Influence of CdTe Thickness on the Properties of Vacuum Evaporated CdSe/CdTe Bilayer

Abstract

Cadmium selenide (CdSe) / cadmium tellurium (CdTe) bilayer was vacuum evaporated onto well cleaned glass substrates. The influence of bottom layer (CdTe) thickness on various properties such as structural, morphological, optical and electrical were studied using the X-ray diffractometer (XRD), atomic force microscopy (AFM), UV-Visible Spectroscopy and I-V measurements respectively. The thickness of the CdTe layer measured using the stylus probe profilometer varied from 550 to 770 nm. XRD pattern of the deposited CdSe/CdTe bilayer shows polycrystalline nature and crystallinity of the bilayer is improved with increase in thickness of the CdTe layer. The root mean square roughness of the deposited bilayer evaluated from the AFM decreases with increase in CdTe bottom layer thickness and the roughness value increases from 4.08 to 2.66 nm. Energy dispersive analysis of X-rays (EDAX) results confirmed the presence ofCadmium (Cd), Selenium (Se) and Tellurium (Te). The optical band gap of the CdTe layers decreases from 2.1 to 1.7 eV for increase in film thickness due to the increase in the grain size. The electrical studies were carried out using two probe measurement and I-V and the resistivity of the film was also measured. The bilayer films deposited in the present work can be used to fabricate multijunction solar cell.