Surface photovoltage measured capacitance: Application to semiconductor/electrolyte system

Abstract

Surface photovoltage measured capacitance (SPMC), a novel technique for determining the properties of semiconducting materials, is introduced. SPMC permits the determination of a semiconductor depletion layer capacitance by measuring changes of the surface potential barrier induced by low intensity chopped light whose photon energy exceeds the band-gap energy. The theory of the SPMC technique is derived, and an equivalent circuit for analyzing the measurements is described. The present technique is compared with the conventional current measured capacitance method, and it is shown that using SPMC the separation of the depletion layer capacitance from the influence of the surface states can be performed by measurements at only one frequency of light modulation. This is a simpler procedure than the frequency dispersion measurement required of conventional capacitance techniques. Measurements of the capacitance-voltage characteristics of a semiconductor/electrolyte system, in particular n-type WS2 exposed to an inert electrolyte, are used as examples to illustrate the capabilities of SPMC.