Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

Jianming Liu,Yan Guo,Zhiwei Li,Xianlin Liu,Huaping Song,Anli Yang,Zhanguo Wang,Hongyuan Wei,Shaoyan Yang,Chengming Li,Xiaoqing Xu,Qinsen Zhu,Chunmei Jiao,Huanhua Wang,Tieying Yang

doi:10.1186/1556-276x-6-69

Abstract

Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate.

Highlights

Group III nitrides are attracting much attention for short-wavelength light emitters and high-temperature electronic devices
Before depositing the thick layer by Hydride vapor-phase epitaxy (HVPE), a template has been predeposited by metal organic vapor-phase epitaxy (MOCVD) [1]
Before depositing GaN thick film, a 60-nm thick low temperature (550°C) GaN buffer layer and a 0.82-μm thick high temperature layer were predeposited on a c-plane sapphire substrate by MOCVD

Summary

Introduction

Group III nitrides are attracting much attention for short-wavelength light emitters and high-temperature electronic devices. Nitride-based devices are mostly heteroepitaxially grown on non-native substrates, such as sapphire (Al2O3), Si, GaAs, and SiC. The conventional method of growing high quality thick film needs two systems. Compared with the conventional growth method, cracks are often produced in GaN thick film grown by HVPE. There are several intriguing aspects for the observed cracks of GaN on sapphire substrates. As the thermal expansion coefficient of GaN is smaller than that of sapphire [3], the film will suffer from biaxial compressive stress during cooling. Etzkorn and Clarke [4] observed cracks in GaN film deposited by HVPE on SiC substrate. The cracks existing in GaN thick films were observed directly and the probable formation mechanism was proposed

Methods

Results

Conclusion