Effect of annealing temperature on the optoelectronic properties of quinary amorphous oxide semiconductor IGZTO thin films

Abstract In this study, novel quinary InGaZnSnO indium gallium zinc tin oxide (IGZTO) thin films deposited on glass substrates using a high-purity IGZTO (atomic ratio In:Ga:Zn:Sn:O = 1:0.5:1.5:0.25: x ) ceramic target via RF magnetron sputtering were annealed in air at room temperature to 450 °C. The effects of annealing temperature on the microstructure, electrical and optical properties of the thin films were systematically investigated. Both the as-deposited and the annealed IGZTO films exhibit amorphous structures. The film annealed at 150 °C demonstrated the best electrical performance, with a carrier concentration of 3.06 × 10 19 cm −3 , a mobility of 35.68 cm 2 V –1 s −1 and resistivity of 5.70 × 10 −3 Ω cm, while the one annealed at 350 °C had a carrier concentration of 3.58 × 10 17 cm −3 and the smoothest surface, with the lowest root mean square (RMS) and average roughness (Ra) of 0.384 nm and 0.278 nm, respectively. As the annealing temperature increased from 150 °C to 450 °C, the optical energy gap (E g ) changed from 3.52 to 3.56 eV, and the Urbach energy (E U ) increased from 170 to 274 meV, indicating the increased disorder and more defects generated after annealing. Oxygen vacancies are found to be the main origin of the conductivity of IGZTO films, and their minimum concentration was found in the film annealed at 350 °C. Thin-film transistors (TFTs) with 350 °C-annealed IGZTO thin film as the active layer exhibit a favorable field-effect mobility of 20.17 cm 2 V –1 s −1 , which is higher than that of most of the reported indium gallium zinc oxide (IGZO) TFTs. Our films are grown by single-target sputtering and their optoelectronic properties are easily regulated by the annealing temperature, so this work demonstrates a facile and convenient method for obtaining IGZTO films with appropriate electrical properties and high-performance IGZTO TFTs.