STRUCTURAL AND ENERGY-GAP VARIATIONS IN (ZNTE)X(CDSE)1-X THIN-FILMS

Thin films (approximately 200 nm thick) of (ZnTe)x(CdSe)1-x in the entire range of composition (0 less-than-or-equal-to x less-than-or-equal-to 1) were prepared by thermal vacuum evaporation maintaining the glass substrates at 303 and 553 K. XRD studies showed that the films were polycrystalline. Wurtzite structure was found in compositions up to x = 0.5. Beyond this composition the zincblende structure was observed. A structural discontinuity was found in a very narrow range of x. Energy gaps estimated from photoconductivity spectral response and optical transmittance spectra were nearly the same and varied non-linearly with composition. The bowing parameters for films prepared at 303 and 553 K were found to be 1.03 and 1.31 eV, respectively. The structural discontinuity and bowing parameter are discussed in detail. Crystallinity (grain size), lattice parameters and bandgap were found to increase with T(s).