Impact of defects on the carrier transport in GaN

GaN layers are found to be highly resistive when grown by molecular beam epitaxy (MBE) using an electron cyclotron resonance (ECR) plasma source. These samples are investigated by Hall effect measurements to gain an insight into the conduction mechanism. Both the carrier concentration and the mobility are found to depend exponentially on the temperature which is attributed to potential barriers caused by electron traps at grain boundaries. A theoretical model developed for polycrystalline 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 exhibits a maximum at the same value. The trap energy and grain size are estimated to be 0.31 eV and 10 to 100 nm, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.