Effect of buffer layer preparation on GaN epilayers grown by gas-source molecular-beam epitaxy

Using gas-source molecular-beam epitaxy, and ammonia as a source of nitroge n, we have investigated the effect of buffer layer preparation on the elect rical and optical properties of GaN epilayers. It is found that the buffer layer thickness and buffer anneal time have a dramatic effect on the Hall m obility and the background carrier density in the layers. With an optimized buffer layer, we have achieved mobility of similar to 190 cm(2)/V s and ha ve correlated this with a defect density as low as 2.1x10(9) cm(-2) in the best layers. The variation of the intensity of defect related lines in phot oluminescence spectra has been used to confirm the decrease of the defect d ensity with increasing mobility in these layers. (C) 2001 American Institut e of Physics.