In this letter, 600-V normally-OFF SiN_x/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) is reported. Normally-OFF operation and low OFF-state gate leakage are obtained by using fluorine plasma ion implantation in conjunction with the adoption of a 17-nm SiN_x thin film grown by plasma-enhanced chemical vapor deposition as the gate insulator. The normally-OFF MIS-HEMT exhibits a threshold voltage of +3.6 V, a drive current of 430 mA/mm at a gate bias of 14 V, a specific ON-resistance of 2.1 mΩ·cm² and an OFF-state breakdown voltage of 604 V at a drain leakage current of 1 μA/mm with V_GS=0 V, and the substrate grounded. Effective current collapse suppression is obtained by AlN/SiN_x passivation as proved by high-speed pulsed I-V and low-speed high-voltage switching measurement results.

In this letter, we investigate the threshold voltage (V _TH ) shift in a p-GaN gate AlGaN/GaN transistor by designed gate-bias pulse measurements. It was found that the forward gate bias causes positive (V _TH ) shift. The dynamics of electron trapping was revealed from the dependences of the consequent (V _TH ) shift on the bias duration at different voltages. A time constant smaller than 0.1 ms for the (V _TH ) shift saturation at 6-V gate bias was obtained. It was also found that the (V _TH ) became inversely proportional to the gate-bias voltages exceeding 7 V. This inverse proportionality of the (V _TH ) shift resulted from the threshold of the hole-injection/electroluminescence (EL) and the sequential optical pumping effect on the electron traps. The EL emission was confirmed by a self- and in-situ photon detection measurement.

A low on-resistance normally-off GaN double-channel metal-oxide-semiconductor high-electronmobility transistor (DC-MOS-HEMT) is proposed and demonstrated in this letter, which features a 1.5-nm AlN insertion layer (ISL) located 6 nm below the conventional barrier/GaN interface, forming a second channel at the interface between the AlN-ISL and the underlying GaN. With gate recess terminated at the upper channel, normally-off operation was obtained with Vth of +0.5 V at ^I DS = 10 μA/mm or +1.4 V from the linear extrapolation of the transfer curve. The lower heterojunction channel is separated from the etched surface in the gate region, thereby maintaining its high field-effect mobility with a peak value of 1801 cm ² /(V·s). The on-resistance is as small as 6.9 Q·mm for a DC-MOS-HEMT with LG/LGS/ ^L GD = 1.5/2/15 μm, and the maximum drain current is 836 mA/mm. A high breakdown voltage (>700 V) and a steep subthreshold swing of 72 mV/decade are also obtained. Index Terms-Double-channel MOS-HEMT (DC-MOSHEMT), field-effect mobility, gate recess, normally-off.

We investigate in detail the influence of AlN passivation on dynamic ON-resistance (R _ON ) and electric field (E-field) distribution in high-voltage AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate based on pulsed I-V measurements, electroluminescence (EL) microscopy, and 2-D physics-based numerical device simulations. It is found that the dynamic RON increase has been significantly suppressed to below 10% at various temperatures ranging from -50 to 200 °C owing to the effective and robust compensation of deep acceptor-like trap states at the AlN/GaN (passivation/cap) interface by the additional positive polarization charges induced in the epitaxial AlN thin passivation layer grown in a plasma-enhanced atomic layer deposition system. To the best of our knowledge, this is the first time that highly suppressed current collapse in an AlGaN/GaN HEMT on a Si substrate within a wide temperature range is ever reported. By monitoring the dynamic RON for 100 consecutive 133-kHz switching cycles, its variation is observed to be less than 2.5%, indicating excellent stability of the passivation effectiveness. The electric field in an AlN-passivated device is found to be well confined at the drain-side gate edge, as shown in EL measurement and numerical simulation results. This phenomenon directly suggests that the virtual gate effect arising from surface trap charging has been effectively alleviated by the AlN passivation technique.

The below bandgap optical transitions of an aluminum nitride (AlN) crystal grown on a tungsten (W) substrate by physical vapor transport (PVT) are investigated by below-bandgap-excited photoluminescence (PL) spectroscopy and first-principles calculations. Oxygen (O) is the only impurity in the AlN-on-W crystal grown by PVT. By analyzing the excitation-power-, excitation-photon-energy-, and temperature-dependence of the PL spectra, the emission peaks of defect complexes involving aluminum vacancy (V_Al) and substitutional oxygen (O_N) with different spatial and atomic configurations, i.e., V_Al–O_N and V_Al–2O_N with O_N featuring axial or basal configurations, are identified. It is revealed that two different charging states coexist in thermal equilibrium for each configuration of V_Al–O_N complexes. The optical transitions between the conduction band and (V_Al–O_N)²⁻ and/or (V_Al–2O_N)¹⁻ contribute the UV emissions and those between the valence band and (V_Al–O_N)¹⁻ or (V_Al–2O_N)⁰ contribute the red emissions.

Solar to fuel energy conversion is one of the momentous topics nowadays considering the urgent demand for clean energy supplies. In this work, the tunable electronic and optical properties of III-nitride/ZnO 2D/2D heterostructures (including GaN/ZnO, AlN/ZnO, and GaN/AlN) by strain engineering were investigated by first-principles calculations. The studied heterostructures feature a small interlayer distance, with the cation of one layer directly above the anion of the other layer, and vice versa. This leads to a strong binding energy and interlayer coupling across the heterostructure. The built-in field induced by the charge redistribution facilitates the photoexcited carrier migration, which is beneficial to the photocatalytic water splitting application. The stable III-nitride/ZnO heterostructures exhibit decent band edge positions with biaxial strain engineering and feature an enhancement of optical absorption under tensile strain. Our results indicate that the III-nitride/ZnO 2D/2D heterostructures are promising photocatalysts for solar to hydrogen generation by water splitting.