GaN High Electron Mobility Transistors Research Articles

Design of 2–16 GHz Non-Uniform Distributed GaN HEMT MMIC Power Amplifier with Harmonic Suppression Network

In this paper, an ultra-wideband (UWB) power amplifier (PA) on a 0.25 μm gallium-nitride (GaN) on silicon carbide (SiC) high-electron-mobility transistor (HEMT) process, operating in Ku-band, is presented. The broadband PA design is based on the four-stage non-uniform distributed amplifier structure. In order to improve the efficiency of the PA, a harmonic suppression network is added at the output of the drain artificial transmission line. At the same time, a capacitor is connected in series at the input of the gate, which is used to compensate for the phase offset of the gate and increase the cut-off frequency of the PA. The final gate width of the first stage is 0.56 μm, and the other three-stage gate widths are all 0.32 μm. Over the frequency range of 2–16 GHz, the simulated results of this NDPA exhibit a power-added efficiency (PAE) of 16.6–27%, a saturated continuous wave (CW) output power of 35–37 dBm, a small signal gain of 9.1–11.6 dB, and output return losses of 5–15 dB.

Dynamic-State Analysis of Inverter Based on Cascode GaN HEMTs for PV Application

With the increase in renewable energy generation, microgrid has put forward higher requirements on the power density and performance of the photovoltaic inverter. In this paper, the dynamic process of inverter based on the cascode Gallium nitride (GaN) high electron mobility transistor (HEMT) for the photovoltaic (PV) application is analyzed in detail. The parasitic inductors and capacitors have been considered in our proposed equivalent model, which can explain the phenomenon that the crossover time of the voltage and current is prolonged by the parasitic parameters. The influence of the parasitic parameters is identified through theoretical analysis. By analyzing the influence of parasitic parameters, the design process of high-frequency inverter can be optimized. A 500 W inverter based on the cascode GaN HEMT is built, and the correctness of theoretical and simulation analysis is verified by the experimental results.

Investigation of back barrier material effects on the scalability of Fe-doped recess-gated AlN/GaN HEMTs for next generation RF power electronics

GaN HEMTs (high-electron-mobility transistors) on SiC (silicon carbide) wafer with back barrier structures have gained much attention owing to the improved sheet charge density through enhanced carrier confinement, which can accomplish further improvement of RF performance. In this simulation work, the influence of different back barrier materials on RF & DC performance of Fe-doped recess gated AlN/GaN HEMT is explored. This paper also investigates the back barrier thickness effects on carrier confinement of each structure; the results show that better confinement of carriers in the GaN channel is accompanied by an optimized thickness for each back barrier material besides which, the performance is comparatively degraded. As back-barrier based structures have the capability to reduce SCEs by enhancing the carrier confinement, the investigation is done to analyse the impact of gate length scalability on the DC & RF characteristics of the proposed device. Lg = 60 nm Fe-doped recess-gated AlN/GaN HEMT with an optimized AlGaN back barrier thickness of 60 nm provided a peak drain current of 4.63 A/mm, the highest transconductance of 2333 mS/mm, and the highest cut-off frequency of 316.6 GHz, and this outstanding DC/RF performance is due to strong carrier confinement and reduced leakage current. This outstanding performance makes them a potential choice for future RF power electronics and MMIC design.

(Invited, Digital Presentation) The Challenges of Overcoming Defects in GaN Hemts for Operation in Extreme Environments

GaN high electron mobility transistors (HEMTs) are known to contain a high density of crystal defects. The material properties of GaN such as high breakdown voltage, carrier mobility, critical electric field strength, and higher thermal conductivity than Si, make it an ideal candidate material for use in power switches in extreme environments. In high power environments (>1.5kV), vertical GaN device geometry is emerging as an effective technique to improve performance, but the more mature lateral GaN HEMT technology is being consistently improved upon to increase breakdown voltage and overall performance in the high-power regime. In high temperature environments, GaNs wide bandgap helps in preventing unwanted thermal generation of carriers, but devices also experience increased gate-leakage current and ohmic contact resistance degradation at high temperatures. The role of defects in these limiting factors of GaN HEMT performance in extreme high power and high temperature environments is reviewed.

(Invited) Micromechanical Aspects of GaN Hemt Performance and Reliability

Performance and reliability of microelectronic devices are governed by the mechanical strain. Typically, strain engineering implies uniformly distributed strain. However, we offer a different perspective by hypothesizing that very small but localized strain (or stress) may have significant impact on the overall behavior of AlGaN/GaN high electron mobility transistors (HEMTs). Micro to nanoscale confined mechanical stress fields may develop unavoidably and are ignored because their spatial average is insignificant. We exploit high resolution techniques such as transmission electron microscopy (TEM) and micro-Raman spectroscopy to spatially resolve the stress field in GaN HEMTs to demonstrate the stress localization and then radiation effects.To study stress localization effects on the global electrical characteristics, we introduced a highly localized strain relief by milling a 20×30 μm2 micro trench about 70 μm deep on the backside of an 800×840 μm2 size HEMT die. The resulting local relaxation of in-plane residual strain was mapped using micro-Raman technique. Our results show that a decrease of only 0.02% strain can decrease the overall output saturation current up to ~20 %. The drop of output current is attributed to reduced two-dimensional electron gas (2DEG) sheet carrier density and electron mobility due to the strain relief in the device layers. However, the mechanistic process of strain relief also causes defect generation at the interfaces, which increases leakage current. Our technique for localized strain re-distribution could be an effective tool to surrogate the influence of inherent localized strain build-up across the channel of electronic devices.To study radiation effects, we exposed the HEMTs to gamma rays (up to 10 megaRads dose at 180 kiloRads per hour). We report the thermal and mechanical responses in terms of the changes in lattice strain and temperature, which were simultaneously characterized by changes in phonon frequency of E2 (high) and A1 (LO) from on- state and unpowered/pinched off reference states. Lower doses of radiation improved the electrical properties, however degradation initiated at about 1 megaRads. We observed about 16% decrease in saturation current and 6% decrease in transconductance at the highest dose. However, leakage current increase by 3 orders of magnitude was the most notable radiation effect. We observed temperature increase by 40% and mechanical stress increase by a factor of three at dose of 10 megaRads compared to the pristine devices. Spatial mapping of mechanical stress along the channel identifies the gate region as mechanically affected area, whereas the thermal degradation was mostly uniform. Transmission electron microscopy showed contrast changes reflecting high vacancy concentration in the gate region. These findings suggest that localized stress (mechanical hotspots) may increases vulnerability to radiation damage by accommodating higher concentration of defects that promote leakage current.Finally, we present experimental results on a novel concept of electron wind force driven room temperature annealing of GaN and SiC devices. This technique was applied on Gamma irradiated HEMT and SiC diodes. We demonstrate full recovery of the HEMTs irradiated to 10 mega-Rads gamma radiation. About 200% performance improvement was recorded for the SiC diodes. Our hypothesis is that mechanical stress waves are instrumental in eliminating interfacial defects.

Interference effects in GaN high electron mobility transistor power amplifier induced by microwave pulses

Owing to the rapid development of wireless communication, radar and pulse power technology, the electromagnetic environment faced by electronic systems is increasingly complex and the intensity of electromagnetic field can be significant. In this study, a new interference phenomenon was observed when the microwave pulses were injected into the gallium nitride (GaN) high electron mobility transistor (HEMT) power amplifier through the output port. We investigated the relationship between the peak power of reverse injection microwave pulses and the duration or the amplitude of the interference by effect experiments. The interference duration could reach the magnitude of millisecond. Deep traps in GaN HEMT power amplifiers are proved to be the cause of this interference effects.

Phonon thermal transport and its tunability in GaN for near-junction thermal management of electronics: A review

The heat dissipation issue has now become one of the most important bottlenecks for power electronics due to the rapid increase in power density and working frequency. Towards the wide bandgap semiconductor GaN high electron mobility transistors (HEMTs), near-junction thermal management is the breakthrough that mainly includes the accurate thermal modeling and effective thermal design for GaN and GaN HEMTs. In this review, we first offer a comprehensive understanding of phonon thermal transport in GaN and GaN HEMTs, including non-equilibrium transport of electrons and phonons in the heat generation process, phonon thermal conductivity, heat spreading, and interfacial thermal transport. Then, we review the current tuning mechanisms and methods for thermal transport in GaN and GaN HEMTs which are classified into three categories according to the particle nature, wave nature, and topological nature of phonons. At last, we conclude by providing our perspectives on challenges and opportunities in the research of phonon thermal transport and its tuning mechanisms in GaN HEMTs.

GaN-Based Multichip Half-Bridge Power Module Integrated on High-Voltage AlN Ceramic Substrate

Power electronic systems employing wide-bandgap GaN transistors promise high efficiency operation and power density but require minimized parasitic circuit elements and an effective cooling concept. This article presents a half-bridge module integrating two 600 V/170 mΩ gallium nitride (GaN) high-electron mobility transistors with their gate drive stages and a fraction of the dc-link capacitance on a patterned multilayer polycrystalline AlN-substrate. The high-voltage isolation at a layer distance of 10 μm and a dense chip-by-chip integration on the GaN half-bridge module enable a compact lateral commutation loop design combined with improved cooling capability of the power transistors. Consequently, the GaN half-bridge module allows for higher load currents at lower device temperature while most parasitic circuit elements are reduced compared to a conventional printed circuit board (PCB) design. The parasitic circuit elements of the GaN half-bridge module and a reference four-layer PCB half-bridge are evaluated using 3D-FEM field simulation and in-circuit measurements. Selected finite element method (FEM) simulation results are validated by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameter measurements and further used to parametrize a lumped commutation loop model. The thermal characterization of the GaN half-bridge module validates the improved cooling capability of the GaN half-bridge power module. Transient switching characteristics are studied in hard-switching mode. The device temperature and converter efficiency are evaluated in dc/dc buck-converter operation.

Impact of the Low Temperature Ohmic Contact Process on DC and Forward Gate Bias Stress Operation of GaN HEMT Devices

In AlGaN/GaN high electron mobility transistors (HEMTs), high temperature processes (such as ohmic annealing with >800°C value) could deform the crystal structure and induce trap states within the bulk and surface. Expanded defect densities cause crucial problems, such as threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> ) instability, current collapse, and high leakages. In this work, a low temperature ohmic contact process (630°C, 10 minutes) is adopted with recess etch, and contact resistances <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; 0.1\Omega ~\cdot $ </tex-math></inline-formula> mm with low sheet resistances are achieved. The positive impact of this low thermal budget process on surface morphology, DC operation, long-term stability, and forward gate bias stress of the device is studied.

Cumulative Hot-Electron Trapping in GaN-Based Power HEMTs Observed by an Ultrafast (10 V/Ns) On-Wafer Methodology

The goal of this article is to advance the understanding of the impact of hard switching on the dynamic performance of GaN-based high electron mobility transistors (HEMTs). To this aim, we developed a fast (10 V/ns) on-wafer system for testing devices in hard switching. The system has been used to study the reliability of several <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W_{G}=2$ </tex-math></inline-formula> mm p-type GaN HEMTs with different <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{\text {GD}}$ </tex-math></inline-formula> or buffer properties. First, we show that by optimizing the drain node capacitance, we can speed up the hard-switching transition to a few ns, even on-wafer level. Second, repeating the experiment by using multiple frequencies, from 1 to 100 kHz, we demonstrate that, in real-world applications, cumulative turn-on stress has a much stronger effect on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathrm {ON}}$ </tex-math></inline-formula> compared with OFF-state stress. Third, by comparing the results on identical devices having shorter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L_{\text {GD}}$ </tex-math></inline-formula> , we pinpoint hot electrons as the main mechanism in the device degradation, ruling out the contribution of self-heating. Finally, by comparing three wafers with different processing conditions (different passivation, different buffer), we suggest that trapping phenomena related to hot electrons happen in ns time scale and that the properties of the buffer can significantly impact the dynamic performance of the devices in hard switching.

Improvement and Reduction of Self-Heating Effect in AlGaN/GaN HEMT Devices

GaN is one of the third-generation broadband semiconductor materials developed rapidly in recent years, and Algan/GanHEMT has a broad application prospect in the fields of high temperature, high power, high frequency and radiation resistance, etc. In recent years, gallium nitride based high electron mobility transistors have been widely used in emerging industries, such as 5G technology, new energy vehicles, unmanned aircraft and other fields, due to their high power and high voltage resistance. However, due to the high power density of HEMT devices, the self-heating effect will lead to a significant increase in the junction temperature of the device, which will seriously affect the performance, reliability, and lifetime of the device. In this paper, the temperature characteristics of GaN high electron mobility transistors (GaN HEMTs) are studied, and the effect of self-heating effect on GaN HEMT devices is analyzed. In order to reduce the device temperature and improve the reliability of the device, a new device structure is proposed in this paper. The new structure replaces the conventional silicon and Si3N4 with highly thermally conductive diamond and SiC as the substrate and passivation layer of the device, which facilitates the heat dissipation from the substrate and passivation layer. Also, the new structure employs a hybrid barrier layer and field plate. Simulation results show that the new structure has about 30% lower temperature peak, 47% higher output current, 28% higher transconductivity, and up to 18.22% higher current collapse rate compared to the conventional structure.

Dual role of 3C-SiC interlayer on DC and RF isolation of GaN/Si-based devices

The impact of Cubic Silicon Carbide (3C-SiC) transition layer on breakdown voltage and frequency performance of GaN high electron mobility transistors is investigated. A combination of distinct material and device characterizations techniques, including Raman spectroscopy, coplanar waveguides, electrical measurements, and Technology Computer-Aided Design (TCAD) simulations, are adopted to inspect the role of the 3C-SiC interlayer. Raman spectra reveal a good quality of the 3C-SiC layer, similar to the mono-crystalline 3C-SiC spectra. A relatively low transmission loss of ∼0.16 dB/mm at 40 GHz is measured for the device with 3C-SiC layer, rather than 2.1 dB/mm for the device without 3C-SiC. In addition, a soft breakdown voltage around 1530 V at 1 μA/mm is achieved, which is three times larger compared with that of the conventional device. The failure mechanism, related to carrier injection at the nucleation layer, is not observed in the structure with the 3C-SiC layer. Instead, TCAD simulations disclose a substantial improvement of the buffer/substrate interface through the suppression of an interface current path.

The 3.4 GHz BAW RF Filter Based on Single Crystal AlN Resonator for 5G Application.

To meet the stringent requirements of 5G communication, we proposed a high-performance bulk acoustic wave (BAW) filter based on single crystal AlN piezoelectric films on a SiC substrate. The fabrication of the BAW filter is compatible with the GaN high electron mobility transistor (HEMT) process, enabling the implementation of the integration of the BAW device and high-performance monolithic microwave integrated circuit (MMIC). The single crystal AlN piezoelectric film with 650-nm thickness was epitaxially grown on the SiC substrate by Metal Organic Chemical Vapor Deposition (MOCVD). After wafer bonding and substrate removal, the single crystal AlN film with electrode layers was transferred to another SiC wafer to form an air gap type BAW. Testing results showed that the fabricated resonators have a maximum Q-factor up to 837 at 3.3 GHz resonant frequency and electromechanical coupling coefficient up to 7.2%. Ladder-type filters were developed to verify the capabilities of the BAW and process, which has a center frequency of 3.38 GHz with 160 MHz 3 dB bandwidth. The filter achieved a minimum 1.5 dB insertion loss and more than 31 dB out-of-band rejection. The high performance of the filters is attributed to the high crystallinity and low defects of epitaxial single crystal AlN films.

Modulating Light Emission Performance of PCSEL via GaN HEMT Driving Circuit

In this study, a paradigm for modulating the light emission performance of photonic-crystal surface-emitting laser (PCSEL) via GaN high electron mobility transistor (HEMT) driving circuit is proposed for the first time. For light detection and ranging (LiDAR) system, a faster pulse repetition frequency with shorter pulse width can provide not only high resolution but also sufficiently precise range resolution. Hereupon, comprehensive analyses for such an integrated system are conducted with not only electro-optical responses but also the corresponding optical behaviors. The relevant electrical characteristics of the employed GaN HEMT are examined at first. Next, the integrated system on a matrix board with its corresponding circuit topology is discussed, illustrating the relevant operating principles. Thereby, sufficient systematical scrutinization for relevant light emissions is performed for both photodiode responses and the optical behaviors under different conditions, paving a holistic panorama for the LiDAR system. Thus, prospects for the next generation LiDAR system in high-power and high-speed operation can be expected.

Wide Bandgap Devices Continue to Evolve for Aerospace Applications

<fig orientation="portrait" position="float" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <graphic orientation="portrait" position="float" xlink:href="bindr-3196232.tif"/> </fig> From electric aircrafts to satellites and unmanned aerial vehicles (UAVs), the need for fuel saving and greenhouse reduction continues relentlessly. As a result, electrification seems to be catching rapidly in aerospace and aviation applications. This demands new generation of power converters, motor drives, and solid-state circuit breakers with unprecedented power density, efficiency, and reliability. Wide bandgap (WBG) power devices, such as silicon carbide (SiC) MOSFETs and gallium nitride (GaN) high-electron mobility transistors (HEMTs) and gate injection transistors (GITs), are regarded as critical candidates for such applications. While WBG devices have been serving the needs of commercial and industrial systems for more than a decade, there are still many challenges for WBG devices and their circuits for aviation applications, which include radiation hardness, extreme operation temperature, high altitude, high-voltage, high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> , and high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i> operation induced issues.

HEMT Inspired GaN Optical Waveguides: Analysis Under Thermal Stress and Prospects

In this paper, high electron mobility transistor (HEMT) inspired aluminium gallium nitride (AlGaN)/gallium nitride (GaN)/aluminium nitride (AlN) optical waveguides are proposed under thermal stress using silicon (Si), silicon carbide (SiC), and sapphire (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) substrates. The interaction of light with the thermal stress range of 20°C to 700°C is analyzed and an optimized framework design by adjusting the core, cladding, and substrate thicknesses is presented in this work. The study suggests that from the dispersion and confinement loss analysis, the SiC substrate-based GaN HEMT is suitable for high temperature and sensing platforms compared with silicon (Si) and sapphire substrates based HEMTs structure. The thermal stress-induced studies will mainly be utilized for sensing, nonlinear applications like tunable supercontinuum generation and spectroscopy in harsh environments. In addition, waveguide analysis based on HEMT inspired GaN optical waveguide proposed here in an optical domain potentially be used in electro-optical modulator application due to its ability to operate in both electrical and optical domain.

Modeling Electrostatics and Low-Field Electron Mobility of GaN FinFETs

Gallium nitride (GaN) high electron mobility transistors (HEMTs) are currently being used for RF applications due to the intrinsically high saturation velocity and high mobility of GaN compared to both Silicon and SiC. However, GaN HEMTs suffer from a variety of issues, such as a lack of E-Mode operation and non-linearity, which impacts their widespread adoption in the RF and low-voltage switching devices. Recent advances in material processing, high aspect ratio epitaxial growth, and etching methods has led to an increased interest in 3-D GaN nanostructures such as AlGaN/GaN MIS FinFET wherein a layer of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> surrounds the AlGaN/GaN fin. Theoretical calculations of transport properties of AlGaN/GaN FinFETs are scarce compared to those of their planar HEMT counterparts. This work employs for the first time self-consistent solution of the coupled 1-D Boltzmann – 2-D Schrödinger – 3-D Poisson problem to yield the channel electrostatics and the transport characteristics of AlGaN/GaN MIS FinFETs. The low field electron mobility in the quasi-1-D region is calculated, using 1-D ensemble Monte Carlo method, as a function of temperature and fin width. Acoustic, piezoelectric and polar optical phonon scattering, and interface roughness scattering at the AlGaN/GaN interface, are incorporated in the theoretical model. Our simulations suggest that E-mode FinFETs can be achieved in ultranarrow fin channels. As suggested experimentally, we confirm via simulation experiments that strain relaxation increases the sheet resistance of the channel.

Prediction of threshold voltage of GaN HEMTs using deep learning model designed by genetic algorithm

This paper demonstrates a novel application of the deep learning (DL) model designed by a genetic algorithm (GA) for modelling the figure of merits (FOMs) of gallium nitride (GaN) based high electron mobility transistors (HEMTs). To the best of our knowledge, it is the first paper that presents an end-to-end methodology to automate the optimization process of a DL model specifically for semiconductor devices. Such design automation of a DL model substantially reduces the barrier to adopting the DL techniques and encourages researchers from the semiconductor field to adopt the potential of deep learning techniques. To optimize and train the DL model, a dataset of 2160 unique GaN HEMTs for various epitaxial structures has been generated by experimentally validated simulation methodology. Four figure of merits (FOMs) i.e., on current (Ion), maximum transconductance (Gm), subthreshold slope (SS) and threshold voltage (Vth) have been extracted to generate the dataset. Any combination of the three FOMs can be used as inputs to train the DL model for predicting the fourth one. In this particular application, Ion, Gm, and SS are used to predict the Vth of the GaN HEMT. The GA converges after 15 generations for the population size of 250. The optimized solution obtained from the GA for the DL model has a batch size of 8, adam optimizer, 4 number of hidden layers with 16, 8, 16 and 16 neurons, respectively, RELU activation function and zero dropout rate. The optimized DL model provides accurate predictions of the FOMs even for unseen inputs at a very low computational cost in real-time (within a second). The performance of the optimized DL model has been also compared with Lasso, Ridge and support vector regression models and their mean square error and R-square are found to be 0.05, 1, 0.29, 0.17 and 0.978, 0.59, 0.88, 0.931, respectively.

Conducted EMI analysis and filters design for a high-low voltage DC/DC converter based on GaN HEMTs in electric vehicle

PurposeThe purpose of this paper is to study conducted electromagnetic interference (EMI) of the high-low voltage DC/DC converter based on GaN high-electron-mobility transistors (HEMTs) in electric vehicle, and design EMI filters to suppress the conducted EMI.Design/methodology/approachThe conducted EMI propagation model is established through simulation and analysis studying the influences of parasitic parameters, operation mode, output power and near-field capacitive coupling effects on conducted EMI of the DC/DC converter and comparing the suppression effects of EMI filters with different topologies to select the best EMI filter.FindingsIt is shown that parasitic parameters, operation mode, output power and near-field capacitive coupling effects can affect the conducted EMI of the DC/DC converter, and EMI filters of the CLC topology can effectively suppress the conducted EMI below the limit of CISPR 25.Originality/valueAnalysis of conducted EMI and design of EMI filters greatly facilitate further explorations and studies on EMI problems of the high-low voltage DC/DC converter based on GaN HEMTs.

Off‐State Drain Leakage Current Mechanism in GaN High Electron Mobility Transistors from Thermal Storage Test

The effect of the thermal storage test on GaN high electron mobility transistor (HEMT) is investigated in this study by observing off‐state drain leakage current and on‐state hysteresis and maximum transconductance. The recovery post thermal stress is also observed which points to native defects within the heterostructure as the leakage values after 72 hrs of recovery are measured to be one order higher than the pristine device. On‐state hysteresis recovery and off‐state drain leakage are dominated by similar defects as observed from the characteristic recovery times. Trap analysis through drain current spectroscopy reveals an additional trap level of EC – 0.83 eV from the thermal storage test. The electrical measurements are in close correlation with the Raman active mode leading to reduced lifetimes (≈0.44 ps) at higher temperatures, where anharmonic phonon decay is observed following the reported Balkanski model. This gives an overall picture of the phonon‐induced defect generation from the thermal stress and the recovery from the reduced scattering probability within the material observed after 72 hrs recovery; also observed within the HEMTs from electrical characterization.