Unpinned (100) GaAs surfaces in air using photochemistry

We have unpinned the Fermi level at the surface of both n- and p-type (100) GaAs in air. Light-induced photochemistry between GaAs and water unpins the surface Fermi level by reducing the surface state density. Excitation photoluminescence spectroscopy shows a substantial decrease in both surface band bending and surface recombination velocity in treated samples, consistent with a greatly reduced surface state density (≅1011 cm-2). Capacitance-voltage measurements on metal-insulator-semiconductor structures corroborate this reduction in surface state density and show that the band bending may be controlled externally, indicating an unpinned Fermi level at the insulator/GaAs interface. We discuss a possible unpinning mechanism.