Subband structure and transport properties of two-dimensional electron gas in AlxGa1-xN/GaN heterostructures

We report on Hall mobility and Shubnikov-de Haas (SdH) measurements of the two dimensional electron gas (2DEG) formed in a series of AlxGa1-xN/GaN heterostructures with different Al composition grown on sapphire substrates. In samples of x = 0.15 and 0.20, we found single periodical oscillations. In a sample of x = 0.30 a double periodical one was clearly resolved, which indicates that more than one subband has been occupied by electrons. Fast Fourier transform (FFT) analysis yielded information about the electron density and subband structure of the 2DEGs. The oscillatory part of the SdH signal was analyzed to extract the quantum scattering time at 4.2 K. It was found that as the increase of the At content, quantum scattering time of the ground subband decreases gradually. We attributed it to the enhanced interface roughness scattering and the onset of the inter-subband scattering in the sample with higher At content. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim