Photoconductivity of thin epitaxial lead-selenide films

The slow component of the photoconductivity signal with a strong dependence of the relaxation time on the temperature, the photon energy, and the excitation intensity has been observed in the epitaxial layers of n- and p-type PbSe/BaF2 of thickness in the range 0.5-2 mu m. When the photon energy is more than twice as large as the band gap, the photoresponse signal reverses sign and the lifetime of the carriers increases. The effect can be explained in terms of the capture of nonequilibrium carriers, which account for the pinning of the Fermi level at the semiconductor surface, into the surface states with a density on the order of 10(13) cm(-2). The effect can also be explained in terms of the spatial separation of the carriers in the region of band bending near the surface. (C) 1996 American Institute of Physics.