Nb/Sb doping effects on the structural, optical, and electrical properties of CdO thin films: role of the hydrogenation—a comparative study

Abstract

Niobium (Nb)- and antimony (Sb)-doped CdO thin films have been prepared on glass substrates by physical vapour deposition method in a vacuum environment. The films were characterized by the X-ray diffraction, optical absorption spectroscopy, and electrical measurements. The structure of the doped film samples preserved the CdO cubic structure. However, the band gap was shifted depending on the dopant type. Besides, it was observed that doping of Nb or Sb ions considerably improved the conduction parameters. However, the most important result was the significant enhancement of the carrier mobility of the host CdO:Nb film, in addition to the increasing in its conductivity and carrier concentration, which was attributed to the formation of multi-electron donors $${\text{Nb}}_{{{\text{Cd}}}}^{v - 2}$$ of v > 2. The band gap of host CdO suffered shrinkage by ~ 7% with Nb doping and widening by ~ 3% with Sb doping that was explained by the simultaneous effects of Moss–Burstein and Urbach phenomena. The influence of annealing of the films in hydrogen atmosphere (hydrogenation) was investigated for a purpose of increasing the carrier concentration and oxygen vacancies. The great effect of the hydrogenation on the conduction parameters was studied and discussed. From the transparent conducting oxide point of view, Nb is sufficiently effective for CdO doping and even emulates other metallic dopants such as Sb, In, Sn, Sc, and Y.