Semiconductor clusters have one extraordinarily important property that on doping and on changes in size, their properties change appreciably and in a controllable way. Current research into semiconductor clusters is focused on the properties of thin films having nanometre range grain size. The wide range of optical and electrical properties of II-VI group compounds make them an important class of materials and competing candidates for silicon and other semiconductor materials in photovoltaic and optoelectronic applications. In this monograph, the structural, spectroscopic and optoelectronic properties of Cadmium Sulfide, Cadmium Telluride and Zinc Oxide thin films are studied in detail. The effects of substrate and grain size on structural and optical properties of these materials are also discussed. Moreover, the synthesis of CdS nanoparticles and fabrication of ZnO thin films by the sol-gel methods and their spectroscopic characterization are described. The ab-initio DFT calculations are carried for the computations of the DOS and band structures of the CdS hexagonal wurtzite, CdTe zinc blende and ZnO hexagonal wurtzite. Effect of Cd dopping in ZnO is also studied theoretically.