Enhanced Carrier Lifetimes and Suppression of Midgap States in GaAs at a Magnetic Metal Interface

We report the first measurement of room temperature carrier lifetimes at a magnetic metal--semiconductor interface, $\mathrm{Fe}/\mathrm{GaAs}(001)\ensuremath{-}(2\ifmmode\times\else\texttimes\fi{}4)$. The lifetimes are significantly enhanced relative to uncoated or sulfur-passivated surfaces, or the $\mathrm{Al}/\mathrm{GaAs}(001)\ensuremath{-}(2\ifmmode\times\else\texttimes\fi{}4)$ interface. These enhanced lifetimes correlate with a corresponding decrease in the density of midgap states which otherwise dominate the character of the GaAs(001) surface. The epitaxial Fe film provides both a ferromagnetic contact and a superior surface-passivating layer which does not pin the Fermi energy.