SYNTHESIS AND CHARACTERIZATION OF CHEMICALLY DEPOSITED Cd1-xPbxS THIN FILMS

A simple and inexpensive chemical bath deposition technique is employed for the deposition of Cd1-xPbxS (0 <= x <= 1) thin films. Cadmium sulphate, lead sulphate and thiourea were used as the basic starting materials. Triethanolamine (TEA) was used as complexing agent. For good quality deposits the various preparative parameters such as deposition temperature, time, speed of substrate rotation and pH of the reaction mixture were optimized to 80 degrees C, 60 min., 65 rpm and 10.5 +/- 0.1 respectively. The 'as-grown' samples were characterized through structural, surface morphological, compositional, optical, electrical and thermoelectric studies. The colour of 'as-grown' samples went on changing from orange yellow to black with increase in composition parameter 'x' from 0 to 1. The thickness of the samples went on increasing with the composition parameter 'x'. The X-ray diffractograms of 'as-grown' samples exhibited polycrystalline nature with presence of cubic phases for CdS and PbS and hexagonal phase for CdS alone. The crystal size determined from XRD and SEM micrographs is observed to increase with 'x' up to 0.175 and later on it decreased. The energy dispersive analysis by X-rays (EDAX) revealed that films are cadmium rich. The optical study at room temperature revealed high coefficient of absorption (104 cm(-1)) with a direct allowed type of transition with band gap energy decreasing continuously from 2.47 eV to 0.49 eV with varying composition parameter 'x'. The electrical resistivity measurements revealed semiconducting nature of the film and it is found that the resistivity of the film decreases with increase in 'x' up to 0.175 and further it increases up to x = 1. The n-type conduction was observed in film from TEP studies.