Surface morphology and optical property of thermally annealed GaN substrates

Boule of GaN crystal was grown with 50 mm diameter and 3 mm thickness by hydride vapor phase epitaxy and cut using a wire saw to produce freestanding wafers. These were, mechanically polished with diamond slurry and followed with chemical mechanical polishing for final surface preparation. Surface morphology was examined by non-contact mode atomic force microscopy before and after thermal annealing process performed at 700, 800, 900, and 1000 °C for 1 h, in air. Wafers with optimum surface quality submitted to thermal annealing treatment at 900 °C were characterized by reduced scratched density and residual stress, and surface roughness of 0.096 nm. Surface quality improvement was confirmed by relatively large recovery of the room temperature near band edge luminescence intensity.