Mobility enhancement and temperature dependence in top-gated single-layer MoS2

The deposition of a high-kappa oxide overlayer is known to significantly enhance the room-temperature electron mobility in single-layer MoS2 (SLM) but not in single-layer graphene. We give a quantitative account of how this mobility enhancement is due to the nondegeneracy of the two-dimensional electron gas system in SLM at accessible temperatures. Using our charged impurity scattering model [Ong and Fischetti, Phys. Rev. B 86, 121409 (2012)] and temperature-dependent polarizability, we calculate the charged impurity-limited mobility (similar to imp) in SLM with and without a high-kappa (HfO2) top-gate oxide at different electron densities and temperatures. We find that the mobility enhancement is larger at low electron densities and high temperatures because of finite-temperature screening, thus explaining the enhancement of the mobility observed at room temperature. similar to imp is shown to decrease significantly with increasing temperature, suggesting that the strong temperature dependence of measured mobilities should not be interpreted as being solely due to inelastic scattering with phonons. We also reproduce the recently seen experimental trend in which the temperature scaling exponent (gamma) of mu(imp).proportional to T -gamma is smaller in top-gated SLMthan in bare SLM. Finally, we showthat similar to 37% mobility enhancement can be achieved by reducing the HfO2 thickness from 20 to 2 nm.