GaP photovoltage transients

Abstract

The photovoltage transients of GaP were examined with the retarding-potential electron-beam technique. Systematic changes in the signal size and shape were noted as the light intensity, chopping frequency, and wavelength were independently varied. The initial rise in the photovoltage signal was linear in light intensity and the maximum signal depended logarithmically on light intensity. The signals decreased in magnitude as chopping frequency was increased. The time dependence of the transients could be described as the difference between two exponential terms. The photovoltage signal was a maximum at 2.82 eV, which corresponds to the lowest-energy direct optical transition. A simple theoretical model which involves the absolute trapping of electrons at the surface is proposed which can account for the observed experimental results.