Effect of substrate temperature on some optical properties of SnO:ZnS4, SnO:CoS4 SnO:CuS4 and SnO:Cr3+ thin films deposited using spray pyrolysis technique

Abstract

Tin oxide (SnO) thin films is one of the most extremely studied oxides because of its usefulness in UV-detector. SnO is known for wide bandgap of 3.6eV which makes it a good candidate for window layers in heterjunction solar cells. Transition metal chalcogenides (TMCs) exhibits unique properties such as high conversion efficiency, good absorption coefficient and good bandgap energy which make their thin films versatile as a coating materials. Spray pyrolysis have been used to deposit SnO (core), SnO/ZnS, SnO/CrS, SnO/CoS and SnO/CuS (biphasic) at 0.1M concentration and different substrate temperatures of 100oC, 150oC and 200oC. The effect of varying substrate temperatures on the optical and structural properties of the SnO (core) and SnO/TMCs (biphasic) films were examined and analysed. The result showed that the optical transmittance decreased with increase in substrate temperature for SnO (core). The result showed that the absorbance of the SnO thin films at various substrate temperatures vary from 0.10 – 0.7. For the biphasic films, SnO/ZnS, SnO/CrS, SnO/CoS and SnO/CuS the absorbance decreases in the neighbourhood of 300nm-350nm, increases from 350nm-600nm and decreases between 600-100nm for the different substrate temperature of 100oC, 150oC and 200oC. The reflectance spectra of SnO films were found fluctuating between maxima and minima while biphasic films altered the reflectance which showed very low reflectance as observed. The bandgap energy for SnO are 2.00eV, 2.10eV, and 2.20eV at 100oC, 150oC and 200oC substrate temperature. The energy band gap increased with substrate temperature. Whereas for biphasic films, the bandgap was in the neighourhood of 1.10eV1.60eV for the different substrate temperature. The extinction coefficient (k) of SnO films increased with increase in substrate temperature while in biphasic films, the extinction coefficient showed significant reduction in magnitude irrespective of the substrate temperature. The refractive index of all the film samples were generally low irrespective of the substrate temperature. The films:SnO and biphasic displayed low value of dielectric constant irrespective of the substrate temperature. The result equally reveals that the optical conductivity for SnO decreases with increase in the substrate temperature.