High-mobility and dilute two-dimensional electron systems exhibit metallic behavior down to the lowest experimental temperatures. In studies of ionic liquid gated insulating silicon, we have observed transitions to a metallic state in low-mobility samples at much higher areal carrier densities than found for samples of high mobility. We have also observed a mobility peak in metallic samples as the carrier density was increased beyond ${10}^{13}{\text{cm}}^{-2}$.

• Received 17 November 2014
• Revised 13 April 2015
• Publisher error corrected 19 June 2015

DOI:https://doi.org/10.1103/PhysRevB.91.241304