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In this work, a p-GaN/AlGaN/GaN hybrid anode diode (HAD) temperature sensor was fabricated by using hydrogen plasma treatment. The zero-temperature coefficient (ZTC) is about 0.7 V from the ${I}$ – ${V}$ characteristics measured at various temperatures. At the forward region below the ZTC bias point, the anode voltage ( ${V}_{{\mathrm {A}}}$ ) at a specific anode current density ( ${I}_{{\mathrm {A}}}$ ) decreases linearly with the increase of temperature, resulting in a sensitivity ranging from 1.64 mV/K (10−5 mA/mm) to 0.69 mV/K (10−2 mA/mm). The leakage current at the reverse bias also presents a temperature-dependent behavior with a sensitivity ranging from 16.76 mA/K (−100 V) to 27.94 mA/K (−5 V). The experimental results can be interpreted well by the two-dimensional variable range hopping model.

In this article, the normally- OFF etching-free p-GaN stripe array gate AlGaN/GaN high-electron-mobility-transistors (PSAG-HEMTs) are designed and experimentally demonstrated through hydrogen plasma treatment. The unique threshold voltage ( ${V}_{TH}$ ) modulation technique based on the PSAG structure is proposed and simulated. Using this method, the ${V}_{TH}$ can be continuously shifted from −0.14 to +1.03 V by just tuning the widths of p-GaN ( ${W}_{p}$ ) and hydrogenated p-GaN (HR-GaN) stripes. To improve breakdown voltage (BV), the PSAG is extended to the drain side based on the 3-D simulation results so that a new electric-field peak is introduced at the edge of the PSAG in the drain side and then the surface electric field is optimized. Besides this, an enhanced conductivity effect is observed and results in a low ON-resistance. The fabricated PSAG-HEMT with $0.75~\mu \text{m}~{W}_{p}$ and 4- $\mu \text{m}$ extension length ( ${L}_{E}$ ) exhibits a positive ${V}_{TH}$ of +0.8 V, a low specific ON-resistance ( ${R}_{\text {ON,sp}}$ ) of 2.73 $\text{m}\Omega \cdot cm^{2}$ , a high BV of 852 V (1449 V) at ${I}_{D} = 1 ~\mu \text{A}$ /mm, and BFOM of 266 MW/cm2 (769 MW/cm2) with substrate grounded (floating), which demonstrate significant improvements over Reference single-gate E-mode and D-mode devices. This work provides a promising architecture for future high voltage normally- OFF p-GaN HEMT devices.

This letter reports the phenomenon of current drops in an AlGaN/GaN heterojunction with CF4 plasma treated in a polar gas ambient. Ungated AlGaN/GaN HEMT with CF4 plasma treatment was tested in ethanol, acetonitrile, and an acetic acid gas ambient, and the current dropped by 52%, 51% and 61%, respectively, which are much higher than the drops (6%, 7%, and 8%) in normal ungated HEMT. On the one hand, based on “ambient doping”, a possible model was proposed to explain this phenomenon. On the other hand, the lower initial current was very important to increase the sensitivity. This means that the initial current should be elaborately designed to achieve maximum sensitivity.

A high-performance temperature sensor based on a p-GaN/AlGaN/GaN hybrid anode diode (HPT-HAD) fabricated by hydrogen plasma treatment is demonstrated. The sensor exhibits accurate and stable temperature responses from 73 to 573 K. The forward anode voltage is linearly proportional to the temperature over the measured temperature range at a fixed current. At a forward current density of 10−7 mA/mm, the device achieves a maximum sensitivity of 1.93 mV/K. The long-time anode current stress measurement reveals that the HPT-HAD shows almost no degradation even at 573 K for 1 h at a current of 100 μA, and the anode voltage shifts only 120 mV at 573 K for 1000 s at 1 nA. This work shows that the HPT-HAD temperature sensor can be reliably operated over a wide temperature range from cryogenic to high temperatures, so can be used in a variety of extreme environments.

A dependable and robust technique for nanomachining is ion implantation. In this work, hydrogen (H) ion implantation was used, for the first time, to passivate p-GaN, except for the gate area, in order to create a normally off p-GaN/AlGaN/GaN high-electron-mobility transistor (HEMT). Ion implantation passivation reduces H ion diffusion in p-GaN, allowing it to withstand temperatures above 350 °C. Through experiments and analyses, the H ion implantation energy and dosage required to passivate p-GaN, by generating Mg-H neutral complexes, were determined to be 20 keV and 1.5 × 1013 cm−2, respectively. After conducting annealing procedures at various temperatures, we discovered that 400 °C was the ideal temperature to effectively obtain a normally off p-GaN HEMT. A threshold voltage of 0.8 V was achievable. The p-GaN HEMT also had a breakdown voltage of 642 V at a gate voltage of 0 V, maximum transconductance of 57.7 mS/mm, an on/off current ratio of 108, an on-resistance of 8.4 mm, and a maximum drain current of 240.0 mA/mm at a gate voltage of 6 V after being annealed at 400 °C.

Electrical characterizations of AlGaN/GaN heterojunctions isolated by N implantation at elevated temperatures were investigated. Three-terminal measurements were carried out to characterize leakage paths, and crystal lattice damage due to implantation was monitored by high-resolution x-ray diffraction. Compared with room temperature implantation, the current leakage was reduced by ∼103 times by the implantation at 300 °C. The low leakage was attributed to low acceptor-like energy levels due to low crystal lattice damage by the “dynamic annealing” effect at high-temperature implantation. The post-annealing process increased the current leakage by two orders of magnitude. This indicates that the implantation isolation process should be conducted after higher temperature processes (>450 °C) in the fabrication of GaN devices. These results can provide valuable information for the fabrication, reliability, and mass production of various GaN-based photonics and electronics.

Herein, a monolithic micro-pixelated light-emitting diode ( μLED) display realized using ion-surface-treatment-based planar-geometry pixelation is reported. A high-resolution blue-emitting μLED array is fabricated by optimizing ion species of a near-surface selectively positioned isolation process. The μLED array exhibiting inhibited surface recombination and higher output power is achieved by using heavy ions, such as fluorine (F−), due to more stable opto-electrical isolation and better process reliability. Furthermore, the low forward voltage of F−-IST-based μLED pixels can effectively improve the wall-plug efficiency for the μLED array with a pixel diameter of 6 μm. Conversely, the poor thermal stability of light hydrogen (H+) ions limits its device applications. Analysis based on a rate equation model reveals that the luminescence mechanism of F−-IST-based μLEDs is dominated by radiative recombination, which will benefit the planar-geometry pixelation for realizing highly efficient full-color microdisplays.

E-mode P-GaN/AlGaN/GaN heterostructure field-effect transistors (HFETs) of various sizes were fabricated, and their parasitic source resistance (RS) was measured. The measurement results showed that RS varied greatly with changing gate bias, and the degree of RS change also differed with the gate bias of different-sized device samples. Through theoretical analysis, it is found that polarization Coulomb field (PCF) scattering caused by the device process and gate bias can affect electron mobility ( $$\mu_{GS}$$ ) in the gate-source region, which causes the variations in $$\mu_{GS}$$ for different-sized devices and same-sized devices under different gate biases. When $$\mu_{GS}$$ changes with the device size and gate bias, the RS will change accordingly. Our study is the first to discover the gate bias dependency of RS for E-mode P-GaN/AlGaN/GaN HFETs due to PCF scattering, which provides a new idea for further in-depth studies on the RS of E-mode P-GaN/AlGaN/GaN HFETs and device performance optimization.

A bulk acoustic wave (BAW) driven magnetoelectric (ME) antenna has narrow operating bandwidth due to its high Q factor, and an effective mechanism for bandwidth enhancement is yet to be explored. This article presents a bandwidth-enhanced magnetoelectric (BWE-ME) antenna made of a Mo/AlN/FeGa sandwich stack, which is composed of three different resonant regions. These resonant regions in the discrete device can be equated as a parallel connection of dual high-overtone bulk acoustic resonators (HBARs) and single film bulk acoustic resonators (FBARs) with tiny frequency shift among the three resonators resulting in bandwidth broadening of the BWE-ME antenna. The resonant mode and return loss curves (S11) are simulated in a two-dimensional finite element method and fitted with the Mason equivalent circuit model. The frequency domain analysis shows that the magnetic flux density bandwidth generated by the multi-resonant mode interaction is 18 MHz, which matches the bandwidth of the measured reference gain S21 curve of the BWE-ME antenna, and the far-field radiated power characterization also shows the corresponding effective bandwidth distributed. The fabricated microelectromechanical systems antenna achieves a fractional bandwidth of 2.7% while maintaining the advantage of small size (0.49 mm2). Discrete composite BAW resonators that effectively combine the multi-resonant regions of HBARs and FBARs have the potential to realize compact and broadband BAW-ME antennas in the future.

A thin SiN x film was deposited on the p-GaN layer before H plasma implantation, which cause four orders of magnitude reduction in gate reverse leakage current. The OFF-state breakdown voltage increases by 89%. It displays a more stable dynamic performance. It is believed that the decrease of gate leakage current is attributed to the increase of trap activation energies in the p-GaN layer, It is concluded that improved dynamic characteristics are owing to the fact that the SiN x film blocks the excessive H plasma into the AlGaN barrier layer and reduces the implantation damage in AlGaN barrier layer.

Vertical GaN trench-gate MOSFETs with ∼130 nm stepped sidewalls in the p-GaN channel layer are studied and two significant influences have been observed compared to the devices with smooth sidewalls. The first effect is the degraded channel mobility of 14.6 cm2 (V·s)−1 to 4.5 cm2 (V·s)−1 which can be attributed to the increased probability of surface acoustic phonons scattering under inversion conditions. Another impact is that only when a drain voltage (V DS) is applied over 30 V can the devices switch on. It can be speculated that the stepped sidewall has a horizontal channel and the transverse electric field is inadequate to drive the electrons at low V DS. According to the investigation, when devices need to be switched at a high V DS, the stepped sidewall morphology should be taken into consideration.

This study has demonstrated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) on Si substrates with a SiNx/SiON composite gate dielectric. The threshold voltage shift in the devices was investigated. The MIS-HEMTs with the SiNx/SiON composite gate dielectric exhibited superior threshold voltage uniformity and small threshold voltage hysteresis than the reference device with SiNx only gate dielectric. The variation of the device threshold voltage was mainly related to trapping process by the interface states, as confirmed by band diagrams of MIS-HEMTs at different gate biases. Based on frequency-dependent capacitance measurements, interface state densities of the devices with the composite and single gate dielectrics were extracted, where the former showed much smaller interface state density. These results indicate that the SiNx/SiON composite gate dielectric can effectively improve the device performance of GaN-based MIS-HEMTs and contribute to the development of high-performance GaN electronic devices.

We present a multiple instance learning class activation map (MIL-CAM) approach for pixel-level minirhizotron image segmentation given weak image-level labels. Minirhizotrons are used to image plant roots in situ. Minirhizotron imagery is often composed of soil containing a few long and thin root objects of small diameter. The roots prove to be challenging for existing semantic image segmentation methods to discriminate. In addition to learning from weak labels, our proposed MIL-CAM approach re-weights the root versus soil pixels during analysis for improved performance due to the heavy imbalance between soil and root pixels. The proposed approach outperforms other attention map and multiple instance learning methods for localization of root objects in minirhizotron imagery.

In this paper, we systematically investigate the effect of hydrogen plasma treatment radio frequency (RF) power, treatment time, and rapid thermal annealing (RTA) on the performance of high-resistivity-cap-layer high-electron-mobility-transistor (HRCL-HEMT). It is found that high RF power contributes to obtain high drain current, but induces more damage. An appropriate RTA process not only can repair the plasma damage but also improves the static characteristics of HRCL-HEMT. Subsequently, a large hydrogen plasma treatment time window of 4 min is demonstrated with an optimized RF power of 2 W and RTA at 350 °C for 5 min. Furthermore, the thermal stability of the optimized HRCL-HEMT is investigated by high temperature test and long-term thermal stress test. No obvious degradation of ${V}_{\text {TH}}$ , ${I}_{G}$ , ${R}_{\text {SH}}$ , and dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ is observed in both before and after passivation devices after 1000-h thermal stress. Finally, gate reliability of the HRCL-HEMT is also analyzed by time-to-failure test. The maximum gate voltage is determined to be 6.28 V for a ten-year lifetime with a failure rate of 1% at 25 °C.

Spin logics provide a shortcut toward logic-in-memory architectures. Here, using a T-type magnetic stack with a perpendicular magnetic layer, an in-plane layer, and a spacing layer in between, we can switch both the in-plane and perpendicular layers and independently control their magnetization without an external magnetic field. By initializing magnetization of the in-plane layer, we can further control chirality (clockwise and counterclockwise) of the current-dependence of perpendicular magnetization. Based on these properties and the majority gate theory, we experimentally construct five Boolean logic gates in a single device in the desired field-free condition, which steps forward to practical spin–orbit torque logics.

In this letter, a device structure of high-resistivity-cap-layer HEMT (HRCL-HEMT) is developed for normally-off p-GaN gate HEMT toward high breakdown voltage and low current collapse. It demonstrates that the breakdown capability and current collapse of the device were effectively improved due to the introduction of a thick HR-GaN cap layer. The fabricated HRCL-HEMT exhibits a high breakdown voltage of 1020 V at ${I}_{\text {DS}} = 10~\mu \text{A}$ /mm with the substrate grounded. Meanwhile, the dynamic ${R}_{\text {on}}$ is only 2.4 times the static ${R}_{\text {on}}$ after off-state ${V}_{\text {DS}}$ stress of 1000 V with the substrate grounded (the OFF to ON switching time interval is set to $200~\mu \text{s}$ ).

The nature of charge transport in GaN-based light-emitting diodes (LEDs) under reverse biases still remains elusive as the bias- and temperature-dependent characteristics of the current can hardly be formulated using a single transport mechanism. In this letter, based on numerical fitting, we develop a combined tunneling-hopping transport model to describe the complete electrical characteristics of the reverse leakage current in InGaN/GaN blue LEDs. This model depicts that the current behaviors are majorly limited by the charge transport process through the depletion region near the neutral n-side, where electrons at the valance band are ready to tunnel into the unoccupied localized gap states in neighborhood near the electron quasi-Fermi level ( ${E}_{\mathrm {fn}}$ ), followed by variable-range hopping or nearest-neighbor hopping via these localized states along a relatively constant ${E}_{\mathrm {fn}}$ , depending on temperature.

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.

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.

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.

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.