An epitaxial structure with high crystal quality

Abstract

The present invention discloses an epitaxial structure with high crystal quality, which comprises, from bottom to top, a substrate, an AlN thin film layer, a high-temperature buffer layer, a non-doped gallium nitride layer, an N-type layer, a multi-quantum well active layer, an electron blocking layer, a P-type layer and a P-type contact layer, wherein the material of the AlN thin film layer is AlN, the material of the high-temperature buffer layer is AlxGa(1‑x)N(0≤x≤1), and the growth temperature is 700-1000°C.

Description

Technical Field

[0001] The invention relates to the technical field of light emitting diodes, and in particular to an epitaxial structure with high crystal quality. Background Art

[0002] LED (Light Emitting Diode) is a semiconductor device that uses energy released during carrier recombination to emit light. LED chips have many advantages such as low power consumption, pure color, long life, small size, fast response time, energy saving and environmental protection.

[0003] In the prior art, due to the large lattice mismatch between the sapphire substrate and GaN, a low-temperature gallium nitride buffer layer needs to be formed between the two to reduce the lattice mismatch. However, due to the very poor crystal quality of the low-temperature gallium nitride buffer layer, the crystal quality of the epitaxial layer grown on it is affected, thereby reducing the overall quality of the epitaxial layer. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an epitaxial structure with high crystal quality, and to form an AlN thin film layer on a substrate to improve the crystal quality of the epitaxial layer.

[0005] In order to solve the above technical problems, the present invention provides an epitaxial structure with high crystal quality, which includes, from bottom to top, a substrate, an AlN thin film layer, a high-temperature buffer layer, a non-doped gallium nitride layer, an N-type layer, a multi-quantum well active layer, an electron blocking layer, a P-type layer and a P-type contact layer, wherein the material of the AlN thin film layer is AlN, the material of the high-temperature buffer layer is AlxGa(1-x)N(0≤x≤1), and the growth temperature is 700~1000℃.

[0006] As an improvement of the above solution, the high temperature buffer layer is formed on the cleaned AlN thin film layer.

[0007] As an improvement of the above solution, the AlN thin film layer is cleaned with an acid solution or an alkaline solution, wherein the acid solution is one or more of sulfuric acid, phosphoric acid and H2O2, and the alkaline solution is KOH and / or NaOH.

[0008] As an improvement of the above solution, the cleaning time of the AlN thin film layer is 2-5 minutes, and the cleaning temperature is 40-60°C.

[0009] As an improvement of the above solution, the growth pressure of the high temperature buffer layer is 100-500 Torr.

[0010] As an improvement of the above solution, the thickness of the AlN thin film layer is 5-50 nm, and the thickness of the high temperature buffer layer is 5-100 nm.

[0011] As an improvement of the above solution, the doping source of the N-type layer is silane, and the doping concentration is 1E18~1E20cm -3 , thickness is 1000~5000nm;

[0012] The doping source of the P-type layer is Mg source, and the doping concentration is 1E18~1E21cm -3 .

[0013] As an improvement of the above scheme, the multi-quantum well active layer includes at least one barrier layer and at least one well layer arranged at intervals from each other, the well layer includes a first N-GaN layer, a current equalization layer arranged on the first N-GaN layer, and a second N-GaN layer arranged on the current equalization layer, and the current equalization layer is formed by doping GaN with one or more of Al, B, and silicon nitride.

[0014] As an improvement of the above solution, the material of the electron blocking layer is AlN or AlGaN, or a superlattice structure formed by AlN, AlGaN and GaN, and the thickness is 1-100 nm.

[0015] As an improvement of the above solution, the doping source of the P-type contact layer is a Mg source, and the doping concentration is 1E20~1E22cm -3 .

[0016] The implementation of the present invention has the following beneficial effects:

[0017] The present invention discloses an epitaxial structure with high crystal quality, which comprises, from bottom to top, a substrate, an AlN thin film layer, a high temperature buffer layer, a non-doped gallium nitride layer, an N-type layer, a multi-quantum well active layer, an electron blocking layer, a P-type layer and a P-type contact layer, wherein the material of the AlN thin film layer is AlN, the material of the high temperature buffer layer is AlxGa(1-x)N(0≤x≤1), and the growth temperature is 700-1000° C. The present invention improves the crystal quality of the epitaxial structure as a whole and reduces the lattice mismatch by the mutual cooperation of the AlN thin film layer and the high temperature buffer layer.

[0018] Furthermore, the high temperature buffer layer of the present invention is formed on the cleaned AlN film layer. Specifically, the AlN film layer is cleaned with an acid solution or an alkali solution, the acid solution is one or more of sulfuric acid, phosphoric acid and H2O2, and the alkali solution is KOH and / or NaOH. After the AlN film layer is cleaned with an acid solution or an alkali solution, its XRD 002 / 102 HW becomes smaller, which effectively reduces the lattice mismatch between the AlN film layer and the high temperature buffer layer, thereby improving the crystal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of the epitaxial structure of the present invention;

[0020] Figure 2 It is a schematic diagram of the structure of the multi-quantum well active layer of the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0022] See also Figure 1 The present invention provides an epitaxial structure with high crystal quality, which includes, from bottom to top, a substrate 10, an AlN thin film layer 20, a high temperature buffer layer 30, a non-doped gallium nitride layer 40, an N-type layer 50, a multi-quantum well active layer 60, an electron blocking layer 70, a P-type layer 80, and a P-type contact layer 90. The material of the AlN thin film layer is AlN, and the material of the high temperature buffer layer is AlxGa(1-x)N(0≤x≤1).

[0023] The function of the AlN thin film layer of the present invention is to reduce the lattice mismatch, and the function of the high temperature buffer layer is to reduce the interface dislocation between AlN and GaN. Since the lattice mismatch between AlN and GaN is relatively small, only about 2%, the present invention forms an AlN thin film layer on the substrate to reduce the lattice mismatch between the substrate and GaN. Since the crystal quality of the high temperature buffer layer is better than that of the low temperature buffer layer, the growth temperature of the high temperature buffer layer can reduce the dislocation between the AlN and GaN interfaces, thereby improving the crystal quality of GaN.

[0024] The present invention forms a high-temperature buffer layer on the AlN film layer, which can improve the crystal quality of the epitaxial layer grown thereon, thereby improving the overall crystal quality of the epitaxial structure. The present invention improves the overall crystal quality of the epitaxial structure and reduces lattice mismatch through the mutual cooperation of the AlN film layer and the high-temperature buffer layer.

[0025] In order to reduce lattice mismatch and improve crystal quality, the high temperature buffer layer of the present invention is formed on the cleaned AlN thin film layer. Specifically, the AlN thin film layer is cleaned with an acid solution or an alkali solution, the acid solution is one or more of sulfuric acid, phosphoric acid and H2O2, and the alkali solution is KOH and / or NaOH.

[0026] After the AlN thin film layer is cleaned with acid or alkali solution, its XRD 002 / 102 HW becomes smaller, which effectively reduces the lattice mismatch between the AlN thin film layer and the high-temperature buffer layer, thereby improving the crystal quality.

[0027] The cleaning time and cleaning temperature have an important influence on the lattice mismatch of the AlN thin film layer. Preferably, the cleaning time of the AlN thin film layer is 2-5 minutes, and the cleaning temperature is 40-60°C.

[0028] The thickness of the AlN film layer and the thickness of the high-temperature buffer layer both play an important role in the crystal quality of the epitaxial structure, especially affecting the warping of the epitaxial layer. Generally speaking, the thinner the thickness of the AlN film layer, the better the crystal quality and the higher the brightness, but it will cause problems such as atomization on the surface of the epitaxial wafer or weakening of the ESD electrical properties. Therefore, the present invention further limits the thickness of the AlN film layer. Preferably, the thickness of the AlN film layer is 5~50nm, and the thickness of the high-temperature buffer layer is 5~100nm. Preferably, the thickness of the AlN film layer is 10~20nm, and the thickness of the high-temperature buffer layer is 5~50nm. More preferably, the thickness of the AlN film layer is 10~15nm, and the thickness of the high-temperature buffer layer is 5~20nm.

[0029] Furthermore, the growth temperature and growth pressure of the high temperature buffer layer play an important role in its crystal quality, so the growth temperature of the high temperature buffer layer is controlled between 700 and 1000°C, and the growth pressure is controlled between 100 and 500 Torr. Preferably, the growth temperature of the high temperature buffer layer is 800 to 850°C, and the growth pressure is 100 to 200 Torr.

[0030] In order to further improve the crystal quality of the epitaxial structure and ensure the luminous efficiency, the present invention further defines other epitaxial structures.

[0031] Specifically, the doping source of the N-type layer is silane, and the doping concentration is 1E18~1E20cm -3 , with a thickness of 1000~5000nm; the doping source of the P-type layer is a Mg source, and the doping concentration is 1E18~1E21cm -3 .

[0032] The material of the electron blocking layer is AlN or AlGaN, or a super lattice structure formed by AlN, AlGaN and GaN, and the thickness is 1-100 nm.

[0033] The doping source of the P-type contact layer is a Mg source, and the doping concentration is 1E20~1E22 cm -3 .

[0034] See also Figure 2, the multi-quantum well active layer 50 includes at least one barrier layer 51 and at least one well layer 52 arranged at intervals from each other. The barrier layer 51 includes a first N-GaN layer 53, a circuit equalization layer 54 arranged on the first N-GaN layer 53, and a second N-GaN layer 55 arranged on the current equalization layer 54; wherein the current equalization layer 54 is formed by doping one or more of Al, B, and silicon nitride in GaN, and the resistivity of the current equalization layer is much greater than that of the first N-GaN layer and the second N-GaN layer. The present invention forms a high-resistivity enhanced diffusion structure by arranging a well layer structure of N-GaN+current equalization layer+N-GaN in the active region, and by compounding the high-resistivity current equalization layer with the low-resistivity N-GaN layer; when the LED having the epitaxial structure of the present invention uses a small current, the congestion effect of the small current can be effectively improved, so that the small current can be expanded laterally and dispersed in the process, and the diffusion effect is enhanced, thereby achieving the effect of low power and high light efficiency.

[0035] Specifically, in the present invention, the low current density refers to a current lower than 500 mA; the doping material in the present invention is selected from one or more of Al, B, and silicon nitride. By doping the above materials, the resistivity of the current equalization layer 34 in the present invention is greater than 10 9 Ω•cm, while the resistivity of the N-GaN layer is ≤3 Ω•cm; the huge difference between the N-GaN layer 33 / 35 and the current averaging layer 34 will form an energy level deformation, making the overall resistance value of the well layer larger, thereby having a better effect of dispersing the current.

[0036] Preferably, the doping material is Al, and the resistivity of the AlGaN layer can be greater than 10 11 Ω•cm, with better current dispersion effect. The Al doping process is simple, the doping temperature is less than 800℃, and it is easy to operate; after doping, the Al content in the AlGaN layer is ≤5 wt%.

[0037] Specifically, referring to the table below, the quality differences between the existing chip and the chip of the present invention are as follows:

[0038]

[0039] The above disclosure is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. An epitaxial structure with high crystal quality, characterized in that From bottom to top, it includes a substrate, an AlN thin film layer, a high temperature buffer layer, a non-doped gallium nitride layer, an N-type layer, a multi-quantum well active layer, an electron blocking layer, a P-type layer and a P-type contact layer, wherein the material of the AlN thin film layer is AlN, the material of the high temperature buffer layer is AlxGa(1-x)N(0≤x≤1), and the growth temperature is 700~1000°C; The high temperature buffer layer is formed on the cleaned AlN thin film layer, the cleaning time is 2-5 minutes, and the cleaning temperature is 40-60°C; The thickness of the AlN thin film layer is 5-50 nm, and the thickness of the high temperature buffer layer is 5-100 nm; The multi-quantum well active layer includes at least one barrier layer and at least one well layer spaced apart from each other, the well layer includes a first N-GaN layer, a current equalization layer disposed on the first N-GaN layer, and a second N-GaN layer disposed on the current equalization layer, and the current equalization layer is formed by doping GaN with one or more of Al, B, and silicon nitride.

2. The epitaxial structure with high crystal quality according to claim 1, characterized in that: The AlN thin film layer is cleaned by using an acid solution or an alkali solution, wherein the acid solution is one or more of sulfuric acid, phosphoric acid and H2O2, and the alkali solution is KOH and / or NaOH.

3. The high crystal quality epitaxial structure according to claim 1, characterized in that: The growth pressure of the high temperature buffer layer is 100-500 Torr.

4. The epitaxial structure with high crystal quality according to claim 1, characterized in that: The doping source of the N-type layer is silane, and the doping concentration is 1E18~1E20cm -3 , thickness is 1000~5000nm; The doping source of the P-type layer is Mg source, and the doping concentration is 1E18~1E21cm -3 .

5. The epitaxial structure with high crystal quality according to claim 1, characterized in that: The material of the electron blocking layer is AlN or AlGaN, or a super lattice structure formed by AlN, AlGaN and GaN, and the thickness is 1-100 nm.

6. The epitaxial structure with high crystal quality according to claim 1, characterized in that: The doping source of the P-type contact layer is a Mg source, and the doping concentration is 1E20~1E22 cm -3 .

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