We have utilized both photoluminescence (PL) and Raman spectroscopy to nondestructively study the surface of polycrystalline electrodeposited CdSe photoelectrodes as a function of surface preparation and aging procedures. The excitation energy dependence of the PL efficiency at 77 K, which depends on surface band bending, is consistent with increased concentration of shallow levels in electrodeposited CdSe compared with single crystal material. No PL was observed for unannealed CdSe films; for annealed, unaged films the spectra at 77 K were qualitatively similar to those of single crystals in that spectral features could be identified with the A exciton at 1.815 eV and with a donor-acceptor-pair band at 1.70 eV exhibiting phonon replicas. The PL and Raman spectra of light-aged electrodes exhibit features which we identify with the formation of a surface layer of CdS and the presence of mixed compounds CdSxSe1−x, which are formed by chemical exchange with the polysulfide electrolyte during light-induced aging. The PL spectra at 4.2 K for the unaged and dark-aged electrodes exhibit sharp lines in the vicinity of 1.81 eV which we identify as due to bound-exciton recombination, but which differ in energy from those exhibited by the light-aged film.

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We have investigated the low-field electrolyte electroreflectance (EER) spectra of polycrystalline electrodeposited N–CdSe in the vicinity of the Eo(A,B) transitions (direct gap at ? = 0). Utilizing the properties of low-field EER, we have studied the distribution of the applied ac voltage in situ in the photoelectrochemical solar cell configuration: (1) By measuring the in-phase and quadrature EER signals as a function of modulation frequency f, we have determined the electrical impedance Z(f) of the interface for 10 Hz<f<10 kHz, at the focus of the incident light. These results are in substantial agreement with direct electrical measurements. (2) By measuring the EER amplitude as a function of applied dc bias voltage, we have found evidence for surface states which contribute to Fermi level pinning; similar evidence was not observed for single-crystal CdSe. These techniques are of general applicability for other semiconductor interfaces with optically transparent junctions, and are well suited to topographical scanning.