Effects of annealing temperature on properties of gallium oxide thin films and ultraviolet detectors

In this work, gallium oxide (Ga₂O₃) thin films are deposited on quartz substrates by radio frequency magnetron sputtering at room temperature and annealed in argon atmosphere at different temperatures. The influences of annealing temperatures in the argon atmosphere on crystal structure, transmittance, surface morphology, and optical band gap of the samples are investigated in detail. It is found that the annealing process can improve the crystalline quality of the film, but high-temperature annealing can also easily cause oxygen elements in the film to escape from the film to form oxygen vacancies, which is evidenced by XPS test results. To obtain the effect of the annealing process on the performance of gallium oxide thin film detector, the metal-semiconductor-metal (MSM) photodetector based on the sample annealed at 800 °C, which is compared with untreated sample operated at a reverse bias voltage of 1.1 V, can achieve excellent comprehensive photo-detection properties for 254 nm ultraviolet light: the light-dark current ratio (<i>I</i>₂₅₄/<i>I</i>_dark), responsivity and specific detectivity are as high as 1021.3, 0.106 A/W and 1.61 × 10¹² Jones, respectively, which are 7.5, 195 and 38.3 times those of the unannealed sample device. And the external quantum efficiency is improved by 51.6%. The rise time of sample detector (0.19/0.48 s) annealed at 800 ℃ decreases compared with that of the unannealed sample (0.93/0.93 s), and the descent time of 800 ℃ detector (0.64/0.72 s)increases compared with that of the unannealed sample (0.45/0.49 s), respectively. By comparing the parameters with those of other current gallium oxide-based MSM photodetectors, it is found that the detector parameters of this work have some gaps compared with the current optimal parameters, which is attributed to the fact that the quartz substrate is selected for this work and not the sapphire substrate that is better matching with gallium oxide, resulting in the poor quality of the film compared with that of the sample on the sapphire substrate, and in this work, the photodetector has the high light-dark current ratio (PDCR) and detection rate (<i>D</i>^*). In the end, the mechanism of increasing oxygen vacancies after being annealed, which leads to the improvement of detector performance parameters, is analyzed in detail.