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A gallium nitride (GaN)-based resonant step-up converter is proposed for the application in the satellite electric propulsion (EP) system. This converter consists of a full-bridge inverter, a resonant tank and a multi-stage Cockcroft-Walton (CW) voltage multiplier to provide a high gain. Additionally, the air-core transformer is introduced due to the megahertz switching frequency allowed by the GaN device. Thus, the limited magnetizing inductance of transformer and the remarkable junction capacitance of diode have to be carefully considered in the resonant tank design, especially after considering that this converter normally operates at the light load in the EP system. In this work, the 4-order LCLC resonant converter is investigated. The recommended parameter selection for the 4-order resonant tank is also provided. A 1.2-MHz, 23-V/2.5-kV, and 6-W prototype is demonstrated. It achieves a low harmonics distortion and a low power loss with the zero voltage switching (ZVS).

This paper proposes a novel ultra-Fast self-powered bidirectional solid-state circuit breaker (SSCB) with voltage overshoot suppression that uses gallium nitride (GaN) switches with very low conduction losses. This SSCB can be used in low and medium AC/DC networks for both short-circuit protection and overcurrent protection. An exhaustive methodology for RCD snubber design applied to SSCBs is provided. A comprehensive review of the technical literature is presented exhibiting that the proposed SSCB reduces conduction losses and detection time in comparison with other similar SSCBs. The performance features of the proposed SSCB are verified through the functional tests that are carried out employing a hardware-implemented prototype. Experimental results confirm that our proposal is able to detect and process the short-circuit failure in 282ns; the authors have not found any faster results in the literature.

This paper presents a high-performance radio frequency (RF) power amplifier (PA) module for which an optimum chip-level packaging structure is proposed to reduce the operating temperature of the RF PA monolithic microwave integrated circuit (MMIC). Because the output power (Pout) and the efficiency of a RF PA module are strongly affected by the thermal characteristics of the PA MMIC, various types of heat spreader materials and thermal interface materials have been examined to implement the PA chip-level packaging structure, and the optimum combination is proposed for a performance enhancement of the PA module in this paper. In addition, the optimum form-factor of the heat spreader was suggested based on a thermal simulation. To verify the proposed PA chip-level packaging structure, a 10 W 618 GHz RF PA MMIC using a commercial 0.25-m gallium nitride high electron mobility transistor process was designed and implemented for radar applications. The operating temperature of the PA MMIC on the proposed chip-level packaging structure shows a dramatic reduction of 24.8 C, and accordingly, the average Pout and average power-added efficiency are enhanced by up to 9.2% and 2.8%, respectively, when compared with a PA module using the conventional chip-level packaging structure.

To fully take the high-frequency advantage of gallium nitride (GaN) devices, this article presents a face-up integrated power module based on the printed circuit board (PCB) embedding technology to tackle the challenges caused by conventional discrete solutions. The proposed GaN module highly integrates a GaN-bare-dies-based full bridge, driving circuits, and decoupling capacitors, in which the advanced bismaleimide-triazine (BT) material is used as the packaging material and the copper-filled laser microvias are used for low-parasitic-inductance and high-thermal-conductivity interconnection. Careful electro-thermal co-design and optimization of power loop is conducted to make the trade-off between power loop inductance and thermal performance. The proposed full bridge power module achieves the lowest power loop inductance of about 0.305 nH in power modules with the same power level. The maximum thermal resistances from the embedded GaN bare dies to top and bottom surface are 3.39 /W and 0.42 /W, respectively. Benefitting from the ultra-low power loop parasitic inductances, the switching speed of GaN devices reaches to 57.5 V/ns, while the voltage overshoot is not higher than 5.35% of the DC bus voltage. The superior performance of the proposed integrated GaN module makes it a promising application prospect in high frequency high power density converters.

In order to suppress the crosstalk in gallium nitride (GaN)-based bridge configuration, a novel negative voltage self-recovery gate drive (NVSRGD) is proposed in this paper. The resistor-capacitor-diode voltage divider is applied to establish the negative gate-source voltage and suppress the impact of positive crosstalk. The antiparallel diode is added to constitute low-impedance Miller current path from the driver integrated circuit (IC) to the GaN device. It works together with the self-recovery gate-source voltage to suppress the negative crosstalk, which not only prevents the GaN device from the negative overstress but also reduces the reverse conduction loss during the dead time. The NVSRGD is composed of a few passive components, which are suitable for integrating into the driver IC. The capacitors and resistors of the NVSRGD are designed to determine the negative voltage level and the restore time. Additive separate negative voltage power supplies or active devices are not needed. The double pulse test based on GS66508B verifies the effectiveness of the proposed method for suppressing the positive and negative crosstalk of GaN devices.

Due to the modulator free structure, the finite-control-set model predictive control (FCS-MPC) needs a high sampling frequency (20kHz-50kHz) for power converter applicationwhile the typical switching frequency is around 20-25% of the sampling frequency. To obtain a high switching frequency, it is not always practical to increase the sampling rate by considering the computational burden in a digital processor. Therefore, increasing the switching frequency without using a high sampling frequency is a critical task for FCS-MPC, particularly applied to silicon carbide (Sic) and gallium nitride (GaN)-based high switching frequency power converters. To solve this problem, this article proposes the multi-rate FCS-MPC (MRFCS-MPC), where the control frequency is allowed to be faster than the sampling frequency. Consequently, the switching frequency can be significantly increased without changing the sampling frequency. The lifting model is built to predict the fast rate state variables based on the low sampling output. Then, the fast rate control inputs within one sampling interval are solved efficiently with a good tradeoff between computational burden and optimized system performance. The experimental motor drive system tests are carried out to verify the effectiveness of the proposed MRFCS-MPC.

Electronic engineering of gallium nitride (GaN) is critical for enhancement of its electrode performance. In this work, copper (Cu) cation substituted GaN (Cu-GaN) nanowires were fabricated to understand the electronically engineered electrochemical performance for Li ion storage. Cu cation substitution was revealed at atomic level by combination of X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), density functional theory (DFT) simulation, and so forth. The Cu-GaN electrode delivered high capacity of 813.2 mA h g−1 at 0.1 A g−1 after 200 cycles, increased by 66% relative to the unsubstituted GaN electrode. After 2000 cycles at 10 A g−1, the reversible capacity was still maintained at 326.7 mA h g−1. The DFT calculations revealed that Cu substitution introduced the impurity electronic states and efficient interatomic electron migration, which can enhance the charge transfer efficiency and reduce the Li ion adsorption energy on the Cu-GaN electrode. The ex-situ SEM, TEM, HRTEM, and SAED analyses demonstrated the reversible intercalation Li ion storage mechanism and good structural stability. The concept of atomic-arrangement-assisted electronic engineering strategy is anticipated to open up opportunities for advanced energy storage applications.

A Gallium nitride (GaN) field effect transistor (FET) can provide superior performance over a Si-MOSFET due to its low on-state resistance and low junction capacitances. However, a GaN-based converter exhibits higher dead-time loss during reverse conduction. Thus, to improve the efficiency, dead-time optimization is required. This paper proposes simple models for dead-time optimization in a GaN-based buck converter under different load conditions. The proposed models are analytical in nature compared to the conventional models available for Si-based converters. A buck converter prototype is designed using a 100 V GaN device (GS61008P from GaN Systems) and the proposed analytical model-based dead-time optimization techniques are validated experimentally. The proposed modeling techniques can be extended for other GaN-based DC-DC converters.

With superb device characteristics, gallium nitride (GaN) power transistors facilitate fast and efficient power conversion and delivery in modern power circuits. To take full advantage of these devices, high switching frequency ( $f_{{SW}})$ operation is highly desirable. However, the lack of GaN compatible high-speed, efficient, and reliable gate drivers has been a formidable design hindrance. In this article, we address three critical design challenges faced in GaN power gate driving, namely bootstrap (BST) level-shifting, switching slew rate (SR) control, and active deadtime $t_{{dead}}$ control. We first propose a BST dynamic level-shifting technique to enable sub-nanosecond $t_{{delay}}$ at high $f_{{SW}}$ . Meanwhile, a dual-SR switching technique is introduced to retain both low switching power and noise. Compared with traditional constant $t_{{dead}}$ controls, the $t_{{dead}}s$ in this design are regulated actively for high efficiency. To validate these techniques, a four-phase GaN-based switching power converter was designed and implemented on a 0.35 μm high-voltage (HV) BCD process. At a $f_{{SW}}$ of 20 MHz and a $V_{{IN}}$ of 20 V, it delivers a maximum power of 8.4 W and a peak efficiency of 84.9%. The gate drivers are fully integrated including all BST capacitors and active BST switches. It achieves regulated rise and fall $t_{{dead}}s$ of 3.2 and 4.7 ns, respectively, for a load range from 50 mA to 1.2 A. The gate switching rise time $t_{R}$ is reduced to 1 ns with a maximum switching SR of 48 V/ns. The converter employs a HV synchronized hysteretic control, which works with the proposed gate drivers seamlessly to demonstrate a dynamic voltage scaling (DVS) Vo up- and down-tracking speeds of 0.33 μs/V and 0.47 μs/V, respectively.

Benefited from the fast switching speed, Gallium nitride (GaN) high electron mobility transistors (HEMTs) have been widely used in high switching frequency converters. However, due to the significant correlation between the turn-off time and operating conditions (more than 20 times difference of the turn-off time between the high load current and small load current for GaN HEMTs), using a fixed dead time will introduce extra dead-time losses in inverters where the output voltage and current are constantly varying. Therefore, this paper proposes a high-efficiency adaptive method to dynamically adjust the GaN-inverter dead-time with operating conditions. An improved transient model including the parasitic inductance and output voltage with bidirectional solution flow has been proposed for GaN HEMTs to increase the accuracy of dead-time adjustment. Based on this model, the dynamic dead-time adjustment can be realized without extra sensors for GaN-inverters. Using the dynamic dead-time adjustment, the experimental results show a peak efficiency of 98.25% in a 1200W inverter with triangular current mode modulation. Compared with using the fixed dead-time, the dynamic dead-time method can reduce the power loss by 26.7% under full load and 49.14% under light load.

We studied the morphological nature of various thin films such as silicon carbide (SiC), diamond (C), germanium (Ge), and gallium nitride (GaN) on silicon substrate Si(100) using the pulsed laser deposition (PLD) method and Monte Carlo simulation. We, for the first time, systematically employed the visibility algorithm graph to meticulously study the morphological features of various PLD grown thin films. These thin-film morphologies are investigated using random distribution, Gaussian distribution, patterned heights, etc. The nature of the interfacial height of individual surfaces is examined by a horizontal visibility graph (HVG). It demonstrates that the continuous interfacial height of the silicon carbide, diamond, germanium, and gallium nitride films are attributed to random distribution and Gaussian distribution in thin films. However, discrete peaks are obtained in the brush and step-like morphology of germanium thin films. Further, we have experimentally verified the morphological nature of simulated silicon carbide, diamond, germanium, and gallium nitride thin films were grown on Si(100) substrate by pulsed laser deposition (PLD) at elevated temperature. Various characterization techniques have been used to study the morphological, and electrical properties which confirmed the different nature of the deposited films on the Silicon substrate. Decent hysteresis behavior has been confirmed by current-voltage (IV) measurement in all the four deposited films. The highest current has been measured for GaN at ∼60 nA and the lowest current in SiC at ∼30 nA level which is quite low comparing with the expected signal level (μA). The HVG technique is suitable to understand surface features of thin films which are substantially advantageous for the energy devices, detectors, optoelectronic devices operating at high temperatures.

An analytical load--pull-based design methodology for three-stage Doherty power amplifiers (PAs) is presented and demonstrated. A compact output combiner network, together with the input phase delays, is derived directly from transistor load--pull data and the design requirements. The technique opens up a new design space for three-stage Doherty PAs with reconfigurable high-efficiency power back-off levels. The method is designed to enable high transistor power utilization by maintaining full voltage and current swings of the main and auxiliary amplifier cells. Therefore, a wide efficiency enhancement range can be achieved also with symmetrical devices. As a proof of concept, a 2.14-GHz 30-W three-stage Doherty PA with identical gallium nitride (GaN) HEMT active devices is designed, fabricated, and characterized. The prototype PA is able to linearly reproduce 20-MHz long-term evolution signals with 8.5- and 11.5-dB peak-to-average power-ratio (PAPR), providing average efficiencies of 56.6% and 46.8% at an average output power level of 36.8 and 33.8 dBm, respectively. Moreover, an average efficiency as high as 54.5% and an average output power of 36.3 dBm have been measured at an adjacent power leakage ratio of -45.7 dBc for a 100-MHz signal with 8.5 dB of PAPR, after applying digital predistortion linearization.

Co-pyrolyzing gallium nitrate hydrate and melamine, melem, or g-C3N4 generates gallium nitride (GaN) for the conversion of methane to acetonitrile (AcCN). The solid-state-pyrolysis-made GaN catalysts exhibited better activity than commercial GaN. Among the as-prepared catalysts, GaN made using g-C3N4 as the nitrogen precursor with a N/Ga ratio of 2 (i.e., GaN-(C3N4)-(2)) was the most attractive: a high initial methane conversion (12.5%), a high initial AcCN productivity (26 μmol/gcat/min), and an accumulated AcCN yield (3309 μmol/gcat) in a 6-h reaction time were obtained. GaN-(C3N4)-(2) had isolated GaN phases and enriched amorphous C and N species (e.g., sp2 N and C≡N groups). A six-fold cavity of g-C3N4 as the docking port of Ga3+ to elevate the GaN dispersion in solid-state pyrolysis was proposed. The analysis of the structure-activity correlation revealed that the accumulated AcCN yield had an inverse trend with respect to the crystallite size of GaN and the sp3/sp2 ratio of the N environment.

Compact model of flexible radio frequency (RF) electronic devices is crucial for flexible circuit designs. In this article, a compact model, including external strain effects for flexible RF gallium nitride (GaN) high-electron-mobility transistor, is presented. First, the carrier density and threshold voltage with external mechanical uniaxial strain is analytically characterized by introducing the strained piezoelectric charge Δ σ , Schottky barrier height $Δ φ_{B}$ , and surface state density $D_{{it}}$ into the model. Then, the variations of the conduction band offset at the AlGaN/AlN and AlN/GaN interfaces are considered. Finally, the complete large-signal model is established after embedding strain effect into intrinsic drain current and nonlinear capacitance models. The proposed model is verified by measurements, including direct current I-V characteristics, small-signal S-parameters up to 40 GHz, and large-signal power performance--output power, efficiency, and gain. The proposed model will be useful for the RF application of flexible electronics.

A method of preparing passive materials suitable for magnetooptic interactions is shown using manganese implantation into gallium nitride (GaN) epitaxial layers, which establishes both dilute ferromagnetism and a three-level optical system with persistence to over 300 K. A sweep of thermal anneal parameters for a high implant dose into Mg-doped p-type GaN films is presented, and the materials are tested for both their magnetization and photoluminescence (PL). The optimal anneal process at 825 °C for 5 min maintains ferromagnetism with $T_{C}$ > 305 K, confirming magnetic alignment at room temperature with a coercivity of ~100 Oe. PL and spectrophotometry of the optimally prepared materials show the effects of the mid-gap defect state on the material's optical characteristics. The anneal process returns the real part index to its baseline dispersion while retaining an onset of absorption starting at the defect level $E_{A}$ = 1.8 eV, signifying a stable mid-gap energy transition with a measured state lifetime of $τ _{PL}$ = 2.7 ns. The scalability of this process for producing three-level transition magnetic materials suggests passive optical or magnetooptic devices can be constructed that interconnect photonic and spintronic effects for emerging system designs and potential applications in quantum information.

In this article, a fully integrated dual-band gallium nitride (GaN) Doherty power amplifier (DPA) based on multi-resonant circuits (MRCs) is presented. A lumped T-type network in combination with the output capacitances of the main and auxiliary transistors is able to realize the quarter-wavelength transformer (QWT) in DPA, and its component values are totally decided by the operating frequency, given a certain characteristic impedance. MRCs are proposed to exhibit the required component values at two different frequencies. By replacing each component in the T-type network with an MRC, a dual-band QWT can be achieved. An integrated dual-band DPA is implemented in a commercial 0.25-μm GaN-HEMT process to validate the proposed method. The fabricated DPA shows a saturated output power of 43.8-44.7/44.4-44.8 dBm, a 6-dB back-off drain efficiency (DE) of 41%-46%/41.5%-47%, and a saturated DE of 49%-52%/56%-59% in 3.35-3.6/4.8-5.2 GHz, with a compact size of 2.8 x 3.5 mm². Applying a 100-MHz OFDM signal with a 7.8-dB peak-to-average power ratio (PAPR), an average efficiency of 37%/40% and an average power of 37/37 dBm are measured at 3.5/5.0 GHz, and the adjacent channel power ratio (ACPR) is better than -49 dBc after digital predistortion (DPD). To the best of our knowledge, the proposed DPA is the first demonstration of fully integrated dual-band GaN DPAs.

Gallium nitride nanowire and nanorod substrates are prospective platforms allowing to control the local strain distribution in graphene films on top of them, resulting in an induction of pseudomagnetic fields. AFM measurements performed in a HybriD mode complemented by SEM allow for a detailed visualization of the strain distribution on graphene surface. Graphene in direct contact with supporting regions is tensile strained, while graphene located in-between is characterized by lower strain. Characteristic tensile strained wrinkles also appear in the areas between the supporting regions. A positive correlation between strain gradient and distances between borders of supporting regions is observed. These results are confirmed by analysis of the Raman D’ band intensity, which is affected by an enhancement of intravalley scattering. Furthermore, scanning tunneling spectroscopy shows a local modification of the density of states near the graphene wrinkle and weak localization measurements indicate the enhancement of pseudomagnetic field-induced scattering. Therefore, we show that nanowire and nanorod substrates provide strain engineering and induction of pseudomagnetic fields in graphene. The control of graphene morphology by modification of distances between supporting regions is promising for both further fundamental research and the exploration of innovative ways to fabricate pseudomagnetic field-based devices like sensors or filters.

Polar GaInN and AlGaN quantum wells (QWs) are widely used in light emitting diodes and laser diodes (LDs). However, the widths of such QWs are usually limited to a few nanometers in order to ensure a sufficiently large overlap between the wave functions of the ground electron and the ground hole state. By increasing the QW width we enter the area of ‘dead’ width where, the overlap of the electron and hole wave functions decreases almost to zero and the luminescence efficiency drastically deteriorates. Therefore, it is assumed that wide QWs are not suitable for light emitters and very wide (8-15 nm) QWs are not considered as a promising gain medium for LDs. Hence such QWs are very rarely studied both experimentally and theoretically. In this work the material gain is calculated for Ga0.8In0.2N/GaN and Al0.8Ga0.2N/AlN QWs with a width varying in the range of 2-15 nm. We observed that the material gain at fixed carrier concentration for these QWs drops to zero with the increase in the QW width and reaches negative values in the width range of ∼4-8 nm even for high carrier concentrations, but after exceeding a certain width to ∼8-12 nm it begins to increase rapidly and reaches the values greater than those observed for narrow QWs. This phenomenon is related to the screening of the built-in electric field by carriers, which is easier for wide QWs, and the reduction of the distance between the energy levels for electrons and holes. For the latter reason, optical transitions between higher energy states make a very significant contribution to the positive material gain .

This letter presents a C-band high-efficiency fully integrated high-power amplifier (HPA) monolithic microwave integrated circuit (MMIC) in 0.25 μm gallium nitride (GaN) high electron mobility transistor (HEMT) technology. The proposed GaN HPA MMIC consists of two amplifying stages, and its output stage includes 8 transistors in parallel. In order to realize the high efficiency, a low-loss harmonic control network (HCN) using a parallel LC resonate block is applied to obtain the optimum load impedance to each transistor employed in the output stage of the HPA at both f0 and 2f0. Thus, the designed GaN HPA can operate in pulse conditions of 100 μs pulse width and 10% of duty cycle over the frequency from 5.6 GHz to 6.3 GHz. The proposed high efficiency GaN HPA MMIC provides an average output power of 45.0 dBm-45.5 dBm (31.6 W-35.5 W) with a power added efficiency (PAE) of 59%-61.8%, and a gain of 26 dB-28.5 dB under a drain voltage of 28 V. The area of the proposed GaN HPA MMIC is 4.2 mm × 4 mm including pads.

This work presents a 48-1V dc-dc converter with an on-chip switch and gallium nitride (GaN) hybrid power conversion. By series connecting a 12-level Dickson switched-capacitor with a two-phase switched-inductor circuit, the capacitors take over most of the 48-V voltage stresses. The circuit, thus, reduces to an equivalent 4-1V converter, making the on-chip 5-V transistor applicable for a 48-V high-voltage design. Due to the easy integration of on-chip switches and superior switch figures of merit over other 48-1V counterparts, this proposed design is able to achieve the highest switching frequency, the lowest external switch count, and the improved power density compared with other prior-state-of-the-arts. The prototype was fabricated using a 0.18-μm BCD process with an evaluation board volume of 17 mm x 15 mm x 2.6 mm. The converter achieves a maximum 8-A loading capacity with the input range from 36 to 60 V and the output from 0.5 to 1 V. The measured peak power efficiency is 90.2%, and the power density is 998 A/in³ considering the power stage volume.

In this article, a monolithically integrated driver fabricated by 12-V depletion mode gallium nitride (dGaN) and enhanced mode GaN (eGaN) driver is proposed. The proposed driver features an internal temperature-compensated (T-compensated) controller to drive an integrated 650-V eGaN power switch. Due to T-compensated characteristics, a slew-rate enhancement driver can be well-controlled by the fast turn-on (FTO) technique which is supplied by an on-chip regulator with reference voltage circuit. Therefore, the Miller plateau voltage can be tracked correctly by the proposed controller so that the switching frequency can be raised up to 50 MHz and the $\textit {dV}_{\mathrm {DS}}$ / dt slew rate can reach 118.3 V/ns for high efficiency and high switching operation.

In order to realize high-sensitivity real-time monitoring of acid-base neutral solutions in the industrial field, it is very important to study how to improve the sensitivity of a pH sensor. Herein, the sensitivity of the pH sensor was improved by using both monolithic integrated planar multi-channel and photoconductive properties of gallium nitride (GaN) high electron-mobility transistors (HEMTs) as a core of the pH sensor. The sensitive area of aluminum gallium nitride/gallium nitride (Al $_{0.25}$ Ga $_{0.75}$ N/GaN) heterojunction HEMT channel surface was increased, and the channel effective resistance was reduced by planar multi-channels. And the photogenerated current was generated by 365-nm ultraviolet (UV) light based on the photoconductive effect. This investigation mainly shows as the sensitivity of the tri-channel was 37.04 μA/pH, which increased 30 times compared with that of the single-channel device under the dual action of planar multi-channel and 365-nm UV light coupling in potassium hydrogen phthalate, mixed phosphate, and borax pH correction buffer solutions. The concept of using the GaN HEMT-based pH sensor for direct quantification of pH values in waste water provides a simple and high-performance method for industrial applications.

In this work, the performance of AlGaN/gallium nitride (GaN) high-electron mobility transistors (HEMTs) with different Fe doping tails was systematically investigated and compared. It is illustrated that the combination of the unintentionally doped (UID) GaN layer and a thinner Fe doping buffer layer would result in a faster slope rate of Fe concentration in the UID GaN layer. The devices with the fastest slope rate of Fe concentration in the UID GaN layer exhibited excellent large signal performance, including the saturated power density ( $P_{sat}$ ) of 9 W/mm and the power-added efficiency (PAE) of 65.6%. In addition, the $P_{sat}$ and the PAE of the device with the fastest slope rate of Fe concentration in UID GaN layer are 27.7% and 14.7%, which are higher than that of the device with the slowest slope rate of Fe concentration under the class AB operation conditions. Pulse I-V measurement results demonstrated that the buffer-related current collapse was more effectively suppressed in the 0.5-μm Fe doping buffer layer because of faster slope rate of Fe concentration in UID GaN layer. Moreover, the frequency-dependent capacitance and conductance measurement results indicated that the current collapse was relevant to deep traps in the UID GaN layer introduced by Fe doping. By reducing the concentration of the deep traps caused by Fe doping, the device showed excellent characteristics of dc and RF. Furthermore, controlling the Fe doping tail was important for designing the GaN-based power amplifier with high $P_{sat}$ and PAE.

We report GaN vertical trench MOS barrier Schottky (TMBS) diodes with embedded p-GaN shielding rings (SRs) and systematically investigate the impact of different structural parameters of the p-GaN SRs on the breakdown performance of the GaN-based vertical TMBS diodes by numerical simulation. The charge coupling effect by the embedded p-n junction at the bottom of the trench homogenize the electric field at the trench corner and alleviate the electric field crowding effect at the Schottky contact region, which can effectively avoid the premature breakdown and improve the reverse blocking capability of the TMBS diodes. The p-GaN SRs can also broaden the overlapped depletion region and shift the pinch-off point into the n−-GaN drift region, thus facilitating the 2-D depletion in the n−-GaN drift layer and boosting the breakdown performance of the conventional TMBS diodes. We found that the doping concentration, thickness, and the width of the p-GaN SRs are closely associated with the electric field distribution and the reverse breakdown characteristics of the GaN-based vertical TMBS diodes. The vertical TMBS diodes with optimal p-GaN SR parameters featured a dramatic improvement in the breakdown voltage from 907 to 1281 V, without an obvious degradation in the ON performance. The proposed TMBS diodes with a p-GaN SR structure can pave the way toward a high-performance GaN vertical power device for high-power and high-efficiency power switch applications.

In this work, a novel n-In x Ga1- x N/N-gallium nitride (GaN) homotype heterostructure is proposed instead of P-GaN/N-GaN homostructure to produce impact-ionization-avalanche-transit-time (IMPATT) diode. Conventional GaN IMPATT device will lose its working ability due to the immature p-type GaN, so this work predicts that the n-In x Ga1- x N/N-GaN IMPATT diode can be an alternative to the GaN p-n IMPATT diode; thus, the difficulty of the p-type doping process is avoided. The dc and RF large-signal output characteristics with different compositions are investigated in detail. The simulation results show that the power and efficiency of the novel structure device increase when the In composition increases. When the In composition is greater than 0.4, the performance of the homotype heterojunction IMPATT is better than that of p-n IMPATT. Moreover, homotype heterojunction IMPATT is better in frequency bandwidth, and it can hold greater bias current density than p-n IMPATT. Meanwhile, the performance of homotype heterojunction IMPATT does not depend on the thickness of the InGaN layer, but it decreases as the thickness of the p-type region in p-n IMPATT increases. As it has greater potential in the application, this work brings a reference for the design and manufacture of IMPATT devices based on wide bandgap semiconductor materials, especially GaN materials.

The submicrometer gate HEMT is fabricated with an ultrathin-barrier (UTB) AlGaN/gallium nitride (GaN) combined with in situ SiN passivation. The sheet resistance of the UTB Al0.2Ga0.8N (4 nm)/GaN heterostructure is effectively reduced by the SiNx passivation layer grown by metal organic chemical vapor deposition (MOCVD), from 6500 to $312~ \Omega $ /⬜. With the 20-nm stress-engineered in situ SiN, the device not only provides a large output current of 1.05 A/mm but also demonstrates promising potential on the RF applications, which gives AlGaN material two records high cutoff frequency ${f} _{\text {T}}/{f} _{\text {max}}$ of 157 GHz/334 GHz for 100-nm gated device and 211 GHz/379 GHz for 70-nm gated device. During the continuous wave (CW) power measurement at 30 GHz, the 70-nm devices exhibit a large output power of 4.6 W/mm associated with a peak power-added efficiency (PAE) of 48.1% and a gain of 11.6 dB ( ${V} _{\text {ds}} =20$ V), and a high PAE of 53.8% with an output power density of 1.9 W/mm and a gain of 10.8 dB ( ${V} _{\text {ds}} =10$ V), respectively. The huge potential of the UTB-AlGaN/GaN is demonstrated for high-frequency and large-output power applications when it is combined with the in situ SiN, which is necessary for future communication systems.

The underlying mechanism responsible for the unique dynamic ON-resistance behavior is unified by demonstrating the presence of critical drain stress voltage, above which dynamic ON-resistance increases significantly, in different gate stacks. Metal–insulator–semiconductor (MIS)- and Schottky-gated HEMTs show similar dependence of critical voltage on various parameters, which establishes that gate-stack design has negligible impact on the observed phenomena. Furthermore, using the physical insights developed, this work proposes a novel surface passivation scheme to improve the dynamic performance of the device. The proposed surface passivation scheme uses p-type Al0.5Ti0.5O (AlTiO), which is deposited over SiN x passivation (or GaN cap), and is shown to be an effective tool in improving the dynamic ON-resistance of the device by modulating the electric field in the GaN buffer. The proposed passivation scheme has avoided the critical voltage to appear for the entire drain stress voltage, stress time, and substrate bias range. Detailed computational analysis in conjunction with electroluminescence (EL) and photoluminescence (PL) studies revealed an electric field redistribution due to the p-type nature of AlTiO deposited over the surface passivation/capping layer, which is responsible for relaxed electric field profile in GaN buffer and observed improvement in dynamic performance. Besides, the new observations have further helped to understand the interplay between surface conditions and GaN buffer, defining its collective role in governing the dynamic performance of GaN HEMTs. Finally, various findings and the proposal in this work have been validated for buffers having higher carbon doping and devices with p-type AlTiO deposited over GaN cap instead of in situ SiN x cap.