Abstract
The ZnS thin films have been deposited by radio frequency magnetron sputtering at room temperature. Post-deposition rapid thermal annealing treatment was done for the films deposited at different powers ranging from 70 to 100 W. One peak is observed for as-deposited and annealed thin films at around 28.48° corresponding to the (111) reflection plane indicating a zincblende structure. The overall intensity of the peaks and the FWHM values of as-deposited films increased after annealing corresponding to the increase in crystallinity. The optical energy bandgap is found in the range of 3.24–3.32 eV. With increasing annealing temperature, the decrease in the Urbach energy values indicating a decrease in localized states which is in good agreement with the XRD results where the crystallinity increased. The surface morphology of the films seems to be composed of Nano-granules with a compact arrangement. Apparently, the grain size increases in the deposited films as annealing temperature increases. The compositional ratio attained close to the stoichiometric ratio of 1:1 after annealing. From the Hall effect measurement, the carrier concentration and mobility are found to increase after annealing. The high carrier concentration and mobility also comply with structural and optical analysis. Best results are found for the film annealed at 400 °C deposited at 90 W.
Highlights
The II–VI semiconductor compound thin films have been investigated for many years because of the multiple applications of these materials, in the field of solar cells, photocatalysts, field-effect transistors, light-emitting devices, and optoelectronic devices [1,2,3,4,5,6,7,8,9,10]
As buffer layer in solar cell, II–VI compounds, such as CdS [7, 11,12,13], Zinc sulfide (ZnS) [9, 14, 15], CdZnS [16,17,18,19,20], CdSe [21, 22], CdSSe [23], etc., have been usually used. This binary/ternary compound thin film is reported to be synthesized by various techniques such as molecular beam epitaxy (MBE) [24], chemical bath deposition [5, 15, 25, 26], sputtering [9, 10, 14, 27, 28], atomic layer deposition [29], etc
One significant peak for the films indicating that the films are of a single crystalline structure and the planes are parallel to the substrate surface [9]
Summary
The II–VI semiconductor compound thin films have been investigated for many years because of the multiple applications of these materials, in the field of solar cells, photocatalysts, field-effect transistors, light-emitting devices, and optoelectronic devices [1,2,3,4,5,6,7,8,9,10]. They achieved over 85% transmittance in the visible light, good crystallinity and the bandgap in the range of 3.3–3.4 eV for the films deposited at 85 and 95 W power.
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