Red light Micro LED high luminous efficiency epitaxial structure

Abstract

The invention discloses a red light Micro LED high luminous efficiency epitaxial structure, which optimizes the current distribution, reduces the electron overflow and enhances the side wall performance by introducing a high energy band transverse expansion layer between a P-type AlInP limiting layer and a P-type GaP current expansion layer, effectively improves the quantum efficiency and the light extraction efficiency, and enhances the high temperature stability and long-term reliability of a device at the same time. The lateral extension layer is of an innovative superlattice structure and is formed by alternating a highly-doped GaP layer, a lowly-doped GaP layer and an Al < x > Ga < 1-x > P layer. The method is suitable for small-size and high-resolution display screens, vehicle-mounted high-temperature displays, low-power-consumption augmented reality glasses and other scenes, and has wide application prospects and industrial value.

Description

Technical Field

[0001] The present invention relates to the technical field of light emitting diodes (LEDs), and in particular to a design and manufacturing method of a red light Micro LED epitaxial structure. Background Art

[0002] With the development of display technology, Micro LED has gradually become the first choice for the new generation of display devices due to its high brightness, low power consumption and high reliability. However, as the size of Micro LED chips gradually decreases, the problem of sudden drop in luminous efficiency is becoming increasingly serious. Especially in the red light band, the problems of carrier leakage and non-radiative recombination caused by material properties are more prominent, which restricts the application of Micro LED in high-resolution display screens, high-temperature automotive displays and ultra-small low-power displays.

[0003] In the prior art, the common metal finger structure can partially alleviate the problem of uneven current distribution, but it still has problems such as severe shading effect, current crowding and poor high temperature stability. These defects significantly reduce the performance and application scope of Micro LED. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a red light Micro LED high-efficiency epitaxial structure, which optimizes the current distribution, reduces electron overflow and enhances the sidewall performance by introducing a high-energy band lateral extension layer between the P-type AlInP confinement layer and the P-type GaP current extension layer, thereby achieving improvements in quantum efficiency and light extraction efficiency.

[0005] The technical solution of the present invention is:

[0006] A red light Micro LED epitaxial structure includes 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 spreading layer, N-type AlGaInP ohmic contact layer, N-type AlInP limiting layer, multi-quantum well layer, P-type AlInP limiting layer, P-type GaP current spreading layer, P-type GaP ohmic contact layer,

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

[0009] Highly doped GaP layer with a doping concentration of 5×10 18 atoms / cm 3 Up to 8×10 18 atoms / cm 3 , thickness is 40 to 80 nm;

[0010] Low-doped GaP layer, doping concentration is 1×10 18 atoms / cm 3 Up to 6×10 18 atoms / cm 3 , thickness is 20 to 40 nm;

[0011] Al x Ga 1-x P layer, doping concentration is 5×10 18 atoms / cm 3 to 1.2×10 19 atoms / cm 3 , with a thickness of 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, a dopant of Si2H6, and a doping concentration of 1×10 18 ~2×10 18 atoms / cm 3 ;

[0014] Preferably, the composition of the N-type AlGaInP etching stop layer is (Al a Ga 1-a ) 0.5 In 0.5 P, where 0≤a≤0.6, thickness 100~200nm, dopant is Si2H6, doping concentration is 1×10 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 500~2500nm, dopant is Si2H6, carrier concentration 1×10 18 ~3×10 18carriers / cm 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, 0.3≤c≤1, thickness 0.5~1.5um, dopant is Si2H6, carrier concentration 3×10 18 ~6×10 18 carriers / cm 3 ;

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

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

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

[0020] Preferably, 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 carriers / cm 3 ;

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

[0022] Preferably, the doping concentration of the highly doped GaP layer is 6×10 18 atoms / cm 3 The doping concentration of the low-doped GaP layer is 3×10 18 atoms / cm 3 , thicknesses are 60nm and 30nm respectively.

[0023] The core principle of the present invention is to improve the performance of red light Micro LED in application scenarios such as small size, high efficiency and high stability through superlattice structure design, material selection and doping optimization. The following is a detailed analysis of the principle of the present invention:

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

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

[0026] (1) Horizontal and vertical current expansion

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

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

[0029] Al x Ga 1-x P layer: As an energy band adjustment layer, its energy band difference promotes the expansion of lateral current and enhances the lateral uniformity of current.

[0030] (2) Suppressing carrier overflow

[0031] The energy band difference of the superlattice structure forms a potential barrier, preventing electrons from overflowing into the P region, reducing non-radiative recombination and improving the recombination efficiency of carriers.

[0032] (3) Sidewall effect optimization

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

[0034] 2.Al x Ga 1-x P Material Selection and Function

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

[0036] (1) Band Regulation

[0037] By adjusting the aluminum content x, the band structure of the material can be precisely controlled, the carrier transport path can be optimized, and local current crowding can be avoided.

[0038] (2) Lattice matching

[0039] Al x Ga 1-x The high lattice matching between the P layer and the surrounding layers reduces the defect density caused by lattice mismatch and improves the overall electrical and optical properties of the material.

[0040] (3) High temperature stability

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

[0042] 3. Principles of doping gradient design

[0043] Doping gradient design is an important optimization point in superlattice structure. Its principles include:

[0044] (1) Current distribution optimization

[0045] Setting a doping gradient between the highly doped and lowly doped layers can form a smoother potential gradient, promote uniform distribution of current, and reduce local hot spots.

[0046] (2) Reduced interface scattering

[0047] The gradient design of doping concentration reduces the scattering of carriers at the heterojunction interface and improves the carrier transport efficiency.

[0048] (3) Improved device stability

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

[0050] 4. There is hope to eliminate the principle of traditional metal finger structure

[0051] By designing a superlattice structure to achieve current expansion, the traditional metal fingers can be eliminated in conjunction with the chip structure, and performance optimization can be achieved based on the following principles:

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

[0053] Simplified process: No need for complicated metal finger manufacturing process, reducing process steps and increasing light output area.

[0054] 5. Summary of working principle

[0055] The present invention achieves the following fundamental improvements through the combined effects of superlattice structure, material selection and doping gradient:

[0056] Quantum efficiency improvement: Improve luminescence efficiency by optimizing carrier distribution and recombination.

[0057] Reduction of non-radiative recombination: Optimize the distribution of current on the chip surface and sidewall areas to suppress the influence of surface states.

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

[0059] Process and structure optimization: Eliminate the metal finger structure to achieve higher light extraction efficiency and a simpler manufacturing process.

[0060] The present invention makes full use of the band regulation advantages and material properties of the superlattice structure, and provides an innovative solution for the development of red light Micro LED in small-size, high-performance application scenarios by optimizing the current transport path, improving the carrier recombination efficiency and enhancing the thermal stability of the device.

[0061] Through the above technical solution, the present invention achieves the following beneficial effects:

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

[0063] 1. Performance Improvement

[0064] (1) Improve quantum efficiency:

[0065] By optimizing the distribution of electrons and holes through the superlattice structure, the probability of carrier recombination is increased, and the quantum efficiency of the device is significantly improved.

[0066] (2) Enhanced light extraction efficiency:

[0067] It is possible to eliminate 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 spreading layer improves hole injection at the chip sidewalls and reduces non-radiative recombination caused by surface states.

[0070] (4) Optimize current distribution:

[0071] Through doping gradient design and band regulation of the superlattice structure, uniform distribution of current in the lateral and vertical directions of the chip is achieved, eliminating local hot spots.

[0072] 2. Enhanced reliability

[0073] (1) Reduce electron overflow:

[0074] The energy band difference formed by the superlattice structure prevents excessive overflow of electrons 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 properties. By adjusting the aluminum content and designing the component gradient, the stability of the device in high temperature environments is improved, making it particularly suitable for automotive and industrial scenarios.

[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 optimized design of the superlattice structure, it adapts to the trend of Micro LED miniaturization and ensures high efficiency even in small size.

[0082] (2) Strong versatility:

[0083] The present 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:

[0086] In large-size displays, high brightness and high resolution are achieved through optimized current distribution.

[0087] (2) In-vehicle head-up display:

[0088] The stability of red light Micro LED under high temperature conditions is improved to meet the stringent requirements of vehicle-mounted displays.

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

[0090] While maintaining extremely small size and low power consumption, it maintains sufficient brightness and contrast to meet the needs of the next generation of wearable display technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 Schematic diagram of the structure of each layer of the red light Micro LED high light efficiency epitaxial structure of the present invention.

[0092] Figure 2 Schematic diagram of the Mg barrier structure in the present invention.

[0093] Figure 3 It is a schematic diagram of the working principle of the high energy band lateral expansion layer in the present invention.

[0094] Figure 4 It is a curve diagram of the relationship between the external quantum efficiency (EQE) and current density (Current Density) of the red light Micro LED high light efficiency epitaxial structure (improved) of the present invention and the traditional red light LED (base). DETAILED DESCRIPTION

[0095] Example 1

[0096] The following layer structures are grown in sequence on the GaAs substrate:

[0097] N-type GaAs buffer layer: thickness 200nm, doping concentration 1.5×10 18 atoms / cm 3 , the dopant is Si2H6;

[0098] N-type AlGaInP etching stop layer: composition is (Al 0.5 Ga 0.5 ) 0.5 In 0.5 P, thickness 150nm, doping concentration 2×10 18 atoms / cm 3 ;

[0099] N-type AlGaInP current spreading layer: Composition: (Al 0.6 Ga 0.4 ) 0.5 In 0.5 P, thickness 1000nm, doping concentration 2.5×10 18 carriers / cm 3 ;

[0100] Multi-quantum well layer: quantum well thickness 4nm, quantum barrier thickness 8nm, 6 pairs in total;

[0101] P-type AlInP confinement layer: thickness 250nm, doping concentration 1×10 18 carriers / cm 3 , the dopant is Cp2Mg;

[0102] P-type GaP current spreading layer: thickness 500nm, doping concentration 3×10 18 carriers / cm 3 ;

[0103] P-type GaP ohmic contact layer: thickness 50nm, doping concentration 1×10 20 carriers / cm 3 .

[0104] Example 2

[0105] Based on Example 1:

[0106] The above-mentioned high energy band lateral extension layer is inserted between the P-type AlInP and P-type GaP current extension layers, and the structure is as follows:

[0107] Highly doped GaP layer: thickness 50nm, doping concentration 7×10 18 atoms / cm 3 , the dopant is Cp2Mg;

[0108] Low-doped GaP layer: thickness 25nm, doping concentration 2×10 18 atoms / cm 3 , the dopant is Cp2Mg;

[0109] Al 0.05 Ga 0.95 P layer: thickness 25nm, doping concentration 5×10 18 atoms / cm 3 , the dopant is Cp2Mg;

[0110] The total number of sublayer structures is 8, and the total thickness is 800 nm.

[0111] from Figure 4 It can be seen that 0.5A / cm 2 By optimizing the structure and adding a high-energy band lateral expansion layer structure, the EQE is increased by more than 55%. The smaller the current, the more significant the improvement in light efficiency.

Claims

1. A red light Micro LED epitaxial structure, comprising the following layer structures grown in sequence on a GaAs substrate: N-type GaAs buffer layer, N-type AlGaInP etching stop layer, N-type AlGaInP current spreading layer, N-type AlGaInP ohmic contact layer, N-type AlInP limiting layer, multi-quantum well layer, P-type AlInP limiting layer, P-type GaP current spreading layer, P-type GaP ohmic contact layer, A high energy band lateral expansion layer is arranged between the P-type AlInP limiting layer and the P-type GaP current expansion layer. The lateral expansion layer is a superlattice structure, including 3 to 15 groups of sublayer structures, wherein the sublayer structure is sequentially arranged from top to bottom by a high-doped GaP layer, a low-doped GaP layer and an Al x Ga 1-x P layer, including: Highly doped GaP layer with a doping concentration of 5×10 18 atoms / cm 3 Up to 8×10 18 atoms / cm 3 , thickness is 40 to 80 nm; Low-doped GaP layer, doping concentration is 1×10 18 atoms / cm 3 Up to 6×10 18 atoms / cm 3 , thickness is 20 to 40 nm; Al x Ga 1-x P layer, doping concentration is 5×10 18 atoms / cm 3 to 1.2×10 19 atoms / cm 3 , with a thickness of 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; The total thickness of the high energy band lateral extension layer is 300 to 1500 nm.

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

3. The red light Micro LED epitaxial structure according to claim 1, characterized in that: x10 18 atoms / cm 3 The composition of the N-type AlGaInP etching stop layer is (Al a Ga 1-a ) 0.5 In 0.5 P, where 0≤a≤0.6, thickness 100~200nm, dopant is Si2H6, doping concentration is 1~3×10 18 atoms / cm 3 .

4. The red light Micro LED epitaxial structure according to claim 1, characterized in that: 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 500~2500nm, dopant is Si2H6, carrier concentration 1×10 18 ~3×10 18 atoms / cm 3 .

5. The red light Micro LED epitaxial structure according to claim 1, characterized in that: The composition of the N-type AlGaInP ohmic contact layer is (Al c Ga 1-c ) 0.5 In 0.5 Among them, 0.3≤c≤1, thickness 0.5~1.5um, dopant is Si2H6, carrier concentration 3×10 18 ~6×10 18 atoms / cm 3 .

6. The red light Micro LED epitaxial structure according to claim 1, characterized in that: The N-type AlInP layer has a thickness of 200-400 nm, a dopant of Si2H6, and a carrier concentration of 1×10 18 ~2×10 18 atoms / cm 3 .

7. The red light Micro LED epitaxial structure according to claim 1, characterized in that: The quantum well thickness of the multi-quantum well layer is 3-5 nm, the quantum barrier thickness is 5-10 nm, and the number of pairs is 2-10 pairs.

8. The red light Micro LED epitaxial structure according to claim 1, characterized in that: The P-type AlInP layer has a thickness of 200-300 nm, a dopant of Cp2Mg, and a carrier concentration of 6×10 17 ~1.2×10 18 atoms / cm 3 .

9. The red light Micro LED epitaxial structure according to claim 1, characterized in that: 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 light Micro LED epitaxial structure according to claim 1, characterized in that: The thickness of the P-type GaP ohmic contact layer is 30-100 nm, the dopant is CBr4, and the carrier concentration is 5×10 19 ~2×10 20 atoms / cm 3 .

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

Images