MONTE-CARLO CALCULATION OF STRAINED AND UNSTRAINED ELECTRON MOBILITIES IN SI1-XGEX USING AN IMPROVED IONIZED-IMPURITY MODEL

An improved Monte Carlo (MC) model for ionized impurity scattering developed in a previous work [L. E. Kay and T.-W. Tang, J. Appl. Phys. 70 1475 (1991)] is used to perform a comprehensive study of majority- and minority-electron mobilities in the Si1-xGe(x) material system for both strained and unstrained cases. This investigation includes calculation of low-field mobilities for wide ranges of doping and Ge mole fraction at both 300 and 77 K as well as high-field studies. A significant improvement in mobility (up to 50%) is observed for transport perpendicular to the growth plane in strained Si1-xGe(x) as compared to the unstrained case. The magnitude of the improvement is dependent on doping (both concentration and type) and germanium content, and is somewhat larger at 77 K. High-field MC simulations show that some strained-mobility enhancement remains even at an electric field of 100 kV/cm. These studies also suggest there is a temperature-dependent Ge content for which mobility is maximized at higher dopings.