Radio frequency power induced changes of structural, morphological, optical and electrical properties of sputtered cadmium oxide thin films

Transparent and conducting cadmium oxide (CdO) thin films were deposited on glass substrates at room temperature using radio frequency (RF) magnetron sputtering method. The carrier concentration and electron mobility are the key factors for the conducting properties of CdO thin films. The grain size, crystallinity, thickness, surface roughness and band gap of CdO thin films play an important role in optical and electrical properties. In this study, dual behaviour of CdO thin films is studied as a function of RF sputtering power. Crystalline quality, micro structure, surface morphology and optical and electrical properties of sputtered CdO thin films were investigated. The structural analysis revealed that the deposited CdO films were polycrystalline in nature with cubic structure (Fm3¯m space group). The grain sizes were found to be increased with increase of RF power from 100 to 150 W and then decreased at high power (200 W). The optical studies revealed that all the films exhibited higher transmittance in visible and near infrared region and the optical energy band gap value decreased from 2.62 to 2.46 eV with increase of RF power. Luminescence spectra exhibited two strong emission peaks at 484 and 519 nm. The resistivity of CdO thin films gradually decreased with an increase of sputtering power and reached a minimum value of 3.041 × 10−4 Ω cm at 200 W. A maximum mobility of 67.01 cm2/Vs was found for the sample prepared at the sputtering power of 150 W.