Characterization of ZnS_xSe_1-x films grown by thermal co-evaporation technique for photodetector applications

Zinc sulfoselenide (ZnS_xSe_1-x, 0.0 ≤ x ≤ 1.0) films were prepared by thermal co-evaporation by taking ZnS and ZnSe as the source materials. The structural and optical properties confirm the composition variation where a systematic shift in the X-ray diffraction peak and absorption edge of the films was witnessed with variation in ‘x’. As ‘x’ varied from 0.0 to 1.0, the bandgap of the films has changed from 2.56 eV to 3.50 eV. The presence of sulfur and selenium vacancy in the deposited films has been confirmed by analysis of photoluminescence spectra. Raman and X-ray photoelectron spectroscopy studies explained the chemical state and revealed the incorporation of oxygen that helped in the enhancement of electrical conductivity and photosensitivity of the samples. The electrical parameter carrier density and resistivity were dependent on the composition parameter and crystallite size of the films. All the films showed n-type conductivity and samples with x = 0.4 showed high photo-response (photosensitivity > 20 for white light) and were suitable for photodetector application. These films showed maximum response (photosensitivity > 20) at 500 nm.