Vacancy-type defects in bulk GaN grown by oxide vapor phase epitaxy probed using positron annihilation

Abstract

Defects in bulk GaN grown by the oxide vapor phase epitaxy (OVPE) method were probed by using positron annihilation spectroscopy. Measurements of the Doppler broadening spectra of the annihilation radiation and lifetime spectra of positrons revealed that the major defect species in OVPE-GaN was Ga vacancy-type defects coupled with oxygen atoms such as VGa(ON)n and VGaVN(ON)n. The formation of vacancy-oxygen complexes was attributed to the high concentration of oxygen incorporated in the samples during their growth process. A correlation between such defect complexes and sample transparencies was observed. An 8-μm-thick epitaxial film grown on OVPE-GaN by using metalorganic vapor phase epitaxy was also characterized. The vacancy concentration in the GaN film was found to be under or close to the detection limit of positron annihilation (1015 cm−3), suggesting that an epitaxial layer can be grown on without being influenced by vacancies in the substrates.