Study of stress in ammonothermal non-polar and semi-polar GaN crystal grown on HVPE GaN seeds

GaN crystals were grown on non-polar and semi-polar HVPE GaN seeds by basic ammonothermal method. Stress distributions were investigated in cross-section of (1 1 -2 0) plane, (1 0 -1 0) plane, (2 0 -2 1) plane and (1 0 -1 1) plane GaN crystal. The cathodoluminescence (CL) images show cross-section information clearly and each examined object consisted of hydride vapor phase epitaxy (HVPE) seed and ammonothermal GaN (AmGaN). The impurity concentration and free carrier concentration were estimated by secondary-ion mass spectroscopy (SIMS) and Hall. Moreover, Raman spectroscopy was used for studying stress distribution in the cross section. Shifts of E-2(high) phonon lines were analyzed to determine stress. Our results indicate that the stress is about 35 MPa in bulk GaN and the stress is less than 60 MPa in the interface of Am-GaN.