High Electron Mobility Transistor Devices Research Articles

Ionizing radiation damage mechanism and biases correlation of AlGaN/GaN high electron mobility transistor devices

In this paper, the total dose effect on AlGaN/GaN high-electron-mobility transistor (HEMT) devices after <sup>60</sup>Co γ-ray irradiation with a total dose of 1 Mrad(Si) was investigated at different biases (<i>V</i><sub>GS</sub> = –3 V, <i>V</i><sub>DS</sub><italic/> = 0.5 V; <i>V</i><sub>GS</sub> = –1.9 V, <i>V</i><sub>DS</sub> = 0.5 V; <i>V</i><sub>GS</sub> = 0 V, <i>V</i><sub>DS</sub> = 0 V). The experimental results were analyzed using 1/<i>f</i> low-frequency noise and direct current electrical characteristics. The electrical parameters degraded mostly under zero bias condition because of the radiation-induced defect charge of the oxide layer and the interface state. Wherein, the saturation drain current was reduced by 36.28%, and the maximum transconductance was reduced by 52.94%. The reason was that the oxide dielectric layer of AlGaN/GaN HEMT devices generated electron-hole pairs under γ-ray irradiation, and most of the electrons were quickly swept out of the oxide region corresponding to the gate-source and gate-drain spacer regions, and most of the holes remained in the oxide. Under the action of the built-in electric field, holes slowly moved towards the interface between the oxide and AlGaN, which depleted the two-dimensional electron gas of the channel.According to the McWhorter model, the low-frequency noise in the AlGaN/GaN HEMT devices results from random fluctuations of carriers, which are caused by the capture and release processes of carriers by traps and defect states in the barrier layer. The extracted defect densities in AlGaN/GaN HEMT devices increased from 4.080 × 10<sup>17 </sup>cm<sup>–3</sup>·eV<sup>–1</sup> to 6.621 × 10<sup>17 </sup>cm<sup>–3</sup>·eV<sup>–1</sup> under the condition of zero bias, and the result was in good agreement with test results of the direct currentelectrical characteristics. The damage mechanism was the radiation-induced defect charge in the oxide layer and the interface state, which increased the flat-band voltage noise power spectral density of the AlGaN/GaN HEMT devices. According to the charge tunneling mechanism, the spatial distribution of defect in the barrier layer was extracted, and the result also proved that the densities of radiation-induced defect charges under zero bias were more than the other biases. The experimental results showed that zero bias was the worst bias for AlGaN/GaN HEMT devices irradiation.

基于感光栅极GaN高迁移率晶体管的新型探测器制备与优化

基于感光栅极GaN高迁移率晶体管的新型探测器制备与优化

A Generic and Efficient Globalized Kernel Mapping-Based Small-Signal Behavioral Modeling for GaN HEMT

The work reported in this article explores a novel Particle Swarm Optimization (PSO) tuned Support Vector Regression (SVR) based technique to develop the small-signal behavioral model for GaN High Electron Mobility Transistor (HEMT). The proposed technique investigates issues such as kernel selection and model optimization usually encountered in the application of SVR to model the GaN based HEMT devices. Here, the PSO algorithm is utilized to find the optimal hyperparameters to minimize the fitness function. To enumerate the efficiency and the generalization capability of the predictors, the performance of the model is investigated in terms of mean square error (MSE) and mean relative error (MRE). A very good agreement is found between the measured S-parameters and the proposed model for multi-biasing sets over the complete frequency range of 1GHz-18GHz. The proposed technique is even used to test the frequency extrapolation capability of the model. A comparative analysis indicates that the proposed PSO-SVR predictor achieves significantly improved computational efficiency and the overall prediction accuracy. To demonstrate the ready usefulness of the modeling approach, the developed model has been incorporated in CAD environment using MATLAB Cosimulation in ADS Ptolemy. Subsequently, the small-signal stability analysis is performed and gain of a power amplifier configuration designed using the proposed GaN HEMT model is determined.

ε-Ga2O3: A Promising Candidate for High-Electron-Mobility Transistors

We predict spontaneous polarization of ε-Ga <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> can achieve a high density of 1014 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> two-dimensional electron gas (2DEG) at the interface of ε-Ga <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> and m-AlN (m-GaN) without doping. Based on the accurately calculated bandgap alignment of ε-Ga <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> , AlN and GaN, we find that the critical thickness of the ε-Ga2O3 to form a mobile 2DEG at the interface on m-AlN and m-GaN substrates is around 1.8 nm, which is much thinner than AlGaN due to its large potential shift. The depletion mode high-electron-mobility transistors (HEMTs) based on ε-Ga <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> are also investigated. The results show that the saturation currents of ε-Ga <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> HEMTs devices are much larger than that of typical AlGaN HEMTs. For the emerging problem of large leakage current from ε-Ga <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> HEMTs device, we present a novel method that can significantly suppress the off-state leakage current of the device by growing an ultrathin AlGaN layer on the top surface of ε-Ga <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> . Therefore, our results can provide a theoretical basis for the potential applications of ε-Ga <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> in fabricating HEMTs for high-power and high-frequency applications.

A Modified Poly-Harmonic Distortion Model Based on the Canonical Piecewise Linear Functions for GaN HEMTs

A novel, large-signal behavioral modeling methodology for Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs), based on the canonical piecewise-linear (CPL) functions, is presented in this paper. The proposed new model employs the poly-harmonic distortion (PHD) model framework, making use of the CPL functions for interpolation of the amplitude of the dominant input signal. The CPL method is also applied to the quadratic PHD (QPHD) model framework, allowing for application to devices operating under high (greater than 3 dB) compression levels. Compared with the standard PHD/QPHD models, which require lengthy tables of parameter values to account for the varying large signal input power(s), the models described in this paper are able to predict transistor behavior at different levels of input power, from the linear region to the strongly nonlinear region (where gain compression exceeds 1 dB), with one single set of model coefficients. The basic theory of the proposed model for both RF and dc responses is provided in the paper. The proposed modeling technique is validated through simulated and experimental data from separate 6 W and 10 W GaN HEMT devices, over a wide range of load conditions and power levels. In addition, a two-dimensional polynomial-based model is used for performance comparison, with the proposed method providing comparable accuracy while requiring significantly fewer model coefficients.

High-Resolution AlGaN/GaN HEMT-Based Electrochemical Sensor for Biomedical Applications

We have investigated the characteristics of pH and salinity sensor derived from the gated AlGaN/GaN high-electron mobility transistor (HEMT) structures in phosphate buffer saline (PBS) and aqueous salt solutions (NaCl + DI). In deionized (DI) water, the HEMT device showed good drain ${I}$ – ${V}$ characteristics, which is very close to the output characteristics of the typical HEMT structures subjected to the air. We observed a significant change in the output drain characteristics curves concerning to the variation in the pH values of PBS solutions, signifying the subsequent potential variation at the AlGaN surface. The output drain current recorded at ${V}_{\text {ds}}= +1$ V was linearly decremented with the pH value. A high sensitivity of $4.32~{\mu }\text{A}$ /mm-pH was obtained. These GaN HEMT structures demonstrated a quick response to the pH changes. It was also investigated that the devices were susceptible toward the aqueous salt solution (NaCl + DI). The percentage change in drain current linearly decreased with decreasing NaCl molar concentration in DI water. We have reported on the change in current with the smaller range of molar concentration of NaCl present in water. Evaluating the sensitivity and response time, we obtained a high sensitivity of 6.48 mA/mm-molar and a response time of 250–350 ms at ${V}_{\text {ds}}= +1$ V. We have also reported on the change in current with the molar concentration of NaCl present in PBS with a high sensitivity of 2.02 mA/mm-molar at ${V}_{\text {ds}}= +5$ V. These outcomes show that the AlGaN/GaN HEMTs are exceptionally promising as a high-sensitivity pH sensor and salinity sensor for biological experiments.

Hydrogen gas ppb-level detection based on AlGaN/GaN high electron mobility transistor with 2.0 nm thick Pt gate layer

In this work, ppb-level H2 gas detection based on the Pt-gated AlGaN/GaN high electron mobility transistor device was obtained through minimizing the H atom diffusion distance by the utilization of a critical Pt gate thickness of ∼2.0 nm. The Ids-Vds curves show that the device exhibits a pinch-off characteristic with an on-to-off ratio of about four orders of magnitude. High response (775% at 100 ppm, 25.4% at 1 ppm) and short response times (2.5 s at 10 000 ppm) are observed at 150 °C. Particularly, the device has a response to trace H2 gas as low as 60 ppb, indicating a small low limit of detection (LOD) &amp;lt; 60 ppb. Its capability to detect very low H2 gas together with a high response makes it promising for trace H2 gas detection such as exhale breath analysis. Moreover, it is found that the H2 detection range depends on the operating temperature, which is useful in real applications that require various H2 gas detection ranges.

Operational Characteristics of Various AlGaN/GaN High Electron Mobility Transistor Structures Concerning Self-Heating Effect.

This study investigated DC characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) considering self-heating effect (SHE) with basic T-gate (BT), drain-side extended T-gate (DSET), and source-bridge FP (SBFP) structures. We analyzed threshold voltage, transconductance, drain saturation current, and breakdown voltage of each structure for device optimization. Experimental data were initially matched with simulated data for the BT structure, then DC characteristics were compared with the drift-diffusion, coupled drift-diffusion and self-heating models for basic T-gate HEMT devices. Breakdown voltages were measured to identify the optimum DSET structure length, while increasing drain-side gate head to 3 µm. An SBFP was also employed where the DSET device showed highest breakdown voltage. Therefore, DC characteristics were compared for three structures and contrasted to reduce SHE. Hot spot and overall temperature were also analyzed for each structure.

(Invited) Novel Channel Engineering for High-Performance AlGaN-Based Transistors

With the advancement of communication technology and the use of higher frequency bands for greater bandwidth, there is an increasing need for power amplifiers that can simultaneously provide high power, linearity, and efficiency. High electron mobility transistors (HEMTs) based on the AlGaN/GaN heterostructure provide state-of-art performance for high frequency power amplifiers [1]. For mm-wave and higher frequencies, significant improvement of performance is necessary to achieve the required performance. This invited talk will address new channel designs that could provide improvement in power density and linearity for future power amplifiers. The first part of this talk will discuss new channel designs to improve the linearity performance of III-Nitride transistors. Transconductance drop is a major source of non-linearity for AlGaN/GaN HEMTs and has been shown to originate from the fundamental transport properties in the 2-dimensional electron gas that forms the conducting channel in such transistors [2]. In this work, we show that replacing the 2D electron gas channel with a 3-dimensional electron gas (3DEG) channel using polarization grading can enable constant transconductance and power gain profiles over the operating regime of the transistor, and therefore improve the linearity performance [3]. We will describe different variations of these polarization graded FETs (PolFETs) including InGaN-based structures, composite 2D/3D channels, and designs for passivation and low leakage [4]. Our results show that novel channel design can enable record performance in terms of two-tone linearity at X-band (10 GHz) frequencies. The second part of the talk will focus on ultra-wide band gap (UWBG) high Al-composition AlGaN based transistors. AlGaN is promising as a high frequency channel material due to its high critical breakdown field and high saturated velocity [5,6]. We will discuss, using detailed simulations and calculations how the high field strength in AlN and AlGaN (above 8 MV/cm) could enable higher power density for mm-wave and THz applications. Achieving the projected performance in actual devices is challenging due to fundamental issues related to the low mobility, charge injection, and electrostatic field management [7]. We will discuss novel designs being pursued to overcome these challenges, including the use of novel heterostructure contacts, scaled devices to enable high-velocity transport, and the integration of extreme dielectric constant materials such as BaTiO3/AlGaN to realize high breakdown fields. These efforts have enabled current state-of-art performance for ultra-wide band gap AlGaN transistors, including 60% AlGaN channel HEMT devices with record cutoff frequency fT up to 40 GHz.

Radiation-Induced DC Parametric Degradation of Enhancement Mode GaN-on-(111)Silicon High-Electron-Mobility Transistors

AlGaN/GaN high-electron-mobility transistors (HEMTs) for applications in radiation environments has required the exact determination of their radiation hardness. Although bulk GaN is the preferred substrate for the epitaxial growth of GaN and AlGaN, (111) silicon is a possible substrate for HEMT devices. The stability of electrical parameters of enhancement-mode (E-mode) GaN HEMTs under gamma irradiation is an essential characterization for reliability. The present work reports the transfer characteristics degradation of E-mode GaN HEMTs under various total dose irradiation from 5krad up to 60Mrads. This represents the first comprehensive total dose study ranging from a few krads up the tens of Mrads. The measured device-to-device variations within groups of devices are presented. The evolutions of critical DC parameters with accumulated total dose is found to be significant at low doses and saturates at high dose levels. The degradation mechanism is very similar to the reported radiation-induced shallow electron traps that trap and release electrons in the near surface GaN and AlGaN layers. Due to the unique properties including high breakdown voltage, high electron mobility and high thermal stability, wide-bandgap semiconductor power electronic devices, especially Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs), have shown great promise in space, defense and nuclear applications, which often involve radiation-hardened electronics that require high radiation tolerance to fluxes of neutrons or gamma ray of devices. To turn the promising potential of GaN HEMTs into reality, investigations on the influence of irradiation on the device performance and reliability are essential. Many studies have investigated the radiation hardness of group III–nitride compound semiconductor devices under various irradiation types, such as electrons, protons, neutrons, and X-rays and at various total irradiation doses. They generally showed higher radiation tolerance compared with Si because of high displacement energy of GaN, demonstrating the favorability of GaN devices in hard radiation environments. Many studies have investigated the influence of 60Co gamma radiation on the device electrical characteristics. However, they were all focusing on depletion mode (D-mode) devices. Enhancement mode (E-mode) GaN-on-Si transistors have been commercially available for years. Their major advantages over D-mode devices are elimination of negative voltage supply and the enabling of direct-coupled FET logic (DCFL) for digital circuits. They also improve the efficiency of commercial DC-DC converters in various power levels and topologies. A previous work on gamma radiation of E-mode GaN-on-Si HEMTs only reported cumulative total doses of up to 1 Mrads (Si). The present work provides a complete coverage of low-to-high irradiation doses from 5krads up to 60Mrads (Si), for commercially available E-mode GaN HEMTs and the devices are characterized to gauge variations in the critical DC parameters. To the best of the author’s knowledge, the present work is the first to investigate the gamma radiation tolerance of E-mode GaN HEMTs covering such a wide range of total doses. This facilitates the observation of the complete degradation behavior of DC parameters in hard radiation applications of the E-mode GaN HEMTs. The devices were supplied in the form of 0.9mm square passivated die with round solder bumps for contacts. They have a rated continuous drain-to-source voltage VDS of 60V, and a rated continuous drain current ID of 1A. These GaN-on-Si devices were fabricated on Si wafers considering process compatibility and cost. An aluminum nitride (AlN) thin layer was grown on the Si wafer to be a seed layer for the AlGaN/GaN heterostructure. Subsequently, the AlGaN/GaN heterostructure was grown on the AlN layer, with a thin AlGaN layer grown above the highly resistive GaN serving as a strained interface between the GaN and AlGaN crystal layers, allowing the creation of a two-dimensional electron gas (2DEG) filled with abundant free electrons with ultra-high mobility. The gate electrode was processed subsequently forming a depletion region under the gate. As an E-mode transistor, the device is turned on by applying a positive bias to the gate. All the irradiations were conducted at room temperature by 60Co gamma-rays with a flux of 318.5Rads (Si)/s, at the dry-cell panoramic gamma irradiator in the University of Maryland Radiation Facilities. The entire irradiation procedure consists of two parts. The first part is higher-dose irradiation with total doses of up to 60Mrads based on two stages. At the first stage, the devices were irradiated at 10Mrads, while at the second stage, the devices were irradiated for another 50Mrads, with three of them taken out after 25Mrads during the second stage. The second part is lower-dose irradiations with total doses of up to 2Mrads. The temperature throughout the irradiation process was monitored to be below 30°C.

Doherty Power Amplifier for LTE-Advanced Systems

The design and implementation of an asymmetrical Doherty power amplifier are discussed, where two Cree GaN High Electron Mobility Transistors (HEMTs) devices are used for designing an asymmetrical Doherty power amplifier to achieve saturated power of 48 dBm and optimal back-off efficiency of 8 dB in the frequency band of 3.3–3.5 GHz. Rogers RO4350B material is used as a substrate material, a back-off of 8 dB was achieved with an average gain of 10 dB. Load-pull data are an important tool for determining the optimum load impedance that the transistor needs to see. Additionally, the measured efficiency was 50% when the designed amplifier was tested by a modulated signal of 8 dB peak-to-average-power ratio when the average output power was 40 dBm. At the same time, the linearity of the designed amplifier was measured and found 31.8 dB which can be improved using a digital pre-distorter. The gain phase measurement can be used as an indicator for compensating the phase difference between the two cells.

Detection of Multiple Samples Based on AlGaN/GaN High Electron Mobility Transistors and Magnetic Microbeads

AbstractSemiconductor biochemical sensors are regarded as robust tools for the detection of various targets. However, re‐use of these sensors is one of the major obstacles hindering further development. To address this problem, a multi‐objective platform was developed based on magnetic beads and the AlGaN/GaN high electron mobility transistor (MBs AlGaN/GaN HEMT) device. Since the magnetic beads are capable of being fixed and released by inductance coils, the platform enables repeatability and multi‐objectivity during testing. To validate the advantages of the platform, metal ions and prostate specific antigen (PSA) were used. In this study, a platform sensing biochemical responses with a sensor was demonstrated to show the characteristics of reusability, multi‐target sensing, and simplicity, resulting in its promising prospects for widespread applications.

Surface states in AlGaN/GaN high electron mobility transistors: Quantitative energetic profiles and dynamics of the surface Fermi level

We present a method to obtain quantitative profiles of surface state charge density and monitor its dynamics under various stress conditions in high electron mobility transistor (HEMT) devices. The method employs optical spectroscopy of the channel current at various bias conditions. We test the method on a classical AlGaN/GaN HEMT structure. To analyze the results, we propose a model, according to which the energy distribution of the surface charge density may be obtained from the derivative of the channel photocurrent. The proposed method is applied to fully fabricated transistors and can be measured under any device bias combination. This way, it is possible to explore the effect of device operating conditions on the surface state charge. This feature should be especially useful in studies of the various surface charge migration effects in nitride HEMTs. An important by-product of the method is a quantitative assessment of the energy position of the surface Fermi level and its dynamics under various bias conditions.

Radiation-Induced DC Parametric Degradation of Enhancement Mode GaN-on-(111)Silicon High-Electron-Mobility Transistors

AlGaN/GaN high-electron-mobility transistors (HEMTs) for applications in radiation environments has required the exact determination of their radiation hardness. Although bulk GaN is the preferred substrate for the epitaxial growth of GaN and AlGaN, (111) silicon is a possible substrate for HEMT devices. The stability of electrical parameters of enhancement-mode (E-mode) GaN HEMTs under gamma irradiation is an essential characterization for reliability. The present work reports the transfer characteristics degradation of E-mode GaN HEMTs under various total dose irradiation from 5krad up to 60Mrads. This represents the first comprehensive total dose study ranging from a few krads up the tens of Mrads. The measured device-to-device variations within groups of devices are presented. The evolutions of critical DC parameters with accumulated total dose is found to be significant at low doses and saturates at high dose levels. The degradation mechanism is very similar to the reported radiation-induced shallow electron traps that trap and release electrons in the near surface GaN and AlGaN layers.

Improved Characterization and Accurate Modelling of Drain Current Derivatives of InP Based High Electron Mobility Transistors Devices.

InP based HEMTs are of great importance, due to their enormous potential in a high-speed modern microwave circuit, power amplifier, and low noise amplifier applications. Therefore, an accurate non-linear equivalent circuit model of HEMTs is very important for an accurate circuit design. This paper presents improved characterization and accurate modelling of drain current derivatives of InP based HEMTs devices. The proposed model is simple, easy to extract, and suitable for implementation in simulation tools. The Ψ function is extended to increase the flexibility of the proposed model. A gate-drain dependent current source is added to increase the S-parameter fitting. A one-dimensional intrinsic multi-bias capacitances model is introduced to avoid convergence failure. The fitting results of the I-V characteristics and its high order derivatives show high accuracy. In addition, S-parameters and Pout for the proposed model are compared with the original Angelov model. The proposed model shows better accuracy.

ScAlN/GaN High-Electron-Mobility Transistors With 2.4-A/mm Current Density and 0.67-S/mm Transconductance

We report the dc and RF performance of ScAlN/GaN high-electron-mobility transistors (HEMTs). The ScAlN/GaN material was epitaxially grown onto a GaN template on a 4-in 4H-SiC substrate by molecular beam epitaxy. The sheet resistance was measured to be 236 ± 4 $\Omega /\square $ across the wafer by the transfer length measurement. Selective area regrowth of highly doped GaN was implemented to reduce contact resistance ( ${R}_{C}$ ) as low as 0.1 $\Omega \cdot \textsf {mm}$ . HEMT devices with $\textsf {2}\times \textsf {150}\,\,\mu \text{m}$ gate width and 140-nm T-gate process show a maximum current density and a transconductance of 2.4 A/mm and 0.67 S/mm, respectively. The extrinsic small-signal gain was measured as a function of drain bias and gate length with extrinsic cutoff frequency and maximum oscillation frequency reported up to 88 and 91 GHz, respectively.

Research and Application of Temperature-sensitive Characteristics of Gate Parameters in GaN high electron mobility transistors

A gallium nitride (GaN) high-electron-mobility transistors (HEMTs) operates in a high-frequency switching state, and its usage reliability is reduced when the temperature increases as a result of the increase of power density and size reduction. To measure the HEMT temperature increase based on the characteristics of the gate-source structure of the HEMT device, this paper proposes the use of reverse gate current as a thermo-sensitive parameter to measure the temperature and improve the temperature characteristics of the parameter by reasonably changing the gate voltage. A theoretical analysis of the reverse gate current components was carried out, and the trends and changes in its temperature characteristics were investigated. The influencing factors affecting the reverse gate current were discussed, and the phenomenon of the current’s sudden change with temperature was explained.

Bayesian Inference-Based Behavioral Modeling Technique for GaN HEMTs

A new, frequency-domain, behavioral modeling methodology for gallium nitride (GaN) high-electron-mobility transistors (HEMTs), based on the Bayesian inference theory, is presented in this paper. Several different probability distribution (kernel) functions are examined for the Bayesian-based modeling architecture, with the optimal kernel function identified through experimental testing. These results are compared to an alternative approach based on the artificial neural networks (ANNs), with the data showing that the proposed approach demonstrates improved accuracy, while at the same time, alleviating the well-known ANN overfitting issue. Model verification is performed at the fundamental and harmonic frequencies using the identified optimal kernel, through comparisons with simulated data from a reference nonlinear circuit model, and with experimental data from separate 2- and 10-W GaN HEMT devices, over a wide range of load conditions. The models can predict accurately the optimal area of the fundamental output power on the Smith chart and the area of optimal power efficiency. Furthermore, the ability of the model to interpolate across input power levels and input frequencies is also tested, with excellent fidelity to the simulated and measured data obtained.

Cumulative dose γ-irradiation effects on material properties of AlGaN/GaN hetero-structures and electrical properties of HEMT devices

The effects of γ-ray irradiation on AlGaN/GaN epitaxial layers and on high electron mobility transistor (HEMT) devices have been systematically investigated. The layer structure and HEMT device has been irradiated cumulatively with γ-ray dose of the order of 16 kGy. The x-ray diffraction (XRD) analysis of irradiated sample shows a lowering in full width at half maximum (FWHM) values along (102) and (002) planes in comparison to the pristine sample due to partial annealing effect. A decrease in the in-plane biaxial stress from 1.20 GPa to 0.75 GPa has been observed. Raman spectrum analysis also corroborates the reduction in stress post γ-ray irradiation. Edge dislocation density is reduced from 2.7 × 108 cm−2 to 1.75 × 108 cm−2 whereas the screw dislocation density remains almost unaffected. Further, Hall measurement shows an improvement in the mobility from 1580 cm2 V−1 s−1 to 2070 cm2 V−1 s−1 with reduction in sheet resistance. This improvement in mobility is attributed due to the decrease in surface roughness as confirmed by atomic force microscopy (AFM) characterization and also due to re-arrangement of the local defect centers as confirmed by cathodoluminescence (CL) imaging analysis. Finally, an increase in drain current from 99.5 mA mm−1 to 121.2 mA mm−1 with reduction in leakage current has been observed in case of HEMT device due to the improvement found in various material parameters.

Design optimization of the graded AlGaN/GaN HEMT device performance based on material and physical dimensions

PurposeTo design and optimize the traditional aluminum gallium nitride/gallium nitride high electron mobility transistor (HEMT) device in achieving improved performance and current handling capability using the Synopsys’ Sentaurus TCAD tool.Design/methodology/approachVarying material and physical considerations, specifically investigating the effects of graded barriers, spacer interlayer, material selection for the channel, as well as study of the effects in the physical dimensions of the HEMT, have been extensively carried out.FindingsCritical figure-of-merits, specifically the DC characteristics, 2DEG concentrations and mobility of the heterostructure device, have been evaluated. Significant observations include enhancement of maximum current density by 63 per cent, whereas the electron concentration was found to propagate by 1,020 cm−3 in the channel.Practical implicationsThis work aims to provide tactical optimization to traditional heterostructure field effect transistors, rendering its application as power amplifiers, Monolithic Microwave Integrated Circuit (MMICs) and Radar, which requires low noise performance and very high radio frequency design operations.Originality/valueAnalysis in covering the breadth and complexity of heterostructure devices has been carefully executed through extensive TCAD modeling, and the end structure obtained has been optimized to provide best performance.