CN100373548C - Method for growing non-polar GaN thick film on lithium aluminate wafer - Google Patents

Abstract

A method for preparing a nonpolar GaN thick film on a lithium aluminate wafer, _comprising : Method 1: using (302) plane γ-LiAlO as a substrate, and preparing a (110) plane by a hydride vapor phase epitaxy method GaN thick film. Method 2: Using the (302) plane γ-LiAlO ₂ as the substrate, a GaN thin film is pre-prepared on the (302) plane γ-LiAlO ₂ substrate by metal-organic chemical vapor deposition to form (110)GaN/( 302) γ-LiAlO ₂ composite substrate, on which the hydride vapor phase epitaxy method is used to prepare a-plane (110) GaN thick film; after peeling off the (302) surface γ-LiAlO ₂ substrate, it can be prepared Non-polar (110) GaN thick film with free-standing substrate. The nonpolar a-plane GaN thick film of the invention can be used for the homoepitaxial growth of GaN and the preparation of nonpolar III-group nitride devices.

Description

Method for growing non-polar GaN thick film on lithium aluminate wafer

technical field

The invention relates to the preparation of GaN-based substrate materials, in particular to a method for growing nonpolar GaN thick films on lithium aluminate wafers.

Background technique

GaN and its ternary and quaternary alloys (AlGaN, InGaN, AlInGaN) have shown broad application prospects in visible light and ultraviolet optoelectronic devices, high-power electronic devices, etc. These devices are typically grown heteroepitaxially on other substrates due to the difficulty in obtaining large-scale GaN bulk single crystals. Epitaxy techniques mainly include the following: molecular beam epitaxy (MBE) method, metal organic chemical vapor deposition (hereinafter referred to as: MOCVD) method and halide vapor phase epitaxy (HVPE) method.

Usually, GaN films grown on commonly used substrates (such as sapphire and 6H-SiC) are along the c-direction, and the c-direction is the polarization axis direction of the GaN wurtzite structure. For the GaN-based heterojunction grown on the (0001) plane, the spontaneous polarization effect and the piezoelectric polarization effect caused by the lattice mismatch stress due to the difference in the electronegativity of the elements on both sides of the heterojunction make A certain concentration of charges is generated at the interface of the heterojunction, and these charges generate a high-intensity built-in electric field in the epitaxial layer, which makes the energy band bend and tilt, and the position of the energy level changes, causing the luminous wavelength to red-shift; at the same time, the interface charge The generated electric field will also cause the positive load carriers to be separated in space, and the overlap of electron and hole wave functions will be reduced, so that the luminous efficiency of the material will be greatly reduced; while the mismatch stress limits the thickness of the quantum well, resulting in the luminous intensity of the material reduce. Nonpolar GaN-based devices can solve this problem, so the preparation of nonpolar GaN-based thin films, thick films and devices and their related mechanisms have become the current international research hotspots of GaN-based materials.

All the planes perpendicular to the (0001) plane in GaN are its non-polar planes, such as the m plane and a plane of GaN, where the m plane: (1100) a plane: (1120). In 1998, the Shanghai Institute of Optics and Mechanics of the Chinese Academy of Sciences first prepared m-plane GaN on γ-LiAlO ₂ (100) by MOCVD [see Journal of Crystal Growth 193, 127 (1998)]. In 2000, German researchers also used MBE to prepare m-plane GaN on (100) γ-LiAlO ₂ substrates [see Nature 406, 865 (2000)]. At present, the m-plane GaN film directly epitaxial on γ-LiAlO ₂ (100) (that is, no buffer layer, no nitriding treatment) has good quality (FWHM of the 1100 peak of the epitaxial film=112arcsec) [see Appl.Phys. Lett.88, 011902 (2006)]. At the same time, people are actively exploring the possibility of preparing non-polar GaN films on common substrates. After several years of unremitting efforts, a-plane GaN can be prepared on r-plane sapphire, SiC and Si(100).

In addition, the manufacture of non-polar GaN devices has also achieved preliminary success. Among them, the use of γ-LiAlO ₂ substrates as initial templates to prepare m-plane GaN films and devices has recently received high attention. The father of Blu-ray, Shuji Nakamura (Nakamura Shuji) used HVPE to prepare m-plane GaN thick film self-supporting substrates on (100) γ-LiAlO ₂ [see (Joumal of Electronic Materials, 34, 357 (2005)], and here A non-polar GaN-based blue light-emitting diode LED was prepared by MOCVD on the bottom [see Jpn.J.Appl.Phys.44, L173 (2005)], and its luminous efficiency has recently made a breakthrough as high as 200 lumens/watt, which is in Levels that cannot be achieved on common substrates such as sapphire.

Contents of the invention

The object of the present invention is to provide a method for growing nonpolar GaN film on a lithium aluminate wafer, that is, on the (302) wafer of γ-LiAlO ₂ , the following expression is: (302) γ-LiAlO ₂ Growth a on the wafer Surface GaN film method.

Technical solution of the present invention is as follows;

A method for growing a nonpolar GaN film on a lithium aluminate wafer, characterized in that it adopts a polished (302) surface γ- _LiAlO substrate, utilizes a hydride vapor phase epitaxy method, or utilizes metal organic chemical vapor deposition and hydrogenation A non-polar (1120) plane GaN film was prepared on a (302) plane γ-LiAlO ₂ substrate by a method combined with gas phase epitaxy.

Scheme 1: Preparation of non-polar (1120) plane GaN film on (302) plane γ-LiAlO ₂ substrate by hydride vapor phase epitaxy method

The polished (302) γ-LiAlO ₂ wafer is cleaned and dried, and then sent to the HVPE system, which is a horizontal quartz reactor with two temperature zones. -1050°C, the purity of various gases fed into the system is greater than 99.9999%. First, the γ-LiAlO ₂ substrate is nitrided with NH ₃ , and then a nucleation layer is grown at 860-1050°C. HCl gas is carried by N ₂ and reacts with metal Ga with a purity greater than 99.9999% to form GaCl, and then N ₂ is used as the The carrier gas respectively introduces GaCl and NH ₃ above the substrate and combines them. The molar ratio of NH ₃ and GaCl is 10-60, the growth temperature is 860-1050°C, and the growth rate is 50-300 μm/h. 100 μm (1120) GaN.

Scheme 2: A non-polar (1120) plane GaN film is prepared on a (302) plane γ-LiAlO ₂ substrate by combining metal organic chemical vapor deposition and hydride vapor phase epitaxy.

With (302) γ-LiAlO ₂ as the substrate, a GaN film is pre-prepared on it by MOCVD method, on this basis, the GaN film is prepared by HVPE method, and then the (302) γ-LiAlO _{2 substrate can be prepared after peeling off the (302) γ-LiAlO 2} substrate A non-polar (1120) GaN self-supporting substrate is produced, and the purity of various gases fed into the MOCVD system and the HVPE system is greater than 99.9999%. The specific steps are: send the polished (302) γ- _LiAlO2 wafer into the MOCVD system, use _N2 as the carrier gas, and grow a low-temperature GaN buffer layer in the temperature range of 500-800°C for 500-4000 seconds, and then increase the temperature To 950-1100 ℃, using N ₂ and H ₂ as carrier gas, grow GaN film, the time is 800-6000 seconds; take out the wafer from the MOCVD system, the (302) γ-LiAlO ₂ liner covered with GaN film The bottom is put into the HVPE system, HCl gas reacts with metal Ga (purity greater than 99.9999%) under the carrying of N ₂ to generate GaCl, and N ₂ gas is used as the carrier gas, and GaCl and NH ₃ are respectively introduced above the substrate to combine, NH The molar ratio of ₃ to GaCl is 10-60, and GaN is continuously grown under the temperature condition of 860-1050° C. to obtain a-plane GaN film.

The method of the invention successfully grows (1120) GaN with a thickness greater than 100 μm. The method can also be used for the homoepitaxial growth of GaN and the preparation of non-polar III-nitride devices.

Detailed ways

Below in conjunction with embodiment the method of the present invention will be further described, but should not limit protection scope of the present invention with this.

Example 1

Send the polished (302) γ- _LiAlO2 wafer into the HVPE system and put it into the growth area. First, the γ- _LiAlO2 substrate is nitrided with _NH3 at 900 °C, and then the nitrided γ-LiAlO2 substrate is nitrided at 800 °C _2. A nucleation layer is grown on the substrate. HCl gas is carried by N ₂ to react with metal Ga to generate GaCl, and then GaCl and NH ₃ are respectively introduced to a place 10 mm above the substrate with N ₂ as the carrier gas. NH ₃ and The molar ratio of GaCl is 10, the growth temperature is 860°C, and the growth rate is 50 μm/h, and a GaN thick film of 250 μm can be grown.

Example 2

Send the polished (302) γ- _LiAlO2 wafer into the HVPE system and put it into the growth area. First, the γ- _LiAlO2 substrate is nitrided with _NH3 at 900 °C, and then the nitrided γ-LiAlO2 substrate is nitrided at 800 °C _2. A nucleation layer is grown on the substrate. HCl gas is carried by N ₂ to react with metal Ga to generate GaCl, and then GaCl and NH ₃ are respectively introduced to a place 10 mm above the substrate with N ₂ as the carrier gas. NH ₃ and The molar ratio of GaCl is 30, the growth temperature is 950°C, and the growth rate is 150 μm/h, and a GaN thick film of 250 μm can be grown.

Example 3

Send the polished (302) γ- _LiAlO2 wafer into the HVPE system and put it into the growth area. First, the γ- _LiAlO2 substrate is nitrided with _NH3 at 900 °C, and then the nitrided γ-LiAlO2 substrate is nitrided at 800 °C _2. A nucleation layer is grown on the substrate. HCl gas is carried by N ₂ to react with metal Ga to generate GaCl, and then GaCl and NH ₃ are respectively introduced to a place 10 mm above the substrate with N ₂ as the carrier gas. NH ₃ and The molar ratio of GaCl is 60, the growth temperature is 1050°C, and the growth rate is 300 μm/h, and a GaN thick film of 300 μm can be grown.

Example 4

Send the polished (302) γ- _LiAlO2 wafer into the MOCVD system, use _N2 as the carrier gas, prepare a layer of GaN buffer layer at 500 °C, the deposition time is 500 seconds, then raise the temperature to 950 °C, and use _N2 Mixed gas with H ₂ as carrier gas, grow GaN film, the growth time is 800 seconds, and finally cool down to room temperature. Tests found that high-quality (1120) GaN films were obtained on (302) γ-LiAlO ₂ wafers. Next, put the (302) γ-LiAlO ₂ substrate covered with (1120) GaN film into the HVPE system. First, HCl gas reacts with metal Ga under the carrying of N ₂ to generate GaCl, and then N ₂ gas is used as the carrier to generate GaCl. gas, GaCl and NH ₃ were introduced above the substrate respectively, and the molar ratio of NH ₃ to GaCl was 10. GaN was grown continuously at a temperature of 860°C, and a complete and high-quality a-plane GaN thick film was obtained.

Example 5

Send the polished (302) γ- _LiAlO2 wafer into the MOCVD system, use _N2 as the carrier gas, prepare a layer of GaN buffer layer at 700 ° C, the deposition time is 1500 seconds, then raise the temperature to 1030 ° C, and use _N2 Mixed gas with H ₂ as carrier gas, grow GaN film, the growth time is 2000 seconds, and finally cool down to room temperature. Tests found that high-quality (1120) GaN films were obtained on (302) γ-LiAlO ₂ wafers. Next, put the (302) γ-LiAlO ₂ substrate covered with (1120) GaN film into the HVPE system. First, HCl gas reacts with metal Ga under the carrying of N ₂ to generate GaCl, and then N ₂ gas is used as the carrier to generate GaCl. Gas, GaCl and NH ₃ were introduced above the substrate and combined, the molar ratio of NH ₃ and GaCl was 30, GaN was grown continuously at a temperature of 950 ° C, and a complete and high-quality a-plane GaN thick film was obtained.

Example 6

Send the polished (302) γ- _LiAlO2 wafer into the MOCVD system, use _N2 as the carrier gas, prepare a layer of GaN buffer layer at 800 ° C, the deposition time is 4000 seconds, then raise the temperature to 1100 ° C, use _N2 Mixed gas with H ₂ as carrier gas, grow GaN film, the growth time is 6000 seconds, and finally cool down to room temperature. Tests found that high-quality (1120) GaN films were obtained on (302) γ-LiAlO ₂ wafers. Next, put the (302) γ-LiAlO ₂ substrate covered with (1120) GaN film into the HVPE system. First, HCl gas reacts with metal Ga under the carrying of N ₂ to generate GaCl, and then N ₂ gas is used as the carrier to generate GaCl. gas, GaCl and NH ₃ were introduced above the substrate respectively, and the molar ratio of NH ₃ to GaCl was 60. GaN was grown continuously at a temperature of 1050°C, and a complete and high-quality a-plane GaN thick film was obtained.

Claims (2)

1. A method for growing nonpolar GaN film on a lithium aluminate wafer, characterized in that the method is carried out in a hydride vapor phase epitaxy system, with polished (302) γ-LiAlO ₂ wafers are cleaned and dried, After that, it is sent to the hydride vapor phase epitaxy system, and the purity of various gases introduced into the system is greater than 99.9999%. The γ-LiAlO ₂ substrate is nitrided with NH ₃ , and then the nucleation layer is grown at 860-1050 ° C, HCl gas Under the carrying of _N2 , react with metal Ga with a purity greater than 99.9999% to generate GaCl, and then use _N2 as a carrier gas to introduce GaCl and _NH3 above the substrate to combine, and the molar ratio of _NH3 to GaCl is: 10 ~ 60, the growth temperature is 860 ~ 1050 ° C, the growth rate is 50 ~ 300 μm / h, can grow thicker than 100 μm

GaN film. 2. A method for growing a nonpolar GaN thick film on a lithium aluminate wafer, characterized in that the method is a combination of metal organic chemical vapor deposition and hydride vapor phase epitaxy, comprising the following steps: ① Send the polished (302) γ-LiAlO ₂ wafer into the metal organic chemical vapor deposition system, use N ₂ as the carrier gas, and grow a low-temperature GaN buffer layer in the temperature range of 500-800°C for 500-4000 seconds, and then Raise the temperature to 950-1100°C, use N ₂ and H ₂ as carrier gas, and grow GaN film for 800-6000 seconds; ②Take out the wafer from the metal-organic chemical vapor deposition system, put the (302)γ- _LiAlO2 substrate covered with GaN film into the hydride vapor phase epitaxy system, HCl gas is carried by _N2 and the purity is greater than 99.9999% Metal Ga reacts to generate GaCl, using N ₂ gas as the carrier gas, respectively introducing GaCl and NH ₃ to the substrate to combine, the molar ratio of NH ₃ to GaCl is 10-60, and the growth continues at 860-1050°C GaN, get

Surface GaN film.