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An optimized top-down approach was utilized to fabricate vertical GaN-on-GaN nanowire Schottky barrier diodes (NWSBDs) in this letter. The suppressed reverse leakage current and enhanced breakdown voltage (BV) of the vertical GaN NWSBDs are attributed to the reduced electric field at the interface of the Schottky junction achieved through the dielectric reduced surface field technique. As-fabricated NWSBD delivers a low turn-on voltage of 0.80 V, a near-unity ideality factor of 1.04, along with a soft BV of 480 V. The measured soft BV is comparable with the avalanche BV of the p–n diode with a similar net doping concentration in the drift region. [ABSTRACT FROM AUTHOR]

An AlGaN-recess-free, ultrathin-barrier (UTB) AlGaN (<6 nm)/GaN heterostructure is presented for the fabrication and integration of AlGaN/GaN enhancement/depletion-mode (E/D-mode) heterojunction field-effect transistors (HFETs), and metal–insulator-semiconductor HFETs (MIS-HFETs). The 2D electron gas in the access region of the UTB-AlGaN/GaN (MIS)HFETs can effectively be recovered by a low-pressure chemical-vapor-deposited SiNx passivation layer (LPCVD-SiNx), which is capable of introducing about 2.75 × 1013 cm−2 positive fixed charges at the LPCVD-SiNx/(Al)GaN interface. LPCVD-SiNx can also serve as a good gate insulator for D-mode MIS-HFETs. Using the self-terminating etching of LPCVD-SiNx on III-nitride as well as a low-damage remote plasma pretreatment, high uniformity E-mode HFETs and low-hysteresis E-mode MIS-HFETs have been fabricated using the GaN-on-Si platform. E/D-mode MIS-HFET inverters with a large logic swing have also been demonstrated on this platform. The UTB-AlGaN/GaN heterostructure is an attractive technology platform for the on-chip integration of power and RF devices with power-driven circuits for GaN-based smart power integrated circuits. [ABSTRACT FROM AUTHOR]

GaN power transistors are attracting increasing attention for next-generation power switching applications. However, GaN power transistors should not be regarded as a direct replacement for silicon power metal–oxide–semiconductor field-effect transistors, since the unique properties of GaN power transistors require special treatment. In this work we review a unique and critical property of GaN power transistors, the dynamic threshold voltage (Vth). GaN power transistors feature a p-GaN gate structure, while the gate metal contacts the p-GaN layer through a Schottky junction. This unique p-GaN gate structure is distinctively different from the silicon metal–oxide–semiconductor gate structure in that the p-GaN layer is actually a floating region without direct electrical contact to the external electrodes of the device. The floating p-GaN layer enables a charge storage process during the switching operation of a p-GaN gate high-electron-mobility transistor. Through carefully designed experiments, the strong correlation between charge storage and the dynamic Vth shift has been revealed; this also serves as an approach to accurately predict the dynamic Vth during switching operation. The influence of the dynamic Vth on power switching applications is discussed. For example, with a positive dynamic Vth shift, the reverse conduction voltage of a GaN power transistor is significantly increased, adding to the power loss. This positive Vth shift also demands a sufficiently high gate drive voltage to ensure that the GaN power transistor can be fully turned on, which reduces the safety margin for the gate reliability of the device. To design a GaN based power switching circuit, accurate simulation of the device/circuit characteristics is necessary. Circuit simulations that do not consider the dynamic Vth lead to a large deviation from the measurement circuit characteristics. We demonstrate that by incorporating the dynamic Vth into the circuit model this deviation can be effectively eliminated. [ABSTRACT FROM AUTHOR]

In this work, enhancement-mode (E-mode) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with high-κ LaLuO3 (LLO) gate dielectric were fabricated by deploying the CF4 plasma treatment technique in a gate-dielectric-first planar process. CF4 plasma treatment can shift the threshold voltage from -2.3 V [for depletion-mode (D-mode) LLO MIS-HEMTs] to 0.6 V (for E-mode LLO MIS-HEMTs). Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results suggest that fluorine ions could penetrate through the polycrystalline/amorphous LLO film and be implanted into the (Al)GaN barrier layer. The primary threshold voltage (VTH) shift mechanism of the E-mode LLO MIS-HEMTs is the negatively-charged fluorine ions in (Al)GaN, while fluorine atoms form chemical bonds with La/Lu atoms in the fluorinated LLO film. The E-mode LLO MIS-HEMTs exhibit a drive drain current density of 352 mA/mm at VGS = 2.5 V and a peak transconductance (Gm) of ∼193 mS/mm. Significant suppression of current collapse and low dynamic ON-resistance are obtained in the E-mode LLO MIS-HEMTs under high-drain-bias switching conditions. [ABSTRACT FROM AUTHOR]

As a thermal sensing and protection module on a GaN smart power IC platform, the first GaN over-temperature protection (OTP) circuit is demonstrated to deliver a desirable triggering signal at the critical temperature. The integrated OTP circuit is realized based on monolithic integration of enhancement-/depletion-mode high electron mobility transistors (HEMT) and HEMT-compatible lateral field effect rectifiers on a baseline AlGaN/GaN-on-Si wafer. The circuit effectively indicates the over-temperature up to 250 °C, and has a power supply rejection radio well above 35 dB. This sensing/protection circuit is expected to provide enhanced reliability to the high-voltage GaN power devices. [ABSTRACT FROM AUTHOR]

In this work, we present a novel device technology of using Schottky source/drain (SSD) in InAlN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MISHEMTs) for off-state breakdown voltage VBD improvement. The Schottky source/drain design can effectively prevent the source carrier injection compared to the conventional MISHEMTs, leading to enhanced VBD in the SSD MISHEMTs. A VBD of 460 V is obtained in an InAlN/GaN SSD MISHEMTs with low specific Ron of 2.27 mΩ·cm2, at a 170% VBD improvement compared to conventional MISHEMTs. Despite the Schottky source/drain used, a SSD MISHEMT with a gate length of 1 µm exhibits respectable drain current density of 416 mA/mm and transconductance of 113 mS/mm. [ABSTRACT FROM AUTHOR]

A boundary-temperature-controlled epitaxy, where the growth temperature of InN is controlled at its maximum, is used to obtain high-electron-mobility InN layers on sapphire substrates by molecular beam epitaxy. The Hall-effect measurement shows a recorded electron mobility of 3280 cm2 V-1 s-1 and a residual electron concentration of 1.47×1017 cm-3 at room temperature. The enhanced electron mobility and reduced residual electron concentration are mainly due to the reduction of threading dislocation density. The obtained Hall mobilities are in good agreement with the theoretical modelling by the ensemble Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

The threshold voltage (Vth) instability in GaN-based metal–insulator–semiconductor high-electron mobility transistors (MIS-HEMTs) with 15-nm atomic-layer-deposited (ALD) Al2O3 as gate dielectrics is systematically investigated by dc current–voltage (I–V), high-frequency capacitance–voltage (C–V) (HFCV), and quasi-static C–V (QSCV) characterizations. Both Al2O3/GaN/AlGaN/GaN MIS diode and GaN/AlGaN/GaN Schottky diode only exhibit tiny threshold-voltage hysteresis (ΔVth) (<10 mV) in double-mode (up and down sweep) HFCV characteristics as the maximum forward bias (VFmax) during the sweep is set to 0 V, while an apparent ΔVth (as large as 0.9 V) emerges as VFmax is increased to +5 V for the MIS diode. The stability of Vth in the corresponding MIS-HEMTs is thus studied by increasing the maximum VGS (VGSmax) in the measurement of transfer characteristics. Significant positive Vth shift occurred once the VGSmax exceeds +1 V, while such Vth-instability is still absent in Schottky-gate AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al2O3/GaN interface account for the Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs. As the filling and emission processes of these interface states are slow, they are successfully captured by low-frequency QSCV techniques. [ABSTRACT FROM AUTHOR]

This paper presents the dc and dynamic characterizations of a GaN-based voltage comparator, fabricated with monolithic integration of enhancement-mode (E-mode) and depletion-mode (D-mode) AlGaN/GaN high electron mobility transistors (HEMTs). The comparator features high gain (>31 dB) and wide bandwidth (>4 MHz), and small propagation delay time (<20 ns) over a wide temperature range up to 250 °C. Its dc gain is still 27.1 dB at 400 °C. These results demonstrate the potential of the AlGaN/GaN HEMT technology for mixed-signal integrated circuits used in GaN power electronics that promises high-voltage, high-current, and high-temperature operation. [ABSTRACT FROM AUTHOR]

We demonstrate a dual-gate (DG) AlGaN/GaN high-electron-mobility transistor (HEMT) structure with enhancement-mode (E-mode) operation. The DG device consists of an E-mode gate and a depletion-mode (D-mode) gate instead of the dual D-mode gate electrodes used in previously reported works; thus no negative voltage supply is required when the DG device is used in amplifier circuits. The E-mode DG HEMTs exhibit similar DC characteristics to E-mode single-gate devices but show a 9 dB gain improvement at 2.1 GHz under the same bias conditions. The power gain improvement can be attributed to the higher output impedance and lower feedback capacitance in the DG structure. [ABSTRACT FROM AUTHOR]