The defect concentration in thin GaN layers was estimated by means of positron annihilation spectroscopy. Positron lifetime and Doppler broadening of the annihilation radiation were used. A comparative study of GaN films grown with different techniques was performed. Specific attention was given to the new low-energy plasma enhanced vapour phase epitaxy (LEPEVPE) growth technique. A very high Ga vacancy density (1019/cm3) was found in a thin GaN layer directly grown by LEPEVPE on a sapphire substrate. However, when a GaN substrate (commercial sample grown by metal organic vapor phase epitaxy) was used as a template for LEPEVPE deposition, the vacancy density of the film was low (about 1016/cm3). This fact provides evidences that the LEPEVPE technique was able to produce high quality GaN layers.

Characterization of Vacancy-Type Defects in Heteroepitaxial GaN Grown by Low-Energy Plasma-Enhanced Vapor Phase Epitaxy. A.Calloni, R.Ferragut, A.Dupasquier, H.von Känel, A.Guiller, A.Rutz, L.Ravelli, W.Egger: Journal of Applied Physics, 2012, 112[2], 024510