HEMT Research Articles

The improvement of device linearity in AlGaN/GaN HEMTs at millimeter-wave frequencies using dual-gate configuration

The linearity performance of the AlGaN/GaN high-electron-mobility-transistors (HEMTs) is critical for circuit applications especially at millimeter-wave frequencies. In this paper, we propose a new dual-gate (DG) configuration for linearity improvement at millimeter-wave frequencies. Using 2D simulation, we observed the improvement in device linearity by placing the additional DC gate in the source-gate access region. Adjusting the bias voltage of the DC gate modulates the horizontal electric field in the channel and controls the acceleration behavior of the channel electrons. Furthermore, such bias adjustment enhances the electron density in the channel to compensate for the transconductance (Gm) degradation. Both of these contribute to the flattening of the Gm profile for linearity improvement. The proposed DG configuration improves the C/I ratio by 10 dB compared to the conventional single gate (SG) device at 38 GHz. Additionally, a 60 % improvement in the cutoff frequency (fT) and maximum oscillation frequency (fmax) is obtained compared to the traditional DG configuration where the second gate is placed in the gate-drain drift region. This is mainly due to the reduction in gate capacitances from the redistribution of the electrons in the device. Such superior characteristics have shown great potential of the proposed device for high linearity applications at millimeter-wave frequencies.

Performance improvement of enhancement-mode GaN-based HEMT power devices by employing a vertical gate structure and composite interlayers*

In this work, p-n junction vertical gate (JVG) and polarization junction vertical gate (PVG) structures are for the first time proposed to improve the performance of GaN-based enhancement-mode (E-mode) high electron mobility transistor (HEMT) devices. Compared with the control group featuring the vertical gate structure, a highly improved threshold voltage (V th) and breakdown voltage (BV) are achieved with the assistance of the extended depletion regions formed by inserting single or composite interlayers. The structure dimensions and physical parameters for device interlayers are optimized by TCAD simulation to adjust the spatial electric field distribution and hence improve the device off-state characteristics. The optimal JVG-HEMT device can reach a V th of 3.4 V, a low on-state resistance (R on) of 0.64 mΩ cm2, and a BV of 1245 V, while the PVG-HEMT device exhibits a V th of 3.7 V, an R on of 0.65 mΩ cm2, and a BV of 1184 V, which could be further boosted when an additional field plate design is employed. Thus, the figure-of-merit value of JVG- and PVG-HEMT devices rise to 2.4 and 2.2 GW cm−2, respectively, much higher than that for the VG-HEMT control group (1.0 GW cm−2). This work provides a novel technical approach to realize higher-performance E-mode HEMTs.

Improved breakdown performance in recessed-gate normally off GaN MIS-HEMTs by regrown fishbone trench

This work develops a regrown fishbone trench (RFT) structure in selective area growth (SAG) technique to fabricate recessed-gate normally off GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs). The RFT structure effectively modulates the electric field at high drain and gate biases, thus allowing the device to feature improved off-state and gate breakdown performance with a high positive Vth of 2 V. The simulated carrier concentration and electric field distributions reveal the mechanism of electric field weakening by RFT architecture. Meanwhile, the current collapse phenomenon is significantly suppressed, and the gate voltage swing is also enlarged. The maximum gate drive voltage of 9.2 V for 10-year reliability of RFT GaN MIS-HEMT, together with the improved linearity and block voltage, broadens the applications of SAG devices. Furthermore, the RFT structure also provides an etching-free method for fabricating normally off GaN MIS-HEMTs with multi-dimensional gates.

Systematic analysis of the principles and application scenarios of Low-Noise Amplifier

As society advances, new ideas and products are increasingly integrated into our daily lives. 5th generation mobile networks tech enables faster, lag-free connectivity, raising performance standards for components like Low-Noise Amplifiers. Summarizing Low-Noise Amplifier tech and applications helps researchers and firms leverage past knowledge and explore innovations. This paper analyzes Low-Noise Amplifier development and application, discussing types, principles, key performance indicators, and circuit structures of basic amplifiers. Five vital Low-Noise Amplifier characteristicsnoise figure, impedance matching, linearity, stability, and gainare examined. The author introduces design and application cases in radio astronomy, navigation systems, and 5th generation mobile networks communications based on Low-Noise Amplifier characteristics and performance requirements. The author concludes that advancing radio frequency tech requires improved Low-Noise Amplifiers, especially for high-frequency signals in 5th generation mobile networks. Promising noise performance enhancements come from technologies like modified high electron mobility transistors on GaAs and InP substrates. Monolithic Microwave Integrated Circuit integration reduces size while maintaining cost-effective performance. Future advancements in these areas could further boost Low-Noise Amplifier performance.

SiC-based high electron mobility transistor

This paper describes the fabrication of a SiC-based high electron mobility transistor (HEMT). A single-crystal 3C–SiC layer was grown on a C-face 4H–SiC substrate, and 2D electron gas was induced at the 3C–SiC/4H–SiC heterointerface due to the unique polarization physics. The measured Hall mobility of the 2DEG was 586 cm2/V s at room temperature. Source, gate, and drain electrodes were fabricated on the 3C–SiC surface. The drain current for the fabricated SiC-HEMT was measured to be 47.5 mA/mm, and the transconductance was estimated to be 13.5 mS/mm.

Normally-off GaON/p-GaN gate HEMTs with selective plasma oxidation: from structural characterization, performance improvement to physical mechanism

In this letter, a p-GaN gate high-electron-mobility transistor (HEMT) with a high threshold voltage and better gate reliability was demonstrated by using selective plasma oxidation (SPO) and an additional low-temperature annealing step before gate metal is evaporated. After the SPO, a gallium oxynitride (GaON) dielectric layer was formed on the surface of p-GaN under the gate metal, and was studied by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, high-resolution transmission electron microscopy and energy dispersion spectroscopy. In addition, the fabricated metal/GaON/p-GaN gate HEMT exhibited a large threshold voltage (V TH) improvement from 1.46 V to 2.47 V. Furthermore, the forward gate breakdown voltage (V GS,BD) increased from 7.55 V to 11.10 V, and the maximum forward gate operating voltage (V GS-max) significantly improved from 5.0 V to 7.80 V for a ten-year lifetime with a 63.2% failure rate. Kelvin probe force microscopy reveals that the surface potential increased after SPO, and the shift of valence band maximum obtained by XPS spectra was 0.7 eV lower than that of the p-GaN, which further improves the Schottky barrier height at the gate metal/GaON interfaces to holes, thereby improving V TH and reducing I GS of the device. As a barrier layer, GaON suppressed the injection of carrier into the depletion region under a high electric field and enhanced the reliability of the gate.

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.

Improvement of AlGaN/ GaN based HEMT with high performance rate for integrated circuit design for wide range of applications

In the current research work, we focused on the design and analysis of a semiconductor device called High-Elec-tron-Mobility Transistor (HEMT) based on the AlGaN/GaN material system. An Aluminum Nitride spacer,Layer of Nucle-ation along with cap as a AlGaN and barrier of GaN with the channel of AlGaN are incorporated to enhance HEMT device performance.The electrical characteristics of the proposed HEMT are an-alyzed. The Drain Current is found to be 0.18A/mm, indicating the device's ability to handle high current levels. The Electron Concentration is observed to have a maximum value of -96.12electrons/cm3 and varying based on the position in the channel for GaN Barrier thickness is 0.15mm. In the analysis of AC such as Gain of the Maximum Unilateral Power is deter-mined to be 83.41dB, indicating the ability of the device to am-plify signals. The Y-parameters, which characterize the de-vice's behavior at various frequencies of operation, are also de-termined. The capacitance between the electrode region Gate-Source (CGSMIN) is found to be 1.70×10^-11 F/mm, and alike The Capacitance between the electrode region the Gate-Drain Ca-pacitance (CGDMIN) is determined to be 4.7×10^-12 F/mm. Fur-thermore, an Electric Field of 96.51×10^3 V/mm is observed, in-dicating the strength of the electric field across the device. For HEMT device the simulation,The TCAD Silvaco software is be-ing practiced.

Construction of AlGaN/GaN high-electron-mobility transistor-based biosensor for ultrasensitive detection of SARS-CoV-2 spike proteins and virions

The COVID-19 pandemic has highlighted the need for rapid and sensitive detection of SARS-CoV-2. Here, we report an ultrasensitive SARS-CoV-2 immunosensor by integration of an AlGaN/GaN high-electron-mobility transistor (HEMT) and anti-SARS-CoV-2 spike protein antibody. The AlGaN/GaN HEMT immunosensor has demonstrated the capability to detect SARS-CoV-2 spike proteins at an impressively low concentration of 10−22 M. The sensor was also applied to pseudoviruses and SARS-CoV-2 ΔN virions that display the Spike proteins with a single virion particle sensitivity. These features validate the potential of AlGaN/GaN HEMT biosensors for point of care tests targeting SARS-CoV-2. This research not only provides the first HEMT biosensing platform for ultrasensitive and label-free detection of SARS-CoV-2.

Theoretical Studies of 2D Electron Gas Distributions and Scattering Characteristics in Double‐Channel n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN High‐Electron‐Mobility Transistors

A detailed analysis of self‐consistent potentials, electric fields, electron distributions, and transport properties of dual‐channel (DC) n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN high‐electron‐mobility transistors (HEMTs) is performed in this article. The 2D electron gas (2DEG) densities and mobility states limited by different scattering mechanisms in channel 1 and channel 2 are obtained, with varying values of doping concentrations, ambient temperatures, Al components, and thicknesses of the back barrier layer. The reduced and increased 2DEG densities are respectively observed in channel 1 and channel 2 with growing Al fractions and thicknesses of the AlxGa1−xN layer. Alloy disorder scattering exhibits a superior effect on carriers in channel 2 due to the lower barrier height and higher permeable electrons, which together with the interface roughness scattering severely depends on the thicknesses and Al fractions of the back barrier layer. Polar optical phonon scattering becomes important at higher temperatures. The trend of individual mobility in channel 1 is exactly opposite to that in channel 2. The parameter variation of the back barrier layer can effectively change the scattering characteristics of the main channel. Low‐temperature mobilities of n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN HEMTs under varied doping concentrations are also obtained. Finally, the results are verified by comparison with the technology computer‐aided design simulations for DC HEMTs.

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.

Enhanced Performance of Ultraviolet AlGaN/GaN Photo‐HEMTs by Optimized Channel Isolation Schemes

AbstractSolar blind ultraviolet (UV) photodetectors utilizing AlGaN/GaN high electron mobility transistor (HEMT) structure offer a very high responsivity, photo‐to‐dark current ratio (PDCR), and detectivity. However, the performance of conventional mesa‐isolated photo‐HEMT is limited due to current leakage paths through the side wall and AlGaN barrier. In this work, apart from conventional mesa‐type isolation, ion implantation and metal‐insulator‐semiconductor (MIS) schemes are adopted to isolate the channels of AlGaN/GaN photo‐HEMTs. A significant reduction in dark current is achieved for MIS photo‐HEMT of around four and three orders of magnitude as compared to those of conventional mesa‐ and ion‐implanted photo‐HEMTs, respectively. Moreover, the responsivity and PDCR of MIS photo‐HEMT are around three and four orders of magnitude higher than those of conventional mesa‐isolated photo‐HEMT. Subsequently, MIS photo‐HEMT on Si substrate has achieved a very high detectivity of 4.63 × 1016 Jones at the UV incidence wavelength of 360 nm. The results presented in this work establish the advantages of MIS photo‐HEMT over other types of photo‐HEMTs. In addition, compatibility with GaN device fabrication technology and significantly enhanced optoelectronic performance suggest AlGaN/GaN MIS photo‐HEMTs as a promising candidate for a variety of advanced UV sensing applications.

Advancements in Tunable and Multifunctional Metamaterial Absorbers: A Comprehensive Review of Microwave to Terahertz Frequency Range

Abstract Over the past two decades, metamaterial absorbers have undergone significant advancements, evolving from microwave single-frequency designs to multi-frequency and broadband absorption, extending into the terahertz band. These absorbers have transitioned from unadjustable to adjustable and multifunctional configurations, enabled by the integration of adjustable materials, mechanical structures, and semiconductor devices. This article provides a comprehensive review of the progress achieved in the microwave to terahertz frequency range over the last five years. Key aspects covered include the absorbing mechanism of metamaterials in the microwave frequency band, with absorption efficiencies exceeding 90% for specific frequency ranges. The development of adjustable absorbers allows for frequency tunability within ±10% of the central frequency, while multifunctional absorbers enable concurrent control over absorption and reflection properties. In the terahertz regime, advanced electromagnetic simulations have led to absorber designs with bandwidths exceeding 50% of the central frequency, resulting in absorption efficiencies above 80% over the entire bandwidth. Integration of gallium nitride-based Gallium Nitride High Electron Mobility Transistors (GaN HMET) provides fast switching speeds below 100 nanoseconds, facilitating rapid reconfiguration of absorber functionalities. These advancements in metamaterial absorbers offer promising prospects for intelligent and integrated designs in future applications.

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.

Al-rich AlGaN high electron mobility transistor gate metallization study up to 600 °C in air

Al-rich AlGaN high electron mobility transistor gate metallization study up to 600 °C in air

Composite channel 100 nm InP HEMT with ultrathin barrier for millimetre wave applications

This study introduces a High Electron Mobility Transistor (HEMT) designed for millimeter-wave applications, utilizing a composite channel structure based on InP and InGaAs-InAs-InGaAs. The proposed device incorporates an ultra-thin 2 nm barsrier layer, a distinctive composite channel topology, and a judicious selection of III-V materials. These features collectively contribute to an improved confinement of electrons within the channel, thereby improving the concentration of two-dimensional electron gas (2DEG), and consequently, enhancing the mobility and speed of the device. The proposed device exhibits a unity current gain frequency (f T) of 249 GHz and a maximum oscillation frequency (f MAX) of 523.9 GHz, accompanied by a current gain of 67.7 dB at 0.1 GHz. The off-state leakage current is maintained within the nanoampere range, and the minimum noise figure (NF MIN) is merely 0.76 dB at 10 GHz. A comparative analysis of DC and RF performance, along with an examination of associated parasitic elements, is conducted among various composite channel HEMTs proposed in recent literature. A quantitative justification is provided for the superiority of InGaAs-InAs-InGaAs channel HEMTs, establishing their heightened f T and f MAX. The proposed InGaAs-InAs-InGaAs channel HEMTs exhibit 1.4 times improved f T and f MAX, coupled with only half the NF MIN in comparison to their InGaAs-InP-InGaAs channel counterparts. To further comprehend the device’s behavior under varying RF conditions, a frequency-dependent intrinsic Field-Effect Transistor (FET) model is presented. This model facilitates the analysis of the device’s performance and allows the identification of the impact of individual parameters on the overall system.

A new gate design combined MIS and p-GaN gate structures for normally-off and high on-current operation

This study proposes a new gate architecture that integrates both a p-GaN gate and a metal–insulator–semiconductor (MIS) structure for a normally-off AlGaN/GaN high electron mobility transistor. Silvaco TCAD simulation software is used to assess the performance of the proposed design. A comprehensive analysis of the device’s transfer, output, and breakdown characteristics is carried out and compared with the conventional p-GaN gate AlGaN/GaN HEMT. The findings indicate that incorporating MIS in conjunction with the p-GaN gate leads to an augmentation in the on-state current density and a reduction in on-resistance. The proposed HEMT exhibits superior attributes, with an 80% increase in drain current compared to the conventional p-GaN gate HEMT, but remains similar to threshold voltage and breakdown voltage. Consequently, the proposed HEMT demonstrates elevated current density and enhances gate control over the channel without modifying the threshold voltage compared to the conventional p-GaN gate HEMT.

In-situ S/TEM DC biasing of p-GaN/AlGaN/GaN heterostructure for E-mode GaN HEMT devices

This work describes an in-situ electrical DC bias study of the E-mode GaN high electron mobility transistor (HEMT) device. A single transistor structure is biased and studied in real-time. The sample was made from an E-mode GaN HEMT device using Focused Ion Beam (FIB) milling and upright lift-off. The device lamella is subjected to forward gate bias to understand the device operation and physical changes under the bias. Active device area and micron level changes due to biasing were studied and identified as crucial factors affecting device reliability during continuous operation. Electric bias-induced physical changes are observed at the p-GaN layer and AlGaN interface on the p-GaN and GaN sides. Localized damage and defect formation, along with elemental diffusion, is observed. The formation of new defects over existing growth defects was seen in the p-GaN/AlGaN/GaN heterostructure. The study helped us identify the exact location of the failure, the region affected under bias, and the occurrence of physical changes due to the electrical bias on the in-situ device. Based on the study, gate breakdown failure and its location at the metal/p-GaN interface are understood to result from physical changes activated by electrical bias.

2–26.5 GHz GaN ultra‐wideband amplifier with over 2 W output power

AbstractA 2–26.5GHz broadband amplifier monolithic microwave integrated circuit (MMIC) based on the 0.15 μm GaN high electron mobility transistor process has been developed. The broadband amplifier adopts a two‐stage distributed amplifier cascade structure, which improves the gain of the broadband amplifier. Further, the capacitive coupling is used to improve the gain bandwidth product of the power amplifier. To improve the output return loss of the wideband amplifier, a tuning stub is introduced at the output of the circuit. The on‐wafer measurement results show that the amplifier has a gain greater than 18 dB, gain flatness less than ±1.4 dB, and saturated output power >35 dBm with a >13% power added efficiency in the whole band.

Effect of High Temperature on the Performance of AlGaN/GaN T-Gate High-Electron Mobility Transistors With ~140-nm Gate Length

Effect of High Temperature on the Performance of AlGaN/GaN T-Gate High-Electron Mobility Transistors With ~140-nm Gate Length