Structural and electrical properties of cadmium-sulpho-selenide solid solutions

Abstract

Complete solid solutions of CdS x Se1−x (0≤x≤1) were synthesized by vacuum fusion of stoichiometric proportions of CdS and CdSe. X-ray diffraction data revealed that they possess the hexagonal wurtzite structure. The unit cell lattice constants vary linearly with the composition parameter,x, following Vegard's law. Thin films of CdS x Se1−x (0≤x≤1) solid solutions could be deposited onto glass substrates by thermal evaporation of the bulk material in 10−4 Pa vacuum. Structural investigation showed that the films are polycrystalline with predominant appearance of the (002) reflecting plane. On annealing at 250°C in 10−2 Pa vacuum atmosphere, aggregation and rearrangement of the as-deposited tiny crystallite occurred, preserving the same crystal structure. The dark electrical resistivity of the films is independent on the film thickness, but it varies appreciably with the composition parameter,x, showing a minimum resistivity of 0.02 Θ cm atx=0.55. The temperature dependence of the resistivity follows the semiconducting behaviour with an extrinsic and an intrinsic conduction below and above 70°C, respectively. The determined activation energies 0.2 eV and 0.8 eV, respectively, correspond to shallow and deep trap levels, respectively.