Study on the Variation of Surface Morphology and Residual Stress Under Various Thermal Annealing Conditions with Bulk GaN Substrates Grown by HVPE

We investigated the effects of different thermal treatment conditions on the surface and internal residual strains of bulk GaN grown by hydride vapor phase epitaxy (HVPE). Thermal annealing was performed at 700-1000 degrees C for 1-5 h in nitrogen atmosphere. The GaN was characterized by atomic force microscopy, energy dispersive spectrometry, X-ray photoelectron spectroscopy, Raman spectroscopy, and by high-resolution X-ray diffractometer. The experimental results demonstrated that thermal decomposition and oxidation occurred on the surface of GaN when exposed to heat over a long time, or even at a low temperature, as compared to thermal decomposition of GaN in ambient nitrogen. The internal residual stress of GaN was relaxed most effectively when annealing at 900 degrees C for 3 h, and it was confirmed that the crystal quality is best under this condition. We also confirmed that the effect of annealing was extremely beneficial because native oxide impurities were removed most effectively in this condition. However, Ga metal or oxide could formed due to the occurrence of slight thermal decomposition on the surface. [GRAPHICS] .