Influence of doping concentrations of Hf on structural and electrical properties of HfxZn1-xO thin films

HfxZn1−xO thin films (x=0, 2.5,3, 7.5, 10 and 15mol %) were deposited on glass substrates using Sol-gel process. The influence of the Hf concentration on the structural, electrical, and optical properties of the films was studied. It is found that Hf ions can be effectively doped into ZnO and all films crystallize in the hexagonal wurtzite structure with a preferred c-axis orientation. The lattice constants of HfxZn1−xO films increase with the Hf contents. The HfxZn1−xO thin films structures of high-Hf-content films remain after annealing at 600 °C for 20 min. The optical band gap increases with the Hf content, but it decreases with the annealing temperature. The reduction of bandgap partly results from grain growth, which is due to the quantum confinement effect of the small grains. Hf doping increases the resistivity of ZnO owing to the disorder of the material structure and the higher bandgap, which results in more carrier traps and less thermally excited carriers in the conduction bands. Two FTIR peaks centered at about 1432 and 1056 cm-1 coexist in the fluorescent spectra. With increasing the Hf contents, the intensity of fluorescent peaks enhances remarkably. The Minimum resistivity reached 6.1 * 10-2 Ὠ cm after annealing with 3% Hf content.