In this work, details of stress time dependent transient ${V}_{\text {T}}$ shift in p-GaN Gate HEMTs are captured using a fast sweeping method. A minimum saturated ${V}_{\text {T}}$ shift ( $\Delta {V}_{\text {T}\_{}\text {Sat}}$ ) independent of stress time at about 4 V gate stress is observed, and electron tunneling process assisted by shallow traps in the AlGaN barrier is introduced as a likely mechanism to explain the phenomena. Under gate stress of 6 V and above, a stress time dependent over-recovery results in a negative ${V}_{\text {T}}$ shift before the final recovery to the fresh state, confirming that hole de-trapping process needs to take a longer time than electron de-trapping process. In addition, under AC gate stress condition, $\Delta {V}_{\text {T}\_{}\text {Sat}}$ shows an opposite trend in cases of low and high forward AC gate bias stresses, which is explained by the difference in the trapping rates of electrons and holes.

In this letter, we demonstrated a normally-off AlGaN/GaN HEMT using p-NiO as a gate stack combined with a recess structure. The fabricated HEMT exhibits a positive threshold voltage of 1.73 V, a saturation output current of 524 mA/mm, a small subthreshold swing of 79.7 mV/dec and a maximum transconductance as high as 143 mS/mm. This is the first time to demonstrate the breakdown characteristics of a p-NiO gate HEMT with a high breakdown voltage of 1205 V and a low specific ON-resistance of 2.22 $\text{m}\Omega \cdot $ cm ² , yielding a competitive Baliga’s figure-of-merit of 0.65 GW/cm ² . The instability evaluation of ${V}_{\text {TH}}$ by step stress and pulse transfer curves shows that the p-NiO gate HEMT has a negligible ${V}_{\text {TH}}$ shift in the entire measured gate bias range, which can be attributed to the counteraction between the electron trapping-induced positive $\text{V}_{\text {TH}}$ shift and hole accumulation induced-negative ${V}_{\text {TH}}$ shift. It is well understood in terms of the carrier transport model based on the large band discontinuity at the interface of the p-NiO/AlGaN type-II heterojunction, which is further verified by transient gate current spectra.

A hybrid photovoltaic–thermal (PV/T) heat pump system is presented, and the model of dynamic characteristics in a hybrid PV/T heat pump system is established. The solar radiation intensity and the evaporation temperature in the PV/T heat pump system have an influence on the solar panel temperature, the solar photovoltaic efficiency, the solar photovoltaic power, and the heat transfer rate of the solar panel in a hybrid PV/T heat pump system. It was concluded that the solar photovoltaic efficiency was 11.2%, 11.1%, and 11%, the solar photovoltaic power was 92.2, 91.7, and 91.3 W, the heat transfer rate of a solar panel was 416, 410, and 405 W, and the coefficient of performance of the PV/T heat pump system was 6.0, 6.9, and 7.9 when the evaporation temperatures in the PV/T evaporator were 5°C, 10°C, and 15°C, respectively.

In this work, temperature-dependent transient threshold voltage (V_T) instability behaviors in p-GaN/AlGaN/GaN HEMTs, with both Schottky gate (SG) and Ohmic gate (OG), were investigated systematically, under negative gate bias stress, by a fast voltage sweeping method. For SG devices, a concave-shaped V_T evolution gradually occurs with the increase in temperature, and the concave peak appears faster with increasing reverse bias stress, followed by a corresponding convex-shaped V_T recovery process. In contrast, the concave-shaped V_T evolution for OG devices that occurred at room temperature gradually disappears in the opposite shifting direction with the increasing temperature, but the corresponding convex-shaped V_T recovery process is not observed, substituted, instead, with a quick and monotonic recovery process to the initial state. To explain these interesting and different phenomena, we proposed physical mechanisms of time and temperature-dependent hole trapping, releasing, and transport, in terms of the discrepancies in barrier height and space charge region, at the metal/p-GaN junction between SG and OG HEMTs.

In this paper, SiNx film deposited by plasma-enhanced chemical vapor deposition was employed as a gate dielectric of AlGaN/GaN high electron mobility transistors (HEMTs). We found that the NH₃ flow during the deposition of SiNx can significantly affect the performances of metal–insulator–semiconductor (MIS) HEMTs. Compared to that without using NH₃ flow, the device with the optimized NH₃ flow exhibited three orders of magnitude lower gate leakage current, two orders of magnitude higher ON/OF drain current ratio, and an increased breakdown field by 69%. In addition, an in situ N₂ plasma surface treatment prepared prior to SiNx deposition can further improve DC performances of MIS-HEMTs to a very low gate leakage current of 10⁻⁹ mA/mm and a high ON/OFF drain current ratio up to 10⁹ by reducing the interface state density. These results demonstrate the great potential for using PECVD-SiNx as a gate dielectric in GaN-based MIS-HEMTs.

In this work, we present an analytical model of dynamic power losses for enhancement-mode AlGaN/GaN high-electron-mobility transistor power devices (eGaN HEMTs). To build this new model, the dynamic on-resistance (Rdson) is first accurately extracted by our ex-traction circuit based on a double-diode isolation (DDI) method for a high operating frequency up to 1 MHz and a large drain voltage up to 600 V, thus the unique problem of an increase in the dynamic Rdson is presented. Then the impact of the current operation mode on the on/off transi-tion time is evaluated by a dual-pulse-current-mode test (DPCT) which including a discontinu-ous conduction mode (DCM) and a continuous conduction mode (CCM), thus the transition time is revised for different current mode. Afterward the discrepancy between the drain current and the real channel current is qualitative investigated by an external shunt capacitance (ESC) meth-od, thus the losses due to device parasitic capacitance are also taken into account. After these improvements, the dynamic model will be more compatible for eGaN HEMTs. Finally, the dynamic power losses calculated by this model are verified to be in good agreement with experimental results. Based on this model, we propose a superior solution with qua-si-resonant mode (QRM) to achieve lossless switching and accelerate switching speed.