Tune-Ability of Physical Properties of Nanocrystalline Cu x Zn1−x Se Thin Films with Copper Concentration

Abstract

Thin films of Cu x Zn 1Àx Se (0 £ x £ 0.20) have been prepared on glass substrates at room temperature by closed space sublimation. The effect of copper (Cu) concentration on the structural, optical and electrical properties of the prepared films has been investigated using x-ray diffraction (XRD), Raman spectroscopy (RS), spectrophotometery and Hall effect measurements. XRD spectra show that all the films are cubic with (111) preferred orientation. The lattice constants, crystallite size, strain, and dislocation density were calculated from the XRD spectra. The structural analysis shows that crystallite size and crystallinity increase while strain and dislocation density decrease up to 10% Cu addition. However, an opposite trend has been observed beyond 10% Cu concentration. RS was carried out to investigate different phonon bands and crystalline phases. The strong reflection corresponding to the (111) texture in the XRD and the observed longitudinal optical (LO) phonon bands at 251 cm À1 and 497 cm À1 in the Raman spectra reveal the formation of single phase zinc-blende structure. The band gap energy decreases from 2.67 eV to 2.24 eV as the Cu concentration is increased from 0% to 20%. Hall effect measurements shows that electrical resistivity (q) is decreased by about three orders of magnitude from 10.4 9 10 À03 X-cm to 47.9 9 10 À03 X-cm while, carrier concentration and mobility (l) is increased with Cu addition.