Subband structure and mobility of two-dimensional holes in strained Si/SiGe MOSFET’s

The hole mobility of $p$-type strained Si metal-oxide-semiconductor field-effect transistors (MOSFET’s) fabricated on a SiGe substrate is investigated theoretically and compared with the mobility of conventional (unstrained) Si $p$-MOSFET’s. Two-dimensional quantization of the holes is taken into account in terms of a self-consistent six-band $\mathbf{k}\mathbf{\cdot }\mathbf{p}$ model for the strained band structure and the confined hole subband states in the inversion channel. The hole dynamics along the inversion channel is studied in terms of ensemble Monte Carlo calculations that take into account all relevant scattering mechanisms. For a Ge concentration of $30\%$ in the substrate, we predict a mobility enhancement of a factor of 2.3 compared to the unstrained $p$-type device. The calculated low-field mobility is in excellent agreement with experimental data for strained ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{0.8}{\mathrm{Ge}}_{0.2}$ and for unstrained Si $p$-MOSFET’s.