Red micro light emitting diode epitaxial wafer and preparation method thereof

Abstract

This invention discloses a red-light-emitting micro-LED epitaxial wafer and its fabrication method, belonging to the field of semiconductor optoelectronic devices. The epitaxial wafer comprises, sequentially disposed on a substrate, an N-type GaAs buffer layer, an N-type AlGaInP current spreading layer, an N-type AlGaInP ohmic contact layer, an N-type AlInP confinement layer, an N-type AlGaInP waveguide layer, a multiple quantum well layer, a P-type AlGaInP waveguide layer, a P-type stress-compensated electron blocking layer, a P-type AlInP confinement layer, a P-type AlGaInP transition layer, a P-type GaP spreading layer, and a P-type GaP ohmic contact layer. The electron blocking layer consists of a periodic AlP / gradient AlGaInP / Al... 0.4 In 0.6 The P / anti-gradient AlGaInP structure effectively suppresses electron leakage, reduces nonradiative recombination, improves quantum efficiency and strain balance, and significantly enhances LED luminous performance.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device technology, and in particular to a red-light micro-emitting diode epitaxial wafer and its fabrication method. Background Technology

[0002] Micro LEDs, as a next-generation display technology, boast advantages such as high brightness, wide color gamut, fast response, low power consumption, and long lifespan. They are widely used in various scenarios including augmented reality (AR), virtual reality (VR), smart wearable devices, micro-displays, automotive displays, and large-size splicing displays. Among these, red Micro LEDs are an indispensable component in full-color display solutions, and their luminous efficiency directly affects the overall display performance.

[0003] Currently, AlGaInP materials are the mainstream approach for achieving red light emission. However, due to the low hole mobility and high electron mobility in AlGaInP, a large number of electrons easily leak from the quantum well region to the P-type region or sidewalls during current injection, leading to increased nonradiative recombination and severely affecting the quantum efficiency and optical output power of the device. To limit electron leakage, existing technologies generally place an electron blocking layer (EBL) between the active region and the P-type confinement layer, often using monolayer AlInP or high-Al-content AlGaInP materials as the blocking layer.

[0004] However, the above structure still has the following drawbacks: On the one hand, it is difficult for a single layer of AlInP or AlGaInP to achieve both high bandgap and lattice matching. When the Al composition is too high, the lattice mismatch with the GaAs substrate is severe, which can easily cause dislocations and defects, thereby affecting the epitaxial quality and luminescence efficiency. On the other hand, the discontinuity of the energy band or the incoordination of stress between the electron blocking layer and the adjacent layer still cannot effectively limit electron overflow, while also affecting hole injection and transport, thus limiting the overall efficiency improvement.

[0005] Therefore, optimizing the electron blocking structure while maintaining epitaxial quality, and achieving coordinated design of electron leakage control, stress balance and band transition, is one of the key technical issues in the current design of red Micro LED epitaxial structures. Summary of the Invention

[0006] This invention provides an epitaxial structure and its fabrication method for improving the luminous efficiency of red-light-emitting diodes (Micro LEDs), belonging to the field of light-emitting semiconductor devices. This epitaxial structure achieves multiple technical goals—suppressing electron leakage, balancing stress, and improving quantum efficiency—by optimizing the design of the electron blocking layer (EBL) and introducing a periodic composite P-type stress compensation layer.

[0007] The technical solution of the present invention is as follows:

[0008] A red-light-emitting diode epitaxial wafer includes the following epitaxial structure layers sequentially disposed on a substrate:

[0009] N-type GaAs buffer layer;

[0010] N-type AlGaInP current-spreading layer;

[0011] N-type AlGaInP ohmic contact layer;

[0012] N-type AlInP confinement layer;

[0013] N-type AlGaInP waveguide layer;

[0014] Multiple quantum well layers;

[0015] P-type AlGaInP waveguide layer;

[0016] P-type stress-compensating electron blocking layer;

[0017] P-type AlInP confinement layer;

[0018] P-type AlGaInP transition layer;

[0019] P-type GaP extended layer;

[0020] P-type GaP ohmic contact layer;

[0021] The P-type stress-compensating electron blocking layer has a periodic structure, and each period includes the following sequentially arranged components:

[0022] AlP layer;

[0023] Al x GaInP gradient layers, in which the Al composition x changes from high to low along the growth direction;

[0024] Al 0.4 In 0.6 P layer;

[0025] Al y In GaInP gradient layers, the Al composition y increases from low to high along the growth direction.

[0026] The P-type stress-compensating electron blocking layer is a periodic structural repeating unit with 3 to 5 cycles.

[0027] The thickness of the AlP layer is 40–80 angstroms.

[0028] The Al x The thickness of the GaInP gradient layer is 30–60 angstroms, and the Al composition varies from 0.6–0.8 to 0.3–0.5.

[0029] The Al y The thickness of the GaInP gradient layer is 30–60 angstroms, and the Al composition varies from 0.4–0.55 to 0.6–0.8.

[0030] The Al 0.4 In 0.6 The thickness of the P layer is 40–80 angstroms.

[0031] The multi-quantum-well layer consists of 3 to 8 pairs of AlGaInP potential wells and Al x The GaInP structure consists of a potential well with a thickness of 30–50 angstroms and a barrier thickness of 50–100 angstroms.

[0032] The above-mentioned method for fabricating the epitaxial wafer of the red light-emitting diode includes the following steps:

[0033] 1) Growing an N-type GaAs buffer layer on a GaAs substrate;

[0034] 2) N-type AlGaInP current spreading layer, N-type AlGaInP ohmic contact layer, N-type AlInP confinement layer and N-type AlGaInP waveguide layer are epitaxially grown sequentially;

[0035] 3) Growth of multiple quantum well layers;

[0036] 4) Epitaxial growth of P-type AlGaInP waveguide layer;

[0037] 5) Grow a P-type stress-compensated electron blocking layer, each cycle including: AlP layer, Al x GaInP gradient layer, Al 0.4 In 0.6 P layer and Al y GaInP gradient layers were grown for 3 to 5 cycles.

[0038] 6) Continue to grow the P-type AlInP confinement layer, P-type AlGaInP transition layer, P-type GaP extension layer, and P-type GaP ohmic contact layer;

[0039] 7) Complete the epitaxial growth of the red-light Micro LED epitaxial wafer.

[0040] To overcome the problems of easy electron leakage, low recombination efficiency of multiple quantum wells, and crystal defects caused by stress mismatch in the epitaxial structure of existing AlGaInP-based red Micro LEDs, this invention proposes a multilayer periodic electron blocking layer, whose structural units sequentially include: a high bandgap material AlP layer, and Al layers with gradually decreasing Al composition. x GaInP layer, Al with fixed composition 0.4 In 0.6The P-stress layer, and the Al composition gradually increasing from low to high. y GaInP layers. The above four layers form a periodic unit, which is repeatedly grown in the electron blocking region for 3 to 5 cycles to form a complete P-type stress-compensated electron blocking structure.

[0041] Among them, the AlP layer possesses an extremely wide band gap and strong electron confinement capability, which can significantly suppress electron leakage from the quantum well region to the P-type region and the LED sidewalls; Al x GaInP and Al y The GaInP layer employs a composition gradient design, which not only creates a continuous valence band potential energy gradient to improve hole migration efficiency, but also achieves stress compensation through stress cancellation, suppressing dislocation defects caused by stress accumulation; Al 0.4 In 0.6 The P-layer has tensile stress characteristics, and combined with the upper and lower AlGaInP gradient layers, it achieves a periodic alternating compression and tension structure, thereby achieving strain equilibrium on a macroscopic level.

[0042] Experiments have shown that, compared with conventional red LEDs using a single-layer AlInP EBL structure, the structure described in this invention can reduce electron leakage current by approximately 12.5% ​​and increase internal quantum efficiency by approximately 14%, significantly improving the low-current luminous efficacy and overall electro-optical performance of the LED device. Because the EBL structure slightly increases the blocking barrier, the operating voltage increases slightly, but the overall photoelectric performance is significantly improved.

[0043] A comprehensive comparison of existing technologies reveals that while some literature has proposed using high-Al content materials (such as AlP) or gradient AlGaInP layers to improve electron confinement and stress management, no method has yet been disclosed for constructing a composite stress-compensated EBL structure using AlP / gradient AlGaInP / tensile stress AlInP / anti-gradient AlGaInP in a periodic manner. The design provided by this invention, based on the coupled optimization of strain engineering and band engineering, is not only innovative in its structural composition but also possesses significant advantages in device performance indicators, effectively supporting the core structure and corresponding technical effects outlined in the claims. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a common red Micro LED epitaxial structure in existing technologies. Its electron blocking layer is usually a single layer of AlInP, which has problems such as severe electron leakage and lattice stress accumulation.

[0045] Figure 2 This is a schematic diagram of the red Micro LED epitaxial wafer structure described in this invention, including the specific order of each epitaxial layer structure. Detailed Implementation

[0046] The structure and fabrication method of the red-light-emitting diode epitaxial wafer of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only for illustrating the technical solutions of the present invention and are not intended to limit the present invention.

[0047] Example

[0048] This embodiment provides a red Micro LED epitaxial wafer based on the AlGaInP material system. The epitaxial structure is grown on a GaAs substrate using Metal-Organic Vapor Phase Epitaxy (MOVPE or MOCVD). Specific structure and process parameters are as follows:

[0049] On the cleaned GaAs substrate 600, an N-type GaAs buffer layer 601 with a thickness of 1500–3000 Å is first grown using an N-type doping source, either SiH4 or Si2H6, with a doping concentration controlled at 1 × 10⁻⁶. 18 ~3×10 18 carriers / cm 3 It is used to eliminate interface defects and serve as a lattice template for subsequent growth.

[0050] An N-type AlGaInP current-spreading layer 200 with a thickness of 5000–10000 Å was sequentially grown on the buffer layer. An N-type doping source, either SiH4 or Si2H6, was used, with a doping concentration of 1 × 10⁻⁶. 18 ~3×10 18 carriers / cm 3 ;

[0051] An N-type AlGaInP ohmic contact layer 201 was grown with a thickness of 5000–15000 Å and a doping concentration greater than 5 × 10⁻⁶. 18 carriers / cm 3 ;

[0052] An N-type AlInP confinement layer 202 with a thickness of 2000–4000 Å was grown using N-type doping. The doping source was Si₂H₆, and the doping concentration was 1 × 10⁻⁶. 18 ~2×10 18 carriers / cm 3 ;

[0053] An N-type AlGaInP waveguide layer 203 with a thickness of 500–1200 Å was grown, and this layer was undoped;

[0054] A multi-quantum well (MQW) layer 204 is grown. This layer is undoped and consists of 3 to 8 pairs of potential well / barrier periods.

[0055] Potential well layer: AlGaInP, with a thickness of 30–50 Å;

[0056] Barrier layer: AlGaInP, thickness 50–100 Å;

[0057] A P-type AlGaInP waveguide layer 205 with a thickness of 500–1200 Å was grown, and this layer was undoped;

[0058] A p-type stress-compensated electron blocking layer 206 was grown, which is a periodic AlP / Al x GaInP / Al 0.4 In 0.6 P / Al y The GaInP structure consists of 3 to 5 cycles, with the following layers and parameters for each cycle:

[0059] AlP layer: thickness 40–80 Å;

[0060] Al x GaInP gradient layer: The thickness is 30-60 Å, the Al content decreases from 0.6-0.8 (near the AlP side) to 0.3-0.5, the In content is designed from low to high, the In content is controlled at 0.45-0.55, and the In content is the lowest near the AlP side;

[0061] Al 0.4 In 0.6 P layer: thickness 40–80 Å;

[0062] Al y GaInP gradient layer: thickness 30–60 Å, Al composition from 0.4–0.55 (close to Al) 0.4 In 0.6 The P-side content increases from 0.6 to 0.8, with the In component designed from high to low, and the In component controlled at 0.45 to 0.55, close to Al. 0.4 In 0.6 The In component was highest on the P side;

[0063] The Al x GaInP and Al y The GaInP layers all form valence band gradients through compositional gradients, while their stress states are similar to those of AlP and Al. 0.4 In 0.6 The P-layers are arranged with alternating tensile and compressive stresses to achieve stress compensation within the structure.

[0064] The 206 p-type stress-compensating electron blocking layer is undoped.

[0065] A p-type AlInP confinement layer 207 with a thickness of 2000–3000 Å was grown using p-type doping with Cp₂Mg as the doping source and a doping concentration of 0.6 × 10⁻⁶. 18 ~1.5×10 18 carriers / cm 3 ;

[0066] A p-type AlGaInP transition layer 208 with a thickness of 200–400 Å was grown using p-type doping with Cp₂Mg as the doping source and a doping concentration of 2 × 10⁻⁶. 18 ~3×10 18 carriers / cm 3 ;

[0067] A p-type GaP current-extended layer 209 with a thickness of 3000–8000 Å was grown using p-type doping with Cp₂Mg as the doping source and a doping concentration of 2 × 10⁻⁶. 18 ~3×10 18 carriers / cm 3 ;

[0068] A p-type GaP ohmic contact layer 210 with a thickness of 300–1000 Å was grown using p-type doping with CBr4 as the doping source and a doping concentration greater than 5 × 10⁻⁶. 19 carriers / cm 3 .

[0069] Except for the P-type stress-compensating electron blocking layer, the composition ratios of the materials in the epitaxial wafers of this invention are well-known in the art and can be adjusted according to specific process requirements. This is not the core of the technical innovation of this invention, and those skilled in the art can determine the appropriate ratio range based on conventional experience.

[0070] The performance of the red Micro LED epitaxial wafer of this invention was compared with that of a conventional structure sample under the same test conditions. The results are as follows:

[0071] The comparison results show that the periodic stress-compensated EBL structure used in this invention significantly reduces electron leakage, improves recombination efficiency, and helps to enhance the luminous performance and reliability of Micro LED devices under low current.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and substitutions without departing from the concept of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A red micro light emitting diode epitaxial wafer, characterized in that, This includes the following epitaxial structure layers sequentially disposed on the substrate: N-type GaAs buffer layer; N-type AlGaInP current-spreading layer; N-type AlGaInP ohmic contact layer; N-type AlInP confinement layer; N-type AlGaInP waveguide layer; Multiple quantum well layers; P-type AlGaInP waveguide layer; P-type stress-compensating electron blocking layer; P-type AlInP confinement layer; P-type AlGaInP transition layer; P-type GaP extended layer; P-type GaP ohmic contact layer; The P-type stress-compensating electron blocking layer has a periodic structure, and each period includes the following sequentially arranged components: AlP layer; Al x GaInP gradient layers, in which the Al composition x changes from high to low along the growth direction; Al 0.4 In 0.6 P layer; Al y GaInP graded layer, whose Al composition y varies from low to high along the growth direction.

2. The red micro light emitting diode epitaxial wafer of claim 1, wherein, The P-type stress-compensating electron blocking layer is a periodic structural repeating unit with 3 to 5 cycles.

3. The red-light-emitting diode epitaxial wafer according to claim 1, characterized in that, The thickness of the AlP layer is 40–80 angstroms.

4. The red micro light emitting diode epitaxial wafer of claim 1, wherein, The Al x The thickness of the GaInP gradient layer is 30–60 angstroms, and the Al composition varies from 0.6–0.8 to 0.3–0.

5.

5. The red micro light emitting diode epitaxial wafer of claim 1, wherein, The Al y The thickness of the GaInP gradient layer is 30–60 angstroms, and the Al composition varies from 0.4–0.55 to 0.6–0.

8.

6. The red micro light emitting diode epitaxial wafer of claim 1, wherein, The Al 0.4 In 0.6 The thickness of the P layer is 40-80 angstroms.

7. The red-light-emitting diode epitaxial wafer according to claim 1, characterized in that, The multi-quantum well layer consists of 3 to 8 pairs of potential wells and barriers, with the potential wells having a thickness of 30 to 50 angstroms and the barriers having a thickness of 50 to 100 angstroms.

8. The method for preparing a red-light-emitting diode epitaxial wafer according to any one of claims 1-7, characterized in that, Includes the following steps: 1) Growing an N-type GaAs buffer layer on a GaAs substrate; 2) N-type AlGaInP current spreading layer, N-type AlGaInP ohmic contact layer, N-type AlInP confinement layer and N-type AlGaInP waveguide layer are epitaxially grown sequentially; 3) Growth of multiple quantum well layers; 4) Epitaxial growth of P-type AlGaInP waveguide layer; 5) Grow a P-type stress-compensated electron blocking layer, each cycle including: AlP layer, Al x GaInP gradient layer, Al 0.4 In 0.6 P layer and Al y GaInP gradient layers were grown for 3 to 5 cycles. 6) Continue to grow the P-type AlInP confinement layer, P-type AlGaInP transition layer, P-type GaP extension layer, and P-type GaP ohmic contact layer; 7) Complete the epitaxial growth of the red-light Micro LED epitaxial wafer.

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