Nanocrystal size control by bath temperature in electrodeposited CdSe thin films

Abstract

The bath temperature dependence of the structure, composition and surface morphology of CdSe thin films electrodeposited on indium-doped tin oxide (ITO) coated glass substrates from a DMSO solution containing CdCl₂ and elemental Se has been investigated. X-Ray diffraction (XRD) and optical absorption results demonstrated that by lowering the bath temperature in the range of 180–130 °C, the nanocrystal sizes of the as-prepared films continuously decreased and crystal quality was improved. Quantitative analysis of the XPS results indicated that the calculated O∶Se ratios also decreased with a lowering of the bath temperature. After annealing in an argon atmosphere at 500 °C for 30 min, the XRD pattern presents a preferred (002) orientation of the hexagonal wurtzite structure, in contrast to the zinc blende structure for the as-deposited films. Also, this preferred orientation was strongly dependent on the bath temperature used in the electrodeposition process. Interestingly, the morphology of the crystalline grains deposited at lower bath temperatures changed from a cauliflower pattern for the as-deposited film to a globular pattern for the annealed film, and the average grain sizes of the annealed film are about 1 µm.