Effect of thermal annealing in different gas atmospheres on the structural, optical, and electrical properties of Li-doped CdO nanocrystalline films

Li-doped CdO thin films with nominal content of about 1% Li were prepared by a vacuum evaporation technique. The samples were annealed in different atmospheres (air, hydrogen, nitrogen, and ammonia gas). The influence of different gas atmospheres on the structural, electrical, and optical properties of the prepared films were systematically studied. Experimental data indicate that Li doping slightly stress the CdO crystalline structure and change its optoelectronic properties. Structural changes under the influence of annealing in different gas atmospheres were also studied in details. The bandgap of Li-doped CdO suffers narrowing that was studied in the framework of the available models. The electrical behaviours of the Li-doped CdO films annealed in different gas atmospheres show that they are degenerate semiconductors and doping improves the conduction properties for example the Li-doped CdO annealed in air shows increase in its conductivity by about 68 times, mobility by about 3 times, and electronic concentration by about 24 times compared with CdO. However, the largest mobility of similar to 44 cm(2)/V s was obtained under annealing in ammonia gas mixed with helium. Thus, from transparent-conducting-oxide point of view, Li is effectively suitable for CdO doping. Furthermore, some phenomenological evaluation of the dependence of bandgap on the carrier concentration of samples is given. (C) 2011 Elsevier Masson SAS. All rights reserved.