Studies on Sn doped cadmium sulfide thin films as highly selective green light photosensors

Thin films of Tin (Sn) doped Cadmium Sulfide (CdS) have been grown by chemical bath deposition technique. It was observed that all fabricated thin films (doped & undoped) were polycrystalline with nanoscaled crystallites and cubic crystal structure of CdS. SEM micrographs show nanorod structure of CdS and Sn doped CdS. EDS analysis shows the deficiency of sulfur and excess of cadmium in the films. UV-VIS spectroscopy confirms increase in band gap with doping of the films. Microstructural analysis shows that the particle size increases with increasing concentration of the Sn on excitation with 483 nm. The gravimetric analysis shows that the thickness of the pure CdS thin film measured is 134.41 nm, which increases with doping concentrations of tin. Electrical conductivity measurements show that the material switches its Negative Temperature Coefficient (NTC) to Positive Temperature Coefficient (PTC) nature with increase in temperature. TEP measurements show n type semiconducting nature of the films which is highly photo sensitive. The pure CdS thin film was observed to be less sensitive to the green light, however, the Sn (3 wt%) doped CdS thin films exhibit enhanced photo response particularly to green light.