A Low-Dark-Current and High-Responsivity Ultraviolet Photodetector Based on a Recessed-Gate AlGaN/GaN Enhanced-Type High-Electron-Mobility Transistor

Abstract

In recent years, an ultraviolet (UV) photodetector (PD) utilizing two-dimensional electron gas (2DEG) formed at the AlGaN/GaN heterostructure as a GaN-based recessed-gate high-electron-mobility transistor (HEMT) has become a hot topic for UV and solar blind detection. Herein, a GaN-based HEMT UV PD with a recessed gate was prepared, and the conductive channel is closed due to the GaN-based recessed gate, which keeps the device normally off without a p-GaN gate or extra gate bias; the 2DEG is fully depleted with an extremely low dark current density of 1.87 × 10 −6 mA/mm under dark conditions. Under 365 nm UV irradiation, the conductive region is restored and the device exhibits a high photo-to-dark current ratio (PDCR) of 7 × 10 8 , a peak responsivity of 1.75 × 10 4 A/W, a high specific detectivity (D*) of 4.87 × 10 16 Jones, and a superior UV-tovisible rejection ratio of 2.9 × 10 6 . Moreover, a fast response time of 1.55/1.60 ms can be maintained, which is ascribed to the use of triethylgallium in intrinsic GaN (i-GaN) epitaxy to achieve improved crystalline quality, the incorporation of a doped AlGaN layer to reduce the scattering of 2DEGs by positive polarity impurities, and the implementation of asymmetric electrodes for rapid separation and transfer of photogenerated electron−hole pairs. The results indicate that our designed recessed-gate AlGaN/GaN HEMT is an ideal UV PD with high responsivity, low dark current, and rapid response time.