GaN High Electron Mobility Transistors Research Articles

Polycrystalline Diamond Film Growth on Gallium Nitride with Low Boundary Thermal Resistance

As the demand for high-frequency and high-power electronic devices has increased, gallium nitride (GaN), particularly in the context of high-electron mobility transistors (HEMTs), has attracted considerable attention. However, the ‘self-heating effect’ of GaN HEMTs represents a significant limitation regarding both performance and reliability. Diamond, renowned for its exceptional thermal conductivity, represents an optimal material for thermal management in HEMTs. This paper proposes a novel method for directly depositing diamond films onto N-polar GaN (NP-GaN) epitaxial layers. This eliminates the complexities of the traditional diamond growth process and the need for temporary substrate steps. Given the relative lag in the development of N-polar material growth technologies, which are marked by surface roughness issues, and the recognition that the thermal boundary resistance (TBRGaN/diamond) represents a critical factor constraining efficient heat transfer, our study has introduced a series of optimizations to enhance the quality of the diamond nucleation layer while ensuring that the integrity of the GaN buffer layer remains intact. Moreover, chemical mechanical polishing (CMP) technology was employed to effectively reduce the surface roughness of the NP-GaN base, thereby providing a more favorable foundation for diamond growth. The optimization trends observed in the thermal performance test results are encouraging. Integrating diamond films onto highly smooth NP-GaN epitaxial layers demonstrates a reduction in TBRGaN/diamond compared to that of diamond layers deposited onto NP-GaN with higher surface roughness that had undergone no prior process treatment.

Internally Harmonic Matched Compact GaN Power Amplifier with 78.5% PAE for 2.45 GHz Wireless Power Transfer Systems

In this paper, a high-efficiency compact power amplifier is designed and fabricated with a 0.25 μm GaN high electron mobility transistor (HEMT) to meet the demands of a high integration level and high efficiency for microwave wireless power transfer (WPT) systems. The proposed power amplifier (PA) is implemented using an internally matched method to achieve a compact circuit size. The output second and third harmonic impedances can be optimized through output matching circuits, eliminating the need for additional harmonic matching networks. This approach simplifies the design of matching circuits and reduces the circuit size. Furthermore, the input third harmonic has been controled for improving the efficiency of DC-to-RF conversion. The total size of the proposed PA is 13.4 × 13.5 mm2. The test results obtained from the continuous wave (CW) testing indicate that the output power of the power amplifier at 2.45 GHz reaches 43.75 dBm. Additionally, the large-signal gain is measured at 15.75 dB, and the power-added efficiency (PAE) achieves a value of 78.5%.

NPDC structure double-channel N-polar E-mode GaN HEMTs: Innovations in enhancing RF and DC performance and mitigating trap effects

—High-electron-mobility transistors (HEMTs) based on gallium nitride (GaN) are favored for their exceptional performance in high-power and high-frequency applications. However, developing dual-channel HEMTs presents challenges due to spontaneous polarization effects and design complexities. This study introduces a novel N-polar E-mode GaN HEMT with a dual-channel structure, featuring recessed drain-source regions and non-alloyed ohmic contacts. TCAD simulations provide theoretical insights and optimization strategies for these structures, focusing on the combination of N-polar GaN and ultra-wide bandgap AlN barrier layers. The optimized device demonstrates a threshold voltage of +1.08 V and a 45.9 % increase in current density. The N-polar double-channel HEMT (NPDC-HEMT) exhibited a 55.75 % improvement in peak transconductance, with Ft increasing from 13.3 GHz to 30.1 GHz and Fmax from 63.7 GHz to 65.9 GHz. Further enhancement was achieved in the T-gate variant (NPDC-T-HEMT), with Ft reaching 52.6 GHz and Fmax 94.4 GHz. The dual-channel design effectively mitigated short-channel effects and current collapse, demonstrating the potential for high-power RF applications.

The Impact of Gate Annealing on Leakage Current and Radio Frequency Efficiency in AlGaN/GaN High-Electron-Mobility Transistors

Gallium Nitride (GaN) high-electron mobility transistors (HEMTs) are highly promising for high-frequency and high-power applications due to their superior properties, such as a wide energy bandgap and high carrier density. The performance of GaN HEMTs is significantly influenced by the interfacial states of the AlGaN barrier, and gate annealing has emerged as a key process for reducing leakage currents and enhancing DC/RF characteristics. This research investigates the impact of gate annealing on AlGaN/GaN HEMTs, focusing on two main aspects: leakage current reduction and improvements in DC and RF efficiency. Through comprehensive electrical analysis, including DC and RF measurements, the effects of gate annealing were experimentally evaluated. The results show a significant reduction in gate leakage current and noticeable improvements in DC/RF performance for the devices that underwent gate annealing. The study confirms that the annealing process can effectively enhance device performance by modifying the material properties at the gate interface.

High-performance InGaZnO power transistors: Effect of device structural parameters

In this work, the effect of offset channel length (Loffset) and the dielectric layer thickness (d) on the InSnO/InGaZnO (ITO/IGZO) dual-active-layer (DAL) high-voltage thin-film transistors (HV-TFTs) is systematically investigated. The characteristics of the DAL HV-TFTs resemble that of GaN high electron mobility transistors, wherein the breakdown voltages (VBD) reach saturation at a certain Loffset, and the on-resistance (Ron) linearly increases with Loffset. The linear fitting of Ron vs Loffset indicates that d has a multifaceted impact on the performance of HV-TFTs. In addition to its theoretical role in transistor models, d also influences the channel doping concentration and sidewall deposition issues in practical devices. The DAL HV-TFT with a 30-nm Al2O3 gate dielectric achieves a remarkable VBD of 450 V, the highest figure of merit of 118.2 kW/cm2, and a positive threshold voltage of 3.65 V. Both experiments and simulations indicate that the breakdown occurs within the semiconductor channel, paving the way for further improvement of the performance.

AI‐assisted Field Plate Design of GaN HEMT Device

AbstractGaN High Electron Mobility Transistors (HEMTs) plays a vital role in high‐power and high‐frequency electronics. Meeting the demanding performance requirements of these devices without compromising reliability is a challenging endeavor. Field Plates are employed to redistribute the electric field, minimizing the risk of device failure, especially in high‐voltage operations. While machine learning is applied to GaN device design, its application to field plate structures, known for their geometric complexity, is limited. This study introduces a novel approach to streamlining the field plate design process. It transforms complex 2D field plate structures into a concise feature space, reducing data requirements. A machine learning‐assisted design framework is proposed to optimize field plate structures and perform inverse design. This approach is not exclusive to the design of GaN HEMTs and can be extended to various semiconductor devices with field plate structures. The framework combines technology computer‐aided design (TCAD), machine learning, and optimization, streamlining the design process.

Nitride spacer aided 0.15 μm AlGaN/GaN HEMT fabrication with optimized gate patterning process

I-line stepper is widely used in large scale device manufacturing with limited achievable critical dimension by itself. With the aid of the spacer sidewall, the critical dimension can be further shrunk down. Spacer sidewall aided process necessitates an additional deposition-etching process, which inevitably results in process related damage under the gate. This paper proposes an optimized spacer sidewall aided gate patterning procedure for 0.15 μm GaN High Electron Mobility Transistors (HEMTs) fabrication. The process is proved to be effective in improving device performance compared to conventional sidewall process by keeping first Si-rich SiN passivation layer integrity at the gate edge. Interface trap density (Dit) and mobility were extracted for both conventional sidewall process and the optimized one with different passivation layers at the gate edge, demonstrating a lower Dit and higher mobility using the optimized process with enhanced device performances, such as higher current, breakdown voltage, and stress state characteristics, compared to the conventional process, which is promising for mass production of 0.15 μm GaN HEMTs.

Growth and performance of n++ GaN cap layer for HEMTs applications

Apart from providing high-quality ohmic contacts to III-N devices, n++ GaN cap layers can eliminate surface-related current collapse effects in high-electron-mobility transistors (HEMTs). Various metal-organic chemical vapor deposition conditions and n-type doping are tested in GaN growth on sapphire by using triethylgallium as a Ga precursor, replacing more conventional trimethylgallium. Consequently, despite relatively low temperature of the growth at 800 °C to facilitate InAlN barrier capping, optimized growth conditions and SiH4 flow provided free electron concentration of 7.2 × 1019 cm−3 and mobility of 103 cm2/Vs. Moreover, electron concentration in the range of 1020 cm−3 is demonstrated by using flow modulation epitaxy. On the other hand, as calibration growths indicated, excessive SiH4 flow alone can lead to high density of edge dislocations and surface undulations without enhancing free electron concentration. 6 nm (Si: 4.2 × 1019 cm−3) and 8 nm thick (Si: 7.2 × 1019 cm−3) n++ GaN cap is implemented in normally-off n++ GaN/InAlN/AlN/GaN HEMTs grown on Si, with a collapse-free performance for the latter case. By calculating energy band and free carrier concentration profiles of the heterostructures it is shown, that free electrons of a sufficiently thick and doped n++ GaN cap can shield the channel from the unstable surface potential.

ScAlInN/GaN heterostructures grown by molecular beam epitaxy

Rare-earth (RE) elements doped III-nitride semiconductors have garnered attention for their potential in advanced high-frequency and high-power electronic applications. We report on the molecular beam epitaxy of quaternary alloy ScAlInN, which is an encouraging strategy to improve the heterointerface quality when grown at relatively low temperatures. Monocrystalline wurtzite phase and uniform domain structures are achieved in ScAlInN/GaN heterostructures, featuring atomically sharp interface. ScAlInN (the Sc content in the ScAlN fraction is 14%) films with lower In contents (less than 6%) are nearly lattice matched to GaN, exhibiting negligible in-plane strain, which are excellent barrier layer candidates for GaN high electron mobility transistors (HEMTs). Using a 15-nm-thick Sc0.13Al0.83In0.04N as a barrier layer in GaN HEMT, a two-dimensional electron gas density of 4.00 × 1013 cm−2 and a Hall mobility of 928 cm2/V s, with a corresponding sheet resistance of 169 Ω/□, have been achieved. This work underscores the potential of alloy engineering to adjust lattice parameters, bandgap, polarization, interfaces, and strain in emerging RE-III-nitrides, paving the way for their use in next-generation optoelectronic, electronic, acoustic, and ferroelectric applications.

Enhanced device performance of GaN high electron mobility transistors with in situ crystalline SiN cap layer

In this paper, a ∼2 nm in situ SiN cap layer on AlGaN barrier layer is grown, which is revealed to be crystalline using high-resolution cross-sectional transmission electron microscopy. Benefitting from superior interface quality of epitaxial crystalline SiN/AlGaN interface, the gate diodes with in situ SiN cap layer feature lower interface trap state density than that with GaN cap layer. By comparing the GaN high electron mobility transistors (HEMTs) with the conventional GaN cap layer, the GaN HEMTs with in situ SiN cap layer exhibit improved device performance, showing higher electron mobility, higher drain current, larger on/off current ratio, and higher transconductance. For breakdown characteristics, the devices with in situ crystalline SiN cap layer show prominent advantages over the GaN cap layer with a 30% breakdown voltage increase to 810 V.

SPICE Simulation Assisted-Dynamic Rds(on) Characterization in 200V Commercial Schottky p-GaN HEMTs Under Unstable Phases

Abstract This paper presents a comprehensive analysis of dynamic and static RDS(ON) in Schottky p-GaN High Electron Mobility Transistors (HEMTs), highlighting the impact of off-state and hot electron trapping on device performance. The authors observed significant hysteresis in the transfer characteristics of a 200V commercial Schottky p-GaN, attributing this to charge trapping effects. A novel experimental setup, employing a multi-pulse test synchronous buck converter circuit with additional gate control and a clamping circuit, enabled precise characterization of dynamic RDS(ON) under varying conditions, including unstable phases with overcurrent. This method effectively mimics solar PV input scenarios, exposing the device to high dv/dt and di/dt stresses, which are critical for evaluating GaN device stability under transient conditions. This research also reveals that increased gate resistance reduces energy losses, challenging traditional expectations by demonstrating the nuanced gate charge dynamics of GaN HEMTs. This study overall contributes to the understanding of GaN device behavior, offering a novel approach for accurately characterizing dynamic RDS(ON) under unstable stages, furtherly advances the GaN device in complex renewable energy power converter applications.

A highly survivable X‐band low noise amplifier based on GaN HEMT technology and impact of pulse width on recovery time

AbstractGaN high electron mobility transistor (HEMT)‐based low noise amplifiers (LNAs) are an integral part of microwave receiver systems to enhance signal‐to‐noise ratio (SNR). The noise of LNA itself becomes critical for systems requiring high SNR, such as imaging and satellite communication systems. This paper discusses the design of a three‐stage LNA operating at the X‐band in the frequency range of 8.0–12.0 GHz. The amplifier's design and small signal, noise, and linearity characterizations are discussed. Stagewise analysis for gain, noise figure (NF), and matching network losses at the design stage results in achieving promising results. The proposed LNA provides a gain of 23.2 dB with dB gain ripple. Its NF is below 1.5 dB, output power at 1 dB gain compression is 16.4 dBm, and third‐order intercept point is 24.7 dBm at 10 GHz. LNA's survivability is validated to input stress as high as 42 dBm. This LNA is the best reported NF and survivability combination in the 8.0–12.0‐GHz frequency range. The reverse recovery time of LNA is measured under two different pulse conditions, and it has been shown that LNA has better recovery times for lower pulse width signals. This LNA finds its applications in radars and satellite communication systems.

Revisiting the effectiveness of diamond heat spreaders on multi-finger gate GaN HEMT using chip-to-package-level thermal simulation

The study of chip-level and package-level heat transfer in a GaN high electron mobility transistor (HEMT) is often disconnected due to limited resources and tools. In this work, device simulation from Silvaco Victory Device is carried forward to the chip-to-package-level simulation using Icepak to provide a complete picture of the proposed thermal management strategies using polycrystalline diamond (PCD) heat spreaders. The max junction temperature, Tj = 105.8 °C and the relative magnitude of max temperature on the GaN surface, ΔTj = 18 % are recorded for the original Si-GaN-Si3N4 chip inside TO-220 at 6.0 Wmm−1. Replacing the Si3N4 with PCD (thermal conductivity of 500 Wm−1 K−1) results in Tj = 98.2 °C and ΔTj = 8 %, while replacing the Si results in Tj = 97.0 °C and ΔTj = 11 %. The top layer PCD spreads the heat from hotspot regions to the surrounding epoxy, while the bottom layer PCD improves the heat path from the hotspots to the base plate. Therefore, the reduction in Tj by the bottom layer PCD is more important than the reduction in ΔTj by the top layer PCD. Implementing both the top and bottom layers of PCD results in the best offers of Tj = 92.9 °C and ΔTj = 6 %. The performance of PCD as heat spreaders in multi-finger gate GaN HEMT suggested by these chip-to-package-level simulations are more reliable than device simulation alone since they cover the complete heat path from generation, conduction within the package, and convection to the ambient air.

Temperature- and gate voltage-dependent I–V modeling of GaN HEMTs based on ASM-HEMT

Abstract In this paper, a temperature and gate voltage dependent current-voltage (I-V) model for Gallium nitride (GaN) high electron mobility transistors (HEMTs) devices is studied. In order to help researchers and designers simulate devices in the absence of experimental data and improve parameter extraction efficiency, the temperature and gate voltage dependence of mobility are discussed and incorporated into the proposed model which is revised from the standard advanced SPICE model (ASM) for GaN HEMTs. The mobility variations with gate voltage from -2 V to 6 V and temperature from 10 K to 1000 K are analyzed. The simulation results of our model are compared with the standard ASM-HEMT model, and the output and transfer characteristics of the device from 270 K to 420 K are simulated. Thereby, our model may simulate various applications of GaN HEMTs at different gate voltages and temperatures in the early stages of design and research.

Time-dependent conduction mechanisms in reversed stepped superlattice layers of GaN HEMTs on 200 mm engineered substrates

Time-dependent conduction in epitaxial superlattice (SL) strain relief layers of GaN high electron mobility transistors on 200 mm engineered substrates with a poly-AlN core was observed and analyzed. This phenomenon occurs when the devices were operated with substrate bias of ∼−300 V for 101–103 s. The formation of the conduction path is related to trap-assisted leakage through the SLs on the engineered substrates; de-trapped carriers spread out vertically and laterally within a portion of the SLs, leading to a higher electrical field across the rest of the layers. This conduction mechanism may be hidden during the devices' normal operation (target 650–1200 V). It could lead to undesired effects during the operation of the devices, such as a time-dependent dynamic Ron. More resistive SLs will potentially reduce the impact of this phenomenon.

Neuromorphic engineering in GaN HEMTs exploiting dendritic dislocations for neuromodulation behaviors and adaptive intelligent power forecasting systems

Gallium nitride (GaN), a prominent III-V semiconductor, plays a pivotal role in the advancement of sophisticated power systems. This study presents an innovative neuromorphic engineering approach utilizing the unique dendritic dislocations extending from bulk to channel within GaN High Electron Mobility Transistors (HEMTs) for three-dimensional charge modulation. This approach dynamically alters charge states and channel potentials in response to multiple parametric stimuli, effectively mimicking neural processing and transmission functions, as well as emulating direct and indirect neuromodulation behaviors observed in human nervous system. The advanced neuromodulation emulation enhances biomimetic diversity, laying a solid foundation for the design of intelligent systems. Comprehensive material and electrical analyses reveal the charging and discharging behaviors of the defect energy levels, underlying the neuromorphic working mechanisms. Additionally, by incorporating artificial neural network algorithms, an intelligent power forecasting system that leverages the device’s diverse neuromorphic traits is developed for real-time and adaptive power management, optimizing efficiency and accuracy in balancing supply and demand, thereby enhancing the cost-effectiveness and sustainability of power systems. The findings highlight the neuromorphic capabilities of GaN devices and open avenues for further exploration into the intelligent power management.

Thermal analysis of GaN HEMTs using nongray multi-speed phonon lattice Boltzmann method under Joule heating effect

Gallium Nitride (GaN) high electron mobility transistors (HEMTs) exhibit superior electrical properties for power and radio frequency applications, but performance is compromised by localized Joule heating, increasing channel temperatures. Precise thermal analysis during design is essential for optimizing device architecture and management strategies. Traditional methods like the Fourier heat diffusion equation (HDE) and the phonon lattice Boltzmann method (PLBM) with the D2Q8 scheme inadequately model phonon ballistic transport at high Knudsen numbers. This study introduces a nongray multi-speed PLBM integrated with the drift-diffusion model to analyze electro-thermal processes in GaN HEMTs. Validated through simulations of thermal conductivities in two-dimensional GaN thin films, the approach examines internal temperature rise in GaN HEMTs under different gate voltages, comparing results with HDE and gray BTE models, and emphasizing the need for non-Fourier effects in thermal analysis. It also evaluates the impact of GaN layer thickness on temperature distribution, providing a robust solution for thermal analysis in GaN HEMTs and other field-effect transistors.

Reduction of interface defects in gate-recessed GaN HEMTs by neutral beam etching

This study investigates and compares the impact of different etching techniques on the fabrication of GaN high electron mobility transistors (HEMTs) between the inductively coupled plasma reactive ion etching (ICP-RIE) and the neutral beam etching (NBE) for the gate recess. By conducting direct current analysis, it was found that devices manufactured using the NBE exhibited superior electrical performance as compared with those produced using the ICP-RIE. These enhanced electrical characteristics include a transconductance of up to 100.4 mS/mm, a threshold voltage (Vth) of −2.3 V, an on/off current ratio of 1.1 × 109, a subthreshold swing (S.S.) of 99.63 mV/dec, and a remarkably low gate leakage current. Additionally, we noted varying degrees of hysteresis in the I–V characteristics were related to process disparities possibly leading to interface defects. Multi-frequency capacitance-voltage (C–V) measurements were used to identify the interface defects at the oxide/AlGaN interface of the gate. The results revealed that devices fabricated using the NBE exhibited a lower interface defect density as compared with those fabricated using the ICP-RIE, thereby elucidating the reduced hysteresis observed in the I–V characteristics. These findings indicated the significant advantages of the NBE process in the fabrication of GaN HEMTs.

Correlation of heat transport mechanism and structural properties of GaN high electron mobility transistors

Grain sizes, impurities, and layer thicknesses in the nm-range affect the heat transport and, hence, hinder proper heat dissipation of GaN-based devices. To obtain a clear picture of heat dissipation, the mechanisms of heat transport must be linked to the structural properties of the nitride-based materials in the device. In this paper, a systematic investigation of the typical layers of GaN high-electron mobility transistor stacks was conducted by time-domain thermoreflectance analysis and Raman measurements. The analyzed layers are the AlN nucleation layer, the Al0.3Ga0.7N transition layer, the AlGaN/AlN superlattice, the C-doped GaN back-barrier, and the uid GaN layer. The results were interpreted using the Born–van Karman model, including the suppression function approach to describe the governing heat transport mechanisms. Investigation of this AlN nucleation layer showed that its phonon scattering is dominated by impurity and grain boundary scattering. The Al0.3Ga0.7N transition layer was shown to have a reduced thermal conductivity not only due to alloy scattering but also because of grain boundary scattering. The AlGaN/AlN superlattice showed a thermal conductivity lower than the Al0.3Ga0.7N transition layer, especially at higher temperatures (7.2 ± 0.2 W/mK vs 14.1 ± 0.4 W/mK at 300 °C). Caused by the enhanced AlGaN/AlN interface density, the thermal conductance was found to be 2 GW/m2 K. The AlGaN/AlN superlattice indicated an anisotropic thermal transport with a factor of ∼1.5. The C-doped GaN layers were analyzed in terms of their size-dictated thermal conductivity, resulting in a reduction of ∼66% from 1 μm to 250 nm at 30 °C. Raman spectroscopy revealed that the thicker the GaN layer, the higher the compressive stress in GaN, which additionally results in a higher thermal transport. The investigations of the heat transport depending on the structural properties enabled an accurate determination of the thermal conductivity of the layer stack. These thermal conductivities served as input parameters for 3D simulation to extract the temperature, in terms of the thermal resistance, of such high-electron mobility transistor stacks. This simulation shows the importance of the GaN layer in terms of thermal management. This work uncovers the thermal transport in GaN-based transistor stacks with the aim to improving the thermal design.

Breakdown voltage enhancement and specific on-resistance reduction in depletion-mode GaN HEMTs by co-modulating electric field

In this letter, a depletion-mode GaN high electron mobility transistors (GaN HEMTs) with high breakdown voltage and low on-resistance are designed and experimentally demonstrated. It combines the gate field plate and partial unintentionally doped GaN (u-GaN) cap layer (gate field plate and partial u-GaN cap HEMTs: GPU-HEMTs) to co-modulate the surface electric field distribution, which results in the electric field peak being far away from the gate edge, thus improving the breakdown voltage and decreasing the on-resistance. The optimized GPU-HEMTs exhibit a larger output current (I DS) of 495 mA mm−1 and a correspondingly smaller specific on-resistance of 4.26 mΩ·cm2. Meanwhile, a high breakdown voltage of 1044 V at I DS = 1 mA mm−1 compared to the conventional GaN HEMTs of 633 V was obtained. This approach is highly effective in simultaneously optimizing the breakdown voltage and the specific on-resistance of GaN HEMTs, while maintaining a large output current.