Long-lived Coulomb gap in a compensated semiconductor<i>—</i>the electron glass

Abstract

We have studied the injection of excess charge into the lightly p-doped compensated GaAs semiconductor layer of a metal-insulator-semiconductor heterostructure. Below a few Kelvin, the length over which excess carriers screen an applied voltage step grows dramatically as the step size is decreased. This nonlinear screening reflects the reduced density of states near the Fermi level caused by electron-electron interactions (the Coulomb gap). The nonlinearities persist for minutes or longer, demonstrating the existence of an electron-glass regime.