Optoelectronic properties of Eu- and H-codoped CdO films

Structural, electrical, and optical properties of lightly (0.8 wt%) Eu-doped CdO thin films post-annealed in hydrogen atmosphere for different durations (15 min, 30 min, and 45 min) were studied. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV–VIS–NIR absorption–reflection spectroscopy. The result indicates that H2 annealing does not change the crystalline CdO structure of the films. The bandgap of the hydrogenated Eu-doped CdO films changes with H2-annealing time following the changing in the carrier concentration. These results were found to be in agreement with the available models of bandgap widening with narrowing. The electrical behaviours of hydrogenated and non-hydrogenated Eu-doped CdO films show that they are degenerate semiconductors with bandgap around 1.8 eV. The Eu-doping of CdO films enhances the electrical conduction and additional enhancement was obtained with H2 low-temperature pre-annealing. It was found that the greatest enhancement of the electrical conduction parameters occurs by annealing of CdO:Eu films in H2 atmosphere for 15–30 min when the conductivity increased by about 90% and the free-electrons concentration increased by about 212% relative to the non-hydrogenated CdO:Eu. From transparent conducting oxide point of view, Eu is sufficiently effective for CdO doping especially when including pre-annealing in H2 atmosphere.