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 authors have experimentally demonstrated enhancement mode (e-mode) AlGaN/GaN high-electron-mobility transistor (HEMT) operation by integrating p-type high-kappa Ω(kappa ) based gate stack.
Abstract: In this paper, for the first time, we have experimentally demonstrated enhancement mode (e-mode) AlGaN/GaN high-electron-mobility transistor (HEMT) operation by integrating p-type high- $\kappa {\mathrm {Al}}_{x}{\mathrm {Ti}}_{1-x}$ O based gate stack. Concentration of Al in Al-Ti-O system was found to be a tuning parameter for the threshold voltage of GaN HEMTs. The high- $\kappa $ properties of ${\mathrm {Al}}_{x}{\mathrm {Ti}}_{1-x}$ O as a function of Al % are studied. Superiority of AlTiO over other p-oxides such as CuO and NiO x is proven statistically. Using the high- $\kappa $ and p-type AlTiO, in conjunction with a thinner AlGaN barrier under gate, 600-V e-mode GaN HEMTs are demonstrated with superior ON-state performance ( $\text{I}_{ \mathrm{\scriptscriptstyle ON}}~\sim ~400$ mA/mm and $\text{R}_{ \mathrm{\scriptscriptstyle ON}} ={8.9}\,\,\Omega $ -mm) and gate control over channel ( $\text{I}_{ \mathrm{\scriptscriptstyle ON}}/\text{I}_{ \mathrm{\scriptscriptstyle OFF}} = {10}^{{7}}$ , SS = 73 mV/dec, and gate leakage <200 nA/mm), beside improved safe operating area reliability.
26 citations
Cites methods from "A Comprehensive Computational Model..."
...A well calibrated simulation setup [26] was used with oxide bandgap taken similar to that of TiO2 (∼ 3....
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TL;DR: In this article, the impact of donor and acceptor states at the Schottky interface of fully recessed AlGaN/GaN Schittky diode is physically modeled using device TCAD and detailed experiments.
Abstract: In this paper, the impact of donor and acceptor states at the Schottky interface of fully recessed AlGaN/GaN Schottky diode is physically modeled using device TCAD and detailed experiments. This allowed us to develop physical insights into recessed AlGaN/GaN diode’s reverse breakdown, reverse leakage, and ON-state performance as a function of interface states and provided design guidelines to engineer fully recessed AlGaN/GaN Schottky diode for the maximum reverse breakdown and least reverse leakage without compromising its ON-state performance. It has been observed that donor states are responsible for high reverse leakage and reduced breakdown performance in Schottky diodes. On the other hand, the presence of acceptor states at the interface improves the diode leakage and breakdown voltage. Experiments involve a number of dry and wet surface treatments to: 1) validate computational findings and 2) find ways to cure or passivate donor states affected Schottky interface/recessed region. The introduction of acceptor traps at the Schottky interface has been proposed and experimentally verified using the Fluorine implant to cure donor state-affected Schottky interface, which improves the breakdown and reverse leakage characteristics significantly.
18 citations
Cites methods from "A Comprehensive Computational Model..."
...Sample without F-plasma shows an abrupt rise in reverse leakage and abrupt fall in breakdown voltage, above a certain donor trap concentration, as predicted using TCAD earlier....
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...2(a), was studied using well-calibrated device TCAD [27]–[29]....
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...To confirm the physical insight developed using TCAD studies and its’ impact on device behavior, the surface treatment with Fluorine plasma is carried out....
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...The experimental findings here corroborate well with TCAD predictions when acceptor states were introduced at the interface, which confirms that the donor and acceptor states may coexist and their relative concentration decides the device’s breakdown and leakage characteristics....
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...These experimental results, which are elaborated in the following, confirm the role of donor states at the anode–semiconductor interface, as predicted in the earlier section using device TCAD....
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TL;DR: In this paper, the distinct failure mechanisms and insights on device degradation of AlGaN/GaN high electron mobility transistors (HEMTs) under electrostatic discharge (ESD) stress conditions are reported.
Abstract: This article reports the distinct failure mechanisms and insights on device degradation of AlGaN/GaN high electron mobility transistors (HEMTs) under electrostatic discharge (ESD) stress conditions. The role of device surface, MESA isolation, and gate Schottky junction in defining the degradation type is discovered. Premature breakdown at the MESA Schottky junction and dislocation induced failure in the active region and their consequences on ESD robustness are reported. Physical mechanisms responsible for snapback instability in transmission line pulsing (TLP) characteristics are discussed. Change in device failure from soft to hard with pulsewidth is revealed. Finally, the role of contact resistivity, surface diffusion, and channel electric field and its fringing effect at contacts are analyzed in context to ESD failure of AlGaN/GaN HEMTs. Various stages of device degradation during TLP stress are captured on-the-fly using high-resolution (HR) optical microscopy and high-speed Si charge-coupled device (CCD) detector. Postdevice failure, damaged regions are analyzed using transmission electron microscopy and scanning electron microscopy together with in situ energy-dispersive X-ray spectroscopy to probe details of failure mechanisms involved. Finally, based on the learning from this article, design guidelines for an ESD robust HEMT are proposed.
14 citations
TL;DR: In this article, the authors proposed a quantitative explanation for this behavior, attributing it to the charging/discharging dynamics of carbon (C)-related buffer traps, which is supported by calibrated 2-D numerical simulations.
Abstract: Dynamic ${R}_{\mathrm{\scriptscriptstyle {ON}}}$ dispersion due to buffer traps is a well-known issue of GaN power high electron mobility transistors (HEMTs), critically impacting their performance and stability. Several works show that the dynamic ${R}_{\mathrm{\scriptscriptstyle {ON}}}$ reaches a maximum for some OFF-state drain–source voltage ( ${V}_{\text{DS},{\mathrm{\scriptscriptstyle OFF}}}$ ) value typically in the range of several hundred volts and then partially recovers to smaller values. In this work, we propose a quantitative explanation for this behavior, attributing it to the charging/discharging dynamics of carbon (C)-related buffer traps. We characterize the dynamic ${R}_{\mathrm{\scriptscriptstyle {ON}}}$ in packaged p-GaN gate AlGaN/GaN HEMTs with a custom measurement setup. We find that in these devices, the relative ${R}_{\mathrm{\scriptscriptstyle {ON}}}$ increase reaches a maximum of 60% for ${V}_{\text {DS}, {\mathrm{\scriptscriptstyle {OFF}}}} \approx 100$ –200 V, partially recovering to about 30% as ${V}_{\text {DS}, {\mathrm{\scriptscriptstyle {OFF}}}}$ is raised to 500 V. We ascribe this behavior to the partial neutralization of C-related acceptor traps in the buffer due to trapping of holes produced by a high-field generation mechanism. This explanation is supported by calibrated 2-D numerical simulations, that successfully reproduce the experimentally observed ${R}_{\mathrm{\scriptscriptstyle {ON}}}$ reduction only when including a hole generation mechanism.
12 citations
TL;DR: In this paper, an optimized normally off GaN-based metal-insulator-semiconductor field effect transistor (MISFET) with an electrode-connected p-i-n diode inserted in the buffer layer was presented.
Abstract: This paper presents an optimized normally off GaN-based metal–insulator–semiconductor field-effect transistor (MISFET) with an electrode-connected p-i-n diode inserted in the buffer layer, i.e., EC-PIN MISFET, and in which the substrate is removed for the suppression of the vertical leakage current. We provide the simulation results of the proposed MISFET. The EC-PIN MISFET with $\text{L}_{\textsf {gd}}= \textsf {6} ~\mu \text{m}$ presents an excellent breakdown voltage of 1400 V, which attributes to the improvement of electric field distribution in the gate–drain region and the suppression of leakage current by EC-PIN. In addition, the specific on resistance of 0.64 $\text{m}\Omega \cdot \textsf {cm}^{\textsf {2}}$ and Baliga’s figure of merit of 3.08 GW $\,\cdot \,\textsf {cm}^{-\textsf {2}}$ are achieved in the optimized EC-PIN MISFET, indicating a good tradeoff between the specific on resistance and breakdown voltage.
10 citations
References
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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
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
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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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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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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