Influence of hydrogenation on the electrical and optical properties of CdO:Tl thin films

Electrical and optical properties of Tl-doped CdO films (CdO:Tl) post-annealed in hydrogen atmosphere for different durations (15 min, 30 min, 45 min, and 60 min) were studied. The prepared films were characterised by the X-ray diffraction method and UV–VIS–NIR absorption–reflection spectroscopy. Experimental data indicate that annealing in H2-atmosphere removes gradually with time the internal structural micro-stress that created as a consequence of Tl doping into CdO structure. The band gap of the hydrogenated Tl-doped CdO samples changes with H2-annealing time following the changing in the free-electron concentration. These results were found to be in agreement with the available bandgap widening and narrowing models. The optical properties were easily explained within the framework of Hamberg band-to-band transitions and classical Drude theory. It was found that the greatest enhancement of the electrical conduction parameters occurs by annealing of CdO:Tl films in H2-atmosphere for 30–45 min when the conductivity increased by about 37% and the free-electron concentration increased by about 6%. The results of the present investigation are important for the transparent conducting oxide preparation technique.