The monolithic red, green, and blue LED according to claim 12, wherein, When the monolithic red, green, and blue LEDs are driven by injected current, the nitride-based quantum well is configured to emit red light with wavelengths between 0.59 µm and 0.76 µm.

14. The monolithic red, green, and blue LED of claim 12, further comprising a first preparation layer formed on the semiconductor substrate and a second preparation layer formed on the first preparation layer, wherein the active region is formed on the second preparation layer, and wherein, The first preparation layer includes an active quantum well and the second preparation layer includes an aluminum-containing bottom layer.

15. The monolithic red, green, and blue LED according to claim 14, wherein, The second preparation layer includes a reflective layer.

16. The monolithic red, green, and blue LED according to claim 14, wherein, The second preparation layer includes a hole-blocking layer.

17. A method for forming a red light-emitting diode, the method comprising: A first barrier layer is grown on a semiconductor template; An underlayer is grown on the first barrier layer, wherein the underlayer contains aluminum; A nitride-based quantum well is grown on the underlying layer. The nitride-based quantum well comprises indium and aluminum and is configured to emit red light at wavelengths ranging from 590 nm to 760 nm. A capping layer is grown on the nitride-based quantum well, wherein the capping layer contains aluminum; A second barrier layer is grown on the capping layer; as well as A p-layer is grown on the second barrier layer.

18. The method according to claim 17, wherein, The Al content of the nitride-based quantum well is between 0.01% and 5%.

19. The method of claim 17, wherein, At least one of the first barrier layer and the second barrier layer comprises aluminum.

20. The method of claim 17, wherein, The underlying layer is an AlGaN layer.

21. The method according to claim 17, wherein, The capping layer is an AlGaN capping layer.

Images