Red light micro led high light efficiency epitaxial structure

Abstract

This invention discloses a high-efficiency epitaxial structure for red Micro LEDs. By introducing a high-energy-bandgap lateral extension layer between a P-type AlInP confinement layer and a P-type GaP current-spreading layer, the current distribution is optimized, electron overflow is reduced, and sidewall performance is enhanced, effectively improving quantum efficiency and light extraction efficiency, while also enhancing the device's high-temperature stability and long-term reliability. This lateral extension layer is an innovative superlattice structure, consisting of a highly doped GaP layer, a low-doped GaP layer, and an Al… x Ga 1‑x The invention is composed of alternating P-layers. It is applicable to small-size, high-resolution displays, high-temperature automotive displays, and low-power augmented reality glasses, and has broad application prospects and industrial value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of Light Emitting Diode (LED), in particular to a design and manufacturing method of a red Micro LED epitaxial structure. BACKGROUND

[0002] With the development of display technology, Micro LED gradually becomes the first choice of new generation display devices due to its high brightness, low power consumption and high reliability. However, with the gradual reduction of the size of Micro LED chip, the problem of sudden drop of light emitting efficiency is increasingly serious. Especially in the red light band, the problems of carrier leakage and non-radiative recombination caused by material characteristics are more prominent, which restricts the application of Micro LED in high-resolution display screens, high-temperature vehicle displays and ultra-small low-power displays.

[0003] In the prior art, although the common metal finger structure can partially alleviate the problem of uneven current distribution, it still has problems such as serious light shielding effect, current congestion and poor high-temperature stability. These defects significantly reduce the performance and application range of Micro LED. SUMMARY

[0004] In order to solve the above problems, the present application provides a red Micro LED high light efficiency epitaxial structure, which introduces a high energy band lateral expansion layer between the P-type AlInP confinement layer and the P-type GaP current expansion layer, optimizes the current distribution, reduces electron overflow and enhances the sidewall performance, and realizes the improvement of quantum efficiency and light extraction efficiency.

[0005] The technical scheme of the present application is as follows:

[0006] A red Micro LED epitaxial structure, comprising the following layer structures grown in sequence on a GaAs substrate:

[0007] N-type GaAs buffer layer, N-type AlGaInP etching stop layer, N-type AlGaInP current expansion layer, N-type AlGaInP ohmic contact layer, N-type AlInP confinement layer, multi-quantum well layer, P-type AlInP confinement layer, P-type GaP current expansion layer, P-type GaP ohmic contact layer,

[0008] A high energy band lateral expansion layer is arranged between the P-type AlInP confinement layer and the P-type GaP current expansion layer, the lateral expansion layer is a superlattice structure, comprising 3 to 15 groups of sublayer structures, the sublayer structure is composed of a high-doped GaP layer, a low-doped GaP layer and an Al x Ga 1-x P layer arranged in sequence from top to bottom, wherein:

[0009] A highly doped GaP layer with a doping concentration of 5 × 10⁻⁶. 18 atoms / cm 3 Up to 8 × 10 18 atoms / cm 3 The thickness is 40 to 80 nm;

[0010] A lightly doped GaP layer with a doping concentration of 1 × 10⁻⁶. 18 atoms / cm 3 Up to 6 × 10 18 atoms / cm 3 The thickness is 20 to 40 nm;

[0011] Al x Ga 1-x The P-layer has a doping concentration of 5 × 10⁻⁶. 18 atoms / cm 3 Up to 1.2 × 10 19 atoms / cm 3 The thickness is 20 to 40 nm, where 0.05 ≤ x ≤ 0.2, and the aluminum element x content gradually increases from 0.05 at the bottom to 0.2 at the top;

[0012] The total thickness of the high-energy band lateral extension layer is 300 to 1500 nm.

[0013] Preferably, the N-type GaAs buffer layer has a thickness of 150~300 nm, the dopant is Si2H6, and the doping concentration is 1×10⁻⁶. 18 ~2×10 18 atoms / cm 3 ;

[0014] Preferably, the composition of the N-type AlGaInP corrosion stop layer is (Al a Ga 1-a ) 0.5 In 0.5 P, where 0 ≤ a ≤ 0.6, thickness 100~200 nm, dopant is Si2H6, doping concentration is 1 × 10⁻⁶ 18 ~3×10 18 atoms / cm 3 ;

[0015] Preferably, the composition of the N-type AlGaInP current spreading layer is (Al b Ga 1-b ) 0.5 In 0.5 P, where 0.3 ≤ b ≤ 1, thickness 500~2500 nm, dopant is Si2H6, carrier concentration 1 × 10⁻⁶ 18 ~3×1018 1.5× 10 3 ;

[0016] Preferably, the composition of the N-type AlGaInP ohmic contact layer is (Al c Ga 1-c ) 0.5 In 0.5 P, wherein 0.3≤c≤1, the thickness is 0.5~1.5um, the dopant is Si2H6, and the carrier concentration is 3× 10 18 ~6× 10 18 carriers / cm 3 ;

[0017] Preferably, the N-type AlInP confinement layer has a thickness of 200~400nm, the dopant is Si2H6, and the carrier concentration is 1×10 18 ~2× 10 18 carriers / cm 3 ;

[0018] Preferably, the quantum well of the multi-quantum well layer has a thickness of 3~5nm, the quantum barrier has a thickness of 5~10nm, and the number of pairs is 2~10;

[0019] Preferably, the P-type AlInP confinement layer has a thickness of 200~300nm, the dopant is Cp2Mg, and the carrier concentration is 6×10 17 ~1.2× 10 18 carriers / cm 3 ;

[0020] Preferably, the P-type GaP current spreading layer has a thickness of 300~800nm, the dopant is Cp2Mg, and the carrier concentration is 1×10 18 ~5× 10 18 carriers / cm 3 ;

[0021] Preferably, the P-type GaP ohmic contact layer has a thickness of 30~100nm, the dopant is CBr4, and the carrier concentration is 5×10 19 ~2× 10 20 carriers / cm 3 .

[0022] Preferably, the high-doped GaP layer has a dopant concentration of 6× 10 18 atoms / cm 3 , the low-doped GaP layer has a dopant concentration of 3× 10 18 atoms / cm 3 , and the thicknesses are 60nm and 30nm, respectively.

[0023] The core principle of the invention lies in improving the performance of red Micro LED in small size, high efficiency, high stability, and other application scenarios through superlattice structure design, material selection, and doping optimization. The following is a detailed analysis of the principles of the invention:

[0024] 1. GaP / Al x Ga 1-x The role of GaP(0.05≤x≤0.2) superlattice structure

[0025] The superlattice structure is a key innovation point of the invention, which uses the alternating stacking of multiple sub-layer materials to achieve the following effects:

[0026] (1) Lateral and vertical current expansion

[0027] Highly doped GaP layer: provides excellent electrical conductivity, promotes vertical current transmission, and improves current distribution uniformity.

[0028] Low-doped GaP layer: by reducing the carrier concentration, reducing the recombination probability of carriers, further optimizing the expansion of current.

[0029] Al x Ga 1-x P layer: as a band adjustment layer, its band difference promotes the expansion of lateral current and enhances the uniformity of current in the lateral direction.

[0030] (2) Suppression of carrier overflow

[0031] The band difference of the superlattice structure forms a potential barrier, preventing electron overflow to the P region, reducing non-radiative recombination, and improving the recombination efficiency of carriers.

[0032] (3) Side wall effect optimization

[0033] By enhancing the lateral current expansion, more holes can be injected into the chip side wall area, reducing the non-radiative recombination problem caused by surface states, and improving the side wall light emission efficiency.

[0034] 2. Al x Ga 1-x P material selection and function

[0035] Al x Ga 1-x P(0.05≤x≤0.2) material plays the following role in the invention:

[0036] (1) Band adjustment

[0037] By adjusting the aluminum content x, the band structure of the material can be accurately controlled, optimizing the carrier transport path, and avoiding local current congestion phenomenon.

[0038] (2) Lattice matching

[0039] Al x Ga 1-x The lattice matching between the P layer and the surrounding layers is high, reducing the defect density caused by lattice mismatch and improving the overall electrical and optical performance of the material.

[0040] (3) High-temperature stability

[0041] Under high-temperature conditions, Al x Ga 1-x P materials can effectively reduce carrier leakage and ensure the long-term reliability of red Micro LED in high-temperature environments such as vehicles.

[0042] 3. Principle of doping gradient design

[0043] Doping gradient design is an important optimization point in superlattice structure, its principle includes:

[0044] (1) Current distribution optimization

[0045] Setting a doping gradient between high-doped and low-doped layers can form a smoother potential gradient, promoting uniform distribution of current and reducing local hot spots.

[0046] (2) Reduction of interface scattering

[0047] Gradual design of doping concentration reduces the scattering of carriers at the heterojunction interface, improving the transport efficiency of carriers.

[0048] (3) Enhancement of device stability

[0049] Gradual doping design helps to reduce current density concentration effect and enhance the stability of the device under high power and high current density.

[0050] 4. Principle of hoping to cancel traditional metal finger structure

[0051] Through the design of superlattice structure to realize current expansion, the traditional metal finger can be cancelled with the chip structure, and the performance optimization is realized based on the following principles:

[0052] Reduce shading effect: metal finger blocks part of the light-emitting area, while the superlattice structure alternative directly improves the light extraction efficiency.

[0053] Simplify the process: without complex metal finger manufacturing process, reduce the process steps, and increase the light-emitting area.

[0054] 5. Comprehensive working principle

[0055] The present application realizes the following principle improvements through the comprehensive effect of superlattice structure, material selection and doping gradient:

[0056] Quantum efficiency improvement: improve light-emitting efficiency by optimizing carrier distribution and recombination.

[0057] Reduced non-radiative recombination: optimize the distribution of current on the chip surface and sidewall area, and suppress the influence of surface state.

[0058] Enhanced high-temperature reliability: through the introduction of Al x Ga 1-x P material and lattice matching optimization, ensure the performance stability of the device at high temperature.

[0059] Process and structure optimization: cancel the metal finger structure, realize higher light extraction efficiency and more simplified manufacturing process.

[0060] The present application makes full use of the band gap regulation advantage of superlattice structure and material characteristics, optimizes the current transport path, improves the carrier recombination efficiency and enhances the thermal stability of the device, and provides an innovative solution for the development of red Micro LED in small size and high performance application scenarios.

[0061] Through the above technical solutions, the present application has the following beneficial effects:

[0062] The beneficial effects of the present application can be summarized as follows from the aspects of performance improvement, reliability enhancement and process optimization:

[0063] 1. Performance improvement

[0064] (1) Improve quantum efficiency:

[0065] Optimize the distribution of electrons and holes through superlattice structure, improve the probability of carrier recombination, and significantly improve the quantum efficiency of the device.

[0066] (2) Enhance light extraction efficiency:

[0067] It is possible to cancel the metal finger design, increase the effective light-emitting area of the chip, reduce the shading effect, and thus improve the overall light extraction efficiency.

[0068] (3) Reduce non-radiative recombination:

[0069] The design of the lateral current expansion layer improves the hole injection of the chip sidewall, and reduces the non-radiative recombination caused by the surface state.

[0070] (4) Optimize current distribution:

[0071] Through the design of doping gradient and the bandgap regulation of superlattice structure, uniform current distribution in both horizontal and vertical directions of the chip is achieved, and local hot spots are eliminated.

[0072] 2. Reliability enhancement

[0073] (1) Reduce electron overflow:

[0074] The bandgap difference formed by the superlattice structure prevents excessive electron overflow from the N region to the P region, reducing carrier leakage.

[0075] (2) Improve high-temperature stability:

[0076] Al x Ga 1-x P material has good lattice matching characteristics, and through the adjustment of aluminum content and component gradient design, the stability of the device in high temperature environment is improved, especially suitable for vehicle and industrial scenes.

[0077] (3) Reduce interface defects:

[0078] Material selection and interlayer doping optimization effectively reduce the interface defect density caused by lattice mismatch, thereby improving the long-term reliability of the device.

[0079] 3. Process optimization

[0080] (1) Adapt to small size chip design:

[0081] Through the optimization design of superlattice structure, it adapts to the trend of small size of Micro LED, and ensures that high efficiency can be maintained under small size.

[0082] (2) Strong universality:

[0083] The invention is applicable to Micro LED chips of different sizes, from large size display screens to small size augmented reality (AR) glasses, and can maintain high efficiency and reliability.

[0084] 4. Application scenario expansion

[0085] (1) High-resolution display screen:

[0086] In large size display screen, high brightness and high resolution are realized through current distribution optimization.

[0087] (2) Vehicle head-up display:

[0088] The stability of red Micro LED under high temperature conditions is improved, meeting the harsh requirements of vehicle display.

[0089] (3) Low-power augmented reality (AR) glasses:

[0090] Under the conditions of extremely small size and low power consumption, sufficient brightness and contrast are maintained, adapting to the needs of the next generation of wearable display technology. BRIEF DESCRIPTION OF DRAWINGS

[0091] Figure 1 A schematic diagram of the layers of the red Micro LED high-efficiency epitaxial structure of the present application.

[0092] Figure 2 A schematic diagram of the Mg blocking structure in the present application.

[0093] Figure 3 A schematic diagram of the working principle of the high-energy band lateral expansion layer in the present application.

[0094] Figure 4 A curve graph showing the relationship between the external quantum efficiency (EQE) and current density of the red Micro LED high-efficiency epitaxial structure (improved) of the present application and the traditional red LED (base).

[0095] Markings in the figure:

[0096] 100 is a GaAs substrate, 200 is a GaAs buffer layer, 300 is an N-type AlGaInP etch stop layer, 400 is an N-type AlGaInP current expansion layer, 500 is an N-type AlGaInP ohmic contact layer, 600 is an N-type AlInP confinement layer, 700 is a multi-quantum well layer, 800 is a P-type AlInP confinement layer, 900 is a high-energy band lateral expansion layer, 1000 is a P-type GaP current expansion layer, 1100 is a P-type GaP ohmic contact layer, 910 is a high-doped GaP layer, 920 is a low-doped GaP layer, 930 is an Al x Ga 1-x P sublayer. DETAILED DESCRIPTION

[0097] Example 1

[0098] The following layer structure is grown on a GaAs substrate in sequence:

[0099] N-type GaAs buffer layer: thickness 200 nm, doping concentration 1.5×10 18 atoms / cm 3 , dopant Si2H6;

[0100] N-type AlGaInP etch stop layer: composition (Al 0.5 Ga 0.5 )0.5 In 0.5 P, thickness 150 nm, doping concentration 2 x 10 18 atoms / cm 3 ;

[0101] N-type AlGaInP current spreading layer: composition (Al 0.6 Ga 0.4 ) 0.5 In 0.5 P, thickness 1000 nm, doping concentration 2.5 x 10 18 carriers / cm 3 ;

[0102] Multiple quantum well layer: quantum well thickness 4 nm, quantum barrier thickness 8 nm, total 6 pairs;

[0103] P-type AlInP confinement layer: thickness 250 nm, doping concentration 1 x 10 18 carriers / cm 3 , dopant Cp2Mg;

[0104] P-type GaP current spreading layer: thickness 500 nm, doping concentration 3 x 10 18 carriers / cm 3 ;

[0105] P-type GaP ohmic contact layer: thickness 50 nm, doping concentration 1 x 10 20 carriers / cm 3 .

[0106] Example 2

[0107] Based on Example 1:

[0108] Insert the above high-energy band lateral spreading layer between the P-type AlInP and P-type GaP current spreading layers, the structure is as follows:

[0109] Highly doped GaP layer: thickness 50 nm, doping concentration 7 x 10 18 atoms / cm 3 , dopant Cp2Mg;

[0110] Lowly doped GaP layer: thickness 25 nm, doping concentration 2 x 10 18 atoms / cm 3 , dopant Cp2Mg;

[0111] Al 0.05 Ga 0.95P layer: thickness 25 nm, doping concentration 5x10 18 atoms / cm 3 , and the dopant is Cp2Mg;

[0112] The total number of sub-layer structures is 8, and the total thickness is 800 nm.

[0113] From Figure 4 It can be seen that the optimized structure increases the high-energy band lateral expansion layer structure EQE by more than 55% at 0.5A / cm 2 The smaller the current, the more significant the light efficiency improvement.

Claims

1. A red light Micro LED epitaxial structure, comprising the following layer structure grown in sequence on a GaAs substrate: an N-type GaAs buffer layer, an N-type AlGaInP etching stop layer, an N-type AlGaInP current spreading layer, an N-type AlGaInP ohmic contact layer, an N-type AlInP confinement layer, a multi-quantum well layer, a P-type AlInP confinement layer, a P-type GaP current spreading layer, and a P-type GaP ohmic contact layer, A high band transverse expansion layer is arranged between a P-type AlInP confinement layer and a P-type GaP current expansion layer, the transverse expansion layer is a superlattice structure, including 3 to 15 groups of sublayer structures, the sublayer structures are composed of high-doped GaP layers, low-doped GaP layers and Al x Ga 1-x P layers arranged from top to bottom, wherein: a highly doped GaP layer with a doping concentration of 5 x 1019 18 atoms / cm 3 to 8 x 1019 18 atoms / cm 3 and a thickness of 40 to 80 nm; a low doped GaP layer with a doping concentration of 1 x 10 18 atoms / cm 3 to 6 x 10 18 atoms / cm 3 and a thickness of 20 to 40 nm; Al x Ga 1-x P layer with a doping concentration of 5 x 10 18 atoms / cm 3 to 1.2 x 10 19 atoms / cm 3 , and a thickness of 20 to 40 nm, wherein 0.05 < x < 0.2, and the aluminum element x content gradually increases from 0.05 at the bottom to 0.2 at the top; a total thickness of the high-energy band lateral expansion layer is 300-1500 nm.

2. The red Micro LED epitaxial structure of claim 1, wherein, The N-type GaAs buffer layer has a thickness of 150-300 nm, a dopant of Si2H6, and a doping concentration of 1×10 18 ~2× 10 18 atoms / cm 3 .

3. The red Micro LED epitaxial structure of claim 1, wherein, The composition of the N-type AlGaInP etching stop layer is (Al a Ga 1-a ) 0.5 In 0.5 P, wherein 0≤a≤0.6, the thickness is 100~200nm, the dopant is Si2H6, and the doping concentration is 1× 10 18 ~3× 10 18 atoms / cm 3 .

4. The red Micro LED epitaxial structure of claim 1, wherein, The composition of the N-type AlGaInP current spreading layer is (Al b Ga 1-b ) 0.5 In 0.5 P, wherein 0.3≤b≤1, the thickness is 500~2500nm, the dopant is Si2H6, the carrier concentration is 1× 10 18 ~3× 10 18 atoms / cm 3 . 5.The red Micro LED epitaxial structure of claim 1, wherein, The composition of the N-type AlGaInP ohmic contact layer is (Al c Ga 1-c ) 0.5 In 0.5 P wherein, 0.3≤c≤1, thickness 0.5~1.5um, dopant is Si2H6, carrier concentration 3x 10 18 ~6x 10 18 atoms / cm 3 . 6.The red Micro LED epitaxial structure of claim 1, wherein, The N-type AlInP confinement layer has a thickness of 200-400 nm, a dopant of Si2H6, and a carrier concentration of 1 x 1018-2 x 1018atoms / cm3. 18 ~2 x 1018atoms / cm3. 18 ~2 x 1018atoms / cm3. 3 ~2 x 1018atoms / cm3.

7. The red Micro LED epitaxial structure of claim 1, wherein, The multi-quantum well layer has a quantum well thickness of 3-5 nm, a quantum barrier thickness of 5-10 nm, and 2-10 pairs of logarithm. 8.The red Micro LED epitaxial structure of claim 1, wherein, The p-type AlInP confinement layer has a thickness of 200-300 nm, is doped with Cp₂Mg, and has a carrier concentration of 6 × 10⁻⁶. 17 ~1.2× 10 18 atoms / cm 3 . 9.The red Micro LED epitaxial structure of claim 1, wherein, The P-type GaP current spreading layer has a thickness of 300-800 nm, a dopant of Cp2Mg, and a carrier concentration of 1×10 18 ~5×10 18 atoms / cm 3 .

10. The red Micro LED epitaxial structure of claim 1, wherein, The p-type GaP ohmic contact layer has a thickness of 30-100 nm, is doped with CBr4, and has a carrier concentration of 5 × 10⁻⁶. 19 ~2×10 20 atoms / cm 3 .

11. The red Micro LED epitaxial structure of claim 1, wherein, The doping concentration of the highly doped GaP layer is 6 × 10⁻⁶. 18 atoms / cm 3 The doping concentration of the low-doped GaP layer is 3 × 10⁻⁶. 18 atoms / cm 3 The thicknesses are 60nm and 30nm, respectively.

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