PHOTOCONDUCTIVITY OF THIN EPITAXIAL LEAD-SELENIDE FILMS

The slow component of the photoconductivity signal with a strong depen dence of the relaxation time on the temperature, the photon energy, an d the excitation intensity has been observed in the epitaxial layers o f n- and p-type PbSe/BaF2 of thickness in the range 0.5-2 mu m. When t he photon energy is more than twice as large as the band gap, the phot oresponse signal reverses sign and the lifetime of the carriers increa ses. The effect can be explained in terms of the capture of nonequilib rium 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 t he spatial separation of the carriers in the region of band bending ne ar the surface. (C) 1996 American Institute of Physics.