We compare the nature of the band bending under GaAs surfaces prepared by alkaline sulfides lsqb;Na2Ssdot;9H2O, (NH4)2Srsqb; with that under oxidized GaAs surfaces. We make the point that Fermi level pinning implies band bending, but band bending does not necessarily imply lsquo;lsquo;pinning.rsquo;rsquo; In either case, even weak light illumination substantially flattens the bands. On ammonium sulfide treated surfaces the fixed and trapped charge density in the dark is only sim;5times;1011electrons/cm2, but these few states are mostly neutralized at lowhyphen;level forward injection. This behavior should not be confused with Fermi level pinning.
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