IMPACT OF DEFECTS ON THE CARRIER TRANSPORT IN GAN

GaN layers are found to be highly resistive when grown by molecular be am epitaxy (MBE) using an electron cyclotron resonance (ECR) plasma so urce. These samples are investigated by Hall effect measurements to ga in an insight into the conduction mechanism. Both the carrier concentr ation and the mobility are found to depend exponentially on the temper ature which is attributed to potential barriers caused by electron tra ps at grain boundaries. A theoretical model developed for polycrystall ine materials is found to excellently describe the data. The mobility shows a pronounced minimum at a room temperature carrier concentration of 2 x: 10(16) cm(-3), whereas the height of the potential barriers e xhibits a maximum at the same value. The trap energy and grain size ar e estimated to be 0.31 eV and 10 to 100 nm, respectively. (C) 1998 Els evier Science B.V. All rights reserved.