UNDERGRADUATE LABORATORY EXPERIMENT - MEASUREMENT OF THE COMPLEX REFRACTIVE-INDEX AND THE BAND-GAP OF A THIN-FILM SEMICONDUCTOR

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-alpha. An energy dependence analysis of a 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.