High quality self-separated GaN crystal grown on a novel nanoporous template by HVPE

Qin Huo,Baoguo Zhang,Haixiao Hu,Yongliang Shao,Yongzhong Wu,Xiaopeng Hao

doi:10.1038/s41598-018-21607-3

Abstract

In this study, a novel nanoporous template was obtained by a two-step etching process from MOCVD-GaN/Al2O3 (MGA) with electrochemical etching sequentially followed by chemical wet etching. The twice-etched MOCVD-GaN/Al2O3 (TEMGA) templates were utilized to grow GaN crystals by hydride vapor phase epitaxy (HVPE) method. The GaN crystals were separated spontaneously from the TEMGA template with the assistance of voids formed by the etched nanopores. Several techniques were utilized to characterize the quality of the free-standing GaN crystals obtained from the TEMGA template. Results showed that the quality of the as-obtained GaN crystals was improved obviously compared with those grown on the MGA. This convenient technique can be applied to grow high-quality free-standing GaN crystals.

Highlights

Gallium nitride (GaN) is an important wide band gap semiconductor that has been applied widely in the optoelectronic[1,2] and high-power high-frequency devices[3] because of its excellent optoelectronic and electronic properties
The full width at half maximum (FWHM) value of the (102) peak for the hydride vapor phase epitaxy (HVPE)-GaN crystal grown on the twice-etched MOCVD-GaN/Al2O3 (TEMGA) template is similar to that from the etching MOCVD-GaN/Al2O3 (ECMGA) template, while the FWHM value of the (002) peak for the HVPE-GaN crystal grown on the TEMGA template is lower than that from the ECMGA template. It means that the density of the screw or mixed dislocations of the HVPE-GaN crystals grown on the TEMGA template is lower than that from the ECMGA template
It is observed that the mapping color near the interface is yellow, the mapping color of the nanoporous buffer layer is a mixture of green and blue and the mapping color of the epitaxial GaN is green. These results indicate that the disorientation near the interface is the largest and the disorientation of the nanoporous buffer layer is the smallest in GaN grown on TEMGA template

Summary

GaN crystal grown on a novel nanoporous template by HVPE

A novel nanoporous template was obtained by a two-step etching process from MOCVDGaN/Al2O3 (MGA) with electrochemical etching sequentially followed by chemical wet etching. The twice-etched MOCVD-GaN/Al2O3 (TEMGA) templates were utilized to grow GaN crystals by hydride vapor phase epitaxy (HVPE) method. To reduce the residual stress and realize the self-separation of GaN crystals, our group has explored several methods, including wet chemical etching[19], high temperature annealing[20,21] and electrochemical etching methods[22], to fabricate the nanoporous GaN buffer layer. It is difficult to obtain high-porosity and large-sized nanoporous structure which is important for the self-separation of GaN crystals by the electrochemical etching method[24]. The much higher porosity of TEMGA template is more efficient to the self-separation of HVPE grown GaN crystals than that of electrochemical etching substrates. The quality of GaN crystals grown by HVPE on TEMGA template and MOCVD-GaN/Al2O3 (MGA) template was researched to indicate the effect of the two-step etching process. The EBSD measurements were carried out at 20 kV with a working distance of 20 mm and a sample tilt of 70°

Result and Discussion

Findings

Conclusion

Additional Information