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, a surface passivation scheme using p-type Al 0.5Ti0.5O (AlTiO), which is deposited over SiN x passivation (or GaN cap), was proposed to improve the dynamic performance of the device.
Abstract: The underlying mechanism responsible for the unique dynamic ON-resistance behavior is unified by demonstrating the presence of critical drain stress voltage, above which dynamic ON-resistance increases significantly, in different gate stacks. Metal–insulator–semiconductor (MIS)- and Schottky-gated HEMTs show similar dependence of critical voltage on various parameters, which establishes that gate-stack design has negligible impact on the observed phenomena. Furthermore, using the physical insights developed, this work proposes a novel surface passivation scheme to improve the dynamic performance of the device. The proposed surface passivation scheme uses p-type Al0.5Ti0.5O (AlTiO), which is deposited over SiN x passivation (or GaN cap), and is shown to be an effective tool in improving the dynamic ON-resistance of the device by modulating the electric field in the GaN buffer. The proposed passivation scheme has avoided the critical voltage to appear for the entire drain stress voltage, stress time, and substrate bias range. Detailed computational analysis in conjunction with electroluminescence (EL) and photoluminescence (PL) studies revealed an electric field redistribution due to the p-type nature of AlTiO deposited over the surface passivation/capping layer, which is responsible for relaxed electric field profile in GaN buffer and observed improvement in dynamic performance. Besides, the new observations have further helped to understand the interplay between surface conditions and GaN buffer, defining its collective role in governing the dynamic performance of GaN HEMTs. Finally, various findings and the proposal in this work have been validated for buffers having higher carbon doping and devices with p-type AlTiO deposited over GaN cap instead of in situ SiN x cap.
5 citations
TL;DR: In this article, the authors presented a breakdownenhanced AlGaN/GaN MISFET with a source-connected P-buried layer combined with field plates (SC-PBL FPs) for a gate-drain spacing of 6μm.
5 citations
TL;DR: In this article, the mobility of the two dimensional electron gas influenced by the optical phonons in Al2O3/AlGaN/AlN/GaN heterostructures is investigated based on the theory of Lei-Ting force balance equation.
5 citations
01 Sep 2017
TL;DR: In this article, the influence of traps on avalanche breakdown of AlGaN/GaN HEMTs is discussed, and the impact of surface and bulk traps on breakdown voltage and device scaling is discussed with associated physics.
Abstract: For the very first time, influence of traps on avalanche breakdown of AlGaN/GaN HEMTs is discussed. Impact of surface and bulk traps on breakdown voltage and device scaling is discussed with associated physics. Surface trap's were found to cause distinct breakdown characteristics with breakdown point varying from gate edge to drain edge, depending on nature, type and concentration. Buffer traps too influence the electric field near gate edge and leakage through the device, thereby affecting breakdown voltage accordingly.
5 citations
Cites background or methods from "A Comprehensive Computational Model..."
...On further increasing the buffer trap concentration, a hole leakage path is formed through the parasitic hole channel on the GaN/AlN interface which is present due to polarization effect [2]....
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...SIMULATION SETUP Simulation setup used in this study is based on the modelling approach as defined in our earlier work [2], with an addition of impact ionization model according to the Chynoweth law [6] with critical field values set for GaN at 3 x 10(6) V/cm....
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...Effect of these traps on device’s DC and RF performance parameters is well explored [2]–[4], however, its impact on breakdown behavior of the device is not well understood....
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TL;DR: In this article, a double-gate double-channel device design is proposed and analyzed for MIS-HEMTs, and a numerical simulation of the design of the double gate double channel is performed.
Abstract: In this work, we have performed numerical simulations of normally-off AlGaN/GaN recessed Metal–Insulator-Semiconductor or MIS-HEMTs. A double-gate double-channel device design is proposed and analy...
4 citations
Cites background or methods from "A Comprehensive Computational Model..."
...Additionally, in order to obtain the same current density as the experimental data, realistic concentrations of fixed charges, donor and acceptor-traps are introduced in accordance with the data reported in the literature [13,14,16,18]....
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...Also it has been shown that the presence of AlN layer increases the product of charge density and mobility in the channel [14]....
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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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