The optical and electrical transport studies of Zn_xCo_1−xS thin films

In an attempt to design and fabricate a suitable II–VI group material of variable optical gap, we have synthesized a series of Zn_xCo_1−xS (0 ≤ x ≤ 0.4) thin films via a facile chemical solution growth technique. To gain insight of the materials properties we have opted for different characterization techniques and are reporting our observations pertaining to the elemental analysis, magneto-topography, optical and electrical transport studies. Excellent agreement of binding energy values for Co2p, Zn2p and S2p levels in elemental analysis concluded the oxidation states as Co²⁺, Zn²⁺ and S²⁻. Magnetic force microscopy confirmed the existence of randomly distributed magnetic domains mimicking the surface topography. The optical studies determined the high absorption coefficient (α ≈ 10⁴ to 10⁵ cm⁻¹) in the as-grown thin films. The optical band gap is found to be increased non-linearly from 1.59 to 2.50 eV as the composition parameter (x) is increased. The D.C. electrical conductivity measurements showed decrease in conductivity with increased composition parameter (x). The thermoelectric studies confirmed degenerative nature of the as-deposited thin films with n-type conduction.