Studies on structural, optical and photoelectron transportation in solution grown nanosize CdS thin films for photosensor application

Abstract

130-136CdS Thin films of different thicknesses have been deposited onto glass substrates at 60°C.The source materials for Cd and S have been used as CdCl2 and NH2-CS-NH2 in ammonia solution respectively. The reaction mechanism involved the preparation of film onto precleaned glass substrate through Cd2+ and S2 ions in aqueous solution. Deposited thin films were annealed in air from 50 to 450oC. The XRD results are presented only for the films annealed from 300 to 450oC, as below 300oC there is no appreciable change in crystal structure. From the XRD patterns, films are seen to be polycrystalline in nature with the formation hexagonal phase. The crystallinity of the films was improved by annealing in air at 400°C. The optical transmittance, reflectance and absorption of annealed CdS thin films with different value of thicknesses are then studied in the energy range 1.1-4.0 eV. The CdS films showed allowed direct optical band gap Eg = 2.38 eV. Films of different thicknesses have same maximum transmittance intensity at same wavelength, 590 nm but refractive index varies in the range 2.15-2.85. The photoconductivity of different thicknesses CdS films has been measured with varying light intensity level as L0.2-L1 and it has been observed that the photoconductivity is changed. The decay time constants and demarcation time (60-80 s) have been calculated by photoconductivity measurement and have same values for all different thicknesses of CdS films. The above results are useful for low cost photosensor device applications