Undergraduate laboratory experiment: Measurement of the complex refractive index and the band gap of a thin film semiconductor

Abstract

A simple experiment to determine the complex refractive index of a semiconductor in thin film form through transmittance measurements is presented. The experiment allows us to obtain, from the real part of the refractive index, the n dispersive law, and from the imaginary part, the absorption coefficient α. An energy dependence analysis of α is done to obtain the semiconductor band gap value and the nature of the optical transition (direct or indirect). Transmittance data of a CdS thin semiconductor film have been analyzed, and a value for the real part of the refractive index, which is very similar to the bulk value, has been obtained. Also, from the absorption coefficient a band gap value of (2.33±0.02) eV for CdS is deduced, in agreement with previously published values.