Optical and microstructural properties of chemically deposited mercury cadmium sulphide thin films

Abstract

Simple, scalable, extremely convenient and idegeneously developed solution growth technique is used to synthesize a series of Hg _x Cd_{1 − x} S thin films for 0 ≤ x ≤ 0.25. The basic source materials were cadmium sulphate, mercuric chloride, and thiourea with TEA and ammonia as the complexing agents. The preparation parameters such as growth temperature (60°C), growth time (90 min), reaction pH (10.8 ± 0.2), rate of mechanical churning (70 ± 2), etc., were optimized. The as-grown films were tightly adherent to the substrate support, smooth, relatively uniform and diffusely reflecting with colour changing through yellowish red to yellowish lead-gray. The terminal layer thicknesses were measured for all the deposits and found to be decreased continuously with increase in [x]. The XRD studies (2θ = 10° to 80°) were also carried out to know the structure of these films. It was observed that the samples are polycrystalline in nature and exhibit dominant hexagonal wurtzite type crystal structure. The analysis of the optical absorption data (300–1000 nm) showed that the optical band gap is of the direct type and the energy gap, E _g, decreased typically from 2.42 to 1.75 eV as x was increased from 0 to 0.25. Scanning electron microscopy showed that the HgCdS deposits appeared to be a network of polycrystals of mixed, irregular shapes and sizes with size decreased with increasing Hg content in CdS.