EFFECTS OF THERMAL-TREATMENT OF LOW-TEMPERATURE GAN BUFFER LAYERS ON THE QUALITY OF SUBSEQUENT GAN LAYERS

The surface morphology and crystalline quality of GaN layers grown by metalorganic chemical vapor deposition on sapphire (0001) substrates w ere investigated for various thermal treatment conditions of low-tempe rature (LT)-grown GaN buffer layers. The surface morphology and crysta lline quality of subsequently grown high-temperature (HT) GaN layers s trongly depended on thermal effects during the temperature ramping pro cess after LT growth of the buffer layers, We have found that the defe ct density and structure are affected by this temperature ramping proc ess, and that the generation of growth pits is closely related to defe cts in the HT-GaN layers, High-quality HT-GaN layers with specular sur face morphology were obtained with optimum growth and ramping conditio ns for the LT-GaN buffer layers. Furthermore, the role of thermal trea tment during the temperature ramping process was identified, and mecha nisms of nucleus formation, HT-growth initiation on the LT-GaN buffer layers, and defect formation are proposed and discussed. (C) 1997 Amer ican Institute of Physics.