Theoretical hole mobility in a narrow Si/SiGe quantum well.

Abstract

Calculations of the hole mobility in a strained SiGe quantum well on (001) Si are carried out for the case of a narrow well in which the subband splittings are large due to quantum-size effects. An envelope-function model for the valence-band structure and hole wave functions in an infinite square well and calculations of scattering rates in a single parabolic band with an isotropic effective mass are used to delineate limitations on mobility imposed by lattice scattering, background impurities, alloy scattering, and interface roughness. Additional scattering mechanisms associated with compositional fluctuations in the SiGe layer are also discussed. Narrow wells (60 \AA{}) with high Ge content (40%) have large subband splittings and exhibit a light mass for hole densities well beyond ${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. Scattering rates in such structures are greatly reduced as a result of the light mass and large subband splittings. Numerical results indicate that hole mobilities in the mid ${10}^{3}$ ${\mathrm{cm}}^{2}$/V s at room temperature and in the mid ${10}^{4}$ ${\mathrm{cm}}^{2}$/V s at low temperature could be possible in narrow SiGe wells as a result of the favorable modifications in band structure and scattering.