Method for Preparing GaN Substrate Material

Abstract

A method for preparing a GaN substrate material includes: performing in-situ epitaxy on a Ga.sub.2O.sub.3 thin film and a GaN thin film in a multifunctional HVPE growth system. First, the Ga.sub.2O.sub.3 thin film is grown on a substrate such as sapphire by an HVPE-like method, and the Ga.sub.2O.sub.3 is nitrided in an ammonia gas atmosphere to form a GaN/Ga.sub.2O.sub.3 composite thin film. Then, a GaN thick film is grown on the GaN/Ga.sub.2O.sub.3 composite thin film by HVPE to obtain a high-quality GaN thick film material. The Ga.sub.2O.sub.3 layer is removed by chemical etching to obtain a self-supporting GaN substrate material. Or, the conventional laser lift-off method is used to separate the GaN thick film from the heterogeneous substrate such as the sapphire to obtain a GaN self-supporting substrate material.

Claims

1. A method for preparing a GaN substrate material, wherein an in-situ epitaxy is performed on a Ga.sub.2O.sub.3 thin film and a GaN thin film in a multifunctional halide vapor phase epitaxy (HVPE) growth system, comprising: firstly, growing the Ga.sub.2O.sub.3 thin film on a substrate by a halide vapor phase epitaxy (HVPE) method, and performing a nitridation on a surface of the Ga.sub.2O.sub.3 thin film in an ammonia gas atmosphere or ammonia-nitrogen mixed gas to form a GaN/Ga.sub.2O.sub.3 composite thin film; then, growing a GaN thick film by the HVPE method on the GaN/Ga.sub.2O.sub.3 composite thin film to obtain a high-quality GaN thick film material; and removing the Ga.sub.2O.sub.3 in an interface layer of the GaN/Ga.sub.2O.sub.3 composite thin film by a chemical etching to obtain a self-supporting GaN substrate material; or, separating the GaN thick film from the substrate by a laser lift-off method to obtain the self-supporting GaN substrate material; wherein growing the Ga.sub.2O.sub.3 thin film by the HVPE method requires the following conditions: oxygen gas and hydrogen chloride or chlorine gas are used as reactant gases, the hydrogen chloride or the chlorine gas reacts with gallium to form gallium chloride as a gallium source, the oxygen gas reacts with the gallium chloride to generate gallium oxide on the substrate at a pressure equal to one bar pressure and a first predetermined temperature of is 900-1150 C., and a ratio of input O atoms to input Ga atoms is (1.515):1.

2. The method for preparing the GaN substrate material according to claim 1, wherein, an annealing is performed at a second predetermined temperature of 800-1100 C. and under ammonia gas atmosphere or ammonia-nitrogen mixed gas for 0.5-5 hours, a surface of the gallium oxide is nitrided to form the GaN/Ga.sub.2O.sub.3 composite thin film for a next epitaxy, an ammonia gas flow rate is 100-5000 sccm, and a flow ratio of ammonia gas to nitrogen gas in the ammonia-nitrogen mixed gas is (0.55):1.

3. The method for preparing the GaN substrate material according to claim 2, wherein, the GaN thick film is continuously in-situ grown on the GaN/Ga.sub.2O.sub.3 composite film by the HVPE method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a schematic diagram showing the reaction principle of growing gallium oxide/gallium nitride by HVPE.

[0015] FIG. 2 is a flowchart of the technical route according to the present invention.

[0016] FIG. 3 is a scanning electron microscope (SEM) image showing the surface morphology of the GaN single crystal layer/Ga.sub.2O.sub.3 composite thin film formed by nitriding according to embodiment 1.

[0017] FIG. 4 is a diagram of the GaN substrate material obtained by growing a GaN thick film on the GaN/Ga.sub.2O.sub.3 composite thin film substrate by HVPE and etching according to embodiment 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The method and process of the present invention include the following parts: preparing a gallium oxide film by an HVPE method; forming a GaN/Ga.sub.2O.sub.3 composite thin film by nitriding the gallium oxide film; and performing an in-situ epitaxy to obtain a GaN thick film by HVPE. The specific flowchart of technical route is shown in FIG. 2.

[0019] On the GaN/Ga.sub.2O.sub.3 composite structure film, in-situ growth of a GaN thick film is continued by HVPE.

[0020] In an HVPE growth system, oxygen gas is newly introduced as a source gas. Ga.sub.2O.sub.3 is performed with an in-situ epitaxy by a method similar to the HVPE growth of the GaN. First, the Ga.sub.2O.sub.3 thin film is grown on a substrate such as sapphire by HVPE, and then Ga.sub.2O.sub.3 is partially or entirely nitrided in an ammonia gas atmosphere to form a GaN/Ga.sub.2O.sub.3 composite thin film. Then, a GaN thick film is grown on the buffer layer by HVPE to obtain a high-quality GaN thick film material. The Ga.sub.2O.sub.3 in the interface layer is removed by chemical etching to obtain a self-supporting GaN substrate material. Or, a conventional laser lift-off method is used to separate the GaN thick film from the heterogeneous substrate such as the sapphire to obtain a GaN self-supporting substrate material.

[0021] A method for preparing a gallium oxide thin film by an HVPE method is provided, where the reaction system mainly includes two temperature regions. In the low-temperature region, the temperature is generally 850-950 C., and gallium reacts with hydrogen chloride or chlorine gas to generate GaCl as a gallium source. Oxygen gas is used as an oxygen source, GaCl and O.sub.2 are mixed and reacted in a high-temperature growth region to obtain the gallium oxide thin film (as shown in FIG. 1). The temperature in the high-temperature region is generally 900-1150 C. The reaction is carried out under normal pressure. The ratio of input O atoms to input Ga atoms is 1.5-15.

[0022] A method for forming a GaN/Ga.sub.2O.sub.3 composite thin film by nitriding a gallium oxide thin film is provided. In the HVPE growth system, after gallium oxide is grown, oxygen gas is stopped. After a period, the GaN/Ga.sub.2O.sub.3 composite film can be obtained by introducing ammonia gas and annealing at a specific temperature for a certain time. The ammonia gas flow rate is 100-5000 sccm, the temperature is 800-1100 C., and the annealing time is 0.5-5 hours.

[0023] After completing the nitriding, the oxygen gas is stopped. After a period, ammonia gas is introduced and maintained at a certain flow rate, and hydrogen chloride gas is introduced to react with gallium to generate GaCl. The growth of GaN is performed on the above GaN/Ga.sub.2O.sub.3 composite film by HVPE to obtain a GaN thick film material with a thickness of generally greater than 10 microns.

[0024] The self-supporting GaN substrate material can be obtained by removing the gallium oxide in the interface layer through chemical etching, or by separating the GaN thick film from the heterogeneous substrate through the traditional laser lift-off method.

[0025] According to one of the implementation modes of the present invention, the preparation of the gallium nitride substrate material includes the following steps.

[0026] 1. A substrate (sapphire) is cleaned and processed.

[0027] 2. A gallium oxide thin film is prepared by an HVPE method. In the low-temperature region, the temperature is generally 850-950 C. Gallium reacts with hydrogen chloride or chlorine gas to generate GaCl as a gallium source. Oxygen gas is used as an oxygen source, GaCl and O.sub.2 are mixed and reacted in a high-temperature growth region to obtain the gallium oxide thin film. The temperature in the high-temperature region is generally 900-1150 C. The reaction is carried out under normal pressure. The ratio of input oxygen gas to input Ga atoms is 1.5-15.

[0028] 3. After the gallium oxide thin film is grown, the oxygen gas is stopped. After a period, ammonia gas is introduced, and a high-temperature annealing treatment is performed. Parameters: the temperature is 800-1100 C., the time is 0.5-5 hours; the gas atmosphere is ammonia gas or ammonia-nitrogen mixed gas, and the ammonia gas flow rate is 100-5000 sccm.

[0029] 4. After completing the annealing and nitridation, GaN thick film is grown by HVPE by adjusting parameters such as temperature and gas flow rate.

[0030] 5. The sample obtained in step 4 is cooled and taken out, and then placed in an acid solution or alkali solution. The oxide in the interface layer is etched to obtain the self-supporting GaN substrate material. The acid can be 30-50% hydrogen fluoride (HF) aqueous solution.

[0031] 6. The sample obtained in step 4 is cooled and taken out. The conventional laser lift-off method is used to separate the GaN thick film from the heterogeneous substrate to obtain the GaN self-supporting substrate material.

Embodiment 1

[0032] A method for preparing a GaN substrate material includes the following steps.

[0033] 1. A sapphire substrate is cleaned and processed by conventional methods.

[0034] 2. A gallium oxide thin film is prepared by an HVPE method. In the low-temperature region, the temperature is set to be 850 C. Gallium reacts with hydrogen chloride to generate GaCl as a gallium source. Oxygen gas is used as an oxygen source, GaCl and O.sub.2 are mixed and reacted in a high-temperature growth region to obtain the gallium oxide thin film. The temperature in the high-temperature region is set to be 950 C. The reaction is carried out under normal pressure. The ratio of input oxygen gas to input Ga is 3.

[0035] 3. After the gallium oxide thin film is grown, the oxygen gas is stopped. After a period, ammonia gas is introduced, and a high-temperature annealing treatment is performed to obtain a GaN/Ga.sub.2O.sub.3 composite structure. Parameters: the temperature is 800 C., the time is 5 hours; the gas atmosphere is ammonia gas, and the ammonia gas flow rate is 200 sccm. The surface SEM diagram of the obtained GaN/Ga.sub.2O.sub.3 composite substrate is shown in FIG. 3.

[0036] 4. After completing the annealing and nitridation, GaN thick film is grown by HVPE after adjusting the temperature in the low-temperature region to be 850 C., the temperature in the high-temperature to be 1050 C., ammonia gas flow rate to be 500 sccm, flow rate of nitrogen gas carried by ammonia gas to be 5 slm, hydrogen chloride flow rate to be 50 sccm, flow rate of nitrogen gas carried by hydrogen chloride to be 500 sccm, and total nitrogen gas flow rate to be 10 sccm.

[0037] 5. The sample obtained in step 4 is cooled and taken out, and then placed in an acid solution. The oxide in the interface layer is etched to obtain a self-supporting GaN substrate material. The acid solution is a 40% HF aqueous solution. The separated self-supporting GaN substrate material is shown in FIG. 4. In FIG. 4, the white part is sapphire, and the black part is gallium nitride. To illustrate the separation effect, sapphire is only partially stripped.

Embodiment 2

[0038] A method for preparing of a GaN substrate material includes the following steps.

[0039] 1. A sapphire substrate is cleaned and processed by conventional methods.

[0040] 2. A gallium oxide thin film is prepared by an HVPE method. In the low-temperature region, the temperature is set to be 870 C. Gallium reacts with chlorine gas to generate GaCl as a gallium source. Oxygen gas is used as an oxygen source, GaCl and O.sub.2 are mixed and reacted in a high-temperature growth region to obtain the gallium oxide thin film. The temperature in the high-temperature region is set to be 900 C. The reaction is carried out under normal pressure. The ratio of input oxygen gas to input Ga is 1.5.

[0041] 3. After the gallium oxide thin film is grown, the oxygen gas is stopped. After a period, ammonia gas is introduced, and a high-temperature annealing treatment is performed to obtain a GaN/Ga.sub.2O.sub.3 composite thin film. Parameters: the temperature is 900 C., the time is 4 hours; the gas atmosphere is ammonia-nitrogen mixed gas, and the total flow rate is 5000 sccm. In this embodiment, the flow ratio of ammonia gas to nitrogen gas is 1:4.

[0042] 4. After completing the annealing and nitridation, GaN thick film is grown by HVPE after adjusting parameters including temperature and gas flow rate.

[0043] 5. The sample obtained in step 4 is cooled and taken out, and then placed in a sodium hydroxide or potassium hydroxide alkali solution. The oxide in the interface layer is etched to obtain a self-supporting GaN substrate material.

Embodiment 3

[0044] A method for preparing of a GaN substrate material includes the following steps.

[0045] 1. A substrate (sapphire) is cleaned and processed.

[0046] 2. A gallium oxide thin film is prepared by an HVPE method. In the low-temperature region, the temperature is set to be 950 C. Gallium reacts with hydrogen chloride or chlorine gas to generate GaCl as a gallium source. Oxygen gas is used as an oxygen source, GaCl and O.sub.2 are mixed and reacted in a high-temperature growth region to obtain the gallium oxide thin film. The temperature in the high-temperature region is 1150 C. The reaction is carried out under normal pressure. The ratio of input oxygen gas to input Ga is 15.

[0047] 3. After the gallium oxide thin film is grown, the oxygen gas is stopped. After a period, ammonia gas is introduced, and a high-temperature annealing treatment is performed to form a GaN/Ga.sub.2O.sub.3 composite thin film. Parameters: the temperature is 1100 C., the time is 1 hour; the gas atmosphere is ammonia gas, and the ammonia gas flow rate is 100 sccm.

[0048] 4. After completing the annealing and nitridation, GaN thick film is grown by HVPE after adjusting the parameters such as temperature and gas flow rate.

[0049] 5. The sample obtained in step 4 is cooled and taken out. The conventional laser lift-off method is used to separate the GaN thick film from the heterogeneous substrate to obtain a GaN self-supporting substrate material.

[0050] It should be understood by those of ordinary skill in the art that the above description is only specific embodiments of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall in the protection scope of the present invention.