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In this paper, we systematically investigated the leakage mechanism of the ion-implantation isolated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) on Si substrate. By means of combined DC tests at different temperatures and electric field dependence, we demonstrated the following original results: (1) It is proved that gate leakage is the main contribution to OFF-state leakage of ion-implantation isolated AlGaN/GaN MIS-HEMTs, and the gate leakage path is a series connection of the gate dielectric Si 3 N 4 and Si 3 N 4 -GaN interface. (2) The dominant mechanisms of the leakage current through LPCVD-Si 3 N 4 gate dielectric and Si 3 N 4 -GaN interface are identified to be Frenkel–Poole emission and two-dimensional variable range hopping (2D-VRH), respectively. (3) A certain temperature annealing could reduce the density of the interface state that produced by ion implantation, and consequently suppress the interface leakage transport, which results in a decrease in OFF-state leakage current of ion-implantation isolated AlGaN/GaN MIS-HEMTs.

In this letter, we report an in-situ predeposition plasma nitridation process, which is adopted to remove the GaN surface oxygen-related bonds and reduce surface dangling bonds by forming Ga-N bonds prior to the low-pressure chemical vapor deposition (LPCVD)Si 3 N 4 deposition. It demonstrates that the Vth hysteresis and current collapse of the device were dramatically improved due to high-quality LPCVD-Si 3 N 4 /GaN interface. The MIS-HEMTs using this in-situ pre-deposition plasma nitridation exhibit a very-low Vth hysteresis of 186 mV at VG-sweep = (-30 V, +24 V), a high breakdown voltage of 881 V with the substrate grounded. Meanwhile, the MIS-HEMT dynamic RON is only 18% larger than the static RON after OFF-state VDS stress of 600 V (the OFF to ON switching time interval is set to 200 μs).

p-doped gallium nitride (GaN) regrowth by epitaxial lateral overgrowth using a SiO2 mask is studied. A comparison between SiO2 and Al2O3 masked p-GaN by cathodoluminescence spectroscopy and scanning electron microscopy indicates that donor-type impurities are related to the SiO2 mask. A domain peak of 3.25 eV induced by shallow-donor and acceptor transitions and the dark contrast of obtuse triangles have been detected in SiO2 masked p-type GaN. Secondary ion mass spectroscopy is simultaneously employed for the analysis of SiO2 and Al2O3 masked p-GaN and identifies that the source of donor-type impurities is from Si atoms. Furthermore, the experimental results of cross-sectional microstructures at different regrowth times have been investigated. It is found that the donor-type impurities tend to cluster in semi-polar 11 2 ¯ 2 facets before the coalescence at the bottom of adjacent triangular stripes starts. The explanation for the non-uniform distribution of impurities is that semi-polar 11 2 ¯ 2 facets exhibit more dangling bond densities than the (0001) plane, and the SiO2 mask exposed to the vapor phase would likely introduce more impurities before the coalescence of GaN stripes.

In this paper, we present a method for removing a high electron mobility transistor (HEMT) silicon substrate using mechanical grinding and deep silicon etching technology and successfully transferred the epitaxial wafer to a PET substrate to achieve the flexible normally-off HEMT. By testing the output characteristics and transfer characteristics of the Si-substrate HEMT and PET-substrate HEMT, we have demonstrated that the PET-substrate HEMT has excellent performance and successfully achieved the mechanical flexibility. Furthermore, we analyzed the physical mechanisms of the change in PET-substrate and Si-substrate HEMT characteristics, as well as flexible HEMT performance under bent and flattened states. The flexible HEMT array demonstrates significant potential in integration with other flexible devices, such as GaN-based micro-LED arrays.

This paper investigates the performance of AlGaN/gallium nitride (GaN) MIS high electron mobility transistors (MIS-HEMTs). The gate dielectric layer and the surface passivation layer are formed by the low-pressure chemical vapor deposition (LPCVD) Si3N4. The LPCVD-Si3N4 MIS-HEMTs exhibit a high breakdown voltage (BV) of 1162 V at $I_{\mathrm{ DS}}= 1~\mu \text{A}$ /mm, a low OFF-state leakage of $7.7 \times 10^{-12}$ A/mm, and an excellent ON/OFF-current ratio of $\sim 10^{11}$ . Compared with the static ON-resistance of 2.88 $\text{m}\Omega \cdot \textrm {cm}^{2}$ , the dynamic ON-resistance after high OFF-state drain bias stress at 600 V only increases to 4.89 $\text{m}\Omega \cdot \textrm {cm}^{2}$ . The power device figure of ${\mathrm{ merit}} = \textrm {BV}^{{\vphantom {R^{l}}{2}}}/R_{{{\mathrm{\scriptscriptstyle ON}.{\mathrm{ sp}}}}}$ is calculated to be 469 $\textrm {MW}\cdot \textrm {cm}^{-2}$ . The LPCVD-Si3N4/GaN interface state density is in the range of (1.4–5.3) $\times 10^{{\vphantom {R^{l}}{13}}}$ eV $^{-1}$ cm $^{-2}$ extracted by the conventional conductance method. Finally, the gate insulator degradation of GaN-based MIS-HEMTs is analyzed by time-dependent dielectric breakdown test. The lifetime is extrapolated to 0.01% of failures after ten years at 300 K by fitting the data with a power law to a gate voltage of 10.1 V.

Minirhizotron technology is widely used to study root growth and development. Yet, standard approaches for tracing roots in minirhiztron imagery is extremely tedious and time consuming. Machine learning approaches can help to automate this task. However, lack of enough annotated training data is a major limitation for the application of machine learning methods. Transfer learning is a useful technique to help with training when available datasets are limited. In this paper, we investigated the effect of pre-trained features from the massive-scale, irrelevant ImageNet dataset and a relatively moderate-scale, but relevant peanut root dataset on switchgrass root imagery segmentation applications. We compiled two minirhizotron image datasets to accomplish this study: one with 17,550 peanut root images and another with 28 switchgrass root images. Both datasets were paired with manually labeled ground truth masks. Deep neural networks based on the U-net architecture were used with different pre-trained features as initialization for automated, precise pixel-wise root segmentation in minirhizotron imagery. We observed that features pre-trained on a closely related but relatively moderate size dataset like our peanut dataset were more effective than features pre-trained on the large but unrelated ImageNet dataset. We achieved high quality segmentation on peanut root dataset with 99.04% accuracy at the pixel-level and overcame errors in human-labeled ground truth masks. By applying transfer learning technique on limited switchgrass dataset with features pre-trained on peanut dataset, we obtained 99% segmentation accuracy in switchgrass imagery using only 21 images for training (fine tuning). Furthermore, the peanut pre-trained features can help the model converge faster and have much more stable performance. We presented a demo of plant root segmentation for all models under https://github.com/GatorSense/PlantRootSeg .

Ba(Ti0.96Sn0.04)O3–xY2O3 (BTS–Y) lead-free piezoceramics are fabricated by the conventional solid state reaction technique. The influences of Y3+ substitution on the phase structure, dielectric properties and piezoelectricity of BTS–Y piezoceramics are investigated. XRD patterns show the ceramics possess a pure perovskite structure. The orthorhombic–tetragonal (O–T) phase transition dielectric peak shifts toward lower temperature with increasing Y3+ content. The compositions x = 0.15 − 0.25% that are at O–T polymorphic phase transition region possess excellent piezoelectricity and the maximum piezoelectric constant d33 of 454 pC/N is obtained at x = 0.2%. The ceramics’ Curie temperatures (TC) are monotonically increased from 71 °C for x = 0 − 86 °C for x = 0.4% due to Y3+ substitution and the usage temperature range of BTS–Y piezoceramics is broadened. Compared with Ca2+ which also decreases the O–T phase transition temperature (TO–T) but hardly affects the TC of BaTiO3-based ceramics, Y3+ substitution seems to be more beneficial for the practical application of the piezoceramics.

Normally off p-gallium nitride (GaN) gate high-electron-mobility transistors (HEMTs) on silicon substrate were fabricated with hydrogen plasma treatment technology, which features a high-resistivity cap layer (HRCL) at the access region. With hydrogen plasma treatment at the access region, the normally off operation was obtained with a threshold voltage of +2.5 V based on the linear extrapolation of the transfer curve. The fabricated HRCL-HEMT with a gate width of 49.7 mm exhibits a maximum drain current of 10 A at V GS = 8 V and a high off-state breakdown voltage of 567 V at V GS = 0 V with substrate grounded. Meanwhile, the HRCL-HEMT also shows low-gate leakage current of 1.3 × 10−7 and 3.3 × 10−10 A/mm at V GS = 8 V and = −30 V, respectively. The positive threshold voltage, high drain current, high-breakdown voltage and low-gate leakage show the potential of HRCL-HEMT for power switching applications.

In this letter, E-mode n-GaN gate heterostructure field effect transistors (HFETs) utilizing polarization induced 2D hole gas (2DHG) have been proposed. It is found that the introduction of the n-GaN cap between the GaN channel layer and the gate metal can effectively deplete the 2DHG in the gate region, resulting in E-mode operation. The simulation results indicate that by adjusting the GaN channel thickness and n-GaN cap doping concentration, threshold voltage of the n-GaN gate p-channel HFETs can be more than |−1.5| V without sacrificing the ON-state current and the ON/OFF ratio, which is enabled to overcome the trade-off observed from conventional p-channel devices.

We report an approach to make two-terminal antenna-coupled AlGaN/GaN high-electron-mobility-transistor self-mixing terahertz detectors. Fluorine ion implantation is used to increase the threshold voltage of the AlGaN/GaN two-dimensional electron gas. An optimal implantation dose can be reached so that the detector responsivity is maximized at zero gate voltage or with the gate floating. The relationship between the ion dosage and the threshold voltage, electron mobility, electron density, responsivity, and noise-equivalent power (NEP) is obtained. A minimum optical NEP of 47 p W / Hz is achieved from a two-terminal detector at 0.65 THz. The capability of two-terminal operation allows for the design of a large array of antenna-coupled high-electron-mobility transistor detectors without the demanding needs of routing negative gate voltage lines around the antenna array and minimizing the gate leakage current.

We report the study of spin–orbit torques in different GaN/NiFe bilayers using a spin-torque ferromagnetic resonance (ST-FMR) method. The GaN/NiFe bilayer based on Ge–GaN and Fe–GaN displayed distinct ST-FMR results, i.e. voltage signal intensity, lineshape, and resonance field. The Ge–GaN/NiFe bilayer exhibited a stronger torque ratio between in-plane torque (τ ∥) and out-of-plane torque (τ ⊥) than the Fe–GaN/NiFe bilayer, which can be ascribed to the difference of Fermi energy level in Ge–GaN and Fe–GaN. Furthermore, the torque ratio of both systems tends to decrease with microwave frequency. Our results may help to understand the spin–orbit torques in GaN.

In this letter, gate leakage mechanisms in different gate contact normally off p-GaN/AlGaN/GaN high electron mobility transistors (HEMTs) have been studied by the temperature-dependent current-voltage (IG-VG) measurement. It is found that two-dimensional variable range hopping is responsible for gate leakage current at the reverse gate bias and low forward gate bias in both high-leakage and low-leakage Schottky gate contact devices. At high forward gate bias, in the case of high-leakage Schottky contact, the dominant current conduction mechanism is found to be thermionic field emission while it is Poole–Frenkle emission (PFE) for the case of low-leakage Schottky contact and the activation energy of trap states for PFE current is derived as 0.6 eV. Besides, related models are also proposed to describe the gate leakage current in p-GaN gate HEMTs and they match well with the experimental gate leakage current within a wide range of temperatures and gate biases.

An AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) on Si substrate was obtained with 18 nm silicon nitride (Si3N4) grown by low-pressure chemical vapour deposition (LPCVD) as the gate insulator. The D-mode MIS-HEMT shows a high I-dss of 16.8 A at V-g = 3 V, a high breakdown voltage (BV) of 600 V and a low-specific on-resistance of 2.3 m Omega.cm(2). The power device figure of merit (FOM = BV2/R-on,R-sp) is calculated as 157 MW.cm(-2). The good insulation effects of LPCVD-Si3N4 were also demonstrated by the low gate leakage current of 154 nA at V-ds = 600 V and V-gs = -14 V. Furthermore, an E-mode device was realised by a low-voltage silicon metal-oxide-semiconductor field-effect transistor in series; the V-th was determined to be 2.6 V. The high I-dss, low-specific on-resistance, high BV and positive V-th show the potential and advantages of GaN MIS-HEMTs for power switching applications.

Gallium Nitride (GaN) Schottky betavoltaic nuclear batteries (GNBB) are demonstrated in our work for the first time. GaN films are grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD), and then GaN Schottky diodes are fabricated by normal micro-fabrication process. Nickel with mass number of 63 ( 63 Ni), which emits β particles, is loaded on the GaN Schottky diodes to achieve GNBB. X-ray diffraction (XRD) and photoluminescence (PL) are carried out to investigate the crystal quality for the GaN films as grown. Current–voltage ( I – V ) characteristics shows that the GaN Schottky diodes are not jet broken down at −200 V due to consummate fabrication processes, and the open circuit voltage of the GNBB is 0.1 V and the short circuit current density is 1.2 nA cm −2 . The limited performance of the GNBB is due to thin effective energy deposition layer, which is only 206 nm to absorb very small partial energy of the β particles because of the relatively high dislocation density and carrier concentration. However, the conversion efficiency of 0.32% and charge collection efficiency (CCE) of 29% for the GNBB have been obtained. Therefore, the output power of the GNBB are expected to greatly increase with growing high quality thick GaN films.

An AlGaN/GaN metal-oxide semiconductor (MOS) high-electron mobility transistor (HEMT) on silicon substrate was obtained with 8 nm Al2O3 gate dielectric films grown using atomic layer deposition. The MOS-HEMT shows a low specific on-resistance of 0.57 Omega.mm(2), a large maximum saturate drain current of 12.5 A and a minimal threshold hysteresis of 0.05 V. Low specific on-resistance, large maximum saturate drain current and minimal threshold hysteresis show that the fabricated MOS-HEMT is very suitable for power switching applications.

In this paper, the authors have fabricated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors employing the low-pressure chemical vapor deposition (LPCVD) SiNx as the gate insulator with field plate structure and the long-term degradation was investigated under off-state stress with degradation process monitoring. The gate leakage and drain leakage under off-state electrical stress showed different change rules while the former was expected to be effectively suppressed by LPCVD-SiNx dielectric. The output and transfer characteristics between the stress were obtained periodically to investigate the degradation process. Through the analysis of the degradation of the parameters and the shifts of the Raman spectra, the inverse piezoelectric effect is believed to be the dominant degradation mechanism.

In this paper, we have studied the performance of Ti/Al/Ni/Au ohmic contact with different Al and Au thicknesses and pretreatments. The temperature dependence of contact resistances (Rc) was investigated and it shows that there are different optimal annealing temperatures with different metal thicknesses and pretreatments. The optimal annealing temperature is affected by Al and Au thickness and AlGaN thickness. The etched AlGaN barrier is useful to achieve good ohmic contact (0.24 Ω·mm) with a low annealing temperature. Only the contact resistances of the samples with 130 nm Al layer kept stable and the contact resistances of the samples with 100nm and 160 nm Al layers increased with the measurement temperatures. The contact resistances showed a similar increase and then keep stable trend for all the samples in the long-term 400 °C aging process. The ohmic metal of 20/130/50/50 nm Ti/Al/Ni/Au with ICP etching is the superior candidate considering the contact resistance and reliability.

In this letter, we have studied the performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with different interface Si donor incorporation which is tuned during the deposition process of LPCVD-SiNx which is adopted as gate dielectric and passivation layer. Current collapse of the MIS-HEMTs without field plate is suppressed more effectively by increasing the SiH2Cl2/NH3 flow ratio and the normalized dynamic on-resistance (RON) is reduced two orders magnitude after off-state VDS stress of 600 V for 10 ms. Through interface characterization, we have found that the interface deep-level traps distribution with high Si donor incorporation by increasing the SiH2Cl2/NH3 flow ratio is lowered. It’s indicated that the Si donors are most likely to fill and screen the deep-level traps at the interface resulting in the suppression of slow trapping process and the virtual gate effect. Although the Si donor incorporation brings about the increase of gate leakage current (IGS), no clear degradation of breakdown voltage can be seen by choosing appropriate SiH2Cl2/NH3 flow ratio.

In this letter, high-resistivity unintentionally carbon-doped GaN layers with sheet resistivity greater than 106 Ω/□ have been grown on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). We have observed that the growth of GaN nucleation layers (NLs) under N2 ambient leads to a large full width at half maximum (FWHM) of (102) X-ray diffraction (XRD) line in the rocking curve about 1576 arc sec. Unintentional carbon incorporation can be observed in the secondary ion mass spectroscopy (SIMS) measurements. The results demonstrate the self-compensation mechanism is attributed to the increased density of edge-type threading dislocations and carbon impurities. The AlGaN/GaN HEMT grown on the high-resistivity GaN template has also been fabricated, exhibiting a maximum drain current of 478 mA/mm, a peak transconductance of 60.0 mS/mm, an ON/OFF ratio of 0.96×108 and a breakdown voltage of 621 V.

In this letter, a double-gate AlGaN/GaN high electron mobility transistor operated in a synchronized switching mode is demonstrated, and improved dynamic performances are obtained. The additional gate sits on top of the conventional gate and stretches 2/4 μm to the source/drain electrodes, respectively. A positive voltage pulse is applied to the top gate and is synchronized with the ON-OFF switching pulse applied to the conventional gate. Such a double-gate driving method significantly improves the dynamic performances of the device. Moreover, it allows us to investigate the dynamic on-resistance in the drift region in detail.

A novel double-gate AlGaN/GaN HEMT, in which an additional top-gate covers the adjacent regions of a normal gate, was proposed and fabricated for the first time to compare the dynamic characteristics of AlGaN/GaN HEMTs with a source field plate (SFP) and a gate field plate (GFP). During the dynamic characterization, the device was configured in two operation modes: One is the SFP mode with the top gate biased at 0 V, and the other is the GFP mode applying the gate pulse signal on the top gate at the same time. Compared with an AlGaN/GaN HEMT without field plates, both GFP and SFP much improve the dynamic performances. Compared with the SFP, the GFP shows better dynamic performances with a ~ 34% reduction of switch-on delay time and ~ 6% reduction of dynamic on-state resistance. Studying the dynamic characteristics and applying negative voltage on the top gate during the off state, the mechanism differences between the GFP and the SFP are discussed in detail.

The transition from hard to soft magnetic behaviour with increasing quenching rate is shown for Nd60WAl10Fe20Co10 melt-spun ribbons with different thickness. Microstructure and magnetic domain structure of ribbons were studied by magnetic force microscopy (MFM). Particle sizes < 5 nm decreasing gradually with increasing quenching rate were deduced from topographic images which differ from large-scale magnetic domains with a periodicity of about 350 nm in all ribbons irrespective the coercivity. This indicates that the magnetic properties of the alloy are governed by interaction of small magnetic particles. It is concluded that the presence of short-range-ordered structures with a local ordering similar to the Al metastable Nd-Fe binary phase is responsible for the hard magnetic properties in samples subjected to relatively low quenching rate.

We proposed a novel AlGaN/GaN enhancement-mode (E-mode) high electron mobility transistor (HEMT) with a dual-gate structure and carried out the detailed numerical simulation of device operation using Silvaco Atlas. The dual-gate device is based on a cascode connection of an E-mode and a D-mode gate. The simulation results show that electric field under the gate is decreased by more than 70% compared to that of the conventional E-mode MIS-HEMTs (from 2.83 MV/cm decreased to 0.83 MV/cm). Thus, with the discussion of ionized trap density, the proposed dual-gate structure can highly improve electric field-related reliability, such as, threshold voltage stability. In addition, compared with HEMT with field plate structure, the proposed structure exhibits a simplified fabrication process and a more effective suppression of high electric field.

GaN-based p–i–n X-ray detectors have been fabricated. We observed using SEM that the surface of a GaN sample has a large number of hexagonal defects. The SEM results show that GaN itself contains numerous screw dislocations that will be the flow channel of leakage current, which in turn increased the reverse-bias leakage current of detectors. We have observed a two-step increase in X-ray photocurrent, which is caused by two different detection mechanisms: photovoltaic and photoconductive, and the total photocurrent ( J p ) to dark current ( J d ) ratio is about 27.7 times and the net photocurrent is about 2.52 µA at 110 V reverse bias. As the X-ray accelerating voltage increases, the photocurrent has a sublinear trend.

X-ray detectors based on Fe doped GaN photoconductors have been fabricated. The dark current I(d) and photocurrent I(p) as a function of bias have been investigated and a large I(p)/I(d) ratio of 180 at 200 V has been obtained in spite of optical quenching. The physical mechanism of the transient performance of the photoconductor has been studied through fitting the experimental data. The functions of photocurrent versus acceleration voltage and current of the X-ray source have been measured and discussed.

In this letter, we report a method by introducing hydrogen plasma treatment to realize normally-off p-GaN/AlGaN/GaN HEMT devices. Instead of using etching technology, hydrogen plasma was adopted to compensate holes in the p-GaN above the two dimensional electron gas (2DEG) channel to release electrons in the 2DEG channel and form high-resistivity area to reduce leakage current and increase gate control capability. The fabricated p-GaN/AlGaN/GaN HEMT exhibits normally-off operation with a threshold voltage of 1.75 V, a subthreshold swing of 90 mV/dec, a maximum transconductance of 73.1 mS/mm, an ON/OFF ratio of 1 × 107, a breakdown voltage of 393 V, and a maximum drain current density of 188 mA/mm at a gate bias of 6 V. The comparison of the two processes of hydrogen plasma treatment and p-GaN etching has also been made in this work.

We characterized an ionic liquid (1-butyl-3-methylimidazolium nitrate, C8H15N3O3) as a photo-electrochemical etchant for fabricating normally-off AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs). Using the ionic liquid, we achieved an etching rate of ∼2.9 nm/min, which is sufficiently low to facilitate good etching control. The normally-off AlGaN/GaN MIS-HEMT was fabricated with an etching time of 6 min, with the 20 nm low-pressure chemical vapor deposition (LPCVD) silicon nitride (Si3N4) gate dielectric exhibiting a threshold voltage shift from −10 to 1.2 V, a maximum drain current of more than 426 mA/mm, and a breakdown voltage of 582 V.

Electrical breakdown characteristics of AlxGa1−xN buffer layers grown on Si(111) are investigated by varying the carbon concentration ([C]: from ∼1016 to 1019 cm−3), Al-composition (x = 0 and 7%), and buffer thickness (from 1.6 to 3.1 μm). A quantitative relationship between the growth conditions and carbon concentration ([C]) is established, which can guide to grow the Ga(Al)N layer with a given [C]. It is found that the carbon incorporation is sensitive to the growth temperature (T) (exponential relationship between [C] and 1/T) and the improvement of breakdown voltage by increasing [C] is observed to be limited when [C] exceeding 1019 cm−3, which is likely due to carbon self-compensation. By increasing the highly resistive (HR) Al0.07Ga0.93N buffer thickness from 1.6 to 3.1 μm, the leakage current is greatly reduced down to 1 μA/mm at a bias voltage of 1000 V.

This letter has studied the performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors on silicon substrate with GaN buffer treated by aluminum ion implantation for insulating followed by a channel regrown by metal–organic chemical vapor deposition. For samples with Al ion implantation of multiple energies of 140 keV (dose: 1.4 × 1014 cm−2) and 90 keV (dose: 1 × 1014 cm−2), the OFF-state leakage current is decreased by more than 3 orders and the breakdown voltage is enhanced by nearly 6 times compared to the samples without Al ion implantation. Besides, little degradation of electrical properties of the 2D electron gas channel is observed where the maximum drain current IDSmax at a gate voltage of 3 V was 701 mA/mm and the maximum transconductance gmmax was 83 mS/mm.

The time-resolved photoluminescence spectra were investigated on the basis of transmission, reflection and photoluminescence studies of the InGaN single quantum well structure grown by metalorganic chemical vapor deposition. It was found that the temporal responses of photoluminescence decay exhibited exponential function. The multi-peak structure of the photoluminescence spectra was attributed to the Fabry-Perot interference effect in the GaN/InGaN/GaN vertical cavity.

Normally-off AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) on Si substrate were fabricated with the fluorine-based treatment technique. By employing a 20nm-thick Al2O3 gate dielectric deposited by atomic layer deposition, the fabricated MOS-HEMT exhibits a large positive threshold voltage of + 3.5V, a maximum gate input voltage of 15V, a maximum saturate drain current of 5.3A and an off-state breakdown voltage of 402V. The high threshold voltage and the large input voltage swing is expected to improve the electromagnetic interference immunity and safety of AlGaN/GaN MOS-HEMT power switches.