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.
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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 article, the authors focused on the relationship between donor parameters (concentration and energy level) and electron density in the channel in AlGaN/GaN heterostructures.
Abstract: As an important step in understanding trap-related mechanisms in AlGaN/GaN transistors, the physical properties of surface states have been analyzed through the study of the transfer characteristics of a MISFET. This letter focused initially on the relationship between donor parameters (concentration and energy level) and electron density in the channel in AlGaN/GaN heterostructures. This analysis was then correlated to dc and pulsed measurements of the transfer characteristics of a MISFET, where the gate bias was found to modulate either the channel density or the donor states. Traps-free and traps-frozen TCAD simulations were performed on an equivalent device to capture the donor behavior. A donor concentration of 1.14×1013 cm-2 with an energy level located 0.2 eV below the conduction band edge gave the best fit to measurements. With the approach described here, we were able to analyze the region of the MISFET that corresponds to the drift region of a conventional HEMT.
38 citations
"A Comprehensive Computational Model..." refers background in this paper
...charge density and AlGaN/GaN HEMT device characteristics [15]; however, the study is limited to surface traps only....
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...have attempted to model polarization charge [6]–[8], [10], [13]– [15], [17], these works limit the polarization effect inside the AlGaN layer by adding a+σ charge at the AlGaN/GaN interface and an equivalent −σ charge at the AlGaN top surface....
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TL;DR: In this paper, the gate leakage current in III-N high-electron mobility transistors is studied using temperature-dependent currentvoltage and capacitance-voltage characteristics.
Abstract: Dependence of gate leakage current on Al mole fraction of AlGaN/GaN high-electron mobility transistors (HEMTs) is studied using temperature-dependent current-voltage and capacitance-voltage characteristics. The reverse leakage current is mostly dominated by Poole-Frenkel (PF) emission in the structures used in this brief. However, it is observed that at higher mole fractions, due to higher electric field across the barrier, Fowler-Nordheim (FN) tunneling also contributes to the gate leakage current even at room temperature and above. An expression for critical temperature below which FN tunneling component becomes comparable with or more than PF emission component is presented. It is concluded that the dominant gate leakage mechanisms in III-N HEMTs are dependent on mole fraction of the barrier material and the temperature. However, the relative strengths of PF emission and FN tunneling are also influenced by various process-dependent parameters.
37 citations
"A Comprehensive Computational Model..." refers background in this paper
...Earlier works suggest Fowler Nordheim (FN) tunneling with Poole-Frenkel emission to be responsible for leakage under reverse bias condition [40], while forward bias current is primarily due to thermionic emission....
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TL;DR: In this paper, a drain-extended FinFET was proposed for highvoltage and high-speed applications, and a 2 × better RON versus VBD tradeoff was shown from technology computer-aided design simulations for the proposed device.
Abstract: A novel drain-extended FinFET device is proposed in this letter for high-voltage and high-speed applications. A 2 × better RON versus VBD tradeoff is shown from technology computer-aided design simulations for the proposed device, when compared with a conventional device option. Moreover, a device design and optimization guideline has been provided for the proposed device.
24 citations
TL;DR: In this paper, the impact of scaling the depth of the shallow trench isolation (STI) region, underneath the gate-to-drain overlap, on the STI drain-extended metal-oxide-semiconductor (DeMOS) mixed-signal performance and hot-carrier behavior is systematically investigated.
Abstract: The impact of scaling the depth of the shallow trench isolation (STI) region, underneath the gate-to-drain overlap, on the STI drain-extended metal-oxide-semiconductor (DeMOS) mixed-signal performance and hot-carrier behavior is systematically investigated in this work. For the first time, we discuss a dual-STI process for input/output applications. Furthermore, the differences in the hot-carrier behavior of various drain-extended devices are studied under the on- and off-states. We found that the non-STI DeMOS devices are quite prone to failure when compared with the STI DeMOS devices in both the on- and off- states. We introduced a more accurate way of predicting hot-carrier degradation in these types of devices in the on-state. We show that scaling the depth of the STI underneath the gate is the key for improving both the mixed-signal and hot-carrier reliability performances of these devices.
19 citations
Additional excerpts
...ness and performance [4], [5]....
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TL;DR: In this paper, the longitudinal optical phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect measurements and also from Infrared (IR) spectroscopy and Raman Spectroscopy.
Abstract: The longitudinal optical (LO) phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect measurements and also from Infrared (IR) spectroscopy and Raman spectroscopy. The Hall effect measurements on AlGaN/GaN heterostructures grown by MOCVD have been carried out as a function of temperature in the range 1.8-275 K at a fixed magnetic field. The IR and Raman spectroscopy measurements have been carried out at room temperature. The experimental data for the temperature dependence of the Hall mobility were compared with the calculated electron mobility. In the calculations of electron mobility, polar optical phonon scattering, ionized impurity scattering, background impurity scattering, interface roughness, piezoelectric scattering, acoustic phonon scattering and dislocation scattering were taken into account at all temperatures. The result is that at low temperatures interface roughness scattering is the dominant scattering mechanism and at high temperatures polar optical phonon scattering is dominant.
17 citations