Observation Of Native Ga Vacancies In Gan By Positron Annihilation

Abstract

Positron annihilation experiments have been performed to identify native point defects in GaN bulk crystals as well as in epitaxial layers. The results show that Ga vacancies are present at concentrations of 1017 – 1018 cm−3 in undoped GaN bulk crystals and layers, whereas the Mgdoped samples are free of Ga vacancies. The Ga vacancies are negatively charged and their concentration correlates with the intensity of the yellow luminescence. We conclude that the Ga vacancies contribute to the electrical compensation of n-type GaN and their acceptor levels are involved in the yellow luminescence transition.

Carbon defects as sources of the green and yellow luminescence bands in undoped GaN

“…For example, in Ref. [54], the YL intensity increased almost linearly with the concentration of Ga vacancies for a few data points. However, the YL band in this paper was measured from the GaN/sapphire interface, where the concentration of various defects (other than V Ga ) is very high and may not be the same across the different samples.…”

Computationally predicted energies and properties of defects in GaN

“…64 This relatively low value seemed to indicate that Ga vacancies would be relatively abundant, a prediction that seemed to be confirmed by positron annihilation experiments. 65,66 The HSE calculations (as well as "shifted GGA") calculations, however, produce a much higher formation energy, about 4.5 eV in HSE. This high value indicates that Ga vacancies are highly unlikely to occur in as-grown GaN, even if the chemical potentials would shift away from the extreme Ga-rich limit.…”

Point Defects in GaN

“…The positron lifetime in the defect-free GaN lattice (τ b ¼ 160 AE 1ps) and the lifetime of positrons trapped at negatively charged V Ga or V Ga -containing complexes (τ V ¼ 235 AE 5ps) have been determined using GaN samples with negligible and high concentrations of the V Ga -containing defects, respectively. Then, the concentration of the V Ga -containing defects, c V , can be found as Oila et al (2001), Reurings and Tuomisto (2007), and Saarinen et al, (1997Saarinen et al, ( , 1998 …”