SYNTHESIS AND CHARACTERIZATION OF THALLIUM SULPHIDE/CADMIUM SULPHIDE AND LEAD SULPHIDE/CADMIUM SULPHIDE THIN FILMS GROWN IN A POLYMER MATRIX BY CHEMICAL BATH DEPOSITION (CBD) METHOD

摘要

Chemical bath deposition of semiconductor thin films is by now recognized as a versatile low-cost method to produce thin films of I-VI, II-VI, III-V, IV-VI and V-VI compounds. This technique is the most cost saving, convenient and simple technique, which is highly reproducible. It makes use of the fact that films can be deposited on substrates whether metallic or not by dipping them into suitable solution baths containing metal salts without applying any external field. CdS/PbS and CdS/TlS thin films were synthesized on the glass substrate by this technique within the pores of polyvinyl alcohol (PVA) at room temperature. The chemical bath for the deposition of CdS is made up of solution of cadmium chloride (CdCl_2), ammonia (NH_3), thiourea ((NH_2) _2CS) and PVA solution. The chemical bath for the deposition of PbS thin film on clean microscope glass slide was achieved by using lead nitrate (Pb(NO_3)_2), sodium hydroxide (NaOH), thiourea ((NH_2)_2CS) and PVA solution. Thallium sulphide (TlS) thin films were deposited on glass substrate using a bath that contains thallium nitrate, sodium citrate, sodium hydroxide, thiourea and PVA solution. A chemical synthesis process for the fabrication of CdS/PbS and CdS/TlS thin films are presented herein. In this present work, these films were annealed in air at 373K and characterized for the structural, morphological and optical properties. These properties were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical spectrophotometer for their potential application in solar energy devices. The optical properties revealed the presence of direct band gaps with energies 1.20 eV for PbS/CdS and 1.40 eV for TlS/CdS thin films. The films show poor transmittance in the visible and near infrared region of the solar spectrum.