Scattering lifetimes due to interface roughness with large lateral correlation length in Al_xGa_1-xN/GaN two-dimensional electron gas

Al_xGa_1-xN/GaN two-dimensional electron gas structures have been grown by molecular-beam epitaxy and exhibited surface roughness defined by the faceted surface morphology of the crystal grains or subgrains, with the grain size being the obvious lateral periodicity. The roughness amplitude varied in a wide range depending on the substrate type and growth conditions. The effect of interface roughness with lateral correlation length of the order of the grain sizes (0.1-1 μm) on the scattering lifetimes is calculated theoretically and compared with experimentally observed lifetime values. We conclude that scattering by long-range interface roughness has little impact on the transport lifetime, but competes with other scattering mechanisms to be the dominant source of small-angle scattering that limits the quantum scattering lifetime.