Synthesis of Single Crystal Gallium Nitride Films on Sapphire by Pulsed Laser Deposition

Pulsed laser deposition has been explored to synthesize gallium nitride films on c-plane sapphire by ablating a pressed GaN target in vacuum. The films were characterized by X-ray diffraction, and high resolution transmission electron microscopy to study the nature of epitaxy, growth, and defect content. Single crystal films with narrow o0-rocking curve width were deposited in the substrate temperature range 700-780°C. High resolution microscopy revealed uniform film surface at lower substrate temperature for films as thin as 150 nm. The predominant extended defects were found to be threading edge dislocations (Burgers vector 1/3<1120>) with the density ~1010 cm-2. The thickness of all these films were in the range 100-150 nm. The coexistence of zincblende phase of GaN alongwith wurtzite phase was found in the film deposited at 780°C. The stabilization of metastable zincblende phase at higher temperature point towards the noneqilibrium nature of laser ablation. These preliminary results indicate the potential of PLD to synthesize high quality GaN films free of hydrogen.