Structural, optical and electrical properties of cerium and gadolinium doped CdO thin films

Cadmium oxide thin films doped with different concentration of cerium (Ce) and gadolinium (Gd) have been prepared by radio frequency magnetron (RF) sputtering. Thin films are deposited on glass substrates at a substrate temperature of 400 °C and pressure of 0.1 mbar in Ar:O2 = 4:1 atmosphere. The structural, optical and electrical properties of deposited film are studied. X-ray diffraction reveals that Ce and Gd doped CdO films have good crystallinity and are apt to grow on (2 0 0) orientation with increasing Ce and Gd doping concentrations. These films are highly transparent with an average transmittance over 80%. With a moderate doping (0.4 at.% Ce and 0.8 at.% Gd), the optical band gap (Eg) blue-shift from 2.59 eV to 2.99 eV. The electrical conductivity increases with increasing Ce and Gd doping concentrations, but for higher doping concentration (0.5 at.% Ce and 1.0 at.% Gd), the conductivity decreases. The increase in carrier concentration due to Ce and Gd doping is the main reason responsible for the increase of and conductivity and the blue shift of band gap.