DEVELOPMENT OF CLOSED SPACE SUBLIMATION TECHNIQUE AND PREPARATION OF Cd­BASED THIN FILMS

Abstract

In the present work, a coating unit for depositing thin films has been developed which works on the technique “Closed Space Sublimation” in which a powdered material is deposited under vacuum. Cadmium Sulfide thin films has been deposited on a glass substrate. Structural, morphological, compositional, optical, and electrical properties of the samples have been determined before and after Indium doping. The main goal doping is to get comparatively high electrically conductive films. The optical properties of the films are also very important from the application point of view so that improvement in conductivity should not be associated at the expense of optical and structural properties of the films. The structure of the films was studied by XRD, SEM and composition of the films was measured by EDX. A model was used for the calculation of optical parameters (optical band gap, refractive index, and films thickness) from the optical transmission spectra recorded by spectrophotometer. Samples of different thickness ranging from 250nm to 900nm were obtained and most of the samples have a band gap near 2.4eV before and after doping, calculated from the transmission data obtained from spectrophotometer. To reduce the resistivity of the thin films, Indium was doped. Indium was thermally evaporated and annealed at different temperatures in order to diffuse it in as-deposited CdS samples. XRD results confirmed the diffusion and formation of new compounds of indium with. cadmium sulfide. Resistivity of 10-1 to 10-2 Ωcm was obtained.