ZnGa2O4 polycrystalline thin-film preparation using hydrothermally synthesized nanoparticles

Polycrystalline ZnGa2O4 (ZGO) thin films were fabricated on quartz substrates using hydrothermally synthesized ZGO nanoparticles with Zn and O deficiencies. The ZGO thin films were formed by annealing the nanoparticle-coated substrate in air at the temperature range of 500–800 °C. Although the annealing process increased the crystallite size and weakened the quantum size effects decreasing the energy gap (Eg), the ZGO thin film annealed at 800 °C still showed high Eg value of 4.59 eV. A photocurrent (IP) was generated in the thin films at an applied voltage of 40 V under irradiation solar-blind (SB) light conditions (with a wavelength of 254 nm), whereas no IP was induced following exposure to ultraviolet light at 365 nm; that is, the ZGO thin films showed the capability to distinguish SB light and non-SB light. In addition, the repetition of the photocurrent response to SB light was confirmed for the ZGO thin film annealed at 800 °C, where the photocurrent increased with the applied voltage. The ratio of the Ip to the dark current (ID, current without irradiation) increased by a factor of 8.8 as the annealing temperature was increased from 500 to 800 °C owing to the decrease in ID. At high-annealing temperatures, the ID was decreased due to the improved crystallinity resulting from the increase in the number of oxygen vacancies. The present ZGO thin films and control of their IP characteristics by the annealing temperature during preparation can aid in future durable SB photodetector applications.