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

We report on the temperature dependence of the mobility of the two-dimensional electron gas in a variable density AlGaN/GaN field effect transistor, with carrier densities ranging from 0.4x1012cm-2 to 3.0x1012cm-2 and a peak mobility of 80,000cm2/Vs. Between 20K and 50K we observe a linear dependence (mobility)^- 1=alpha*T indicating that acoustic phonon scattering dominates the temperature dependence of the mobility, with alpha 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 which account for thermal broadening and the temperature dependence of the electron screening. Our data imply a deformation potential D=12-15 eV.