Preparation and Properties of Mixed Metal Sulfide Thin Films for Photosensor Applications

Abstract

The present work reported in this thesis involves studies on binary metal sulfides namely ZnS, CdS, and SnS along with the investigations on the ternary compounds: Cux(ZnS)1-x, ZnxCd1-xS, and ZnxSn1-xS thin films deposited using a vacuum thermal evaporation method on glass substrates. The above compounds were selected due to their optimal direct band gap energy values. Substrate temperature plays an essential role in controlling the crystallite size, structural phase, surface morphology, and optoelectrical properties of the films. By varying the substrate temperature, the binary films were optimized to form a stoichiometric film and the various properties of the films were analyzed as a function of substrate temperature. All the films were found to be free from any pinholes and cracks. The band gap energy for the stoichiometric ZnS, CdS, and SnS thin films was found to be 3.49 eV, 2.42 eV, and 1.54 eV, respectively. Both CdS and SnS films displayed exceptional photodetector properties and the photosensitivity was found to be highest at 10.93 for the stoichiometric SnS films. The Cux(ZnS)1-x films exhibited outstanding p-type conductivity with very high transparency and thereby, suggesting that the films can be used as a p-type transparent conducting layer. The various properties of the ZnxCd1-xS and ZnxSn1-xS thin films were tuned by altering the composition of the films. A successful band gap engineering was achieved for the ternary compound thin films. The ZnxCd1-xS and ZnxSn1-xS films were analyzed for photodetector application and the various parameters such as photoconductivity (L), photosensitivity (S), photoresponsivity (R), recovery time (τd), and response time (τr) of the films were calculated. The present study reveals a maximum photosensitivity of 43.38 for the Zn0.10Sn0.90S thin films.