Scaling and the metal-insulator transition in Si/SiGe quantum wells

Abstract

The existence of a metal-insulator transition at zero magnetic field in two-dimensional (2D) electron systems has recently been confirmed in high-mobility Si-metal-oxide-semiconductor field-effect transistors. In this work, the temperature dependence of the resistivity of gated Si/SiGe/Si quantum-well structures has revealed a similar metal-insulator transition as a function of carrier density at zero magnetic field. We also report evidence for a Coulomb gap in the temperature dependence of the resistivity of the dilute 2D hole gas confined in a SiGe quantum well. In addition, the resistivity in the insulating phase scales with a single parameter ${T}_{0}\ensuremath{\propto}|{n}_{c}\ensuremath{-}{n}_{s}{|}^{z\ensuremath{\nu}}$ where $z\ensuremath{\nu}=1.6\ifmmode\pm\else\textpm\fi{}0.2,$ ${n}_{c}$ is the critical carrier density, and ${n}_{s}$ is the 2D carrier density. This dependence is sample independent. These results are consistent with the occurrence of a metal-insulator transition at zero magnetic field in SiGe square quantum wells driven by strong hole-hole interactions.