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 × 10 ¹² to 3.0 × 10 ¹² cm ^-2 and a peak mobility of 80 000 cm ²/V s. Between 20 and 50 K we observe a linear dependence μ _zc ^-1 = αT, indicating that acoustic phonon scattering dominates the temperature dependence of the mobility, with a 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 = 12-15 eV.