Ar+ Ion Implantation Induced Surface, Structural and Optical Modifications in Cadmium Selenide Thin Films

Among the groups II-VI semiconductors, cadmium selenide (CdSe) is a direct and wide band gap semiconductor. In comparison to Si films, CdSe semiconducting thin film have superior carrier mobility and, therefore, can be employed in solar cells as an absorber layer. In the present work, firstly thin films of CdSe were electrodeposited on the indium doped tin oxide (ITO) substrates. For the deposition, a bath containing cadmium sulfate and selenium dioxide solution was used. Prior to electrodeposition, ITO substrates were cleaned by an ultrasonicator using de-ionized water and acetone to remove impurities. After successful deposition of the film of thickness 120 nm, these were characterized by UV-Visible spectrophotometer, RF-530 Spectrofluorophotometer and four-probe setup with programmable current-voltage (I-V) source meter. The as-deposited CdSe thin films were implanted with 80 keV Ar+ ions at different fluencies i.e. 1 x 10(15) ions/cm(2), 5 x 10(15) ions/cm(2), 1 x 10(16) ions/cm(2) and 5 x 10(16) ions/cm(2). The effect of Ar+ ion implantation on the surface properties of CdSe thin films is studied with respect to lattice disorder. Defects created on implantation may give rise to new energy levels within the energy band gap that may serve as the trapping or recombination centers for the charge carriers depending upon the positions of the new energy levels. This alters the properties of the material and hence the characteristics of the device based upon the material.