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

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 $T_0\propto |n_c-n_s{|}^{z\nu }$ where $z\nu =1.6\mathrm{}\pm 0.2,$ $n_c$ 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.