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

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 × 108, a peak responsivity of 1.75 × 104 A/W, a high specific detectivity (D*) of 4.87 × 1016 Jones, and a superior UV-to-visible rejection ratio of 2.9 × 106. 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.