The p-GaN gate high electron mobility transistor (HEMT) with a 2.0 × 10^-5 cm² sensitive area as a UV photodetector (PD) has been designed and fabricated in this study. AlGaN/gallium nitride (GaN) heterostructure was adopted to get a 2-D electron gas (2DEG) as a conductive channel, resulting in a high photoresponsivity of 8.07 × 10⁴ A/W, a sharp cutoff wavelength at 360 nm, high UV-to-visible rejection ratio of 1.80 × 10⁶, rise and decay time of 0.12 and 1.0 ms, respectively. The dark current of 5.44 × 10^-7 A, the photocurrent of 4.42 × 10^-3 A at 5 V, the external quantum efficiency (EQE) of 2.77% × 10⁵%, and the detectivity of 8.31 × 10¹⁴ Jones for the UV PD were determined under a low UV light intensity of 5 mW/cm² at 360-nm UV illumination. The obtained results show that the performance of as-fabricated UV PD based on AlGaN/GaN HEMT is significantly improved compared to the literature. This device, which has lower noise equivalent power (NEP) and enhanced detectivity features compared to existing ones, is a promising candidate for military and space applications.

A novel ohmic-like p-GaN gate high-electron-mobility transistor (HEMT) with a built-in diode (BD) was proposed and fabricated in this work. Compared with the conventional Schottky-contact type p-GaN gate, ohmic-like contact can avoid the formation of high electric field in the Schottky depletion region and eliminate gate degradation caused by the Schottky junction failure. Good electrical match between the reverse BD and the PIN junction in the gate-stack is critical to device operation, especially at a high gate voltage. The reverse built-in hybrid anode diode (HAD) can withstand a high reverse bias and limit a relatively low gate leakage current (10 $^{-\text{1}}$ mA/mm) even under the forward gate voltage of 100 V. No obvious degradation has been observed after the high temperature and longtime high gate voltage stress. Meanwhile, it has negligible impacts on the other characteristics, showing great potential for practical applications.

In this work, we carried out research on the photoresponsivity of a high-performance p-GaN high-electron mobility transistor-based ultraviolet photodetector at low temperatures. The device exhibited an extraordinary responsivity of 2.8 × 106 A/W at 100 K, demonstrating its great potential in frigid environment. Meanwhile, the mechanism of interaction between photo-generated carriers and defects is also discussed. The quantitative analysis of the decay behavior reveals that two trap levels determined the decay behavior in different temperature intervals. It provides constructive evidence for understanding the persistent photoconductivity behavior and can be meaningful in further improvement of the device performance.

In this work, we present a low-damage p-GaN surface processed by atomic layer etching (ALE), enabling high-performance Ohmic contacts. The mechanism underlying surface modifications introduced by various etching processes were studied in detail. Compared to conventional dry etch, ALE preserves the pristine surface stoichiometry comparable to as-grown p-GaN, effectively suppressing the formation of detrimental surface defects. Crucially, this atomic-level controlled process minimizes the increase in downward band bending and maintains the intrinsic surface electrical properties. Thus, metal contacts fabricated on the ALE-processed p-GaN exhibit an excellent Ohmic behavior. Collectively, these results not only establish low-surface-degradation contacts, but also provide a fundamental understanding required for advancing GaN-based device physics and designs.

Through a novel pulsed I-V test with an extra pre-state at sub-millisecond timescales, the effects of positive charges storage and depletion in gate stack on dynamic threshold voltage (VTH) instability are characterized and studied in p-GaN gated enhancement-mode high electron mobility transistor (E-HEMT). Due to the time-dependent transport behaviors of carriers, the causes of negative VTH shifts have been analyzed theoretically and successfully distinguished, which are mainly attributed to the hole accumulation or hole trapping in the p-GaN gate. Moreover, the distinct deviations have been revealed through the drain current transient curves under positive gate stress combined with pre-pulsed negative voltage. The detailed transport process of holes is inquired comprehensively through evaluating the temperature-dependent current transient characteristics. And the traps energy levels and band offset have been given out experimentally. This study focuses on the mechanism and in-depth influence of carrier behaviors on the gate performance, demonstrating that the proposed method is a powerful tool for distinguishing dynamic carrier transport processes, and can help with the further improvement of the dynamic instability and reliability of the GaN-based HEMTs.