GaN High Electron Mobility Transistors Research Articles

Inverse Piezoelectric and Trap Effects With Temperature Dependence in AlGaN/GaN HEMTs Under Narrowband Microwave Pulses

This article aims to study the thermal effect, inverse piezoelectric effect, and trap effect of aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high-electron mobility transistors (HEMTs) with injection of narrowband (NB) microwave pulses where sensitive semiconductor devices are often disturbed or even damaged by intentionally electromagnetic interference. A series of AlGaN/GaN HEMT-based power amplifiers is designed and measured by utilizing an NB microwave system. The thermal analysis is performed by observing the temperature and thermal stress distributions over the structure and the temperature transient response in different dc conditions. Moreover, in the inverse piezoelectric analysis, the elastic energy density of AlGaN is calculated using a simulated vertical electric field and compared with the critical value of the material itself. Lastly, to fully understand these two failure mechanisms above on the device degradation, the influences of traps generated by these two effects above are investigated by analyzing the electron movement, trap behavior, and output drain current.

Modeling and Prediction of Common Mode Electromagnetic Interference in GaN-Based Switching Power Converters

Behavioral models of common mode (CM) electromagnetic interference (EMI) are proposed herein for a GaN high-electron-mobility transistor (HEMT) synchronous buck converter. First, a CM noise model is developed using a linear equivalent circuit that consists of a voltage source, current source, and two noise impedances. The behavioral parameters of the CM model are then extracted by changing the input-side shunt impedances. A GaN HEMT buck converter setup is then built using switching frequencies of 100 kHz, 200 kHz, and 500 kHz to verify the validity of the CM EMI behavioral model. A comparison between the experimental and predicted results indicated that the proposed CM EMI model of GaN-based power converters was able to predict well the CM EMI current in the 150 kHz–30 MHz frequency range.

The effect of the barrier thickness on DC and RF performances of AlGaN/GaN HEMTs on silicon

In this study, the effect of barrier thickness on the DC and RF performances of AlGaN/GaN high-electron mobility transistors (HEMTs) on silicon for millimeter wave applications is experimentally investigated. GaN HEMT devices with different barrier thicknesses were fabricated and characterized. While the device with the thinnest barrier exhibited the highest extrinsic transconductance (gm) resulting from the shortest gate-to-channel distance, such configuration suffered from the lowest unit current-gain cut-off frequency (fT) due to the increase of the total gate capacitance. Moreover, degradation in the output power was observed for devices with thinner barriers. Such degradation was related to the severe knee walkout as evidenced from drain-lag characterization.

Recent Progress of E‐mode Gallium Nitride Metal–Insulator–Semiconductor ‐High Electron Mobility Transistors with Hybrid Ferroelectric Charge Trap Gate (FEG‐HEMT) for Power Switching Applications

Aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure devices have proven to be highly effective for high‐frequency power amplifiers and power switching applications with improved performance compared to those made with traditional silicon technology and other advanced semiconductor technologies. The development of enhancement‐mode (E‐mode) AlGaN/GaN high electron mobility transistors (HEMTs) and metal–insulator–semiconductor HEMTs (MIS‐HEMTs) has been a focus in recent years due to their potential applications. Arising from the concept of a flash‐memory‐like hybrid ferroelectric charge storage structure, the high‐performance hybrid ferroelectric charge storage gate (FEG) GaN HEMT has gradually gained a great deal of attention due to the concept being a useful and versatile tool to realize E‐mode operations. This article attempts to review the latest progresses in this technology, including alternative improvements and device characteristics. Future challenges for the E‐mode FEG‐HEMT are also discussed.

Surface morphology evolution of N-polar GaN on SiC for HEMT heterostructures grown by plasma-assisted molecular beam epitaxy

The surface morphology evolution of N-polar GaN with growth time was investigated and compared with Ga-polar GaN. N-polar GaN directly grown on SiC substrates was found to have slower 3D-to-2D growth transformation and less coalescence than the Ga-polar counterpart, resulting in rougher surface morphology, whereas the AlN nucleation layer accelerated 3D-to-2D transformation, resulting in smoother surface morphology. N-polar GaN was found to have mound-type surface morphology with clustered atomic steps, unlike the regular screw-type dislocation-mediated step-flow growth observed for Ga-polar GaN. This was explained by the lower diffusion of adatoms on the N-polar surface due to its higher surface energy and higher Ehrlich–Schwoebel barrier. In addition, the increased III/V ratio in N-polar GaN growth was found to reduce the surface roughness from 2.4 nm to 1 nm. Without Si doping, the N-polar GaN high electron mobility transistor (HEMT) heterostructures grown under optimized conditions with smoother surface morphologies exhibited a sheet carrier density of 0.91 × 1013 cm−2 and a mobility of 1220 cm2 (V s)−1. With Si δ-doping, the sheet carrier density was increased to 1.28 × 1013 cm−2 while the mobility was reduced to 1030 cm2 (V s)−1. These results are comparable to the state-of-the-art data of plasma-assisted molecular beam epitaxy-grown N-polar GaN HEMT heterostructures on SiC substrates.

X-band MMICs for a Low-Cost Radar Transmit/Receive Module in 250 nm GaN HEMT Technology

This paper describes Monolithic Microwave Integrated Circuits (MMICs) for an X-band radar transceiver front-end implemented in 0.25 μm GaN High Electron Mobility Transistor (HEMT) technology. Two versions of single pole double throw (SPDT) T/R switches are introduced to realize a fully GaN-based transmit/receive module (TRM), each of which achieves an insertion loss of 1.21 dB and 0.66 dB at 9 GHz, IP1dB higher than 46.3 dBm and 44.7 dBm, respectively. Therefore, it can substitute a lossy circulator and limiter used for a conventional GaAs receiver. A driving amplifier (DA), a high-power amplifier (HPA), and a robust low-noise amplifier (LNA) are also designed and verified for a low-cost X-band transmit-receive module (TRM). For the transmitting path, the implemented DA achieves a saturated output power (Psat) of 38.0 dBm and output 1-dB compression (OP1dB) of 25.84 dBm. The HPA reaches a Psat of 43.0 dBm and power-added efficiency (PAE) of 35.6%. For the receiving path, the fabricated LNA measures a small-signal gain of 34.9 dB and a noise figure of 2.56 dB, and it can endure higher than 38 dBm input power in the measurement. The presented GaN MMICs can be useful in implementing a cost-effective TRM for Active Electronically Scanned Array (AESA) radar systems at X-band.

Enhanced quantum oscillations and scattering effect in quaternary InAlGaN/GaN two-dimensional electron gas

Quantum transport properties of a large bandgap In0.15Al0.79Ga0.06N/GaN quaternary GaN high electron mobility transistor (HEMT) heterostructure are studied at low temperatures up to 2 K. Herein, we report the first evidence of weak localization in a quaternary GaN two-dimensional electron gas (2DEG) system. We observe negative magnetoresistance behavior and extracted dephasing time (τΦ) using a Hikami–Larkin–Nagaoka model at 2.2 K. Linear dependency of dephasing rate with temperature (τΦ−1∝T) is established below 20 K. Furthermore, Shubnikov–de Haas quantum oscillation induced by 2DEG is observed using perpendicular magnetic (B⊥) field strengths up to 14 T. From the temperature-dependent oscillation amplitude, we extracted an effective mass m*≈0.237me. The dominance of small-angle scattering in the 2DEG channel is identified from less than unit ratio (τq/τt≪1) of quantum lifetime (τq) to the Hall transport lifetime (τt). In our study, we have demonstrated that the In0.15Al0.79Ga0.06N/GaN quaternary heterostructure possesses high dephasing time (τΦ=5.4 ps) and larger quantum lifetime (τq=0.102 ps) indicating better suitability and a way forward to high-power–high-frequency GaN HEMT development.

Ultrasensitive Real-Time Detection of Pb2+ Ions Using g-C3N4 Nanosheets

The quick and easy monitoring of heavy metals in drinking water is utmost important due to their harmful effects on human health. In this work, GaN based high electron mobility transistor (HEMT) sensor has been fabricated using optical lithography and explored as a prospective sensor for the determination of trace Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions present in the water. Graphitic carbon nitride was synthesized by single step combustion method. The g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanosheets were used to functionalise the gate area of the fabricated GaN HEMT sensor to investigate the presence of Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> metal ions in water. The g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> functionalized sensor exhibited sensitivity of around 0.46 μA/ppb with 0.32 ppb as Limit of detection (LoD) much below the international set standards. Moreover, the real time measurements on lake water were performed using the developed GaN HEMT sensor to detect the presence of Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions in real samples in a fast and ultrasensitive manner. We anticipate that the reported work will certainly serve as proof-of-concept to develop heavy metal ion sensors.

Analysis of Trapping Effect on Large-Signal Characteristics of GaN HEMTs Using X-Parameters and UV Illumination.

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave (X21FB) and small-signal forward gain (X2111S) at fundamental frequency increased, whereas the large-signal second harmonic output wave (X22FB) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X21FB and X2111S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors.

Epitaxial growth of AlGaN/GaN HEMTs on patterned Si substrate for high voltage power switching applications

In this work, a series of AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on patterned (Al)GaN-on-Si seed layers by metalorganic chemical vapor deposition (MOCVD) to study the effect of the (Al)GaN buffer thickness and its aluminum content on the vertical breakdown voltage. The atomic force microscopy (AFM) analysis performed on the GaN seed layers shows a perfectly smooth, MOCVD-like morphology with a threading dislocation density (TDD) around 2 × 109 cm−2. We succeeded to regrow up to 10 μm and 5 μm crack-free GaN + HEMT and Al0.30G0.70N + HEMT structures, respectively and scanning electron microscopy (SEM) revealed limited lateral growth on mesas with few microscopic defects while AFM show the same surface morphology of HEMT structures as ones grown on planar substrates. NiAu Schottky contacts were deposited on the regrown (Al)GaN HEMTs as well as on (Al)GaN seed layer structures. No breakdown was noticed up to 200 V for the regrown Al0.30Ga0.70N (3 μm) HEMT and the GaN seed layer structures and the leakage current remained in the range of 1 nA. However, the leakage current in the regrown GaN (5 μm) structure reached rapidly 1 mA. Such a high leakage was not noticed for non-patterned devices. Thus, it is possibly attributed to silicon contamination in the regrown GaN layer. On the other hand, the absence of noticeable leakage in the regrown 3 μm thick Al-rich AlGaN buffer HEMT opens the way to a new competitive solution for high power electronics applications on silicon substrate.

Electric Field Modulation in the Channel by Lateral Thickness Distribution of High-k Films Formed on GaN HEMTs to Improve Breakdown Voltage

High breakdown voltage owing to a quasi-uniform electric field, upon loading a high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{k}$</tex-math> </inline-formula> film in the gate–drain region, was recently investigated. However, the uniform high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{k}$</tex-math> </inline-formula> film has a limit to modulate the electric field distribution, and the electric field near the gate side is stronger than that near the drain side. This study proposes the modulation of the high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{k}$</tex-math> </inline-formula> film thickness between the drain and gate of a gallium nitride (GaN) high electron mobility transistor (HEMT) in the lateral direction for electric field distribution control in the channel. Compared to a uniform film, the electric field near the gate can also be weakened and possesses a negative gradient compared to a conventional electric field slope. Based on the simulation results, the voltage at which impact ionization occurs can be increased by 20%. This can be explained using the smaller gate leakage current and improved electric field distribution. Furthermore, the maximum electric field increased in the present structure when the slope of the electric field was negative.

A Broadband Voltage Variable Attenuator With High-Power Tolerance and Compact Size Based on Dual-Gate GaN HEMTs

To achieve broadband and high-power tolerance voltage variable attenuator (VVA), this paper replaces the single-gate High Electron Mobility Transistor (HEMT) with a dual-gate HEMT based on the distributed stacked structure VVA proposed by Qorvo, which can effectively reduce the chip area and cost while ensuring the bandwidth and power tolerance. To verify the effectiveness of this method, a DC-30GHz single-gate HEMT structure VVA and a DC-30GHz dual-gate HEMT structure VVA were designed and implemented based on the 0.25μm GaN process, respectively. The experimental results show that compared with the single-gate HEMT VVA, the 0.1dB power compression point ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IP-0.1dB</i> ) of the dual-gate HEMT VVA increases by more than 8 dB, and the insertion loss decreases by 0.9dB, the dynamic range increases by 4dB, and the chip area is reduced by 27%. To the best of our knowledge, this is the first report of a VVA based on a dual-gate HEMT structure, which suggests that a multi-gate HEMT device is certainly a better choice for achieving a broadband VVA or switch with high power tolerance with limited chip area and cost.

Thermal Performance of Cu Electroplated GaN/AlGaN High-Electron-Mobility Transistors with Various-Thickness Si Substrates

Thermal dissipation is an important issue for power devices. In this work, the impact of thermal effects on the performance of Cu electroplated GaN-based high-electron-mobility transistors (HEMTs) are considered. Electrical, thermometry and micro-Raman characterization techniques were used to correlate the effects of improved heat dissipation on device performance for GaN HEMTs with different thicknesses of Si substrate (50, 100, 150 μm), with and without an additional electroplated Cu layer. GaN HEMTs on electroplated Cu on Si (≤50 μm) demonstrate an enhanced on/off current ratio compared to bare Si substrate by a factor of ~400 (from 9.61 × 105 to 4.03 × 108). Of particular importance, surface temperature measurements reveal a much lower channel temperature for thinner HEMT devices with electroplated Cu samples compared to those without.

Resonant Mechanism for a Long-Distance Wireless Power Transfer Using Class E PA and GaN HEMT

This paper presents a study on long-distance wireless power transfer (WPT), which formulates the voltage gain in terms of the coupling coefficient between the power transmitting unit (PTU) and the power receiving unit (PRU) coils. It is proposed that maximum power transfer efficiency (PTE) can be reached when maximum voltage gain is achieved under a matching condition between the coil quality factor and the coupling coefficient. In order to achieve maximum power delivered to load (PDL), we need to elevate the input voltage as high as the high breakdown-voltage of gallium nitride (GaN) high-electron mobility transistors (HEMT) along with class E amplifier circuit topology. In order to promote voltage gain, knowledge of the coupling coefficient between two coils including the factors of the coil diameter, wire diameter, coil turns, and the coil resistance are derived. It was observed that a lower coil resistance leads to a reduced parallel quality, which facilitates long-distance wireless power transfer. Experimental results support the findings that the maximum PTE occurred at the maximum voltage gain existing at a specific distance matches the coupling coefficient between coils. A maximum power point tracking (MPPT) method is also developed to achieve maximum PDL. At a distance of 35 cm, experiments with more than 100 W successfully receive a PTE of 57% at the PRU when the received voltage reached 1.4 kV. This is used to verify the concepts and analysis that are proposed in this paper.

Improved drain lag by reduced surface current in GaN HEMT via an ultrathin HfO2 blanket layer

This paper reports the influence of an ultrathin 1.5 nm atomic-layer-deposited HfO2 blanket layer as a gate dielectric on GaN high-electron-mobility transistors (HEMTs) grown on a 4H-SiC substrate. Transistors with a gate length of 250 nm and a source-to-drain distance of 3 µm were manufactured. The proposed technique involves HfO2 deposition at 250 ∘C prior to the gate metallization with no additional lithography steps. This approach reduced the drain lag by 83% compared to the conventional design with no gate dielectric. The HfO2 layer suppressed the parasitic lateral conduction from the gate, reduced surface trapping, and improved gate electrostatics. The manufactured devices exhibited nearly three orders of magnitude decreased surface leakage, better turn-on behavior, and improved cut-off frequency f T linearity by 16%. High quality metal-oxide interface formation was confirmed by the conductance method. Results demonstrate that the blanket HfO2 deposition is a promising approach to improve the current dispersion characteristics and gate electrostatics of GaN HEMTs without incurring major changes to the established fabrication techniques.

Effects of GaN channel downscaling in AlGaN–GaN high electron mobility transistor structures grown on AlN bulk substrate

In this work, two series of AlGaN/GaN/AlN high electron mobility transistor (HEMT) heterostructures have been grown by molecular beam epitaxy on AlN bulk substrates. The effects of reduction in the GaN channel thickness as well as the AlGaN barrier thickness and composition on structural and electrical properties of the heterostructures have been studied. The material analysis involved high-resolution x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. In a first series of HEMT structures grown with an aluminum content of 30% in the AlGaN barrier, the channel downscaling results in a reduction in the GaN strain relaxation rate but at the expense of degradation in the mean crystal quality and in the electron mobility with a noticeable increase in the sheet resistance. An opposite trend is noticed for the three-terminal breakdown voltage of transistors, so that a trade-off is obtained for a 50 nm width GaN channel HEMT, which exhibits a sheet resistance of 1700 Ω/sq. with transistors demonstrating three-terminal breakdown voltage up to 1400 V for 40 μm gate to drain spacing with static on resistance Ron = 32 mΩ cm2. On the other hand, a second series of HEMT structures with high aluminum content AlGaN barriers and sub-10 nm GaN channels have been grown perfectly strained with high sheet carrier densities allowing to preserve sheet resistances in the range of 880–1050 Ω/sq.

A Comprehensive Overview of the Temperature-Dependent Modeling of the High-Power GaN HEMT Technology Using mm-Wave Scattering Parameter Measurements

The gallium-nitride (GaN) high electron-mobility transistor (HEMT) technology has emerged as an attractive candidate for high-frequency, high-power, and high-temperature applications due to the unique physical characteristics of the GaN material. Over the years, much effort has been spent on measurement-based modeling since accurate models are essential for allowing the use of this advanced transistor technology at its best. The present analysis is focused on the modeling of the scattering (S-) parameter measurements for a 0.25 μm GaN HEMT on silicon carbide (SiC) substrate at extreme operating conditions: a large gate width (i.e., the transistor is based on an interdigitated layout consisting of ten fingers, each with a length of 150 μm, resulting in a total gate periphery of 1.5 mm), a high ambient temperature (i.e., from 35 °C up to 200 °C with a step of 55 °C), a high dissipated power (i.e., 5.1 W at 35 °C), and a high frequency in the millimeter-wave range (i.e., from 200 MHz up to 65 GHz with a step of 200 MHz). Three different modeling approaches are investigated: the equivalent-circuit model, artificial neural networks (ANNs), and gated recurrent units (GRUs). As is shown, each modeling approach has its pros and cons that need to be considered, depending on the target performance and their specifications. This implies that an appropriate selection of the transistor modeling approach should be based on discerning and prioritizing the key features that are indeed the most important for a given application.

Ti3 C2 Tx MXene van der Waals gate contact for GaN high electron mobility transistors.

Gate controllability is a key factor that determines the performance of GaN high electron mobility transistors (HEMTs). However, at traditional metal-GaN interface, direct chemical interaction between metal and GaN can result in fixed charges and traps, which can significantly deteriorate the gate controllability. In this study, Ti3 C2 Tx MXene films were integrated into GaN HEMTs as the gate contact, wherein van der Waals heterojunctions were formed between MXene films and GaN without direct chemical bonding. The GaN HEMTs with enhanced gate controllability exhibited an extremely low off-state current (IOFF ) of 10-7 mA/mm, a record high ION /IOFF current ratio of ∼1013 (which is six orders of magnitude higher than conventional Ni/Au contact), a high off-state drain breakdown voltage of 1085V, and a near-ideal subthreshold swing of 61mV/dec. This work shows the great potential of MXene films as gate electrodes in wide-bandgap semiconductor devices. This article is protected by copyright. All rights reserved.

Electrical Characteristics of Gated Anode Diodes Based on Normally Off Recessed‐Gate GaN High‐Electron‐Mobility Transistors for Rectenna Applications

AlGaN/GaN high‐electron‐mobility transistor (HEMT)‐based gated‐anode diodes (GADs) for a 5.8 GHz rectenna application are proposed. An anode of the GAD is formed by connecting a gate and a drain of a normally off GaN HEMT. Herein, a wide recessed HEMT structure reported in the previous article is modified to a buried‐type recessed gate HEMT structure. The gate‐to‐cathode distance is optimized to maximize device performance. Typical direct current (DC) characteristics of the HEMTs are a threshold voltage (Vth) of +0.4 V and a maximum drain current (Imax) of 450 mA mm−1. GADs using the HEMTs show the characteristics of maximum forward current (If) of 600 mA mm−1 and reverse breakdown voltage (BVr) of more than 100 V. The GAD using the recessed gate structure HEMT is shown to significantly improve If and BVr simultaneously compared to the previous work using the wide recessed gate structure. The rectifying performance of a bridge‐type rectifier simulated with SPICE model of the GAD shows radio frequency (RF)–DC conversion efficiency of 84% and RF input power of 13 W at 5.8 GHz using four GADs with each gate width (Wg) of 400 μm.

Total-ionizing dose irradiation induced degradation behavior and mechanism of the Cascode GaN HEMTs

In this article, the effects of total ionizing dose (TID) irradiation and the annealing treatment on the degradation of the commercial Cascode GaN high-electron-mobility transistors (HEMTs) were investigated, and low frequency noise method (LFN) was carried out to analyze the defects. The DC characteristics show that the device after TID irradiation with different doses exhibits a negative drift of threshold voltage (V th) and a remarkable increase of drain-source current (I ds) with respect to the fresh one. Meanwhile, with increasing doses of the TID irradiation, the off-state drain leakage current increases, while the drain-source resistance decreases. The gate-lag characteristic gets better for the Cascode GaN HEMTs after TID irradiation. The transfer characteristics, output characteristics, blocking characteristics and capacitance characteristics of the devices can partly be restored by annealing treatment, but there is no pronounced influence on the gate-lag characteristics and drain-source resistance. The trap density extracted by the LFN method decreases in the Cascode GaN HEMTs after TID irradiation. The degradation behavior and mechanism of the Cascode GaN HEMTs under TID irradiation are analyzed. The experimental results may provide a useful reference for the design and space application of the Cascode GaN HEMTs.