Charged impurity scattering in two-dimensional materials with ring-shaped valence bands: GaS, GaSe, InS, and InSe

The singular density of states and the two Fermi wave vectors resulting from a ring-shaped or "Mexican hat" valence band give rise to unique trends in the charged impurity scattering rates and charged impurity limited mobilities. Ring-shaped valence bands are common features of many monolayer and few-layer two-dimensional (2D) materials including the III-VI materials GaS, GaSe, InS, and InSe. The wave-vector dependence of the screening, calculated within the random phase approximation, is so strong that it is the dominant factor determining the overall trends of the scattering rates and mobilities with respect to temperature and hole density. Charged impurities placed on the substrate and in the 2D channel are considered. The different wave-vector dependencies of the bare Coulomb potentials alter both the magnitudes and the temperature dependencies of the mobilities. Moving the charged impurities 5 angstrom from the center of the channel to the substrate increases the mobility by an order of magnitude by suppressing the large wave-vector backscattering across the outer Fermi ring.