High hole injection efficiency GaN-based light emitting diode epitaxial structure and preparation method thereof

Abstract

The invention relates to a GaN-based light emitting diode epitaxial structure with high hole injection efficiency and a preparation method thereof. The epitaxial structure sequentially comprises a first semiconductor layer, an active layer, a low-temperature P-type layer and a second semiconductor layer which are arranged on the substrate, and the low-temperature P-type layer is arranged between the active layer and the P-type GaN and sequentially comprises a hole expansion layer, a hole storage layer and a hole layer. The hole expansion layer is composed of a periodic structure formed by AlN layers and low-doped Mg-GaN layers alternately. The hole storage layer is of a periodic structure composed of a GaN layer, an InGaN layer and a low-doped Mg-AlGaN layer. The hole layer is of a periodic structure of a P-type AlInGaN layer and an MgN layer and is formed in an Mg source pulse deposition mode. According to the structure, the multi-cycle heterogeneous layer design is combined with doping regulation and deposition process optimization, the Mg acceptor activation rate and the hole injection efficiency are improved, the defect density and the electron leakage are reduced, and the structure is suitable for being applied to a small-current Micro LED.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lighting, and in particular to a GaN-based light-emitting diode epitaxial structure with high hole injection efficiency and a preparation method thereof. Background Art

[0002] A light-emitting diode (LED) is a device that emits light by combining electrons and holes in a semiconductor heterostructure. Due to its advantages such as small size, low power consumption, long life, and fast response time, it has been widely used in various fields such as lighting, display, backlighting, and communications. In recent years, with the growing demand for miniaturization and high-resolution displays, MicroLED technology, as a core solution for the next generation of display technology, has attracted widespread attention from industry and academia. MicroLED offers significant advantages such as high brightness, high pixel density, high contrast, wide color gamut, and low power consumption, making it particularly suitable for applications with extremely high performance requirements, such as wearable devices, in-vehicle displays, and virtual reality.

[0003] In the epitaxial structure of GaN-based blue light LEDs, multiple quantum wells are often used as the active layer, which has a PN junction structure composed of n-type and p-type GaN layers on the top and bottom respectively. However, due to factors such as the large effective mass and low mobility of the holes themselves, as well as the low activation rate of Mg doping in p-type GaN, the effective injection of holes has always been an important bottleneck limiting the performance of LED devices. On the one hand, due to the poor mobility of holes, they are mainly distributed in a few quantum wells close to the p-type layer side, resulting in uneven recombination efficiency of electrons and holes in the entire active layer, limiting the photon output efficiency. On the other hand, the activation energy of the acceptor impurity Mg in GaN is relatively high (about 160-200meV), and it is difficult to achieve a high concentration of hole effective carriers (usually only 10 17 -10 18 atoms / cm 3 order of magnitude), thereby affecting the conductivity and injection capability of the p-type layer.

[0004] Furthermore, due to their small effective mass and high mobility, electrons easily cross the quantum barrier in the active region and leak into the p-type region, triggering non-radiative recombination and further reducing the external quantum efficiency. This "electron overflow" phenomenon is particularly severe in small-sized MicroLED devices, where the operating current density is lower and the importance of hole injection efficiency becomes even more prominent. To alleviate these issues, existing technologies have proposed several improvements, such as introducing an electron blocking layer (EBL), using AlGaN or InGaN intercalation to manipulate the band structure, and utilizing superlattice structures to enhance Mg activation. However, these improvements have not fundamentally resolved the issues of low hole injection efficiency and poor Mg doping activity. This is especially true in low-temperature, low-current operating environments, where the coordinated optimization of p-type doping activation and hole transport remains challenging.

[0005] Therefore, how to construct an efficient epitaxial structure with good crystal quality, high Mg activation rate, strong hole injection ability and suitable for MicroLED applications is one of the key technical issues that urgently need to be broken through in the current field of LED device design and preparation. Summary of the Invention

[0006] The purpose of the present invention is to provide an improved high-hole injection efficiency GaN-based light-emitting diode epitaxial structure and its preparation method. By introducing a multi-period low-temperature P-type composite structure layer before the second semiconductor layer (p-type GaN), the following goals are achieved: effectively improving the hole injection efficiency and spatial distribution uniformity in the active region; enhancing the degree of Mg doping activation and increasing the hole concentration; suppressing electron overflow and reducing the probability of non-radiative recombination; and improving the device's electro-optical conversion efficiency, making it particularly suitable for high-performance MicroLED applications.

[0007] The technical solutions of the present invention are as follows: A high hole injection efficiency GaN-based light-emitting diode epitaxial structure comprises the following structural layers sequentially arranged on a substrate: a first semiconductor layer, an active layer, a low-temperature P-type layer, and a second semiconductor layer; The first semiconductor layer comprises a buffer layer, an undoped GaN layer and an n-type GaN layer; The active layer comprises at least one InGaN / GaN multiple quantum well structure; The low-temperature P-type layer is provided between the active layer and the second semiconductor layer, and specifically comprises: a) Hole expansion layer: a periodic structure consisting of an AlN layer and a low-Mg-doped GaN layer alternating with each other. The thickness of the AlN layer is 0.5-5 nm, the thickness of the low-Mg-doped GaN layer is 1-10 nm, and the Mg concentration is 1×10 18 -1×10 19 atoms / cm 3 , the number of cycles is 1-20; b) Hole storage layer: a periodic structure consisting of GaN layer, InGaN layer and low Mg-doped AlGaN layer, with GaN thickness of 1-20nm, InGaN thickness of 1-5nm, low Mg-doped AlGaN thickness of 1-20nm, In composition of 0.01-0.2, Al composition of 0.01-0.2, and Mg concentration of 1×10 19 -1×10 20 atoms / cm 3 , the number of cycles is 1-20; c) Hole layer: a periodic structure consisting of alternating P-type AlInGaN layers and MgN layers. The thickness of the AlInGaN layer is 1-20 nm, the thickness of the MgN layer is 1-10 nm, and the Mg doping concentration is 1×10 20 -1×10 21 atoms / cm 3 , the number of periods is 1-20, the In component of the AlInGaN layer is 0.01-0.2, and the Al component is 0.01-0.2; The second semiconductor layer includes an electron blocking layer and a P-type GaN layer.

[0008] The method for preparing the above-mentioned light-emitting diode epitaxial structure comprises the following steps: 1) Providing a patterned substrate; 2) The following structural layers are deposited on it in sequence: The buffer layer, the undoped GaN layer and the n-type GaN layer form a first semiconductor layer; InGaN / GaN multiple quantum well structure, forming the active layer; The low-temperature P-type layer is deposited in the following periodic structure: a) Hole expansion layer: AlN layers and low-Mg-doped GaN layers are alternately deposited at 800-900°C, 50-500 torr pressure, and N2 / NH3 atmosphere; b) Hole storage layer: GaN layer, InGaN layer, and low-Mg-doped AlGaN layer are alternately deposited at 800-900°C, pressure 50-500 torr, and N2 / NH3 atmosphere; c) Void layer: P-type AlInGaN layer and MgN layer are alternately deposited by pulsed deposition of Mg source at 700-800°C, pressure 50-500 torr, and N2 / NH3 / H2 atmosphere, specifically including: Introducing Al source / In source / Ga source and nitrogen source to deposit AlInGaN layer; Turn off the metal source, introduce only the nitrogen source and turn on the Mg source to form the MgN layer; Repeat the above deposition steps to form a periodic structure; 3) Depositing an electron blocking layer and a P-type GaN contact layer to form a second semiconductor layer.

[0009] To further enhance hole injection efficiency, the hole expansion layer utilizes a periodically arranged AlN layer and a low-Mg-doped GaN layer for synergistic effect. The AlN layer's high barrier effectively inhibits electrons from escaping from the active layer to the P-type region, reducing non-radiative recombination. Furthermore, the low-Mg-doped GaN layer enhances the uniform vertical expansion of holes by regulating the Mg doping concentration. This periodic structure facilitates the formation of a continuous "channel"-like path, enhancing the spatial transport capability of holes. Furthermore, appropriate Mg doping can achieve a lower work function, helping to reduce the turn-on voltage of the Micro LED.

[0010] The hole storage layer utilizes a stepped periodic structure of GaN / InGaN / low-Mg-doped AlGaN. This structure, through differences in bandgap width, creates a "barrier-well" distribution, confining holes to the InGaN layer for effective accumulation. Simultaneously, the AlGaN layer, doped with a small amount of Mg, provides enhanced driving force for hole injection, improving overall injection efficiency and further reducing operating voltage. By regulating the energy band arrangement, this structure achieves the synergistic optimization of controlling hole injection direction and increasing local concentration.

[0011] The vacancy layer is a periodic structure of P-type AlInGaN and MgN, wherein the MgN layer is deposited using a Mg source pulse deposition method, in which the Mg source is statically introduced and ammonia is passed through to form a thin layer of MgN after the metal source is turned off. This method can significantly reduce the risk of defect formation caused by Mg agglomeration under high temperature conditions. At the same time, since Mg is introduced during the interruption stage of the GaN layer, even if a GaN-MgN-GaN stacking structure is formed locally, its dislocation is not easy to propagate along the epitaxial direction. When AlInGaN continues to grow, the stacking dislocation no longer expands due to the lack of Mg source interference. This structural design not only suppresses defect expansion, but also improves the activation efficiency of Mg acceptors, and cooperates with the low activation energy auxiliary effect of In atoms to effectively improve the hole concentration and crystal quality of the P-type layer.

[0012] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Significantly improved hole injection efficiency: Through the composite periodic layer design, a continuous transition structure of expansion, storage, and high doping is formed in the hole injection path, significantly improving the injection depth and distribution range of holes in the active layer, overcoming the problem of hole localization; 2. Improved Mg doping activation rate: By introducing Mg source pulse deposition technology, the introduction of Mg atoms is separated from GaN growth, effectively reducing the hydrogen passivation effect, improving the Mg acceptor activation rate, and thus increasing the hole concentration; 3. Reduce defect density and electron leakage: The band regulation effect of each periodic layer in the structure and the blocking effect of periodic interfaces on defect propagation significantly reduce electron overflow and non-radiative recombination, improving the overall crystal quality and reliability of the device; 4. Suitable for MicroLED low current density working environment: This structure is particularly suitable for MicroLED epitaxial structure design under small size and low driving current conditions. It can control energy consumption while ensuring high brightness and has good industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic cross-sectional structure diagram of a high-efficiency light-emitting diode epitaxial structure for improving hole injection efficiency according to the present invention.

[0014] The structural layers represented by the numbers in the figure are described as follows: 100: patterned substrate; 200: first semiconductor layer; 201: buffer layer; 202: undoped GaN layer; 203: n-type GaN layer; 300: active layer; 301: quantum well layer; 302: Quantum barrier layer; 400: low temperature P-type layer; 410: hole expansion layer; 411: AlN layer; 412: low Mg-doped GaN layer; 420: hole storage layer; 421: GaN layer; 422: InGaN layer; 423: low Mg-doped AlGaN layer; 430: cavity layer; 431: P-type AlInGaN layer; 432: MgN layer; 500: second semiconductor layer; 501: electron blocking layer; 502: P-type GaN layer. DETAILED DESCRIPTION

[0015] The light emitting diode epitaxial structure and its preparation method provided by the present invention are further described below with reference to the examples. It should be understood that this embodiment is merely an illustrative description and is not intended to limit the scope of protection of the present invention. Example

[0016] like Figure 1As shown, the epitaxial structure of the high hole injection efficiency GaN-based light-emitting diode described in this embodiment includes: The following epitaxial layers are grown in sequence on the sapphire patterned substrate 100: 1. First semiconductor layer 200: Buffer layer 201: thickness of about 30 nm; Undoped GaN layer 202: about 1.5 μm; n-type GaN layer 203: about 2 μm, Si doping concentration of 1×10 19 atoms / cm 3 .

[0017] 2. Active layer 300: Quantum well layer 301: InGaN thickness 2.5nm, In composition approximately 0.16; The growth temperature is 720-800℃ and MOCVD is completed in an ammonia / nitrogen atmosphere.

[0018] Quantum barrier layer 302: GaN with a thickness of about 8 nm; The number of multiple cycles is 3-5; The growth temperature is 850-920℃ and MOCVD is completed in an ammonia / nitrogen / hydrogen atmosphere.

[0019] 3. Low-temperature P-type layer 400: Hole expansion layer 410: AlN layer 411: thickness 1.8 nm; Low Mg-doped GaN layer 412: thickness 6.1 nm, Mg concentration 7×10 18 atoms / cm 3 ; The cycle number was 11, the V / III ratio was about 2000, the temperature was 850°C, the pressure was 150 torr, and the nitrogen source atmosphere was N2 / NH3.

[0020] Hole storage layer 420: GaN layer 421: 12nm; InGaN layer 422: 2.5 nm, In composition 0.1; Low Mg-doped AlGaN layer 423: 8nm, Al composition 0.08, Mg concentration 2.5×10 19 atoms / cm 3 ; The number of cycles was 8, the growth temperature was 850°C, the pressure was 150 torr, and the nitrogen source atmosphere was N2 / NH3.

[0021] Cavity layer 430: P-type AlInGaN layer 431: thickness 7.2 nm, In composition 0.07, Al composition 0.08, Mg concentration 2.8×10 20 atoms / cm 3 ; MgN layer 432: thickness 3.5 nm; Cycle number 10, growth temperature 750℃, pressure 150 torr, growth atmosphere N2 / NH3 / H2; Pulse deposition process: In each cycle, the AlInGaN layer is first deposited, and then the Mg source is statically introduced.

[0022] 4. Second semiconductor layer 500: Electron blocking layer 501: Al 0.2 Ga 0.8 N, thickness 20 nm, growth temperature 970 °C; P-type GaN contact layer 502: thickness of about 120 nm, Mg concentration of 5×10 19 atoms / cm 3 , used for ohmic contact.

[0023] The structure shown in the figure above is a preferred embodiment of the epitaxial wafer of the present invention, and structures such as electrode contacts and electrode patterning layers are not shown. Its process can be integrated with conventional LED manufacturing methods.

[0024] This structure achieves comprehensive performance optimization such as increased hole concentration, suppressed electron leakage, reduced defect density and improved quantum efficiency by designing multiple hole regulation functional layers, combined with temperature zone deposition and pulsed Mg source activation technology. It is particularly suitable for low current density MicroLED chip structures.

[0025] Samples 1-7 prepared by the present invention in Table 1 and the comparison samples currently produced in mass production were prepared using the same chip process conditions to form 3 mil*5 mil chips. The parameters of the comparison samples are as follows: low-temperature P-type GaN layer thickness 20 nm, Mg doping concentration 2.1E+20 atoms / cm 3 , tested at a current of 2 mA, the results are shown in Table 2, and the photoelectric efficiency is improved by 3.8%~7.3%.

[0026] Table 1 parameter Thickness of hole expansion layer AlN layer / low Mg-doped GaN layer (nm) <![CDATA[Low Mg-doped GaN layer, Mg doping concentration (atoms / cm 3 )]]> Hole expansion layer overlap period Thickness of hole storage layer GaN layer / InGaN layer / low Mg-doped AlGaN layer (nm) <![CDATA[Mg doping concentration of low-doped Mg-AlGaN layer (atoms / cm 3 )]]> Hole storage layer overlap period Thickness of P-type AlInGaN layer / MgN layer in the hole layer (nm) <![CDATA[Mg doping concentration of P-type AlInGaN layer (atoms / cm 3 )]]> Hole layer overlap period Sample 1 1.8 / 6.1 7E+18 11 12 / 2.5 / 8 2.5E+19 8 7.2 / 3.5 2.8E+20 10 Sample 2 2.3 / 6.6 6.5E+18 13 12 / 2.5 / 8 2.5E+19 8 7.2 / 3.5 2.8E+20 10 Sample 3 1.5 / 5.6 7.5E+18 9 12 / 2.5 / 8 2.5E+19 8 7.2 / 3.5 2.8E+20 10 Sample 4 1.8 / 6.1 7E+18 11 15 / 2.8 / 12 3.5E+19 6 7.2 / 3.5 2.8E+20 10 Sample 5 1.8 / 6.1 7E+18 11 10 / 2.3 / 7 1.5E+19 10 7.2 / 3.5 2.8E+20 10 Sample 6 1.8 / 6.1 7E+18 11 12 / 2.5 / 8 2.5E+19 8 6.7 / 3.2 2.5E+20 8 Sample 7 1.8 / 6.1 7E+18 11 12 / 2.5 / 8 2.5E+19 8 7.7 / 3.8 3E+20 12 Table 2 parameter Improved lighting efficiency Brightness (mW) Sample 1 7.30% 2.083 Sample 2 5.90% 2.056 Sample 3 3.80% 2.015 Sample 4 4.30% 2.024 Sample 5 6.50% 2.067 Sample 6 5.30% 2.044 Sample 7 6.10% 2.059 Comparison sample - 1.941

Claims

1. A GaN-based light-emitting diode epitaxial structure with high hole injection efficiency, characterized in that: The invention comprises the following structural layers sequentially arranged on a substrate: a first semiconductor layer; active layer; Low temperature P-type layer; a second semiconductor layer; in: The first semiconductor layer comprises a buffer layer, an undoped GaN layer and an n-type GaN layer; The active layer includes at least one InGaN / GaN multiple quantum well structure; The low-temperature P-type layer is provided between the active layer and the second semiconductor layer, and specifically comprises: a) Hole expansion layer, a periodic structure formed by alternating AlN layers and low-Mg-doped GaN layers; b) Hole storage layer, a periodic structure formed by alternating GaN layers, InGaN layers, and low-Mg-doped AlGaN layers; c) a hole layer, comprising a periodic structure formed by alternating P-type AlInGaN layers and MgN layers, wherein the MgN layers are prepared by pulsed deposition of a Mg source; The second semiconductor layer includes an electron blocking layer and a P-type GaN layer.

2. The epitaxial structure according to claim 1, wherein: The thickness of the AlN layer in the hole expansion layer is 0.5-5 nm, the thickness of the low-doped Mg-GaN layer is 1-10 nm, and the number of periods is 1-20.

3. The epitaxial structure according to claim 1, wherein: The In composition of the InGaN layer in the hole storage layer is 0.01-0.2, and the Al composition of the low-Mg-doped AlGaN layer is 0.01-0.

2.

4. The epitaxial structure according to claim 1, wherein: The Mg doping concentration in the hole layer is 1×10 20 to 1×10 21 atoms / cm 3 , the number of cycles is 1-20.

5. The epitaxial structure according to claim 1, wherein: The MgN layer is formed by introducing only a nitrogen source and a Mg source under the condition of shutting off the metal source.

6. The epitaxial structure according to claim 1, wherein: The electron blocking layer is an AlGaN layer.

7. The method for preparing a light-emitting diode epitaxial structure according to claim 1, wherein: The steps include: 1) Providing a patterned substrate; 2) The following structural layers are deposited on it in sequence: The buffer layer, the undoped GaN layer and the n-type GaN layer form a first semiconductor layer; InGaN / GaN multiple quantum well structure, forming the active layer; The low-temperature P-type layer is deposited in the following periodic structure: a) Hole expansion layer: AlN layers and low-Mg-doped GaN layers are alternately deposited at 800-900°C, 50-500 torr pressure, and N2 / NH3 atmosphere; b) Hole storage layer: GaN layer, InGaN layer, and low-Mg-doped AlGaN layer are alternately deposited at 800-900°C, pressure 50-500 torr, and N2 / NH3 atmosphere; c) Void layer: P-type AlInGaN layer and MgN layer are alternately deposited by pulsed deposition of Mg source at 700-800°C, pressure 50-500 torr, and N2 / NH3 / H2 atmosphere, specifically including: Introducing Al source / In source / Ga source and nitrogen source to deposit AlInGaN layer; Turn off the metal source, introduce only the nitrogen source and turn on the Mg source to form the MgN layer; Repeat the above deposition steps to form a periodic structure; 3) Depositing an electron blocking layer and a P-type GaN contact layer to form a second semiconductor layer.

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