Modeling of optical and electrical behavior of semiconducting thin films: Application to sprayed CdS on transparent substrates

Abstract

Both the optical absorption coefficient α, and the carrier density N, of semiconducting thin films are analytically investigated in relation with their deposition substrate influence. It is shown that these two properties are sensitive to the film thickness d, particularly when incident monochromatic light is very close to the film transmission cutoff wavelength. α behaves according to the α≊f(d−1) type of function while N obeys the law N≊f(d−m) whose precise form varies with m value and depends on the substrate influence. Experimental results report on sprayed CdS films respectively deposited on glass, SnO2, and ITO substrates which illustrate the suitability of the model proposed. The film absorption coefficient is affected by the migration phenomenon at the film-substrate interface, the rate of the migration depending upon the substrate involved. m≊1 obtained with SnO2 and m≊2 with ITO indicate different CdS film interface properties, typical of the substrate used.