Structural Characterization and Electrical Conductivity Percolation in (CdTe)1-x Tex

Abstract

AbstractSamples of the (CdTe)1-xTex diphasic system were grown by HWFE on glass plates kept at temperatures between 150 and 260 °C. The films have excess elemental tellurium varying between 12 and 67 vol%. X-ray analyses showed the samples to be diphasic with CdTe in the cubic phase and Te in the hexagonal phase. The excess tellurium concentration increased as the substrate temperature diminished. The critical volume fraction for conductivity percolation in the (CdTe)1-xTex system was determined to be around 0.4, which indicates a non-random distribution of the excess Te. Raman spectroscopy was used to characterize the Te phase across the conductivity percolation threshold. The integrated intensity of the first-order A1 mode increases dramatically at the percolation transition. Second-order Raman scattering from Te is also seen, but only for those samples with over 38 vol% Te. In addition, the A1 mode is shifted to higher energies in films with concentrations below the transition point, revealing that Te goes from a state of tensile stress into a relaxed state as the films pass from low to high conductivity. These results indicate that simultaneously with the Te network connectivity there occurs aggregation of the excess Te, which was initially located at the grain surfaces. This mechanism relieves the strain and gives rise to high conductivity and extended vibrational modes resembling those of bulk elemental tellurium at volume concentrations around 40% and above.