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 (E_g), the ZGO thin film annealed at 800 °C still showed high E_g value of 4.59 eV. A photocurrent (I_P) 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 I_P 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 I_p to the dark current (I_D, 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 I_D. At high-annealing temperatures, the I_D 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 I_P characteristics by the annealing temperature during preparation can aid in future durable SB photodetector applications.