CdSe nanocrystalline thin films: composition, structure and optical properties

Abstract

Nanocrystalline CdSe semiconductor thin films of different crystalline sizes have been synthesized by cathodic electrodeposition onto indium tin oxide glass and titanium electrodes. The composition of as-grown films, their crystalline structure and band gap were evaluated as a function of deposition current density and temperature. Particle induced X-ray emission and Rutherford backscattering spectrometric analysis indicate that the samples are free from any foreign impurity and the Cd to Se ratio changes at very low electrolysis current density. Crystalline size estimated from Grazing angle X-ray diffraction (GXRD) is found to be varied between 7 and 19nm for different samples. A lattice contraction of 1.00% has been estimated from the GXRD measurement. Optical absorption shows size quantization effect marked by a blue shift by 0.52eV from its standard bulk band gap value 1.7eV. Crystalline size estimated from the blue shift is found to be much smaller compared to that determined from GXRD. Both GXRD and transmission electro microscopy (TEM) studies of CdSe nanocrystals reveal the cubic phase of the samples and the sizes estimated from both GXRD and TEM analysis are found to be comparable.