Electrical properties of high quality MBE-grown GaN thin films on intermediate-temperature buffer layers

High quality GaN thin films were grown by RF-plasma assisted molecular beam epitaxy on an intermediate-temperature buffer layer (ITBL). The electrical properties of the GaN films were systematically characterized by Hall coefficients and low-frequency noise measurements. The results show a systematic change in the electrical properties, which vary as a function of the ITBL thickness. Room temperature Hall mobility increases steadily from 87 cm² V^-1 s^-1, for GaN films grown on a conventional low-temperature buffer layer (LTBL), to 390 cm² V^-1 s^-1, for a sample grown with an 800 nm-thick ITBL inserted between the LTBL and the top epitaxial layer. The Hooge parameter reaches a minimum value of 7.34×10^-2 for an optimal ITBL thickness of 800 nm. The observed improvements in the electrical properties are attributed to the relaxation of residual strain in the overgrown GaN by use of the ITBL