In this article, we experimentally investigate the degradation mechanisms of GaN high-electron mobility transistors (HEMTs) with p-type gate during long-term high-temperature reverse bias (HTRB) stress and negative bias temperature instability (NBTI) stress. Based on a number of stress/recovery experiments, we demonstrate that HTRB stress could lead to hole emission in the p-GaN layer, making threshold voltage (Vth) positively shift, while NBTI stress could result in detrapping at the AlGaN/GaN interface or the AlGaN layer and make Vth negatively shift. It is also found that the temperature rise can suppress the positive Vth shift and accelerate its recovery process in HTRB experiments.

This work investigates the degradation mechanism of 1.2 kV silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET) under positive or negative long-term high-temperature gate bias (HTGB) stress. After positive long-term HTGB stress, the device shows a positive shift in threshold voltage ( ${V}_{\text {th}}{)}$ and an increase in ON-state resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}{)}$ , which mainly results from the electron traps at or near the SiC/SiO2 interface. While subjected to negative HTGB stress, the drift of $V_{\text {th}}$ is time-dependent and correlated with the gate bias. For the device biased at a low gate voltage of −10 V, due to the hole traps at or near the interface, its ${V}_{\text {th}}$ exhibits negative shift all the time. But the drift of ${V}_{\text {th}}$ for the device biased at a higher voltage of −20 V is decreased first with the stress time, then is increased with the stress time, which may result from the hole traps and the additional electron traps introduced by the tunneling effect. Through the low-frequency noise technology, it is demonstrated that the trap density of the device biased at higher negative gate voltage of −20 V has been increased up to three times.

We have investigated the effect of hot electron stress on the electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs) of hydrogen poisoning. The AlGaN/GaN HEMTs were biased at the semi-on state, and they suffered from the hot electron stress. The devices of hydrogen poisoning were degraded, while there is almost no degradation for the fresh ones. The hot electron stress leads to the significantly positive shift of threshold voltage and the notable decrease of drain-to-source current for the AlGaN/GaN HEMTs of hydrogen poisoning. For the AlGaN/GaN HEMTs of hydrogen poisoning, the trap density increases by about one order of magnitude after the hot electron stress experiment. The physical mechanism can be attributed to electrically active traps due to the dehydrogenation of passivated point defects at AlGaN surface, AlGaN barrier layer, and heterostructure interface. The results of this paper may be useful in the design and application of AlGaN/GaN HEMTs.

In the article, a new thermal resistance measurement method for GaN high electron mobility transistor (HEMTs) is proposed based on temperature sensitive electrical parameter (TSEP) with the use of MOS switches to connect the drain–source at the beginning of the measurement processes. Compared with traditional methods, the connection of the source and drain reduces the delay caused by the matching circuit. In our experiments, we measured a GaN HEMT at 48 V with a power consumption of 5.28 W. The delay time was less than ${2}~\mu \text{s}$ , and the thermal resistance was 9.85 °C/W. We also measured the thermal resistance at the same current-different voltages and different voltages-same power. The results show that the thermal resistance of the GaN HEMT increases with the increase of the power and voltage. Furthermore, the results have been verified by infrared (IR) and simulation methods. Compared with Raman thermography and IR, this method can conveniently measure the thermal resistance of GaN HEMTs without breaking the package, and the temperature accuracy was ±2 °C or better. And the thermal resistance information of each layer of structure, such as the chip-solder-carrier, can be extracted by structural function method to improve the thermal design of GaN HEMTs.

In this article, the degradation behavior of the electrical characteristics of AlGaN/GaN HEMTs subjected to radio frequency (RF) overdrive stress has been studied. Trap analysis based on low-frequency noise (LFN) and electroluminescence (EL) characterizations was carried out for AlGaN/GaN HEMTs before and after RF stress. The experimental results show that drain-to-source current of AlGaN/GaN HEMTs after RF stress is obviously lower than that of the fresh devices. The maximum change of drain-to-source current was up to 79 mA in the saturation zone. The threshold voltage drifted forward and gate-lag characteristic became worse for the AlGaN/GaN HEMTs after RF stress. The EL characterizations also showed the nonuniformity of channel illumination intensity, which indicates the distribution of electron of the channel nonuniform. Trap analysis was performed by using the LFN method, and the LFN results showed that the trap density increased by about one order of magnitude in the AlGaN/GaN HEMTs after RF stress, which would lead to more depletion of the channel two-dimensional electron gas (2DEG) electrons. The mechanism of increasing trap density could be attributed to defects induced by RF stress at AlGaN surface and AlGaN barrier layer. The experimental results may offer a useful reference in the design and application of RF of AlGaN/GaN HEMTs.

The related recovery effect of hydrogen on AlGaN/gallium nitride (GaN) high-electron-mobility transistors (HEMTs) irradiated by high-fluence protons was investigated in this article. The results show that under the same temperature and time conditions, the recovery effect induced by thermal hydrogen annealing is better than that of ordinary thermal annealing. Compared with the ordinary thermal annealing, the high-fluence proton-irradiated device experienced a 65-mA additional increase in saturation current at the gate-to-source voltage (V _gs ) of 0 V, a 0.074-V additional negative shift of the threshold voltage, a more significant increase in reverse gate leakage current and better gate lag after the hydrogen treatment. The defect densities are extracted by the low-frequency noise method. It shows that the trap density decreases from 8.32 × 10 ¹⁷ to 6.84 × 10 ¹⁷ cm ^-3 ·eV ^-1 after ordinary thermal annealing and then decreases from 6.84 × 10 ¹⁷ to 3.85 × 10 ¹⁷ cm ^-3 ·eV ^-1 after hydrogen treatment of an irradiated AlGaN/GaN HEMT. The mechanism for the decrease of trap density after the hydrogen treatment could be attributed to the H-passivated defects in the structures of AlGaN/GaN HEMTs.