A Comprehensive Computational Modeling Approach for AlGaN/GaN HEMTs
TL;DR: In this paper, the impact of surface and bulk traps on two-dimensional electron gas, device characteristics, and gate leakage is accounted for, and a new approach to accurately model the forward gate leakage in Schottky gate devices is proposed.
Abstract: This paper for the first time presents a comprehensive computational modeling approach for AlGaN/GaN high electron mobility transistors. Impact of the polarization charge at different material interfaces on the energy band profile as well as parasitic charge across the epitaxial stack is modeled and studied. Furthermore, impact of surface and bulk traps on two-dimensional electron gas, device characteristics, and gate leakage is accounted in this paper. For the first time, surface states modeled as donor type traps were correlated with gate leakage. Moreover, a new approach to accurately model the forward gate leakage in Schottky gate devices is proposed. Finally, impact of lattice and carrier heating is studied, while highlighting the relevance of carrier heating, lattice heating, and bulk traps over the device characteristics. In addition to this, modeling strategy for other critical aspects like parasitic charges, quantum effects, S/D Schottky contacts, and high field effects is presented.
Citations
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TL;DR: In this article, the effect of carbon-doping in GaN buffer on the performance of AlGaN/GaN HEMTs is discussed. But the authors focus on the degradation of the breakdown voltage, leakage current, sheet charge density, and dynamic ONresistance.
Abstract: Physics behind the improvement in breakdown voltage of AlGaN/GaN HEMTs with carbon-doping of GaN buffer is discussed. Modeling of carbon as acceptor traps and self-compensating acceptor/donor traps is discussed with respect to their impact on avalanche breakdown. Impact of carbon behaving as a donor as well as acceptor traps on electric field relaxation and avalanche generation is discussed in detail to establish the true nature of carbon in GaN that delays the avalanche action. This understanding of the behavior of carbon-doping in GaN buffer is then utilized to discuss design parameters related to carbon doped buffer. Design parameters such as undoped channel thickness and relative trap concentration induced by carbon-doping are discussed with respect to the performance metrics of breakdown voltage, leakage current, sheet charge density, and dynamic ON-resistance.
54 citations
Cites background or methods from "A Comprehensive Computational Model..."
...These surface traps are taken to compensate hole density on surface [14] and the concentration value is selected so as to achieve the required nS and the gate leakage [14]....
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...This hole density is attributed to polarization charges present at the GaN/AlN interface and is discussed in detail in our earlier work [14]....
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...An unintentional (n-type) doping of 1×1015 cm−3 is considered in the GaN buffer [14]....
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...reported in [14]....
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...Modeling aspects related to channel transport, mobility, and sheet charge density (nS) were calibrated with experimental data according to framework described in our earlier work [14]....
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TL;DR: In this paper, the breakdown behavior of drain-connected field plate-based GaN HEMTs was investigated and the proposed vertical and dual-field-plate designs were proposed to alleviate the channel electric field by uniformly distributing it vertically into the buffer region.
Abstract: TCAD studies are performed to develop physical insights into the breakdown behavior of drain-connected field plate-based GaN HEMTs. Using the developed insights, to mitigate the performance bottleneck caused by the lateral drain-connected field plate design, we have proposed novel vertical-field-plate designs. The proposed designs alleviate the channel electric field by uniformly distributing it vertically into the GaN buffer region. As a result, the proposed vertical and dual-field-plate design offer ${2} \times $ and ${3} \times $ improvements in breakdown voltage, respectively, compared with the design without field plate. Similarly, compared with a design with a lateral field plate, a 50% improvement in the breakdown voltage was seen with dual-field-plate architecture. RF power amplifier (PA) performance extracted using load-pull simulations demonstrates an improved RF PA linearity at higher drain bias, improved output power, efficiency, and PA gain for HEMTs with dual- and vertical-field-plate designs.
35 citations
Cites methods from "A Comprehensive Computational Model..."
...Electron mobility, contact resistance, surface trap charges, and so on were calibrated with experimental data, which has been elaborated in our earlier work [23]....
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...A well-calibrated Technology CAD setup, as described and used in our earlier works [23]–[25], has been used here....
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TL;DR: In this paper, a modified Si-doping profile in the GaN buffer is proposed to lower the Cdoping concentration near GaN channel to mitigate the adverse effects of acceptor traps.
Abstract: In part I of this paper, we developed physical insights into the role and impact of acceptor and donor traps—resulting from C-doping in GaN buffer—on avalanche breakdown in AlGaN/GaN HEMT devices. It was found that the donor traps are mandatory to explain the breakdown voltage improvement. In this paper, silicon doping is proposed and explored as an alternative to independently engineer donor trap concentration and profile. Keeping in mind the acceptor and donor trap relative concentration requirement for achieving higher breakdown buffer, as depicted in part I of this paper, silicon & carbon codoping of GaN buffer is proposed and explored in this paper. The proposed improvement in breakdown voltage is supported by physical insight into the avalanche phenomena and role of acceptor/donor traps. GaN buffer design parameters and their impact on breakdown voltage as well as leakage current are presented. Finally, a modified Si-doping profile in the GaN buffer is proposed to lower the C-doping concentration near GaN channel to mitigate the adverse effects of acceptor traps in GaN buffer.
31 citations
Cites background or methods from "A Comprehensive Computational Model..."
...electron density, mobility and related transport parameters are calibrated with the experimental data as per the framework discussed in our earlier work [23]....
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...the one described in our earlier work [23], and is discussed in...
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TL;DR: In this paper, the authors show that the RON increase and decrease during stress and recovery experiments in carbon-doped AlGaN/GaN power metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs).
Abstract: RON degradation due to stress in GaN-based power devices is a critical issue that limits, among other effects, long-term stable operation. Here, by means of 2-D device simulations, we show that the RON increase and decrease during stress and recovery experiments in carbon-doped AlGaN/GaN power metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) can be explained with a model based on the emission, redistribution, and retrapping of holes within the carbon-doped buffer (“hole redistribution” in short). By comparing simulation results with front- and back-gating OFF-state stress experiments, we provide an explanation for the puzzling observation of both stress and recovery transients being thermally activated with the same activation energy of about 0.9 eV. This finds a straightforward justification in a model in which both RON degradation and recovery processes are limited by hole emission by dominant carbon-related acceptors that are energetically located at about 0.9 eV from the GaN valence band.
30 citations
References
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TL;DR: In this paper, a comprehensive study of the transport dynamics of electrons in the ternary compounds, Al/sub x/Ga/sub 1-x/N and In/sub ng/g/ng/s/n g/n/g n/g 1.x/n, is presented, which includes all of the major scattering mechanisms.
Abstract: We present a comprehensive study of the transport dynamics of electrons in the ternary compounds, Al/sub x/Ga/sub 1-x/N and In/sub x/Ga/sub 1-x/N. Calculations are made using a nonparabolic effective mass energy band model. Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab initio band models. The effects of alloy scattering on the electron transport physics are examined. The steady state velocity field curves and low field mobilities are calculated for representative compositions of these alloys at different temperatures and ionized impurity concentrations. A field dependent mobility model is provided for both ternary compounds AlGaN and InGaN. The parameters for the low and high field mobility models for these ternary compounds are extracted and presented. The mobility models can be employed in simulations of devices that incorporate the ternary III-nitrides.
421 citations
"A Comprehensive Computational Model..." refers methods in this paper
...In this work these parameters are adopted from [38], which were extracted using Monte Carlo simulations and offer good agreement with mobility measured....
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...[38], which is adopted in this work while using model parameters extracted from Monte Carlo simulations [38]:...
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...Model given below, as adopted from [38], reasonably approximates the low field mobility...
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TL;DR: In this paper, a novel heterojunction AlGaN/AlN/GaN high-electron mobility transistor (HEMT) is discussed, where the insertion of the very thin AlN interfacial layer (/spl sim/1 nm) maintains high mobility at high sheet charge densities by increasing the effective /spl Delta/E/sub C/ and decreasing alloy scattering.
Abstract: In this letter, a novel heterojunction AlGaN/AlN/GaN high-electron mobility transistor (HEMT) is discussed. Contrary to normal HEMTs, the insertion of the very thin AlN interfacial layer (/spl sim/1 nm) maintains high mobility at high sheet charge densities by increasing the effective /spl Delta/E/sub C/ and decreasing alloy scattering. Devices based on this structure exhibited good DC and RF performance. A high peak current 1 A/mm at V/sub GS/=2 V was obtained and an output power density of 8.4 W/mm with a power added efficiency of 28% at 8 GHz was achieved.
418 citations
TL;DR: AlGaN-GaN power high-electron mobility transistors (HEMTs) with 600-V breakdown voltage are fabricated and demonstrated as switching power devices for motor drive and power supply applications.
Abstract: AlGaN-GaN power high-electron mobility transistors (HEMTs) with 600-V breakdown voltage are fabricated and demonstrated as switching power devices for motor drive and power supply applications. The fabricated power HEMT realized the high breakdown voltage by optimized field plate technique and the low on-state resistance of 3.3 m/spl Omega/cm/sup 2/, which is 20 times lower than that or silicon MOSFETs, thanks to the high critical field of GaN material and the high mobility in 2DEG channel. The fabricated devices also demonstrated the high current density switching of 850 A/cm/sup 2/ turn-off. These results show that AlGaN-GaN power-HEMTs are one of the most promising candidates for future switching power device for power electronics applications.
409 citations
"A Comprehensive Computational Model..." refers methods in this paper
...The simulation studies in [10] and [11] have presented effect of gate connected [10] and source connected [11] field plates on the breakdown voltage of the device, which was further extended by Saito et al....
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...on-resistance (Vbr-Ron ) trade-off [11]....
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TL;DR: In this paper, the advantages and limitations of the current-transient methods used for the study of the deep levels in GaN-based high-electron mobility transistors (HEMTs), by evaluating how the procedures adopted for measurement and data analysis can influence the results of the investigation.
Abstract: This paper critically investigates the advantages and limitations of the current-transient methods used for the study of the deep levels in GaN-based high-electron mobility transistors (HEMTs), by evaluating how the procedures adopted for measurement and data analysis can influence the results of the investigation. The article is divided in two parts within Part I. 1) We analyze how the choice of the measurement and analysis parameters (such as the voltage levels used to induce the trapping phenomena and monitor the current transients, the duration of the filling pulses, and the method used for the extrapolation of the time constants of the capture/emission processes) can influence the results of the drain current transient investigation and can provide information on the location of the trap levels responsible for current collapse. 2) We present a database of defects described in more than 60 papers on GaN technology, which can be used to extract information on the nature and origin of the trap levels responsible for current collapse in AlGaN/GaN HEMTs. Within Part II, we investigate how self-heating can modify the results of drain current transient measurements on the basis of combined experimental activity and device simulation.
320 citations
TL;DR: On montre, en generalisant l'equation d'etat du gaz d'electrons afin d'inclure les effets des gradients de densite, que cette description peut etre etendue pour inclure le comportement quantique observe dans des couches d' inversion forte.
Abstract: The diffusion-drift description of electrons and holes in a semiconductor is frequently used to obtain a detailed understanding of the physics and engineering of semiconductor devices. We show that, by generalizing the equation of state of the electron gas to include density-gradient dependences, this standard description can be extended to describe much of the quantum-mechanical behavior exhibited by strong inversion layers.
316 citations
"A Comprehensive Computational Model..." refers methods in this paper
...to that of Schrödinger equation and to have acceptable numerical cost, density gradient quantum correction model [22], [23] is deployed in this work, while using Schrödinger equation to...
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