Influence of sapphire nitridation on properties of gallium nitride grown by metalorganic chemical vapor deposition

The properties of 1.2 mu m thick GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The different nitridation schemes of sapphire strongly affect the dislocation structure of GaN films resulting in a decrease of the dislocation density from 2x10(10) to 4x10(8) cm(-2) for shorter NH3 preflow times. Room- and low-temperature electron transport characteristics of these films are specifically affected by the dislocation structure. A 300 K electron mobility as high as 592 cm(2)/V s was obtained for a short ammonia preflow whereas a long nitridation caused the mobility to drop to 149 cm(2)/V s. Additionally, the photoluminescence quality deteriorates for samples with a long sapphire nitridation time. (C) 1996 American Institute of Physics.