Characterization of vacancy-type defects in heteroepitaxial GaN grown by low-energy plasma-enhanced vapor phase 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 (10¹⁹ 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 10¹⁶ cm⁻³). This fact provides evidences that the LEPEVPE technique is able to produce high quality GaN layers.