Metal–insulator transition in Si/SiGe heterostructures: mobility, spin polarization and Dingle temperature

Abstract

For zero temperature we calculate the mobility of the two-dimensional electron gas in Si/SiGe heterostructures for charged-impurity scattering and interface-roughness scattering. Multiple-scattering effects lead to a metal–insulator transition (MIT) at low electron density, in agreement with experiment. Comparing the electron density dependence of the calculated mobility with experimental data of a recently developed insulator-gate field-effect transistor we conclude that (i) many remote charged impurities are present at the SiGe/Al2O3 interface (zi = 490 Å) and (ii) interface-roughness scattering (Λ ≈ 100 Å) is important at higher electron density or (iii) few nearby charged impurities are present at the Si/SiGe interface (zi = 0 Å). We calculate the mobility of the fully spin-polarized electron gas and compare the critical densities of the MIT of the non-polarized and the fully spin-polarized electron gas. The Dingle temperature (single-particle scattering time) is discussed. The temperature dependence of the mobility is also considered.