Molecular beam epitaxy growth and characterization of GaN and AlxGa1−xN on 6H-SiC

Abstract

We have investigated the growth of undoped and doped GaN and AlGaN films on both on-axis and 3.5° off-axis 6H-SiC substrates. Scanning electron microscopy showed that the films were smooth and crack free. The typical x-ray rocking curve half-width of the GaN (0002) peak using Cu Kα x rays was found to be between 9 and 15 arcmin for a 1 μm film. The crystalline quality improved with increasing thickness. The best films were obtained at the highest growth temperature (800 °C) with a 40–50 nm AlN buffer layer grown at the same temperature. The n-type doping up to 4.0×1020 cm3 was accomplished with silicon, with a 40%–50% activation rate. A calibration curve correlating the n-type carrier concentration in the film with the Si effusion cell temperature was established. The undoped AlxGa1−xN film (x≊0.1) was found to be n type, with a carrier concentration of 7.0×1018/cm3.