Radio frequency magnetron sputtered CdO thin films for optoelectronic applications

Abstract

In this study, CdO thin films were deposited on glass substrates by using radio frequency magnetron sputtering with different deposition times. The effects of the deposition time on the structural, morphological, optical, and electrical properties of CdO thin films were investigated. The thicknesses of the CdO thin films ranged from 310 to 960 nm. The X-ray diffraction patterns demonstrated that the CdO thin films were polycrystalline with cubic structures. The texture coefficients were greater than unity, thereby indicating the high texturing of the films. The morphological properties of the CdO thin films were analyzed by field emission scanning electron microscopy and atomic force microscopy (AFM). The film deposited for 30 min was highly uniform with a nanopyramidal structure. The AFM images showed that the roughness of the films increased with the deposition time. Compositional information obtained by energy dispersive spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of cadmium (Cd2+) and oxygen (O2−) on the deposited films. Optical analyses showed that the films exhibited electronic transitions from the direct transition type and the optical energy gap value ranged from 2.2 to 2.4 eV. The overall transmittance of the deposited films was between 60% and 98% in the visible region. The photoluminescence spectra contained two strong emission peaks at 484 and 519 nm. The electrical properties of the films were determined using a Hall Effect instrument. The maximum mobility (158.5 cm2 Vs−1) was observed after a deposition time of 30 min.