Photovoltaic Effect in GaS and GaSe Crystals

Evidence of photovoltaic effect in highly resistive GaS and GaSe is reported. In both semiconductors a saturation vs. light intensity at relatively low levels of illumination and a polarity inversion for h v < Eg are observed. The characteristics of the photovoltage may be explained assuming that barriers are formed at the contacts by surface states. This is also supported by a quenching of the photovoltage observed by irradiation of the samples with two different wavelengths. Peaks are present in the spectral response at energies corresponding to transitions at higher critical points.