Optical investigation of the electrical properties of a polycrystalline–semiconductor–electrolyte interface using electroreflectance

Abstract

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.