Helicity dependent temporal profile of the semiconductor thin film photoresponse

We demonstrate that the transverse photovoltage pulses generated in the thin CuSe/Se semiconductor nanocomposite film irradiated by circularly and linearly polarized femtosecond laser beams have different durations, indicating the dependence of the relaxation time of the photogenerated carriers on their spin. For the linearly polarized excitation beam, the photovoltage is a unipolar pulse that reverses polarity when the polarization azimuth changes sign, while its duration is polarization independent. For the left- and right-circularly polarized excitation beams, the photovoltage pulses are also unipolar having the same amplitude and duration but the opposite polarities. However, the temporal profile of the photoresponse changes drastically when the excitation beam is elliptically polarized. Specifically, it can be either a unipolar or bipolar pulse depending on the degree of the circular polarization of the excitation beam. We show that the observed helicity-sensitive temporal profile of the photoresponse originates from the interference of photocurrents generated in the subsurface layer of the film due to the linear and circular surface photogalvanic effects.