Demonstration of AlGaN/GaN-based ultraviolet phototransistor with a record high responsivity over 3.6 × 107 A/W

In this work, we demonstrate a high-performance ultraviolet phototransistor (UVPT) based on the AlGaN/GaN high-electron mobility transistor (HEMT) configuration. When the device is biased at off state, the peak photoresponsivity (R) of 3.6 × 107 A/W under 265 nm illumination and 1.0 × 106 A/W under 365 nm illumination can be obtained. Those two R values are one of the highest among the reported UVPTs at the same detection wavelength under off-state conditions. In addition, we investigate the gate-bias (VGS) dependent photoresponse of the fabricated device with the assistance of band structure analysis. It was found that a more negative VGS can significantly reduce the rise/decay time for 265 nm detection, especially under weak illumination. This can be attributed to a largely enhanced electric field in the absorptive AlGaN barrier that pushes the photo-generated carriers rapidly into the GaN channel. In contrast, the VGS has little impact on the switching time for 365 nm photodetection, since the GaN channel has a larger absorption depth and the entire UVPT simply acts as a photoconductive-type device. In short, the proposed AlGaN/GaN HEMT structure with the superior photodetection performance paves the way for the development of next generation UVPTs.