Low-temperature mobility of holes in Si/SiGe p-channel heterostructures

Abstract

We present a theory of the low-temperature mobility of holes in strained SiGe layers of Si/SiGe p-channel heterostructures. Our theory must not be based on the unclear concept of interface impurity charges assumed in the previous calculations, but takes adequate account of the random deformation potential and random piezoelectric field. These appear as effects arising from both lattice mismatch and interface roughness. It is proved that deformation potential scattering may be predominant over the well-known scattering mechanisms such as background doping, alloy disorder, and surface roughness for a Ge content x ≳ .0.2, while piezoelectric scattering is comparable thereto for x ≳ 0.4. Our theory turns out to be successful in providing a good quantitative explanation of recent experimental findings not only about the low value of the hole mobility but also its dependence on carrier density as well as its decrease with Ge content.