Channel High Electron Mobility Transistors Research Articles

Numerical modeling of highly sensitive resonant detection of THz radiation using a multichannel dispersive plasmonic HEMT

The resonant detection of terahertz radiation using a dispersive AlN/GaN multichannel high-electron-mobility transistor (HEMT) is analyzed and modeled in this paper. The proposed full-wave model is based on the concurrent solution of the complete hydrodynamic model (CHM) and Maxwell’s equations. The CHM is derived from the first three moments of the Boltzmann transport equation (BTE). Considering the variations of the electron temperature and transport parameters along the HEMT channel, this model well characterizes the electron–wave interaction in the device for both low- and high-field conditions. Moreover, the effect of the optical phonon modes of the GaN buffer, which cannot be ignored in the target terahertz frequency band, is described using the Lorentz dispersive model. Employing the developed model, the transmission spectrum of the device is extracted numerically using the finite-difference time-domain (FDTD) method for grating-gate single-, double-, and three-channel HEMT structures. The results show that, at a lattice temperature of 300 K for a GaN grating-gate HEMT with gate periodicity of 680 nm and gate width of 520 nm, at given resonance frequency and overall electron concentration, the resonance depth improves by about 2.7 dB in the three- compared with the single-channel structure. Moreover, it is shown that the detection performance of such a structure at 300 K is similar to the single-channel HEMT at a reduced temperature of 120 K. Therefore, the multichannel HEMTs can show notably improved resonant detection performance, enabling the design of resonant detectors with enhanced sensitivity at room temperature.

Analysis of MIS-HEMT Device Edge Behavior for GaN Technology Using New Differential Method

A new differential method for accurate extraction of electrical parameters of high-electron mobility transistor (HEMT) devices for gallium nitride (GaN) technology is proposed. This method, presented here for the first time, is used to study the mobility degradation with gate length, allowing an analysis of the contribution of the gate edge region to the total metal-insulator semiconductor (MIS)-HEMT device conductance. First, an analytical model is proposed to account for the relative conduction of the edges and the main flat part of the channel HEMTs. Second, the differential method allows the split-CV mobility extraction of each part, allowing a precise analysis of the resistive contribution of each region of the HEMT devices. This study has been performed over a large range of channel lengths for two normally OFF HEMT GaN wafers having different recess depths.

Modeling Bias Dependence of Self-Heating in GaN HEMTs Using Two Heat Sources

This article proposes a new approach for modeling self-heating in gallium nitride (GaN) high-electron-mobility transistors (HEMTs). The proposed approach utilizes two heat sources to model the effects of the relatively uniform heat generation when the device is in the linear regime and the concentrated heat generation in the high-field area after the device pinches off. Compared to traditional single heat source modeling approaches, the proposed approach yields a model that can accurately capture the bias dependence of the heat and temperature distribution in the GaN HEMT channel without resorting to the more resource-intensive electrothermal simulations. It also leads to a simple yet accurate analytical expression for the maximum channel temperature using thermal resistances that have clear geometric dependence.

Interdependence of Electronic and Thermal Transport in AlxGa1–xN Channel HEMTs

Aluminum gallium nitride (AlGaN) high electron mobility transistors (HEMTs) are candidates for next-generation power conversion and radio frequency (RF) applications. Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> N channel HEMT devices (x = 0.3, x = 0.7) were investigated using multiple in-situ thermal characterization methods and electro-thermal simulation. The thermal conductivity, contact resistivity, and channel mobility were characterized as a function of temperature to understand and compare the heat generation profile and electro-thermal transport within these devices. In contrast to GaN-based HEMTs, the electrical output characteristics of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.70</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.30</sub> N channel HEMTs exhibit remarkably lower sensitivity to the ambient temperature rise. Also, during 10kHz pulsed operation, the difference in peak temperature between the AlGaN channel HEMTs and GaN HEMTs reduced significantly.

A 0.5 nJ/b 60 GHz ultra wideband transmitter for short range wireless sensor network applications

AbstractA novel monolithic microwave integrated circuit (MMIC) design of ultra wide band (UWB) transmitter at 60 GHz with simple architecture and high‐range resolution ability is presented in this paper. Implemented with 0.1 μm 100 GHz GaAs positive channel high electron mobility transistor (PHEMT) technology offered by OMMIC, the transmitter comprises a millimeter wave oscillator, a buffer amplifier (BA), a medium power amplifier (MPA) and two UWB Pulse Generators (UWBPG). For the sake of the goal on reducing the entire transmitter consumption, the oscillator is controlled by one UWBPG and another UWBPG drives the BA and MPA simultaneously. The transmitter has infinite isolation level to minimize the interference with neighboring devices. For a pulse repetitive time of 5 ns, pulse width of 500 ps and supply voltage of 3 V, the transmitter consumes only 101 mW and has a peak transmit power of 9.2 dBm corresponding to 0.5 nJ per pulse energy consumption, which is suitable for future short range wireless sensor network (WSN) applications.

High‐Breakdown‐Voltage AlGaN Channel High‐Electron‐Mobility Transistors with Reduced Surface Field Technique

In this article, reduced surface field (RESURF) AlGaN channel high‐electron‐mobility transistors (HEMTs) are proposed and investigated through 2D simulation for the first time. p+ doping is designed to form the RESURF structure, and the impact of the p+ doping density and length on breakdown characteristics is investigated. The breakdown voltage (BV) can be improved from 819 V for a conventional HEMT to 1746 V for a RESURF HEMT with a p+ doping density of 5 × 1018 cm−3 and length of 4 μm. Although the specific on‐resistance (RON) increases from 1.45 to 2.16 mΩ cm2, the power figure of merit (FOM) increases from 2.49 × 108 to 8.28 × 108 V2 Ω−1 cm−2 by utilizing a RESURF structure. By increasing the Al component of the RESURF AlGaN channel HEMT, the BV can be improved from 1746 to 2199 V. However, the RON also increases from 3.68 to 8.04 mΩ cm2, which leads to a decreasing of the power FOM. Simulation and analysis suggest that RESURF AlGaN channel HEMTs have great potential in power electronic applications.

Breakdown voltage enhancement in GaN channel and AlGaN channel HEMTs using large gate metal height**Project supported by the National Key Science & Technology Special Project of China (Grant No. 2017ZX01001301), the National Key Research and Development Program of China (Grant No. 2016YFB0400100), and the National Natural Science Foundation of China (Grant Nos. 51777168 and 61801374).

A large gate metal height technique is proposed to enhance breakdown voltage in GaN channel and AlGaN channel high-electron-mobility-transistors (HEMTs). For GaN channel HEMTs with gate–drain spacing LGD = 2.5 μm, the breakdown voltage VBR increases from 518 V to 582 V by increasing gate metal height h from 0.2 μm to 0.4 μm. For GaN channel HEMTs with LGD = 7 μm, VBR increases from 953 V to 1310 V by increasing h from 0.8 μm to 1.6 μm. The breakdown voltage enhancement results from the increase of the gate sidewall capacitance and depletion region extension. For Al0.4Ga0.6N channel HEMT with LGD = 7 μm, VBR increases from 1535 V to 1763 V by increasing h from 0.8 μm to 1.6 μm, resulting in a high average breakdown electric field of 2.51 MV/cm. Simulation and analysis indicate that the high gate metal height is an effective method to enhance breakdown voltage in GaN-based HEMTs, and this method can be utilized in all the lateral semiconductor devices.

Global modeling of terahertz plasmonic high electron mobility transistor using a complete hydrodynamic model

The global modeling of an unbiased/biased ungated high electron mobility transistor (HEMT) is presented. The complete hydrodynamic model is employed for the full-wave analysis of the structure, using the finite-difference time-domain numerical method. This model is based on the first three moments of the Boltzmann transport equation combined with Maxwell’s equations. Using the three moments of the transport equation, in contrast to the usual first two moments, allows us to take into account the variation of the transport parameters with the energy and the temperature. Therefore, the complete characteristics of the plasmons’ propagation along the ungated HEMT channel for low- and high-field conditions are achieved. Moreover, by applying this model to a metallic grating gate HEMT as a tunable resonant detector, the transmission spectra are obtained for various temperatures and electron densities for low- and high-field conditions. The results show the characteristics of the surface plasmons’ propagation are highly influenced by the excitation field level and accordingly cause transport parameter variations that can be described completely by our developed model.

Growth behavior of GaN on AlN for fully coalesced channel of AlN-based HEMT

We investigated the growth behavior of GaN grown on AlN along with V/III ratio and pressure variation, and found out the lateral growth regime for the fully coalesced channel layer of the AlN-based double-hetero structure high electron mobility transistor (HEMT). When the V/III ratio increases and pressure decreases, compressive stress in the GaN channel increases, and pit formation occurs to release the stress. The AlN-based HEMT structure was grown and the device was fabricated with an optimized channel layer. The two-dimensional electron gas mobility, sheet density, and sheet resistance were 1480 cm2 V−1 s−1, 1.32 × 1013 cm−2, and 319 Ω/sq., respectively, at room temperature. The device was characterized; direct current output result showed that the maximum current was ∼620 mA mm−1, on-resistance was 6.4 Ω mm, transconductance was ∼140 mS mm−1, and current on/off ratio was ∼104, respectively.

Extreme Temperature Operation of Ultra-Wide Bandgap AlGaN High Electron Mobility Transistors

High Aluminum content channel (Al0.85Ga0.15N/ Al0.7Ga0.3N) High Electron Mobility Transistors (HEMTs) were operated from room temperature to 500°C in ambient. The devices exhibited only moderate reduction, 58%, in on-state forward current. Gate lag measurements at 100 kHz and 10% duty only showed a slight reduction in pulsed current from DC at 500°C and high gate voltages. Interfacial trap densities were $2 \times 10^{11}$ over the range 25–300°C and $3 \times 10^{12}$ cm $^{-2}$ from 300–500°C from the subthreshold swing. These low interfacial trap densities and the near ideal gate lag measurement indicate high-quality epi layers. The insulating properties of the barrier layer led to low gate induced drain leakage current of $\sim 10^{-12}$ A/mm and $\sim 10^{-8}$ A/mm at 25 and 500°C, respectively. Low leakage current was enabled by the high Schottky barrier of the Ni/Au gate, 1.1 eV and 3.3 eV at 25 and 500°C, respectively. These properties of the AlGaN channel HEMTs demonstrate their potential for high power and high temperature operation.

Simulation and Performance Evaluation of In Ga P/In Ga As/Ga As Dual Channel HEMT

An InGaP/InGaAs/GaAs dual channel High Electron Mobility transistor (HEMT) with three δ doped layers with different doping densities is modeled and simulated in this paper by using two dimensional ATLAS simulation package from Silvaco software. Different DC performances (Drain characteristic and Transfer characteristics) at various voltage levels are analyzed and results are compared by taking the gate length of 500nm and 800nm at two different temperature levels (250k and 300k) to determine the efficiency of the device for high speed digital device applications. The paper describes the effect of parasitic access resistance on device gate length and effect of mobility by varying temperature. High drain current drivability, large carrier densities and better saturation characteristics are realized because of the inclusion of InGaAs channel instead of GaAs DC structure and schottky behavior of InGaP layer. The studied double channel HEMT with proper dimensions and accurate doping profile makes it a promising device for high performance electronics device applications.

Multidimensional thermal analysis of an ultrawide bandgap AlGaN channel high electron mobility transistor

Improvements in radio frequency and power electronics can potentially be realized with ultrawide bandgap materials such as aluminum gallium nitride (AlxGa1−xN). Multidimensional thermal characterization of an Al0.30Ga0.70N channel high electron mobility transistor (HEMT) was done using Raman spectroscopy and thermoreflectance thermal imaging to experimentally determine the lateral and vertical steady-state operating temperature profiles. An electrothermal model of the Al0.30Ga0.70N channel HEMT was developed to validate the experimental results and investigate potential device-level thermal management. While the low thermal conductivity of this III-N ternary alloy system results in more device self-heating at room temperature, the temperature insensitive thermal and electrical output characteristics of AlxGa1−xN may open the door for extreme temperature applications.

(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.

Temperature‐Dependent Characteristics of AlGaN/GaN Nanowire Channel High Electron Mobility Transistors

In this work, three AlGaN/GaN nanowire channel high electron mobility transistors (NC‐HEMTs) with different channel widths have been fabricated. The temperature dependent characteristics of NC‐HEMTs are studied and compared with conventional HEMT. The results show that the on‐state current density of NC‐HEMTs have weaker temperature dependence, and the threshold voltage variation of NC‐HEMTs is lower. In addition, the temperature characteristics of the drain‐induced barrier lowering of NC‐HEMT are first reported. Moreover, there are two main scattering mechanisms that influence the transconductance characteristics of NC‐HEMT, phonon scattering and Coulomb scattering, which correspond to different gate voltage biases.

Visible- and solar-blind photodetectors using AlGaN high electron mobility transistors with a nanodot-based floating gate

AlGaN-channel high electron mobility transistors (HEMTs) were operated as visible- and solar-blind photodetectors by using GaN nanodots as an optically active floating gate. The effect of the floating gate was large enough to switch an HEMT from the off-state in the dark to an on-state under illumination. This opto-electronic response achieved responsivity >108 A/W at room temperature while allowing HEMTs to be electrically biased in the off-state for low dark current and low DC power dissipation. The influence of GaN nanodot distance from the HEMT channel on the dynamic range of the photodetector was investigated, along with the responsivity and temporal response of the floating gate HEMT as a function of optical intensity. The absorption threshold was shown to be controlled by the AlN mole fraction of the HEMT channel layer, thus enabling the same device design to be tuned for either visible- or solar-blind detection.

Electron mobility calculation for two-dimensional electron gas in InN/GaN digital alloy channel high electron mobility transistors

The InN/GaN digital alloy is a superlattice-like nanostructure formed by periodically stacking ultra-thin InN and GaN layers. In this study, we calculate the electron mobility in InN/GaN digital alloy channel high electron mobility transistors (HEMTs) by performing a single-particle Monte Carlo simulation. The results of the simulation show that alloy-induced scatterings have little impact and the electron mobility significantly improves as the effective indium mole fraction of the channel increases. This contrasts with InGaN alloy channel HEMTs, where alloy disorder and random dipole scatterings have a strong impact and the electron mobility decreases as the indium mole fraction of the channel increases.

Comparative performance evaluation of lateral and vertical GaN high-voltage power field-effect transistors

We have evaluated specific on-state resistance (Ron,sp) and switching performance of various GaN power field-effect transistors (FETs) with 600 and 1200 V ratings using analytical calculation and numerical simulation. The normally-off GaN power FET family includes lateral p-GaN gate high electron mobility transistors (HEMTs), lateral metal-oxide-semiconductor (MOS) channel HEMTs, current aperture vertical electron transistors (CAVETs) and vertical U-shaped trench-gate MOS field-effect transistors (UMOSFETs). This study shows the advantages of vertical GaN power FETs over lateral GaN power HEMTs. These advantages include lower Ron,sp and smaller switching energy loss, especially at higher blocking voltages (1200 V). At 600 V, lateral P-GaN gate HEMTs are competitive with vertical power FETs. Vertical GaN CAVETs perform better than both lateral HEMTs and vertical UMOSFETs at both voltage ratings, benefiting from its lowest Ron*QG figure-of-merit.

Study of deep traps in AlGaN/GaN high-electron mobility transistors by electrical characterization and simulation

The localization of deep traps in normally-off AlGaN/GaN metal-oxide-semiconductor channel high-electron mobility transistors has been established by means of capacitance and current deep level transient spectroscopies (DLTS). Electrical simulations of the total current density between the drain and source contacts, the electron density, and the equipotential line distribution helped to understand the transport mechanisms into the device and to determine the zone probed by DLTS measurements. By changing the drain-source voltage in current DLTS or the reverse bias in capacitance DLTS, we demonstrated that we can choose to probe either the region below the gate or the region between the gate and drain electrodes. We could then see that defects related to reactive ion etching induced surface damage, expected to be formed during the gate recess process, were located only under the gate contact whereas native defects were found everywhere in the GaN layer. Thanks to this method of localization, we assigned a trap with an EC – 0.5 eV to ion etching induced damage.

Operation Up to 500 °C of Al0.85Ga0.15N/Al0.7Ga0.3N High Electron Mobility Transistors

AlGaN channel high electron mobility transistors (HEMTs) are the potential next step after GaN channel HEMTs, as the high aluminum content channel leads to an ultra-wide bandgap, higher breakdown field, and improved high temperature operation. Al0.85Ga0.15N/Al0.7Ga0.3N (85/70) HEMTs were operated up to 500 °C in ambient causing only 58% reduction of dc current relative to 25 °C measurement. The low gate leakage current contributed to high gate voltage operation up to +10 V under Vds = 10 V, with $\text{I}_{\mathrm{ ON}}/\text{I}_{\mathrm{ OFF}}$ ratios of $> 2 \times 10^{11}$ and 3 $\times \,\,10^{6}$ at 25 and 500 °C, respectively. Gate-lag measurements at 100 kHz and 10% duty cycle were ideal and only slight loss of pulsed current at high gate voltages was observed. Low interfacial defects give rise to high quality pulsed characteristics and a low subthreshold swing value of 80 mV/dec at room temperature. Herein is an analysis of AlGaN-channel HEMTs and their potential future for high power and high temperature applications.

Communication—Potential of the π-Gate InAs HEMTs for High-Speed and Low-Power Logic Applications

Composite channel (In0.65Ga0.35As/InAs/ In0.65Ga0.35As) high electron mobility transistors (HEMTs) with π-gate structure were investigated for high-speed and low-power logic applications. The conventional and tri-gate MESA HEMTs were compared with the π-gate device for evaluation. The π-gate device exhibited the best maximum transconductance value of 1584 mS/mm, on-state current of 332mA/mm, subthreshold swing (SS) of 78.1 mV/decade, and ION/IOFF ratio of 3 × 104 at VDS = 0.5 V at room temperature. These results indicated that the designed π-gate InAs devices improve the electrical characteristics of InAs HEMTs for high-speed and low-power logic applications.