Abstract

GaAs surfaces routinely exhibit mid-gap Fermi-level pinning, where regardless of doping level or type, the surface Fermi-level lies about 0.8eV below the conduction-band edge. Until recently, unpinned GaAs has only been observed in certain electrolytes, at high-quality hetero junction interfaces, or in vacuum on cleaved (110) surfaces. Our group reported recently that (100) GaAs could be unpinned photochemically by spraying deionized water on a laser-illuminated sample that was mounted on a spin-coater typically used for photoresist. The response of band-edge photoluminescence to changes in excitation wavelength was used to measure the surface Fermi-level position. Both n- and p-type material responded to this treatment, showing that the Fermi-level was in fact unpinned and not simply repinned close to one band edge. Hg/PMMA/GaAs capacitors on unpinned surfaces showed control of the surface Fermi-level.

© 1987 Optical Society of America