Effects of annealing on cadmium selenide nanocrystalline thin films prepared by chemical bath deposition

CdSe thin films were deposited on the glass substrates by chemical bath deposition method at 80 °C using cadmium acetate and sodium selenosulphate as source materials and ethylene diamine tetra acetic acid (EDTA) as a chelating agent with concentrations 0.025, 0.075 and 0.1 M. The various preparative parameters such as composition, solution temperature, pH of the solution and deposition time were optimized for depositing good quality CdSe films. The deposited CdSe thin films are annealed in the air atmosphere for 3 h at 350 °C. The structural, optical, morphological and electrical properties of as deposited and annealed samples were studied. The crystallite size of the film was estimated by Scherrer's formula and the dislocation density was evaluated using the high intense X-ray diffraction peaks. The phase change of CdSe from cubic to hexagonal after annealing at 350 °C was confirmed from the X-ray diffraction pattern. The thickness of the film is found to be 0.6 μm using interferometery technique. The optical properties were studied using UV–vis and photoluminescence spectrometer. The optical band gap of the film has been estimated to be 2.1 and 1.84 eV for as deposited and annealed films. The photoluminescence band shows red shift with increasing particle size after annealing at a higher temperature. The homogeneous crystalline grains were observed from SEM as well as AFM images. The as-deposited and annealed CdSe films exhibit negative Hall coefficient, which confirms n-type conductivity. The Hall mobility, resistivity, carrier concentration and conductivity were evaluated.

Research highlightsIn the present work, CdSe thin films have been deposited on the glass substrates by chemical bath method at 80 °C using cadmium acetate, sodium selenosulphate and ethylene diamine tetraacetic acid (EDTA) as a chelating agent with different molar concentrations like 0.025, 0.075 and 0.1. The addition of a small quantity of EDTA enhances the spreading of crystalline films during the deposition process without affecting the properties of material and increases the lateral growth of thin films and also discussed the annealing properties of CdSe thin films.