Acoustic phonon scattering in a low density, high mobility AlGaN∕GaN field-effect transistor

We report on the temperature dependence of the mobility μ of the two-dimensional (2D) electron gas in a variable density AlGaN∕GaN field-effect transistor, with carrier densities ranging from 0.4×1012to3.0×1012cm−2 and a peak mobility of 80000cm2∕Vs. Between 20 and 50K we observe a linear dependence μac−1=αT, indicating that acoustic phonon scattering dominates the temperature dependence of the mobility, with α being a monotonically increasing function of decreasing 2D electron density. This behavior is contrary to predictions of scattering in a degenerate electron gas, but consistent with calculations that account for thermal broadening and the temperature dependence of the electron screening. Our data imply a deformation potential D=12–15eV.