Coverage Dependent Surface Photovoltage Induced by Synchrotron Radiation at Metal/GaAs Interfaces

Contact potential difference measurements of synchrotron radiation-induced surface photovoltage (SPV) are performed on GaAs(110) as a function of metal coverage and temperature. On low doped n-samples, the low temperature SPV (0.55 eV) is almost equal to the total band bending at submonolayer coverage and discharges with a time constant of hours. Above a monolayer, the rate of discharging increases dramatically, emphasizing the role of charge leakage through the overlayer. The room temperature SPV is considerably smaller (0.2 eV) and its coverage dependence does not correlate with that of band bending. A metal-dependent enhancement of SPV is found. No significant SPV is detected on highly doped p-GaAs.