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Journal ArticleDOI

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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Journal ArticleDOI
TL;DR: In this paper, a systematic study on the physics of avalanche instability and safe operating area (SOA) reliability in AlGaN/GaN high-electron-mobility transistor (HEMT) using submicroseconds pulse characterization, poststress degradation analysis, well-calibrated TCAD simulations, and failure analysis by scanning electron microscopy (SEM) and transmission electron microscope (TEM).
Abstract: This paper reports the very first systematic study on the physics of avalanche instability and safe operating area (SOA) reliability in AlGaN/GaN high-electron-mobility transistor (HEMT) using submicroseconds pulse characterization, poststress degradation analysis, well-calibrated TCAD simulations, and failure analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Impacts of electrical and thermal effects on SOA boundary and avalanche instability are investigated. Trap-induced cumulative nature of degradation is studied in detail. The root cause for avalanche instability in AlGaN/GaN HEMTs is investigated. Postfailure SEM, energy dispersive X-ray (EDX), and TEM analysis reveal distinct failure modes in the presence and absence of carrier trapping.

10 citations


Cites methods from "A Comprehensive Computational Model..."

  • ...To validate this argument, TCAD simulations were performed using setup explain in our earlier works [16]–[18]....

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Journal ArticleDOI
01 Sep 2021-Silicon
TL;DR: In this article, AlGaN/GaN High Electron Mobility Transistor (HEMT) with stacked passivation (Diamond/SiN) is proposed and investigated.
Abstract: In this paper, AlGaN/GaN High Electron Mobility Transistor (HEMT) with stacked passivation (Diamond/SiN) is proposed and investigated. The implementation of stacked passivation in HEMT has been shown to be effective in suppressing self-heating effect. Under the gate-terminal, the peak channel temperature of HEMT with stacked passivation is 384 K, whereas it is 393 K for conventional HEMT. The reduction of channel temperature in the proposed device is attributed to good heat-spreading via diamond. The thermal resistance (RTH) is extracted and it is found that RTH of proposed HEMT is 17% lower than that of the conventional HEMT. The transconductance of the proposed GaN-HEMT is also improved by 12%. Furthermore, the maximum drain current of 800 mA/mm at VGS = 0 V and VDS = 5 V is obtained for the proposed HEMT with a gate length of 0.25 μm. The proposed device is considered as one of the most attractive candidates for future high frequency and high-power applications over a wide range of operating temperatures.

10 citations

Journal ArticleDOI
TL;DR: In this paper, physical insights into the complex interplay of surface and buffer traps governing breakdown characteristics of AlGaN/GaN HEMTs are developed by well-calibrated TCAD simulations.
Abstract: Physical insights into the complex interplay of surface and (GaN) buffer traps governing breakdown characteristics of AlGaN/GaN HEMTs are developed by well-calibrated TCAD simulations. Impact of surface traps in correlation with 1) acceptor traps in case of Fe doping and 2) self-compensating traps (corresponding to C doping) in the GaN buffer on breakdown characteristics of AlGaN/GaN HEMTs is discussed. The explorations include defect-related traps as well as traps induced by intentional buffer doping by carbon/iron. The computational findings corroborate well with the experimentally observed electric field profile for devices with different buffer doping conditions. Developed insights have allowed to discuss the collective impact of surface as well as buffer traps on device design to improve breakdown characteristics.

10 citations


Cites background or methods from "A Comprehensive Computational Model..."

  • ...Source/drain Ohmic contacts are modeled as Schottky contact with lower work function and high n-type doping at the contact/GaN interface [18]....

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  • ...The computational framework used in this work is adopted from our earlier works in [9], [10], and [18] and is discussed in...

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Journal ArticleDOI
TL;DR: In this paper, a fabless design approach for the lateral optimization of a low voltage GaN power HEMT was proposed to minimize the figure-of-merit (RDS) for a targeted breakdown voltage.

9 citations

Journal ArticleDOI
TL;DR: In this paper, the degradation of the Schottky diode during both free-wheeling operation (high forward current injection) and reverse blocking state (high-voltage stress) was studied.
Abstract: Pulse reliability of AlGaN/GaN recessed Schottky diode is studied under transient overstress conditions, typically encountered in power converters. Degradation of the Schottky diode during both free-wheeling operation (high forward current injection) and reverse blocking state (high-voltage stress) is studied. Defect generation and the associated degradation were found to be uncorrelated with the nature of interface formed due to various surface treatments (at metal/GaN Schottky interface). During forward conduction, trap-assisted Schottky interface degradation is studied using on-the-fly ${I}$ – ${V}$ and ${C}$ – ${V}$ characterization under high-current stress. Under high-voltage stress, in the reverse blocking mode, mechanical strain evolution and defects generation were found to be dominant degradation modes, which are studied in detail using on-the-fly micro-Raman spectroscopy. Post-failure analysis was performed using SEM, TEM, and EDX, which reveals distinct failure signatures at the safe operating area (SOA) boundary. TCAD simulations are used to gain deeper physical insights into the observed degradation mechanism. Finally, a qualitative failure model, explaining the distinct failure physics, is presented based on observations and findings, from various electrical, optical, Raman spectroscopy, and electron microscopy investigations.

9 citations


Cites methods from "A Comprehensive Computational Model..."

  • ...To understand the underlying physics, diode structure was simulated using the well-calibrated TCAD setup explained in our earlier works [16]....

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References
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Journal ArticleDOI
TL;DR: In this article, the authors investigated the role of spontaneous and piezoelectric polarization on the carrier confinement at GaN/AlGaN and AlGaN/GaN interfaces.
Abstract: Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in heterostructures with AlGaN barrier layers of different Al concentrations (0.15

2,581 citations

Journal ArticleDOI
TL;DR: In this paper, a combination of high resolution x-ray diffraction, atomic force microscopy, Hall effect, and capacitance-voltage profiling measurements is used to calculate the polarization induced sheet charge bound at the AlGaN/GaN interfaces.
Abstract: Two dimensional electron gases in Al x Ga 12x N/GaN based heterostructures, suitable for high electron mobility transistors, are induced by strong polarization effects. The sheet carrier concentration and the confinement of the two dimensional electron gases located close to the AlGaN/GaN interface are sensitive to a large number of different physical properties such as polarity, alloy composition, strain, thickness, and doping of the AlGaN barrier. We have investigated these physical properties for undoped and silicon doped transistor structures by a combination of high resolution x-ray diffraction, atomic force microscopy, Hall effect, and capacitance‐voltage profiling measurements. The polarization induced sheet charge bound at the AlGaN/GaN interfaces was calculated from different sets of piezoelectric constants available in the literature. The sheet carrier concentration induced by polarization charges was determined

1,439 citations

Journal ArticleDOI
TL;DR: In this paper, the origin of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructure field effect transistors is examined theoretically and experimentally.
Abstract: The origin of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructure field effect transistors is examined theoretically and experimentally. Based on an analysis of the electrostatics, surface states are identified as an important source of electrons. The role of the polarization-induced dipole is also clarified. Experimental Hall data for nominally undoped Al0.34Ga0.66N/GaN structures indicate that ∼1.65 eV surface donors are the actual source of the electrons in the 2DEG, which forms only when the barrier thickness exceeds 35 A.

1,015 citations


"A Comprehensive Computational Model..." refers background in this paper

  • ...[24] suggested that polarization charges alone are not sufficient to explain 2DEG profile and proposed that sur-...

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Journal ArticleDOI
TL;DR: In this paper, an analytical expression for the electron and hole mobility in silicon based on both experimental data and modified Brooks-Herring theory of mobility was derived, which allows one to obtain electron and holes mobility as a function of concentration up to \sim 10^{20} cm-3 in an extended and continuous temperature range (250-500 K) within ± 13 percent of the reported experimental values.
Abstract: An analytical expression has been derived for the electron and hole mobility in silicon based on both experimental data and modified Brooks-Herring theory of mobility. The resulting expression allows one to obtain electron and hole mobility as a function of concentration up to \sim 10^{20} cm-3in an extended and continuous temperature range (250-500 K) within ± 13 percent of the reported experimental values.

886 citations


Additional excerpts

  • ...in [37] and Farahmand et al....

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Journal ArticleDOI
TL;DR: In this paper, the authors reported the highest reported microwave power density for undoped sapphire substrated AlGaN/GaN HEMT's on the same wafer.
Abstract: Surface passivation of undoped AlGaN/CaN HEMT's reduces or eliminates the surface effects responsible for limiting both the RF current and breakdown voltages of the devices. Power measurements on a 2/spl times/125/spl times/0.5 /spl mu/m AlGaN/GaN sapphire based HEMT demonstrate an increase in 4 GHz saturated output power from 1.0 W/mm [36% peak power-added efficiency (PAE)] to 2.0 W/mm (46% peak PAE) with 15 V applied to the drain in each case. Breakdown measurement data show a 25% average increase in breakdown voltage for 0.5 /spl mu/m gate length HEMT's on the same wafer. Finally, 4 GHz power sweep data for a 2/spl times/75/spl times/0.4 /spl mu/m AlGaN/GaN HEMT on sapphire processed using the Si/sub 3/N/sub 4/ passivation layer produced 4.0 W/mm saturated output power at 41% PAE (25 V drain bias). This result represents the highest reported microwave power density for undoped sapphire substrated AlGaN/GaN HEMT's.

752 citations


"A Comprehensive Computational Model..." refers background in this paper

  • ...Mitigation of RF dispersion [25], [26], drain and gate lag effects...

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