High mobility electron gases in Si/Si0.77Ge0.23 quantum wells at 1.7 K.

Abstract

Calculations have been carried out to investigate the factors which limit the low temperature, low field mobilities of two dimensional electron gases formed in the X2-valley quantum wells of tensile strained Si/Si0.77Ge0.23 modulation doped structures. The electronic charge density in the system has been solved in conjunction with Poisson's equation to derive a self-consistent solution for the bound sheet charge density. Details of the self-consistent ground state wavefunction are fed into a simple calculation to derive the low field drift mobility. Remote ionized donor impurities in the supply layer and roughness at the SiGe spacer/Si well interface are found to be the main sources of electron scattering in the case of high mobility gases grown on SiGe virtual substrates at 800 °C. The comparatively poor electron mobilities observed for experimental samples produced at the lower growth temperature of 600 °C show an inverse square law dependence of mobility on sheet carrier density, the characteristic for roughness scattering.