High-mobility GaN epilayer grown by RF plasma-assisted molecular beam epitaxy on intermediate-temperature GaN buffer layer

High-mobility GaN thin films were grown by RIF plasma-assisted molecular be am epitaxy on (0 0 0 1) sapphire. A conventional low-temperature buffer lay er and an intermediate-temperature buffer layer (ITBL) were first deposited before the growth of the epitaxial layer. Electron mobility is found to va ry strongly with the ITBL thickness with value as high as 460 cm(2)V(-1)S(- 1) obtained from the sample grown on a 800 nm ITBL on top of a low-temperat ure buffer layer. A systematic shift in the photoluminescence peak position , following the same trend as the mobility, suggests the relaxation of resi dual strain in the top GaN epitaxial layer by utilizing an ITBL. Detailed c haracterizations of G-R noise indicate reduction of deep levels by over an order of magnitude for the sample with 800 nm ITBL compared to the control sample which has the same total thickness but with only the low-temperature buffer layer. (C) 2001 Elsevier Science B.V. All rights reserved.