Effects of Processing on the Properties of Polycrystalline CdTe Grown by Various Deposition Techniques

Enhanced performance of CdS/CdTe polycrystalline heterojunction cells has been observed following post-deposition chemical and temperature processing. However, correlation of the effects of the CdCl₂ and 300-500 °C treatments with the resulting film properties seems to vary with the origin of the material. This paper examines and compares the effects of these treatments on the physical, structural, chemical, compositional, and electrooptical properties of polycrystalline CdTe films produced by sputtering, close-spaced sublimation, physical vapor deposition and metallo-organic chemical vapor deposition. Atomic-force microscopy (AFM) is used to investigate nanostructural differences among the films, especially the presence of small grains (not observable by Scanning Electron Microscopy [SEM]) in the vicinity of grain boundaries. The change in structure in these intergrain regions and annihilation of these <300 angstroms grains following processing are observed and correlated with the passivation and change of electronic defect levels.