Red light Micro light emitting diode epitaxial wafer and preparation method thereof

Abstract

The invention discloses a red light Micro light emitting diode epitaxial wafer and a preparation method thereof. The epitaxial wafer comprises a GaAs substrate, an N-type layer, a multi-quantum well active layer and a P-type layer which are sequentially arranged from bottom to top, the multi-quantum well active layer comprises a plurality of AlGaInP quantum well layers and quantum barrier layers which are alternately arranged, a hole injection layer is inserted between at least part of quantum well structures, and the hole injection layer is composed of a first N-type doped sub-layer, a P-type doped sub-layer and a second N-type doped sub-layer which are connected in sequence; the materials of the three sub-layers are (Al < x > Ga < 1-x >) < 0.5 > In < 0.5 > P (x is greater than or equal to 0.5 and less than or equal to 0.9), and the doping concentration is in gradient distribution along the thickness direction. By introducing the N-P-N structure hole injection layer, the hole injection efficiency is improved, electron leakage and Mg diffusion are inhibited, and the luminous efficiency of the red light Micro LED is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor optoelectronic devices, and in particular to an epitaxial wafer for red light Micro LEDs (Micro LEDs) and a preparation method thereof. Background Art

[0002] Micro LED, with its technological advantages such as high brightness, wide color gamut, and high reliability, has broad application prospects in fields such as microdisplays, consumer electronics, and giant displays, and is considered a key direction for the next generation of display technology. Micro LED, with its advantages of high resolution, fast response, low energy consumption, and long life, has shown great potential in virtual reality (VR), augmented reality (AR), smart wearable devices, electronic billboards, and other fields. Micro LED also has broad application prospects in biosensing, optogenetics, and visible light communications.

[0003] However, while Micro LED technology is developing rapidly, it is also facing many technical challenges. One of the key issues is the low luminous efficiency of red Micro LED. As the chip size decreases, the conventional structure of red Micro LED has problems such as low hole injection efficiency and severe electron leakage. Specifically, Figure 1 In the conventional red Micro LED epitaxial structure shown, due to the large effective mass and low mobility of holes and the high mobility of electrons, injected electrons can easily cross the multi-quantum well (MQW) and escape into the P-type region of the LED structure, or even leak out of the chip sidewalls. Furthermore, during the fabrication process of red Micro LEDs, dry etching is typically used to form a mesa structure. This etching process introduces surface defects such as vacancies and dangling bonds on the LED sidewalls. These defects act as non-radiative recombination centers, causing some carriers to recombine non-radiatively on the sidewalls rather than radiatively in the quantum wells, further reducing the device's quantum efficiency. These factors collectively lead to a significant decrease in the external quantum efficiency (EQE) of red Micro LEDs when driven at small chip sizes and low currents.

[0004] In response to the need to improve the luminous efficiency of Micro LEDs, the industry has attempted to alleviate the above-mentioned problems by adjusting the epitaxial structure. For example, increasing the magnesium (Mg) acceptor doping concentration in the P-type AlInP confinement layer hopes to increase the hole concentration and enhance recombination. However, heavy Mg doping brings new problems: Mg has a serious diffusion effect and easily diffuses into the multi-quantum well active region during the growth process, becoming a non-radiative recombination center, which in turn leads to a further decrease in luminous efficiency. Therefore, how to improve the hole injection efficiency of red light Micro LEDs and reduce electron leakage without introducing additional non-radiative recombination has become a technical difficulty and research hotspot in the current red light Micro LED field. Summary of the Invention

[0005] To address the issues of insufficient hole injection and severe electron leakage in the aforementioned red Micro LED epitaxial structure, the present invention provides a novel structure for a high-efficiency red Micro LED epitaxial wafer and its manufacturing method. By inserting a hole injection layer into the traditional AlGaInP-based multi-quantum well structure, this invention optimizes the carrier injection and recombination processes, significantly improving the device's luminous efficiency.

[0006] The red light Micro LED epitaxial structure of the present invention includes: a GaAs substrate, and an N-type GaAs buffer layer, an N-type AlGaInP current spreading layer, an N-type AlGaInP ohmic contact layer, an N-type AlInP limiting layer, a multi-quantum well active layer (an AlGaInP multi-quantum well structure with a hole injection layer inserted therein), a P-type AlInP limiting layer, a P-type AlGaInP transition layer, a P-type GaP current spreading layer, and a P-type GaP ohmic contact layer, which are epitaxially grown on the substrate in sequence. Among them, the multi-quantum well is composed of alternating AlGaInP quantum wells and AlGaInP quantum barriers, which can be, for example, 3 to 12 pairs of potential wells / barriers; the hole injection layer is inserted into the multi-quantum well structure (it can be inserted evenly between each quantum well, or several layers can be inserted unevenly as needed) to form the quantum well optimized active layer of the present invention. The hole injection layer adopts (Al x Ga 1-x ) 0.5 In 0.5 The P material (where 0.5≤x≤0.9) is constructed from three sublayers, doped with Si, Mg, and Si, forming an N-type / P-type / N-type "sandwich" doping structure. This NPN hole injection layer is the core innovation of this invention, providing additional holes within the quantum well active region and regulating the band structure, thereby effectively improving carrier recombination efficiency.

[0007] The novel structure of the red Micro LED epitaxial wafer provided by this invention is an improvement on the conventional structure. The entire epitaxial stacked structure includes the following layers from bottom to top:

[0008] GaAs substrate: provides the base material for epitaxial growth, preferably using wafer-level GaAs single crystal as the substrate.

[0009] N-type GaAs buffer layer: The initial epitaxial layer grown on the substrate, typically several thousand angstroms thick, is used to improve lattice matching and surface flatness. This layer is doped with N-type impurities such as silicon (Si) to make it n-type conductive, providing a good carrier transport transition.

[0010] N-type AlGaInP current spreading layer: Grown on the GaAs buffer layer, this layer is composed of AlGaInP material. Its function is to spread the current laterally in the n-type region, improving the uniformity of current distribution below the active area. This layer is doped with Si to achieve n-type conductivity and is typically several thousand angstroms thick.

[0011] N-type AlGaInP ohmic contact layer: Immediately above the current spreading layer, this layer is also made of AlGaInP. This layer has a high Si doping concentration, achieving a low-resistance N-type ohmic contact. The thickness can also be increased to reduce the device's series resistance, typically ranging from several thousand to tens of thousands of angstroms.

[0012] N-type AlInP confinement layer: This carrier confinement layer, located below the active area, is made of AlInP doped with n-type Si. This layer has a large bandgap and primarily serves to form a potential barrier below the active area, limiting electron diffusion and leakage (and, to a certain extent, hole escape), thereby effectively confining carriers near the active area. Its thickness is typically around 0.2–0.4 μm.

[0013] Multi-quantum well (MQW) active layer: This is the light-emitting active layer of the LED, consisting of several pairs of alternating AlGaInP quantum wells and AlGaInP quantum barriers. In the traditional structure, the active region is not doped to maintain high radiative recombination efficiency. In the present invention, the active layer is optimized and several hole injection layers are inserted into the quantum well structure. A hole injection layer can be inserted between each pair of quantum well / quantum barrier structures, or inserted at some of the quantum well intervals as needed. In general, multiple hole injection layers are distributed throughout the active region. The hole injection layer adopts (Al x Ga 1-x ) 0.5 In 0.5 P material (0.5≤x≤0.9), with a thickness of tens of angstroms, consists of three sublayers: the first sublayer is an N-type Si-doped (AlGaInP) thin layer, the second sublayer is a P-type Mg-doped (AlGaInP) thin layer, and the third sublayer is an N-type Si-doped (AlGaInP) thin layer. Typically, the first and third sublayers are about The thickness of the second sublayer is about By inserting such a composite NPN doped layer into the quantum well region, two functions are achieved: First, the central P-type sublayer acts as a hole source, close to the quantum well, providing an additional supply of hole carriers. Second, the N-type doped sublayers sandwiched on either side, due to their energy band difference with the P-type layers, form a built-in electric field, which acts as a barrier near the quantum well, preventing high-speed electrons from continuing to leak into the P-type region and inhibiting the diffusion of Mg impurities into the quantum well. Notably, the doping concentration of each sublayer of the hole injection layer of the present invention is gradiently distributed along the thickness direction to further optimize performance: the N-type sublayer region near the central P-type layer has a higher Si doping concentration, providing a stronger electron barrier and space charge region; while the P-type sublayer has a lower Mg doping concentration near the interface with the N-type sublayer and a slightly higher concentration in the middle, ensuring a supply of holes while minimizing Mg diffusion into adjacent layers. Multiple such hole injection layers, alternating with quantum wells / quantum barriers, form an optimized active region, significantly improving the efficiency of hole injection and carrier recombination.

[0014] P-type AlInP confinement layer: A P-type carrier confinement layer located above the active region, made of AlInP and doped with Mg to form a p-type. This layer has a large energy gap and acts like an electron blocking layer (EBL) in a traditional LED, blocking the leakage of higher energy electrons in the active region to the P-type current expansion layer. At the same time, it also serves as the upper confinement layer of the quantum well, helping to confine holes in the active region. The thickness of this layer is about 0.2–0.3 μm, and the Mg acceptor doping concentration is higher than that of the P-type sublayer of the hole injection layer, but it still needs to be controlled within a certain range to avoid Mg diffusion (typical doping concentration is about 10 18 cm -3 level).

[0015] P-type AlGaInP transition layer: Grown on the P-type AlInP confinement layer, it is composed of AlGaInP material and doped with Mg to make it p-type. Since growing GaP directly on the AlInP confinement layer will have discontinuities in lattice and conductivity type, an AlGaInP transition layer is inserted to achieve a smooth transition between materials and energy bands. This layer can also further expand the band gap to reduce carrier absorption loss. The typical doping concentration is about 2×10 18 ~3×10 18 cm -3 .

[0016] P-type GaP current spreading layer: A p-type GaP layer grown on top of the transition layer is used to spread the current laterally in the P-type region. GaP has a high resistivity, so this layer needs to be thick enough (several thousand angstroms) to facilitate lateral current spreading while maintaining good lattice continuity. Doping with acceptor impurities such as Mg or C makes it p-type, and the doping concentration is usually around 2×10 18 cm-3 about.

[0017] P-type GaP ohmic contact layer: The topmost contact layer is made of heavily doped P-type GaP. Due to the high intrinsic resistance of GaP, its resistivity needs to be reduced by heavy acceptor doping (such as carbon doping) to achieve low-resistance ohmic contact. The typical thickness is hundreds of angstroms, and the doping concentration needs to be >5×10 19 cm -3 Such a high acceptor concentration can be achieved by using a carbon source such as CBr4 as a dopant. The ohmic contact layer ensures good ohmic contact between the metal electrode and the P-type GaP, reducing the contact resistance.

[0018] In summary, the red light Micro LED epitaxial structure of the present invention, based on the functional layers of the conventional structure, prominently introduces a hole injection layer as an innovative structure. By inserting a series of doping-optimized hole injection layers (NPN three-sublayer structure) within the multi-quantum well active region, the dual purpose of replenishing hole carriers in the quantum wells and blocking unnecessary carrier diffusion and leakage is achieved. This new structure effectively alleviates the problems of insufficient hole injection and electron leakage in red light Micro LEDs, structurally ensuring that more electrons and holes recombine and emit light within the quantum wells, thereby improving external quantum efficiency and device performance.

[0019] The red light Micro LED epitaxial wafer of the present invention is grown using metal organic chemical vapor deposition (MOCVD) technology. The entire growth process is as follows:

[0020] Growth environment preparation: Place the cleaned GaAs single crystal substrate into the MOCVD reaction chamber. During the growth process, the reaction chamber temperature is controlled at approximately 700-750°C. Depending on the material composition of the layer to be grown, corresponding precursor gas sources are introduced at different stages, including trimethylgallium (TMGa), trimethylaluminum (TMAl), and trimethylindium (TMIn) as Group III element sources, and arsine (AsH3) and phosphine (PH3) as Group V element sources. Doping sources are introduced as needed: silane (SiH4) or disilane (Si2H6) is used as an N-type doping source, cyclo Cp2Mg (ethyl magnesium, Cp2Mg) is used as a P-type doping source, and carbon tetrabromide (CBr4) can be used as an additional acceptor carbon doping source.

[0021] N-type GaAs buffer layer growth: First, an N-type GaAs buffer layer is epitaxially grown on a GaAs substrate. The thickness of this layer is controlled to be approximately To ensure the formation of a smooth transition layer. During the growth, arsenic source (AsH3) and gallium source (TMGa) are introduced to form GaAs. During the growth of the buffer layer, an appropriate amount of N-type doping gas source (Si2H6 or SiH4) is introduced to control the silicon doping concentration to about 1×10 18~3×10 18 cm -3 After the buffer layer is deposited, the arsenic source can be stopped to terminate the growth of the layer.

[0022] N-type AlGaInP current spreading layer growth: Next to the buffer layer, an N-type AlGaInP current spreading layer is grown on it. At this stage, a phosphorus source (PH3), an aluminum source (TMAl), a gallium source (TMGa), and an indium source (TMIn) are introduced to grow together to form an AlGaInP alloy layer. The flow ratio of TMAl / TMIn / TMGa is adjusted to obtain the required Al, Ga, and In composition ratio (the band gap of AlGaInP can be adjusted according to the Al content). The thickness of this layer grows to about To ensure sufficient lateral current expansion capability. During the growth process, N-type doping source SiH4 / Si2H6 is introduced to control the silicon doping concentration to about 1×10 18 ~3×10 18 cm -3 , making it an n-type layer. The growth temperature is still maintained above 700℃ to ensure the crystal quality.

[0023] N-type AlGaInP ohmic contact layer growth: N-type AlGaInP ohmic contact layer is grown on the current spreading layer. Its material is the same as the lower layer (AlGaInP), but the doping concentration needs to be significantly increased to achieve low-resistance ohmic contact characteristics. By increasing the Si doping source flow rate, the silicon doping concentration reaches more than 5×10 18 cm -3 (as high as possible), while growing the layer thickness to about This highly doped n+AlGaInP layer ensures good contact with the subsequently formed N-type electrode and low contact resistance.

[0024] N-type AlInP confinement layer growth: Next, grow the N-type AlInP confinement layer. Aluminum source (TMAl), indium source (TMIn), and phosphorus source (PH3) are introduced to form the AlInP layer. The ratio of Al to In can be adjusted to obtain the desired band gap (usually AlInP is close to the direct band gap range to provide a large band gap difference). A silicon source such as SiH4 is maintained for n-type doping, and the doping concentration is controlled at approximately 1×10 18 ~2×10 18 cm -3 The layer grows to a thickness of approximately As the electron confinement / blocking layer below the active area, its material quality must be high and the interface must be smooth to prepare for subsequent quantum well growth.

[0025] Multi-quantum well active layer growth (including hole injection layer insertion): The multi-quantum well (MQW) active region of the red LED is grown on the N-type confinement layer. First, the first layer of AlGaInP quantum barrier is grown on the AlInP layer: the TMGa / TMIn / TMAl flow rate is switched to the set ratio to obtain the AlGaInP barrier layer, and the thickness is grown to about Then stop the TMGa / TMAl flow to form a stationary slab structure. Then grow the AlGaInP quantum well: reduce the Al source flow or switch the composition to obtain a smaller bandgap AlGaInP well layer with a thickness of about After the quantum well layer is completed, the next quantum barrier is grown, and so on. According to the design, the active region contains, for example, 3 to 12 pairs of quantum well / quantum barrier structures, all completed under a PH3 protective atmosphere, and unintentionally doped (no doping source is introduced to maintain intrinsic properties). In particular, the present invention inserts a hole injection layer during the growth of the quantum well structure: conventional AlGaInP growth is suspended between specific quantum well / quantum barrier layers, and a layer (Al x Ga 1-x ) 0.5 In 0.5 The hole injection layer P can be inserted after each pair of quantum wells, or it can be inserted unevenly (for example, inserting a layer every few pairs of quantum wells), depending on the design optimization plan. The growth of each hole injection layer includes the following sub-steps:

[0026] (1) First sublayer (N-type layer): TMAl, TMGa, TMIn and PH3 are introduced to maintain (Al x Ga 1-x )InP alloy matrix growth, while introducing silane / disilane as N-type doping source. Control the growth thickness to about During the growth process, the silicon source flow rate is adjusted to achieve gradual doping: at the beginning of this sub-layer, the silicon doping concentration is set to be low (for example, about 4×10 16 cm -3 ), and then gradually increase it, and when the sub-layer is nearing the end (about to transition to the P-type layer), the Si doping concentration is increased to about 1×10 17 ~3×10 17 cm -3 This allows the first sublayer to have the highest N-type carrier concentration near the middle P layer.

[0027] (2) Second sublayer (P-type layer): Immediately after the first sublayer, switch the N-type doping source to zero and turn on the P-type doping source such as Cp2Mg to grow the middle P-type (Al x Ga 1-x )InP layer. The thickness is controlled at about During the growth of this sub-layer, in order to suppress the diffusion of Mg into the adjacent N-type layer, a two-way gradient doping strategy is adopted: only a low concentration of Mg (about 1×10 17 cm -3 ), and then gradually increase the Mg source flow rate in the middle stage of the sub-layer to increase the doping concentration to the highest (up to about 4×10 17 ~6×10 17 cm -3 ), and then the Mg source is reduced near the end of the second sublayer (the interface with the third sublayer) to reduce the Mg concentration back to the initial low value. This "first increase and then decrease" Mg doping distribution ensures sufficient hole concentration in the center of the P-type layer, while the Mg concentration is lower near the interfaces on both sides of the N-type layer, reducing the driving force for Mg atoms to diffuse into adjacent layers.

[0028] (3) The third sublayer (N-type layer): After the P-type sublayer is completed, the Mg source is turned off again and the Si doping source is reintroduced to continue growing the third N-type (Al x Ga 1-x )InP. The thickness is also about The Si doping concentration gradient of the third sub-layer is similar to that of the first sub-layer, but in the opposite direction: a higher Si doping concentration (e.g., about 1×10 17 ~3×10 17 cm -3 ), and then gradually decreases the Si concentration as the distance from the P-type layer interface increases, and drops to about 4×10 16 ~8×10 16 cm -3 In this way, the third sublayer close to the P-type layer provides strong electron blocking and electric field effects, while the far end is doped shallowly to reduce the obstruction of holes entering the subsequent quantum wells.

[0029] Completion of the growth of the above three sub-layers constitutes a complete hole injection layer. Then continue to resume the growth of conventional AlGaInP quantum wells / quantum barriers. If the design requires the insertion of multiple layers of hole injection layers, repeat the above insertion process at the corresponding position. After the entire active area is grown, it contains a predetermined number of quantum well structures and hole injection layer structures. Growth of P-type AlInP confinement layer: After the growth of the multi-quantum well active layer (including the hole injection layer) is completed, switch the material source and epitaxially grow a P-type AlInP confinement layer on it. TMAl, TMIn, and PH3 are introduced to form the AlInP layer, and Cp2Mg is introduced to realize Mg acceptor doping. Control the Mg source flow rate to make the doping concentration approximately (0.6–1.5)×10 18 cm -3, so that the layer is moderately doped p-type (the doping concentration must be sufficient to block electrons but not too high to prevent Mg from diffusing into the active area). The growth thickness is controlled at about The thickness is comparable to that of the N-type confinement layer below, forming a symmetrical upper and lower confinement structure that clamps the active area.

[0030] Growth of P-type AlGaInP transition layer: Grow a P-type AlGaInP transition layer on the P-type AlInP layer. Introduce TMGa, TMAl, TMIn and PH3 to grow AlGaInP, and continue to introduce Cp2Mg for P-type doping. The main function of this layer is to transition from AlInP to GaP material, so the thickness does not need to be too thick. It is usually grown until the Al composition gradient transition is completed (for example, a few hundred angstroms to a few thousand angstroms). The doping concentration can be increased to about 2×10 18 ~3×10 18 cm -3 to ensure sufficient hole concentration and good conductivity.

[0031] Growth of P-type GaP current spreading layer: Continue to deposit P-type GaP current spreading layer on the transition layer. Switch the material source to TMGa and PH3 to grow GaP layer while maintaining Cp2Mg doping. The thickness of GaP current spreading layer grows to about So that the current can be fully expanded in the P-type region. The Mg doping concentration is controlled at about 2×10 18 ~3×10 18 cm -3 , maintaining a high hole concentration. Since GaP material itself has poor conductivity, sufficient doping concentration and thickness must be ensured to reduce lateral resistance.

[0032] Growth of P-type GaP ohmic contact layer: Finally, grow a P-type GaP ohmic contact layer on the top layer. Continue to introduce TMGa and PH3 gas source to form GaP, and introduce high concentration of acceptor impurities to achieve heavy doping. Here, CBr4 is preferably used as the carbon doping source to obtain a very high acceptor concentration (>5×10 19 cm -3 ), making GaP highly doped P++ type conductive. This layer grows to about After the ohmic contact layer is grown, all precursors are turned off, the reaction chamber temperature is lowered, and the epitaxial wafer is removed.

[0033] After completing the MOCVD growth of each layer in the above order, the red light Micro light-emitting diode epitaxial wafer of the present invention is obtained. Compared with the conventional epitaxial structure, the method of the present invention adds the process step of the hole injection layer in the multi-quantum well growth process, and optimizes and controls the doping scheme. This manufacturing method can ensure that the hole injection layer is accurately embedded in the specified position of the active area, and realizes the required doping gradient distribution, thereby achieving the functional effect of the structural design intention. The epitaxial wafer finally prepared can show higher light output efficiency and lower leakage current when it is subsequently made into a Micro LED device through processes such as lithography, electrode preparation and chip cutting. This preparation method is mature and feasible, suitable for existing MOCVD industrial production lines, and is expected to be widely used in the field of red light Micro LED displays.

[0034] Compared with the prior art, the structure of the present invention has the following beneficial effects:

[0035] Enhanced hole injection and recombination: The hole injection layer inserted into the multi-quantum well contains a P-type doped sublayer, which generates and injects more holes close to the quantum well. Because the P-type doped layer is located closer to the active area, holes can be injected into the quantum well more quickly and achieve radiative recombination with electrons, reducing the loss of electrons that jump across the active area to the P region or sidewalls, thereby significantly improving the light efficiency of red light Micro LEDs under low current driving.

[0036] Internal electric fields suppress carrier leakage and diffusion: The hole injection layer adopts an N-type-P-type-N-type heterogeneous doping structure, and the P-type doping concentration of this injection layer is preferably lower than that of the adjacent P-type AlInP confinement layer. The NPN three-sublayer structure forms an internal built-in electric field from N to P, which effectively blocks the movement of positive charge. This means that it prevents the diffusion of P-type doped Mg atoms into the quantum well, while also forming a potential barrier for fast-moving electrons, preventing excessive leakage into the P region. As a result, electrons are better confined in the quantum well to participate in radiative recombination, reducing ineffective leakage.

[0037] Optimized Graded Doping Configuration: The doping concentrations of each sublayer of the hole injection layer are carefully designed with gradients along the thickness. The Si doping concentrations of the first and third N-type sublayers gradually increase from a low value farther from the middle layer, reaching a peak near the interface with the middle P-type sublayer. The higher N-type carrier concentration provides strong screening and blocking near the P-type layer, limiting Mg diffusion and electron overflow, while the doping is shallower farther from the P-type layer to ensure that hole entry is not excessively suppressed. Furthermore, the doping concentration of the central P-type sublayer increases and then decreases, with the Mg doping concentration being highest at the center and lowest near the interfaces with the N-type sublayers on both sides. This design ensures sufficient holes while minimizing the driving force for Mg diffusion into the quantum well. This graded doping of the hole injection layer effectively balances the trade-off between enhanced injection and suppressed diffusion, significantly improving the device's internal quantum efficiency.

[0038] Through this structural optimization, the present invention's red Micro LED epitaxial wafer achieved significant performance improvements in experiments. Comparative test results showed that the external quantum efficiency of chips using the present structure increased by approximately 30% compared to conventional structures, demonstrating that this novel structure can effectively address key bottlenecks in the field of high-efficiency red Micro LEDs and holds significant value for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 : Schematic diagram of a conventional epitaxial structure. This figure shows the hierarchical structure of a conventional red light Micro LED epitaxial wafer and the numbering of each layer. From bottom to top, they are: GaAs substrate (numbered 500), GaAs buffer layer (501), N-type AlGaInP current spreading layer (100), N-type AlGaInP ohmic contact layer (101), N-type AlInP confinement layer (102), AlGaInP multi-quantum well active layer (103, including several pairs of AlGaInP quantum wells / quantum barriers, without inserting special layers), P-type AlInP confinement layer (104), P-type AlGaInP transition layer (105), P-type GaP current spreading layer (106) and P-type GaP ohmic contact layer (107). In this conventional structure, the multi-quantum well region is only composed of alternating AlGaInP quantum wells and quantum barriers, and does not include additional structures such as hole injection layers. When driven by external current, electrons are injected from the N-type region into the active region. Due to the lack of sufficient hole supply and electron blocking mechanism, some electrons will cross the quantum well and run to the P-type region and chip sidewall defects, making it impossible for them to recombine with holes in the quantum well to emit light, resulting in a decrease in luminous efficiency.

[0040] Figure 2 : Schematic diagram of epitaxial structure 1 of the present invention. This figure is Example 1 of the new structure of the red light Micro LED epitaxial wafer provided by the present invention. The structure of each layer from bottom to top is the same as Figure 1 Similarly, the numbers are: GaAs substrate (600), GaAs buffer layer (601), N-type AlGaInP current expansion layer (200), N-type AlGaInP ohmic contact layer (201), N-type AlInP confinement layer (202), multi-quantum well optimized active layer (203), P-type AlInP confinement layer (204), P-type AlGaInP transition layer (205), P-type GaP current expansion layer (206), P-type GaP ohmic contact layer (207). Among them, the active region 203 includes several pairs of AlGaInP quantum well / quantum barrier structures, and is inserted with multiple hole injection layers (represented by the yellow highlighted "hole injection layer" in the figure). In this embodiment, the hole injection layer is uniformly inserted between each quantum well layer, for example, one hole injection layer is sandwiched between every two quantum wells. The hole injection layer is composed of an N / P / N three-layer structure of (AlGaInP) material, and its doping design is as described above, providing additional holes and forming an electron barrier. By Figure 1 The comparison shows that compared with the traditional structure, Figure 2 A new hole injection layer structure (the layer marked in yellow) is introduced into the active area (203), which effectively alleviates the problems of insufficient hole injection and electron overflow, and improves the luminous efficiency of the LED from a structural perspective.

[0041] Figure 3 : Schematic diagram of epitaxial structure 2 of the present invention. This figure shows another embodiment of the red light Micro LED epitaxial structure of the present invention, and its layer composition is similar to Figure 2 It is basically the same, but shows another way of inserting the hole injection layer into the active region. The labels of the layers from bottom to top are: GaAs substrate (700), GaAs buffer layer (701), N-type AlGaInP current expansion layer (300), N-type AlGaInP ohmic contact layer (301), N-type AlInP confinement layer (302), multi-quantum well active layer (303), P-type AlInP confinement layer (304), P-type AlGaInP transition layer (305), P-type GaP current expansion layer (306), P-type GaP ohmic contact layer (307). Figure 2 compared to, Figure 3 The active region 303 in the diagram also incorporates multiple hole injection layers, but these insertions can be unevenly distributed. For example, as shown in this figure, two hole injection layers are inserted above, below, and in the middle of the active region, separating the multiple quantum wells into groups. This layout demonstrates that the number and spacing of hole injection layers can be adjusted based on actual needs to achieve optimal carrier injection and recombination between different quantum well layers. Figure 3The structure shown also improves the distribution of holes in the quantum well and the confinement of electrons through the action of the hole injection layer, further verifying that the structure of the present invention can significantly improve the luminescence performance of red light Micro LEDs under different implementation modes. Figure 4 : Comparison curve of the external quantum efficiency (EQE) of red light Micro LEDs with the structure of the present invention and the conventional structure. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0043] Example 1:

[0044] like Figure 2 As shown in FIG, a specific epitaxial structure of a red light micro light-emitting diode epitaxial wafer includes the following layers from bottom to top:

[0045] GaAs substrate 600;

[0046] N-type GaAs buffer layer 601, with a thickness of SiH4 or Si2H6 was used as the doping source with a doping concentration of 1×10 18 ~3×10 18 carriers / cm 3 ;

[0047] N-type AlGaInP current spreading layer 200, with a thickness of Using Si as a doping element;

[0048] N-type AlGaInP ohmic contact layer 201, with a thickness of Doping concentration is greater than 5×10 18 carriers / cm 3 ;

[0049] N-type AlInP confinement layer 202, with a thickness of Use Si doping;

[0050] The quantum well optimized active layer 203 includes a plurality of AlGaInP quantum well and quantum barrier pairs (3 to 12 pairs) and a multi-layer hole injection layer embedded therein;

[0051] The P-type AlInP confinement layer 204 has a thickness of Cp2Mg was used as the P-type doping source with a concentration of 0.6×10 18 ~1.5×10 18 carriers / cm3 ;

[0052] P-type AlGaInP transition layer 205, with a thickness of several hundred to several thousand The doping concentration is 2×10 18 ~3×10 18 carriers / cm 3 ;

[0053] The P-type GaP current spreading layer 206 has a thickness of

[0054] The P-type GaP ohmic contact layer 207 has a thickness of CBr4 is used for heavy doping, with a doping concentration greater than 5×10 19 carriers / cm 3 .

[0055] The hole injection layer is arranged in a quantum well structure and consists of the following three layers:

[0056] The first sublayer: thickness is Si doped, the initial concentration is 4×10 16 ~6×10 16 carriers / cm 3 , linearly increasing to the highest concentration of 1×10 17 ~3×10 17 carriers / cm 3 ;

[0057] Second sublayer: thickness is Mg-doped, doping concentration from 1×10 17 ~3×10 17 Linearly increasing to 4×10 17 ~6×10 17 carriers / cm 3 Then, it linearly decreases back to the original concentration;

[0058] The third sublayer: thickness is Symmetrically with the first sublayer, the Si doping concentration decreases linearly from the highest value to 4×10 16 ~8×10 16 carriers / cm 3 .

[0059] The hole injection layer material is (Al x Ga1- x ) 0.5 In 0.5 P, where x is 0.5 to 0.9.

[0060] The above structure constructs an NPN type charge control structure by inserting multiple hole injection layers into the multi-quantum well structure. On the one hand, it enhances the hole injection capability, and on the other hand, it inhibits electron cross-region and Mg diffusion, thereby improving the recombination efficiency and light output efficiency.

[0061] Example 2: Epitaxial preparation method

[0062] The epitaxial structure is sequentially grown on a GaAs substrate by a metal organic chemical vapor deposition (MOCVD) process, the method comprising:

[0063] Substrate preparation: Select n-type conductive GaAs single crystal substrate and polish the surface;

[0064] Buffer layer growth: At a temperature of 700-750°C, TMGa and AsH3 are introduced to grow the GaAs buffer layer, and SiH4 is introduced to achieve N-type doping;

[0065] Growth of n-type AlGaInP region: TMAl, TMIn, TMGa, and PH3 are introduced to form AlGaInP, and the doping concentration is controlled to form the extension layer and contact layer in sequence;

[0066] Confinement layer growth: grow AlInP confinement layer, doped with Si;

[0067] Multiple quantum well structure and hole injection layer insertion:

[0068] Three sublayers of hole injection layer are inserted between each pair of quantum well / barrier structures;

[0069] When growing each sub-layer, the Si and Mg doping concentrations are controlled separately to achieve concentration gradient;

[0070] Growth of the p-type region: AlInP confinement layer, AlGaInP transition layer, GaP current spreading layer and ohmic contact layer are grown in sequence, using Cp2Mg and CBr4 as P-type doping sources;

[0071] Complete the epitaxial structure.

[0072] This embodiment corresponds to Figure 2 structure, which can be extended to Figure 3 The hole injection layer is a structure with unequal spacing.

[0073] Effect verification

[0074] The red light Micro LED prepared by the above embodiment is compared with the traditional structure device. Figure 4As shown in the figure, under the same driving current conditions, the external quantum efficiency (EQE) can be improved by about 30%, verifying that the optimized structure of the present invention has obvious advantages in improving light efficiency compared with the conventional structure, and is particularly suitable for Micro LED chips and low current driving application scenarios.

Claims

1. A red light micro light emitting diode epitaxial wafer, characterized in that: Including the following settings from bottom to top: GaAs substrate; N-type GaAs buffer layer; N-type AlGaInP current spreading layer; N-type AlGaInP ohmic contact layer; N-type AlInP confinement layer; Multiple quantum well active layer; P-type AlInP confinement layer; P-type AlGaInP transition layer; P-type GaP current spreading layer; P-type GaP ohmic contact layer; The multi-quantum well active layer includes a plurality of alternately arranged AlGaInP quantum well layers and quantum barrier layers, and a hole injection layer is provided between at least part of the quantum well structures. The hole injection layer includes the following layers arranged in sequence: The first sublayer is N-type doped (Al x Ga 1-x ) 0.5 In 0.5 P material; The second sublayer is P-type doped (Al x Ga 1-x ) 0.5 In 0.5 P material; The third sublayer is N-type doped (Al x Ga 1-x ) 0.5 In 0.5 P material; Wherein, x is a value between 0.5 and 0.9, the doping element of the first sublayer and the third sublayer is Si, the doping element of the second sublayer is Mg, and the doping concentrations of the three sublayers are distributed in a gradient along the layer thickness direction.

2. The epitaxial wafer according to claim 1, wherein: The thickness of the first sublayer and the third sublayer in the hole injection layer is The thickness of the second sublayer is 3. The epitaxial wafer according to claim 1, wherein: The doping concentration of Mg in the second sub-layer first increases to a maximum value along the thickness direction and then decreases, and the maximum value is located in the middle.

4. The epitaxial wafer according to claim 1, wherein: The hole injection layers are distributed in the multi-quantum well active layer at equal intervals, or are distributed unevenly at different quantum well intervals.

5. The method for preparing a red light emitting micro diode epitaxial wafer according to any one of claims 1 to 4, characterized in that: The steps include: 1) Providing a GaAs substrate, and sequentially growing thereon by metal organic chemical vapor deposition (MOCVD): N-type GaAs buffer layer; N-type AlGaInP current spreading layer; N-type AlGaInP ohmic contact layer; N-type AlInP confinement layer; Multiple quantum well active layer; P-type AlInP confinement layer; P-type AlGaInP transition layer; P-type GaP current spreading layer; P-type GaP ohmic contact layer; 2) When growing the multi-quantum well active layer, AlGaInP quantum barrier layers and quantum well layers are alternately grown, and a hole injection layer is inserted between at least part of the quantum well structure, wherein the hole injection layer comprises: In the first sublayer, Si doping source is introduced for N-type doping, and the doping concentration is linearly increased from the initial value to the maximum value; The second sublayer is doped with a Mg doping source for P-type doping, and the doping concentration is linearly increased from the initial value to the maximum value and then linearly decreased; The third sublayer is doped with Si doping source for N-type doping, and the doping concentration decreases linearly from the maximum value to the initial value; 3) Control the thickness of each sub-layer: the first and third sub-layer Second sublayer 6. The method according to claim 5, characterized in that: The epitaxial growth temperature is controlled at 700-750° C., the precursor gas source includes TMGa, TMAl, TMIn, AsH 3 , and PH 3 , the N-type doping source is SiH 4 or Si 2 H 6 , and the P-type doping source is Cp 2 Mg or CBr 4 .

7. The method according to claim 5, characterized in that: The hole injection layer is made of (Al x Ga1- x ) 0.5 In 0.5 P, where x A value between 0.5 and 0.

9.

8. The method according to claim 5, characterized in that: The hole injection layers are inserted into the multi-quantum well active layer at equal or unequal intervals, and the number of inserted layers is 2 to 6.

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