Photoluminescence and Raman studies of cadmium telluride, cadmium sulfur telluride alloys and cadmium sulfide/cadmium telluride thin-film solar cells

The performance of CdS/CdTe thin-film solar cells is strongly determined by the properties of the CdS/CdTe interface region which forms during the heat treatment of the solar cell. In this dissertation near resonant Raman scattering and photoluminescence (PL) spectroscopy have been used to analyze the interface region of CdS/CdTe solar cells. From these measurements the co-existence of two phases at the solar cell CdS/CdTe interface has been confirmed and their composition measured. For single phase CdS{dollar}sb{lcub}rm x{rcub}{dollar}Te{dollar}sb{lcub}rm 1-X{rcub}{dollar} alloys the LO phonon modes have been modeled according to the modified random element isodisplacement model (MREI) and force constants between atoms have been determined. Photoluminescence measurements revealed that the thickness of the interdiffused layer at the CdS/CdTe interface is about 5000 A. It was found from PL measurements that if oxygen is mixed into the sputter gas during the CdTe deposition the interdiffusion across the junction and the diffusion of chlorine from the CdTe surface are inhibited.; In addition, resonant excitation of donor-bound excitons in single-crystal CdTe showed evidence that lower polaritons serve as a mediator for the formation of donor-bound excitons. By measuring Stokes shifts of two-electron transitions the ionization energies of the associated donors have been found.; Furthermore, a tunable diode laser with a tuning range between 776 and 794 nm and a fiber optics device which provides sample cooling to temperatures down to 4 K has been designed, constructed and used as part of this dissertation.