Characterization of vacancy-typedefects in heteroepitaxial GaN grown by Low-Energy Plasma-Enhanced VaporPhase Epitaxy

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 has been given to the new low energy plasma enhanced vapor phase epitaxy (LEPEVPE) growth technique. A very high Ga vacancy density (10^19 cm^-3) 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) is used as a template for LEPEVPE deposition, the vacancy density of the film is low (about 10^16 cm^-3). This fact provides evidences that the LEPEVPE technique is able to produce high quality GaN layers.