Monte Carlo simulations of hole transport in SiGe and Ge quantum wells

Abstract

Monte Carlo simulations have been carried out to investigate factors which influence hole transport at 300 K for moderate electric fields .104–106 V m−1/ within compressively strained Si1−xGex .x D 0:15 ! 0:30/ quantum wells deposited on Si. Drift mobilities in the range 900–1200 cm2 V−1 s−1 have been calculated for pseudomorphic structures with well widths 60 ! 110 Å, and trends in the mobility have been identified. SiGe alloy disorder and interface roughness are the main factors which limit the mobility; inelastic LO phonon scattering is less significant owing to the large phonon energy 60 MeV and hence comparatively large threshold carrier wavevector for the onset of scattering. The mobility in SiGe is compared with that simulated for an experimental Ge=Ge0:7Si0:3 structure. The simulated drift mobility ratio for Ge/GeSi versus SiGe/Si is 10:1, a result which is consistent with recent measurements. There are two main reasons for this—a comparatively low in-plane heavy hole effective mass and significantly reduced alloy scattering. This is despite greater surface roughness derived from the reported experimental data.