Energy-Saving ZnGa₂O₄ Phototransistor Improved by Thermal Annealing

The development of phototransistors is attributed to material stability, and energy saving has remained a challenge. This is particularly important for single-crystalline ZnGa2O4 epitaxial thin films essential for applications in sensing, energy conversion, and storage. We report herein that high-temperature thermal annealing with 800 °C in N2 ambient for 1 h could significantly improve epilayer quality, which has been used to fabricate the phototransistor. It was found that the off current of the annealed sample decreased to be ∼2 pA and IDS induced by the visible current (at 450 nm) response can be reduced from 2 × 10–8 to 3 × 10–9 A as compared with that of the as-grown phototransistor. It could have resulted from the higher crystallinity and lower defect density after the annealing treatment. The responsivity of a ZnGa2O4 phototransistor is 4.74 × 102 A/W at 240 nm, in which the rejection ratio is improved to 1.54 × 102. Moreover, the resulting ZnGa2O4 phototransistor has an excellent 0.4 s response time. The above results demonstrate that the high superiority of annealed ZnGa2O4 can be applied in the deep ultraviolet photodevices.