Dong-Sing Wuu, Ray-Hua Horng, Wei-Hao Tseng and Wei-Tsung Lin

Institute of Electrical Engineering, Da-Yeh University, Chang-Hwa, Taiwan 515, ROC

The behavior and role of a GaN buffer layer has been investigated using a specially designed two-flow horizontal metalorganic chemical vapor deposition. In this reactor, the NH₃ (mixed with N₂) and carrier gas are supplied separately using the upper-flow and lower-flow lines. The two-flow design is used to prevent the pre-reaction for the reactive gases, and to prevent NH₃ decomposing H₂ and N₂ at high temperature directly with increasing the N₂ gas in the reactor. It is demonstrated that GaN with improved crystal quality can be obtained by a two-step growth process consisting of the growth of a thick GaN layer (T_s=1050° C) on a thin low-temperature GaN buffer layer (T_s=550° C). Results will be discussed in terms of a change in growth mode induced by the surface roughness.