The Effect of Oxygen Partial Pressure and Annealing Process on the Characteristics of ZnGa₂O₄ MSM UV Photodetector

Abstract

In this work, ZnGa2O4 solar-blind photodetectors (PD) based on a metal-semiconductor-metal (MSM) structure was fabricated by radio frequency (RF) magnetron sputtering method. The transmittance of the material shows larger than 80% cross the visible light region. As a wide bandgap and high transparency semiconducting material, ZGO is a potential candidate for UV-detection applications. The ZGO MSM PD with no oxygen flow during sputtering exhibits a responsivity of 4.46 × 10−2 A/W under illumination at wavelength of 260 nm, rejection ratio of 1.75 × 104. The performance can be enhanced with proper thermal annealing process. With an annealing process at temperature of 200°C, the responsivity and rejection ratio are 0.203 A/W and 1.12 × 105, respectively.

Zinc Gallium Oxide—A Review from Synthesis to Applications

“…Therefore, both dark current and photocurrent are decreased due to an increase in partial oxygen pressure. However, the ratio of I ph /I dark did not reach a higher value with increasing partial oxygen pressure [20].…”

“…MSM photodetectors possess low capacitance and have the potential for large-area detectors [89]. Therefore, MSM ZnGa 2 O 4 photodetectors in Reference [20,85,90,91] are taken into consideration. Their process parameters and optimized performances are listed in Tables 7 and 8, respectively.…”

“…In addition to the annealing method, increase in the partial oxygen pressure also changes the concentration of oxygen vacancies [20], resulting in less oxygen vacancies or less carriers in the ZnGa 2 O 4 thin films. The concentration of oxygen vacancies directly affects photocurrent and dark current because the concentration of carriers is directly proportional to the current.…”

“…The authors concluded that the Schottky barrier was responsible for this phenomenon [85]. Increasing the oxygen flow rate also results in enhancing the DUV-visible rejection ratio, but it is not feasible because less oxygen flow during sputtering can create more oxygen vacancies which could be excited by UV light [20]. In addition to the aforementioned methods above, post-annealing can transform the broad spectral response of the photodetector to sharp spectral response.…”

“…ZnGa 2 O 4 phosphors possess intrinsic blue emission characteristics, and the doping of metal ions may lead to a shift in its emission wavelength [18] and manifest various functional properties that can be applied to optoelectronic devices [19]. Recently, ZnGa 2 O 4 thin films have been investigated for deep-ultraviolet photodetectors [20]. Porous ZnGa 2 O 4 microspheres are synthesized by a facial glucose-mediated microwave hydrothermal method followed by annealing, in order to investigate the photocatalytic degradation of gas-phase aromatic pollutants, where porous ZnGa 2 O 4 microspheres confirmed a much higher activity and stability than TiO 2 under 254 nm UV irradiation [21].…”