Hole Mobility in Germanium as a Function of Substrate and Channel Orientation, Strain, Doping, and Temperature

We present a comprehensive study of hole transport in germanium layers on “virtual” substrates using a full band Monte Carlo simulation approach, considering alternate “virtual” substrate and channel orientations and including the impact of the corresponding biaxial strain, doping, and lattice temperature. The superior mobility in strained germanium channels with orientation on a (110) “virtual” substrate is confirmed, and the factors leading to this enhancement are evaluated. The significant decrease in strain-and-orientation-induced mobility enhancement due to impurity scattering in doped material and at increasing lattice temperature is also demonstrated. Both factors determine how efficiently the mobility enhancement translates into transistor performance enhancement. Additionally, we shine light on the question of which factor has stronger impact in mediating the increase in mobility due to strain-the breaking of degeneracy for the heavy- and light-hole bands at the point or the reduction in the density of states.