Metal-insulator transition at $B=0\mathrm{}$ in $p$-type SiGe

Observations are reported of a metal-insulator transition in a two-dimensional hole gas in asymmetrically doped strained SiGe quantum wells. The metallic phase, which appears at low temperatures in these high-mobility samples, is characterized by a resistivity that decreases exponentially with decreasing temperature. This behavior, and the duality between resistivity and conductivity on the two sides of the transition are very similar to that recently reported for high-mobility Si metal-oxide-semiconductor field-effect transistors.