GaN High Electron Mobility Transistors Research Articles

Comprehensive empirical modeling of ScAlN/AlGaN/GaN ferroelectric HEMT

This correspondence introduces a concise depiction of a high electron mobility transistor (HEMT) utilizing a model that incorporates the effect of ferroelectric (FE) polarization on the empirical expression for drain current. This is accomplished by modifying the basic Shockley equation (S.E) for MESFET. The model employed in this investigation is particularly geared towards investigating the impact of the counterclockwise hysteresis effect due to the use of dielectric ScAlN on the transfer characteristics ( Id−Vgs ), which is mainly attributed to trapping and de-trapping of charge carriers at the dielectric/semiconductor interface. Modifying the S.E. made it possible to replicate the behavior observed in experimental HEMT accurately. We reported the modified drain current empirical expressions for the ScAlN/AlGaN/GaN HEMT that considers the FE polarization. The results of this study showed good agreement between the Id−Vgs characteristics obtained from the analytical and experimental data, with a root mean square deviation (RMSD) error of 0.97% and a mean squared error error of 0.94%. This analytical drain current model, presented herein for the first time, incorporates a limited number of fitting parameters. Therefore, enhancing the computational efficiency to assess the performance of FE GaN HEMTs for usage in wide-area electronics.

Dual-Module Ultrawide Dynamic-Range High-Power Rectifier for WPT Systems

Rectifier plays a pivotal role in wireless power transfer systems. While numerous studies have concentrated on enhancing efficiency and bandwidth at specific high-power levels, practical scenarios often involve unpredictable power inputs. Consequently, a distinct need arises for a rectifier that demonstrates superior efficiency across a broad range of input power levels. This paper introduces a high-power RF-to-DC rectifier designed for WPT applications, featuring an ultrawide dynamic range of input power. The rectification process leverages a GaN (gallium nitride) high electron mobility transistor (HEMT) to efficiently handle high power levels up to 12.6 W. The matching circuit was designed to ensure that the rectifier will operate in class-F mode. A Schottky diode is incorporated into the design for relatively lower-power rectification. Seamless switching between the rectification modes of the two circuits is accomplished through the integration of a circulator. The proposed rectifier exhibits a 27.5 dB dynamic range, achieving an efficiency exceeding 55% at 2.4 GHz. Substantial improvement in power handling and dynamic range over traditional rectifiers is demonstrated.

Multiphysics simulation study of thermal stress effects in nanoscale FinFETs heterogeneously integrated with GaN high-power device on silicon substrate

Heterogeneous integration enables high-density integration to improve system functionality, but meanwhile brings reliability concerns due to the intensification of temperature and thermal stress. However, research on thermal stress effects in nanoscale transistors within heterogeneous integrated circuit is still very limited up to now. Multiphysics computation for the heterogeneous integration of nanoscale p-FinFET with GaN high electron mobility transistor (HEMT) on silicon substrate is performed. Firstly, self-heating of GaN HEMT induced thermal stress is simulated. Then, thermal stress effects induced by the GaN HEMT on quantum transport in the FinFET at different locations are compared and analyzed, including the hole effective mass, hole average velocity, on/off-state current, and on-off ratio. Moreover, the impacts of crystal orientation configurations are further discussed. Simulation results show that the impact of thermal stress on FinFET is highly dependent on the Si crystal orientation and its location relative to GaN HEMT. Taking the FinFET with (001)/[110] confinement/transport orientation, which is at a distance of RFET and an angle of φ from the GaN HEMT as an example, thermal stress induces the significant reductions in Ion and Ioff of FinFET at φ = π/2 and φ = 3π/2, and the increases of Ion and Ioff in FinFET at φ = 0 and φ = π, but has small impact on FinFETs located diagonally to the GaN HEMT.

GaN HEMT for High-performance Applications: A Revolutionary Technology

Background: The upsurge in the field of radio frequency power electronics has led to the involvement of wide bandgap semiconductor materials because of their potential characteristics in achieving high breakdown voltage, output power density, and frequency. III-V group materials of the periodic table have proven to be the best candidates for achieving this goal. Among all the available combinations of group III-V semiconductor materials, gallium nitride (GaN), having a band gap of 3.4eV, has gradually started gaining the confidence to become the next-generation material to fulfill these requirements. Objective: Considering the various advantages provided by GaN, it is widely used in AlGaN/GaN HEMTs (High Electron Mobility Transistors) as their fundamental materials. This work aimed to review the structure, operation, and polarization mechanisms influencing the HEMT device, different types of GaN HEMT, and the various process technologies for developing the device. Methods: Various available methods to obtain an enhancement type GaN HEMT are discussed in the study. It also covers the recent developments and various techniques to improve the performance and device linearity of GaN HEMT. Conclusion: Despite the advantages and continuous improvement exhibited by the GaN HEMT technology, it faces several reliability issues, leading to degradation of device performance. In this study, we review various reliability issues and ways to mitigate them. Moreover, several application domains are also discussed, where GaN HEMTs have proven their capability. It also focuses on reviewing and compiling the various aspects related to the GaN HEMT, thus providing all necessary information.

Enhanced Performance of GaN HEMTs in X‐band Applications Using SixN/Si3N4 Bilayer Passivation Technique

In order to achieve high‐performance gallium nitride (GaN) high‐electron‐mobility‐transistors (HEMTs) capable of operating in the X‐band, a bilayer passivation technique is employed. The technique involves creating a stacked passivation layer consisting of a 20‐nm Si‐rich silicon nitride (SixN) passivation layer and a 100‐nm N‐rich silicon nitride (Si3N4) passivation layer. This effectively reduces radio frequency scattering in GaN HEMTs without compromising the breakdown voltage (BV). On the one hand, the SixN passivation layer effectively suppresses the surface states of devices, resulting in low current collapse. On the other hand, the Si3N4 passivation layer can effectively reduce gate leakage caused by the SixN passivation layer, allowing the device to reliably operate at higher voltages. Consequently, a GaN HEMTs with SixN/Si3N4 bilayer passivation achieve a low current collapse of 5% and a high BV of 157 V. The device features a current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) of 57.9 and 96.8 GHz, respectively. Additionally, it exhibits excellent radio frequency performance in the X‐band, with an output power density (Pout) of 13.7 W mm−1 and power added efficiency of 60.8% at a drain voltage (VD) bias of 50 V.

Novel Temperature Calibration Method of E-Mode and D-Mode GaN Power Modules Considering Dynamic ON-Resistance

This paper presents a method for measuring temperature using the temperature sensitive parameter (TSP) of a GaN power module. Current collapse occurs in GaN high electron mobility transistors (HEMTs). This results in dynamic on-resistance because of trapped electrons. Thus, dynamic conditions should be considered to accurately measure thermal characteristics. GaN HEMTs are operated in the enhanced mode (E-mode) and depletion mode (D-mode). In this study, E-mode and D-mode GaN power modules are designed to compare their thermal characteristics. Among three common temperature-measurement methods, this work employs the TSP-based approach in consideration of the device operation, instead of those using thermo-sensitive optical or material properties. The calibration is conducted in steady-state and dynamic-state. The ambient temperature is estimated using steady-state calibration data. Power cycling is examined for considering dynamic conditions. It is confirmed that dynamic on-resistance changes according to the cycle period, on time, and number of cycles. Experiments are conducted using different values of these parameters. Finally, an equation for temperature is obtained from the experimental results. The equation precisely estimates temperature with an error of 0.7%.

Study of MoN gate impact on GaN high electron mobility transistor

AbstractIn this letter, molybdenum nitride (MoN) gate AlGaN/GaN HEMT has been investigated with MoN developed in various physical vapour deposition (PVD) conditions. The Schottky gate is studied through forward and reverse characteristics with different processed MoN, which is compared with the standard Ni gate. Similar DC and radio frequency (RF) performances are obtained with MoN and Ni gate, while MoN demonstrated higher reliability than Ni gate through RF aging test.

A novel small-signal equivalent circuit model for GaN HEMTs incorporating a dual-field-plate

An accurate and novel small-signal equivalent circuit model for GaN high-electron-mobility transistors (HEMTs) is proposed, which considers a dual-field-plate (FP) made up of a gate-FP and a source-FP. The equivalent circuit of the overall model is composed of parasitic elements, intrinsic transistors, gate-FP, and source-FP networks. The equivalent circuit of the gate-FP is identical to that of the intrinsic transistor. In order to simplify the complexity of the model, a series combination of a resistor and a capacitor is employed to represent the source-FP. The analytical extraction procedure of the model parameters is presented based on the proposed equivalent circuit. The verification is carried out on a 4 × 250 μm GaN HEMT device with a gate-FP and a source-FP in a 0.45 μm technology. Compared with the classic model, the proposed novel small-signal model shows closer agreement with measured S-parameters in the range of 1.0 to 18.0 GHz.

Current collapse suppression in AlGaInN/GaN HEMTs with thin unintentionally doped GaN channel and AlN back barrier grown on single-crystal AlN substrate

A high-electron-mobility transistor (HEMT) structure consisting of a 15-nm-thick quaternary AlGaInN top barrier layer, a thin 200-nm-thick unintentionally doped (UID) GaN channel layer, and an AlN back barrier was grown on a single-crystal AlN substrate by metal–organic chemical vapor deposition. The HEMTs fabricated on the grown heterostructure exhibited DC pinch-off characteristics with no large negative resistance owing to the high thermal conductivity of the AlN substrate. The 2-μm-gate-length devices showed the maximum current density of 500 mA/mm and the peak transconductance of 120 mS/mm with the threshold voltage of approximately −4 V. The off-state leakage was less than 30 μA/mm thanks to the thin UID-GaN channel with good crystal quality. The pulsed I–V characteristics for the fabricated HEMTs showed much smaller drain current decreasing compared to the same structured HEMTs with a C-doped GaN back barrier on a SiC substrate. This indicates that the UID-GaN channel grown on the AlN substrate had no harmful impurity levels that cause the current collapse phenomenon. The above-mentioned results demonstrate that the combination of the thin UID-GaN channel and the AlN back barrier works effectively in GaN HEMTs, and it will contribute to the device design and fabrication for future high-power/high-frequency applications.

Temperature-induced degradation of GaN HEMT: An in situ heating study

High-power electronics, such as GaN high electron mobility transistors (HEMTs), are expected to perform reliably in high-temperature conditions. This study aims to gain an understanding of the microscopic origin of both material and device vulnerabilities to high temperatures by real-time monitoring of the onset of structural degradation under varying temperature conditions. This is achieved by operating GaN HEMT devices in situ inside a transmission electron microscope (TEM). Electron-transparent specimens are prepared from a bulk device and heated up to 800 °C. High-resolution TEM (HRTEM), scanning TEM (STEM), energy-dispersive x-ray spectroscopy (EDS), and geometric phase analysis (GPA) are performed to evaluate crystal quality, material diffusion, and strain propagation in the sample before and after heating. Gate contact area reduction is visible from 470 °C accompanied by Ni/Au intermixing near the gate/AlGaN interface. Elevated temperatures induce significant out-of-plane lattice expansion at the SiNx/GaN/AlGaN interface, as revealed by geometry-phase GPA strain maps, while in-plane strains remain relatively consistent. Exposure to temperatures exceeding 500 °C leads to almost two orders of magnitude increase in leakage current in bulk devices in this study, which complements the results from our TEM experiment. The findings of this study offer real-time visual insights into identifying the initial location of degradation and highlight the impact of temperature on the bulk device’s structure, electrical properties, and material degradation.

Damage Effects and Mechanisms of High-Power Microwaves on Double Heterojunction GaN HEMT

In this paper, simulation modeling was carried out using Sentaurus Technology Computer-Aided Design. Two types of high electron mobility transistors (HEMT), an AlGaN/GaN/AlGaN double heterojunction and AlGaN/GaN single heterojunction, were designed and compared. The breakdown characteristics and damage mechanisms of the two devices under the injection of high-power microwaves (HPM) were studied. The variation in current density and peak temperature inside the device was analyzed. The effect of Al components at different layers of the device on the breakdown of HEMTs is discussed. The effect and law of the power damage threshold versus pulse width when the device was subjected to HPM signals was verified. It was shown that the GaN HEMT was prone to thermal breakdown below the gate, near the carrier channels. A moderate increase in the Al component can effectively increased the breakdown voltage of the device. Compared with the single heterojunction, the double heterojunction HEMT devices were more sensitive to Al components. The high domain-limiting characteristics effectively inhibited the overflow of channel electrons into the buffer layer, which in turn regulated the current density inside the device and improved the temperature distribution. The leakage current was reduced and the device switching characteristics and breakdown voltage were improved. Moreover, the double heterojunction device had little effect on HPM power damage and high damage resistance. Therefore, a theoretical foundation is proposed in this paper, indicating that double heterojunction devices are more stable compared to single heterojunction devices and are more suitable for applications in aviation equipment operating in high-frequency and high-voltage environments. In addition, double heterojunction GaN devices have higher radiation resistance than SiC devices of the same generation.

Influence of electrical field on the susceptibility of gallium nitride transistors to proton irradiation

Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 1012 to 3.76 × 1014 cm2, and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According to in-situ Raman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability.

Impact of Carbon Doping on Vertical Leakage Current in AlGaN‐Based Buffer Layer Grown on Silicon Substrate

The buffer leakage phenomena have a large effect on high‐power and fast‐switching GaN high electron mobility transistor devices. Herein, the buffer leakage mechanism in a GaN‐on‐Si substrate with AlGaN buffer layers is investigated by using samples with various carbon concentrations. Comparing the leakage current with crystallinity and impurity concentration, it is found that the vertical leakage current is dominated by both threading dislocations and bulk impurities. Increasing the carbon concentration of buffer layers suppresses leakage current in the bulk conducting regime in high electric fields but increases it in the dislocation conducting regime in low electric fields. These results indicate that the optimal carbon concentration of buffer layers depends on the target electric field.

Suppressed current collapse and improved threshold voltage stability of AlGaN/GaN HEMT via O2 plasma treatment

A comprehensive study about the effects of O2 plasma treatment on the dynamic performance of AlGaN/GaN high electron mobility transistors (HEMTs) is presented. The drain current transient spectroscopy indicated a much decelerated and mitigated current degradation process for the HEMT with O2 plasma treatment. Upon negative gate bias stressing, current collapse of 10.7 % and minor threshold voltage shift of 0.16 V were achieved by O2 plasma treatment. In addition, current collapse ratio of the HEMTs as a function of stress/recovery time showed that the HEMT with O2 plasma treatment had a superior performance in various on-off conditions. Particularly in high-frequency switching events, current collapse ratio was reduced from about 50 % to 0.2 %. At last, the quality of AlGaN/metal interface with O2 plasma treatment is demonstrated by capacitance-frequency measurements, with the interface trap density Dit is estimated to be 1.39 × 1012 cm−2 eV−1. These results indicate that GaN HEMT with O2 plasma treatment is a promising technology in power switching applications.

Temperature rise detection in GaN high-electron-mobility transistors via gate-drain Schottky junction forward-conduction voltages

An electrical measurement method for the junction temperature and thermal resistance of GaN high-electron-mobility transistors (HEMTs) is discussed. It is based on the forward voltage drop across the gate-drain Schottky diode. During measurement of this temperature-sensitive parameter, the source is left floating while the drain is grounded. Previous studies have shown that the hot spot in GaN HEMTs is near the gate side, close to the drain. The forward voltage drop across the gate-drain diode yields higher and more consistent temperatures relative to those using the forward voltage drop across the gate-source Schottky diode. This method could potentially provide more accurate data for thermal management and reliability analyses of GaN-based HEMTs. The maximum temperature of the sample was 44.8 °C on the grate-drain side and approximately 40.5 °C on the gate-source side when the sample exhibited 3.44W thermal power consumption for 1 min. Hence, the proposed method is practical and instructive.

Alleviation of the on-state dynamic conductance decline in a GaN high electron mobility transistor with heavy carbon doping

Carbon doping is a standard blocking-voltage-enhancing technique for commercial silicon substrate-based AlGaN/GaN power switching transistors, although the incorporation of carbon into GaN may deteriorate the dynamic on-state resistance (dy-R on) properties of the device. Commonly, researchers have believed that the greater the carbon doping, the greater the deterioration in dy-R on. Surprisingly, in this work, the opposite was observed: the dy-R on value decreased as the carbon concentration increased, particularly when the density exceeded several 1017 cm−3. This phenomenon is explained by the effect of electric field-induced band-to-band electron tunneling into the two-dimensional electron gas (2DEG) conduction channel, originating from the ionization of acceptor-like nitrogen site carbon atoms (CN) in the device off-state with large drain bias. Simulation data indicated that negatively ionized CN may generate a much larger electric field in samples with higher carbon doping, which may induce a narrower 2DEG back energy band barrier that increases the possibility of electron band-to-band tunneling.

Investigation of RF performance of Ku-band GaN HEMT device and an in-depth analysis of short channel effects

In this paper, we have characterized an AlGaN/GaN High Electron Mobility Transistor (HEMT) with a short gate length (Lg ≈ 0.15 μm). We have studied the effect of short gate length on the small signal parameters, linearity parameters and gm-gd ratio in GaN HEMT devices. To understand how scaling results in the variation of the above-mentioned parameters a comparative study with higher gate length devices on similar heterostructure is also presented here. We have scaled down the gate length but the barrier thickness(tbar) remained same which affects the aspect ratio (Lg/tbar) of the device and its inseparable consequences are the prominent short channel effects (SCEs) barring the optimum output performance of the device. These interesting phenomena were studied in detail and explored over a temperature range of −40 °C to 80 °C. To the best of our knowledge this paper explores temperature dependence of SCEs of GaN HEMT for the first time. With an approach to reduce the impact of SCEs a simulation study in Silvaco TCAD was carried out and it is observed that a recessed gate structure on conventional heterostructure successfully reduces SCEs and improves RF performance of the device. This work gives an overall view of gate length scaling on conventional AlGaN/GaN HEMTs.

Revolutionizing Fe doped back barrier AlGaN/GaN HEMTs: Unveiling the remarkable 1700V breakdown voltage milestone

This research investigates the enhanced device breakdown capabilities of silicon-based AlGaN/GaN High Electron Mobility Transistors (HEMT). By incorporating various back barrier materials, a significant improvement in peak electric field and breakdown voltage is observed. Specifically, the integration of iron (Fe) doping into the Gallium Nitride (GaN) back barrier layer, combined with different back barrier materials such as Aluminum Gallium Nitride (AlGaN) and Indium Gallium Nitride (InGaN), results in an impressive increase of up to 1700 V. This improvement is attributed to the reduction of peak electric field at the gate edge. The optimized layer configurations significantly contribute to the overall performance of silicon substrate GaN HEMT devices, making them promising candidates for high-voltage applications in electric vehicles and high-power applications.

Integration of low-thermal-budget In2O3 NMOS inverter and GaN HEMT for power electronics

Herein, we demonstrated an “interposer”-style integration of In2O3 FET-based gate-driver circuitry wire bonded to an AlGaN/GaN high electron mobility transistor (HEMT) device grown on a GaN-on-Si substrate, and its feasibility for power electronics was discussed. The normally-on AlGaN/GaN HEMT exhibited a threshold voltage of −2.8 V, with a maximum drain current density of 265 mA/mm. The device also showed good off-state performance, such as a high ON/OFF ratio (Ion/Ioff) of ∼1010 with a breakdown voltage of ∼445 V and an off-state leakage current of ∼10−12 A. The low-temperature processed In2O3 driver circuitry exhibited a high gain of ∼64 and a maximum operating frequency of 2 kHz. The temperature-dependent study of the voltage transfer characteristics (VTC) of In2O3 driver circuitry exhibited stable operation up to 125 °C. An integrated In2O3 driver circuitry with GaN HEMT was demonstrated, marked by a 50 mA/mm drain current for circuit response of one cycle during the ON state. These results pave the way for future monolithic integration of oxide semiconductor-based gate-driver circuitry with power switches for energy-efficient integrated circuits.

Insights into dynamic switching behavior and electric field distribution of depletion-mode GaN HEMT with bonding pad over active layout

Bonding pad over active (BPOA) layout, which stacks traditional horizontal structure pad electrodes vertically above the active area, is an area-effective device architecture and packaging-enabled solution for GaN-based high electron mobility transistors (HEMTs). In this work, the dynamic switching and electric field distribution of such layout, as well as associated capacitance–voltage and trapping characteristics, are comprehensively studied on D-mode GaN-on-sapphire HEMT by performing numerical simulations. In terms of different pad electrodes covering the active area, BPOA is composed of various structures such as gate-related and drain-related BPOAs (i.e. G-BPOA and D-BPOA), among which G-BPOA exhibits inferior switching characteristics due to the additional introduction of Miller capacitance that prolongs the device switching, while breakdown voltage of D-BPOA is 400–900 V lower than other BPOA counterparts due to the interplay between D-BPOA and the drain electrode. Furthermore, the effects of trap capture cross section and trap density on switching characteristics are evaluated. These results highlight the differences in electrical characteristics of various structures within the BPOA layout, and provide valuable insights into BPOA device design and performance improvement.