Tetyana V. Torchynska

ZnO-based transparent conducting oxide (TCO) has many advantages over In or Cd containing TCOs. But the electrical conductivity of ZnO films are lower than those in widely used In₂O₃:Sn (ITO) layers. In this paper, a method to improve the conductivity of ZnO films is proposed. The impact of doping by two donor-type elements, Ga (or Al) and In, on the characteristics of ZnO layers is presented. Two sets of films grown by spray pyrolysis were studied. The first set includes films with 2.0 at% In and varied Ga concentrations 0.5–3.0 at%. The second set includes films with 1.0 at% In and Al content varied 0.5–3.5 at%. Then, all films were thermally treated at 400°C for 4 h in a N₂ ambience. The variation of morphology, compositions, crystal structure, transmittance, and emission versus doping have been monitored. All films are characterized by the wurtzite crystalline structure, sharp transmittance edges, bright photoluminescence confirmed the high crystallinity of films. Using impurities with small (Ga, Al) and higher (In) ionic radii compared to Zn allows varying stresses and shifting an onset of self-compensating effect to significant doping levels. This improves electrical characteristics and reaches a resistivity of 5.5 × 10⁻⁴ Ω cm in Ga/In or 3.55 × 10⁻³ Ω cm in Al/In doped ZnO films. The factors that influence the variation of crystal structure, transmittance, and emission versus Ga (or Al) contents have been analyzed. Obtained high-quality ZnO films with the optimal donor concentrations are interesting for optoelectronic applications as the transparent conducting oxides.