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 significan tly influenced by the duration of exposing the sapphire substrate to a mmonia prior to the GaN growth initiation. The different nitridation s chemes of sapphire strongly affect the dislocation structure of GaN fi lms resulting in a decrease of the dislocation density from 2x10(10) t o 4x10(8) cm(-2) for shorter NH3 preflow times. Room- and low-temperat ure electron transport characteristics of these films are specifically affected by the dislocation structure. A 300 K electron mobility as h igh 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. Addit ionally, the photoluminescence quality deteriorates for samples with a long sapphire nitridation time. (C) 1996 American Institute of Physic s.