Low temperature buffer growth to improve hydride vapor phase epitaxy of GaN

Two-step growth of hydride vapor phase epitaxy (HVPE) was optimized to grow high-quality, thick GaN film on the (0001) sapphire substrate using ammonia, chlorinated gallium and nitrogen carrier gas. Chlorinated Ga and NH3 were used to grow GaN-buffer layers at a temperature range of 550–650°C for 1 to 7 min. The main growth of approximately 30 μm thick GaN film was performed at 1125°C for 30 min. Surface roughness after the low temperature buffer growth was measured by atomic force microscopy (AFM), and its effect on thick GaN film was characterized by double crystal X-ray diffractometry (DCXRD) and electron microscopy techniques (SEM and TEM). Direct correlation between AFM roughness (in terms of the RMS value) of the buffer layer surface and crystalline quality of the GaN film was observed. It is suggested that the smooth surface of low temperature grown GaN is critical in obtaining good quality GaN film in HVPE.