On the modelling of interface roughness scattering in AlGaN/GaN heterostructures

AlGaN/GaN heterostructures are attractive for high-power radiofrequency applications due to the wide bandgap of GaN and the high values of spontaneous and piezoelectric polarisation in such material systems, which lead to high breakdown voltages and high 2D carrier concentrations. It is of particular interest to accurately model the 2DEG mobilities in these structures, as different scattering mechanisms can limit the total mobility at different temperatures and carrier concentrations. In this paper, we present a semi-classical modelling framework for low-field mobility in AlGaN/GaN heterostructures, focussing especially on the impact of interface roughness (IFR) scattering on the low-temperature mobility. The framework is validated by comparing calculated mobility values with experimental data, and different ways of modelling the IFR scattering are investigated. A non-linear IFR scattering model is used to obtain the best match to measured data for different Al-contents in the AlGaN layer in case of a low potential barrier at the heterointerface, while the temperature dependence of mobility with a high potential barrier in an AlGaN/AlN/GaN system is best matched with IFR models where the squared scattering matrix elements depend linearly on the roughness power spectrum.