Effect of annealing conditions on the optical properties and surface morphologies of ((2)over-bar 0 1)-oriented -Ga₂O₃ crystals

The bulk properties of beta-Ga2O3 are sensitive to temperature and atmosphere; therefore, suitable annealing conditions are required. This study was performed to investigate the effects of annealing conditions on the ((2) over bar 0 1) surface of beta-Ga2O3 crystal using atomic force microscopy, optical transmission/ luminescence spectroscopy, and X-ray photoelectron spectroscopy. Annealing was performed in air and in evacuated glass capsules at different temperatures. After annealing at 900 degrees C in air, the sample became a colorless insulator, and faceting was observed. On the other hand, sample decomposition was observed after annealing in the evacuated capsules. While, after annealing at 300 degrees C in air, step-terrace formation was observed. With increase of the annealing temperature, faceting was observed after annealing at 600 degrees C exposing the (1 0 0) and (0 0 1) surfaces. These results demonstrate the need for optimized annealing conditions for different surface orientations to obtain desirable beta-Ga2O3 surfaces for heterointerfaces.