OPTICAL PARAMETER ANALYSIS OF THIN ABSORBING FILMS MEASURED BY THE PHOTOVOLTAGE METHOD

A special method for measuring the optical parameters of thin absorbing films is presented. Within the method the radiation transmitted through the layer is measured. The transmitted radiation is detected by the space charge region which is located in the substrate at the interface with the layer. The space charge region acts as a photodetector placed just behind the layer. In this paper the method is applied to characterize a system of an absorbing ZnSe film on a GaAs substrate. The values of the optical parameters of the film are evaluated. This means that the valne of the thickness and the spec- tral dependences of both the refractive index and extinction coefficient are determined. The spectral dependences of both optical constants are deter- mined in the visible range. Finally, the comparison of our results obtained by this method with the results obtained from ellipsometric and reflectance measurements is presented. PACS numbers: 78.20.Ci, 72.40.+w The optical parameters are usually measured by standard methods like re- flectance, ellipsometry and so on. The measurements can be influenced by some negative factors (e.g., roughness). In this case an alternative method of measure- ment of optical parameters is being developed. The method is based on the exis- tence of surface space charge region in the semiconductor substrate at the interface between the layer and the substrate. The space charge region acts as a photode- tector placed just behind the layer. A measure of the radiant flux passing through the layer is the photovoltage in the space charge region. The principle has beer} used to. observe exciton absorption in a superlattice (1) and has been verified for measurement of non-absorbing thin films (2). The application of this method to absorbing thin film — semiconductor substrate system measurement is described in this paper. .The application of the method to the absorbing layer is the next step to apply this method for the analysis of thin films with rough boundaries.