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 ammoni a, chlorinated gallium and nitrogen carrier gas. Chlorinated Ga and NH3 wer e used to grow GaN-buffer layers at a temperature range of 550-650 degrees C for 1 to 7 min. The main growth of approximately 30 mu m thick GaN film w as performed at 1125 degrees C for 30 min. Surface roughness after the low temperature buffer growth was measured by atomic force microscopy (AFM), an d its effect on thick GaN film was characterized by double crystal X-ray di ffractometry (DCXRD) and electron microscopy techniques (SEM and TEM). Dire ct correlation between AFM roughness (in terms of the RMS value) of the buf fer layer surface and crystalline quality of the GaN film was observed. It is suggested that the smooth surface of low temperature grown GaN is critic al in obtaining good quality GaN film in HVPE. (C) 1999 Elsevier Science S. A. All rights reserved.