Effective mass and mobility of holes in strained Si1-xGex layers on (001) Si1-yGey substrate

The directional density-of-state effective masses of the valence bands of a strained Si_1-xGe_x layer for the (001) growth direction are calculated using k×p and strain Hamiltonians. The mobilities are then calculated as functions of temperature and doping concentration for various Ge contents using the relaxation time approximation and the known valence-band structure. The nonparabolicity and warped nature of the valence bands are included in the mobility calculation. Under the biaxial strain present in the film, all the directional effective masses except the longitudinal heavy hole mass at the Γ point are shown to be strongly affected by the strain. Comparatively, the strain effect becomes weak for large k values. The mobility of the strained layer becomes anisotropic under strain. Both the longitudinal and the transverse mobilities are higher than that of the relaxed alloy with the same Ge content