MICRO THROUGH NANOSTRUCTURE INVESTIGATIONS OF POLYCRYSTALLINE CDTE - CORRELATIONS WITH PROCESSING AND ELECTRONIC-STRUCTURES

This paper provides first-time correlations of the nanoscale physical structure with the macroscale electronic and optical properties of CdT e/CdS thin films for several standard deposition techniques. Atomic fo rce microscopy (AFM) was used to determine the micro and nanostructure s of polycrystalline CdTe thin films used in photovoltaic (PV) cell fa brication. Photoluminescence (PL) was used to determine band gap, rela tive defect density, and photoexcited carrier lifetime. Cross-sectiona l scanning tunneling microscopy (STM) was used to determine the nanosc ale electronic properties. Nanostructural features (nanograins), beyon d the spatial resolution of conventional scanning electron microscopy (SEM), were observed and characterized in as-deposited CdTe. The corre lations of the proximal probe measurements of the physical and electro nic structure with the optically determined electronic properties were used to show the effects of the chemical and heat processing, directl y and conclusively. A particularly striking effect with important impl ications for PV applications is the diffusion of sulfur across the CdT e/CdS interface during heat treatment.