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 degrees C in N-2 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 similar to 2 pA and I-DS induced by the visible current (at 450 nm) response can be reduced from 2 x 10(-8) to 3 x 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 x 10(2) A/W at 240 nm, in which the rejection ratio is improved to 1.54 x 10(2). 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.