Spectroscopic and electrical analysis of vacuum co-evaporated Cd_xZn_1-xTe thin films

Cd_xZn_1-xTe (CZT) films with different compositions were grown by thermal co-evaporation method, in which cadmium telluride (CdTe) and zinc telluride (ZnTe) were used as the source materials. The structural, morphological and optical properties of the films were characterized by x-ray diffraction (XRD), UV–Visible spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), photoluminescence (PL) and Raman spectroscopy. Detailed analysis has shown that films were having cubic phase with orientation along (111) plane and the optical band gap reduced from 2.17 to 1.53 eV when x was varied from 0 to 1. SEM micrographs confirmed the homogeneity of the films. Depending on the composition, Raman peaks of CZT samples were mixture of the fundamental modes of the CdTe and ZnTe and indicate “trigonal” lattice of Tellurium (Te). Analysis of PL spectra suggested tellurium as isoelectronic exciton traps, recombination of carriers in the surface traps and donor-acceptor pair present in the samples. Under electrical properties, p to n-type conversion was witnessed for x = 0.4 and above. Optical bad gap of about 1.60 eV with minimum Urbach energy (28.88 meV) and favourable electrical properties has led to conclude that CZT films with x = 0.8 may be suitable for solar cell absorber.