Theoretical Electron Mobility Analysis in Thin-Body FETs: Dependence on Substrate Orientation and Biaxial Strain

Results of recent mobility measurements in ultrathin-body FETs are analyzed theoretically for different substrate orientations. A Monte Carlo method incorporating the degenerate statistics exactly is used for calculations of the mobility. Due to volume inversion, the mobility in double-gate ultrathin-body (110) FETs is enhanced in comparison with the mobility of single-gate structures, in the whole range carrier concentrations. In contrast, the mobility in a double-gate (100) 3 nm thick structure plotted as a function of the carrier concentration per channel sinks below the single-gate mobility value for high effective fields. It is shown that degeneracy effects play a crucial role in mobility degradation for (100) double-gate FETs, as they lead to the opening of additional intersubband scattering channels. Biaxial strain has little influence on the mobility of ultrathin-body FETs. Simulation results are in good agreement with recent mobility measurements