Studies on DC reactive magnetron sputtered CdO:C thin films for optoelectronic devices

Abstract

Cr doped CdO thin films were deposited on glass substrates by DC reactive magnetron sputtering method with individual Cd and Cr metallic targets. The effect of Cr concentration (1% to 5%) on structural, electrical and optical properties of CdO films was investigated. The structural studies reveal that the films are polycrystalline with preferred orientation along (2 0 0) plane. The shift of the diffraction peak (2 0 0) towards higher angles with the increase of Cr concentration indicates the presence of stress in the films. SEM images consist of agglomerates and no distinguished grains are seen. Energy Dispersive Analysis of X-rays (EDAX) is carried out for the compositional analysis of prepared thin films. The optical transmittance of 85 % and minimum resistivity of 1.73 × 10-4 Ω.cm is obtained for 3% Cr doped CdO thin films. A blue shift of the band edge has been observed for the Cr doped CdO films with the increase of Cr Concentration. This blue shift is due to Burstein -Moss effect, which arises due to increase in free carrier concentration. The optical band gap of Cr doped CdO thin films increases from 2.35 to 2.85 eV with the increase of Cr concentration. The optical constants such as absorption coefficient (a), extinction coefficient (k) and refractive index (n) were determined from the optical transmission data.