THE EFFECT OF THE GROWTH-PARAMETERS ON THE OPTICAL-PROPERTIES OF RF-SPUTTERED CDS FILMS

We present an experimental study of the optical properties of RF-sputtered CdS Films. A method is proposed for a fine analysis of transmission measurements, which allows one to increase the accuracy in the determination of the optical constants and thickness but also to get an order of magnitude of the film surface roughness. The effect of the plasma composition and substrate temperature on the optical properties are investigated. The introduction of hydrogen and the increase of the substrate temperature lower the absorption before the fundamental edge. Increasing the argon pressure during the growth gives porous films with lower apparent refraction indexes. An attempt of interpretation of the subgap absorption in terms of the Franz-Kledysh effect is presented: on the assumption that the built-in electric field covers a large part of the grains, values of the intergranular barrier height are deduced. Light scattering in the samples suggests that the film roughness was in the range 50-250 angstrom.