Characteristics of ZnO Layers Grown on GaN Template Under Argon Pressure by Pulsed Laser Deposition

Abstract

We employed epi-GaN substrates for ZnO film growth, and studied the deposition and post-annealing effects. ZnO films were grown by pulsed laser deposition (PLD) method. The as-grown films were annealed for one hour under atmospheric pressure air. We investigated ZnO morphology after annealing. The post-annealed ZnO films grown at Tg = 700 °C have very smooth surfaces and the rms roughness is about 0.5 nm. Finally, we inserted ZnO post-annealed buffer layer between ZnO epi-layer and GaN/sapphire substrates. It is confirmed by AFM that growth temperature of 700 °C helps the films grow in step-flow growth mode. It is observed by cathode luminescence spectrum that the ZnO film grown at 700 °C has very low visible luminescence, indicating the decrease of the deep level defects. It is also revealed by Hall measurements that carrier concentration is decreased by increasing the growth temperatures. Thermal treatment and post-annealed ZnO buffer layer can be used to fabricate ZnO hetero-epitaxy.