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Title: Nanowire Radial Heterostructures as High Electron Mobility Transistors

Abstract

We report the rational synthesis of dopant-free GaN/AlN/AlGaN radial nanowire heterostructures and their implementation as high electron mobility transistors (HEMTs). The radial nanowire heterostructures were prepared by sequential shell growth immediately following nanowire elongation using metal-organic chemical vapor deposition (MOCVD). Transmission electron microscopy (TEM) studies reveal that the GaN/AlN/AlGaN radial nanowire heterostructures are dislocation-free single crystals. In addition, the thicknesses and compositions of the individual AlN and AlGaN shells were unambiguously identified using cross-sectional high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM). Transport measurements carried out on GaN/AlN/AlGaN and GaN nanowires prepared using similar conditions demonstrate the existence of electron gas in the undoped GaN/AlN/AlGaN nanowire heterostructures and also yield an intrinsic electron mobility of 3100 cm{sup 2}/Vs and 21,000 cm{sup 2}/Vs at room temperature and 5 K, respectively, for the heterostructure. Field-effect transistors fabricated with ZrO{sub 2} dielectrics and metal top gates showed excellent gate coupling with near ideal subthreshold slopes of 68 mV/dec, an on/off current ratio of 10{sup 7}, and scaled on-current and transconductance values of 500 mA/mm and 420 mS/mm. The ability to control synthetically the electronic properties of nanowires using band structure design in III-nitride radial nanowire heterostructures opens up new opportunities for nanoelectronics andmore » provides a new platform to study the physics of low-dimensional electron gases.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [2];  [1]
  1. Harvard University
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Shared Research Equipment Collaborative Research Center
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1003393
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nano Letters; Journal Volume: 6; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHEMICAL VAPOR DEPOSITION; DESIGN; DIELECTRIC MATERIALS; ELECTRON GAS; ELECTRON MOBILITY; ELECTRONS; ELONGATION; GASES; IMPLEMENTATION; MONOCRYSTALS; PHYSICS; SYNTHESIS; TRANSISTORS; TRANSMISSION ELECTRON MICROSCOPY; TRANSPORT

Citation Formats

Li, Yat, Xiang, Jie, Qian, Fang, Gradecak, Silvija, Wu, Yue, Yan, Hao, Blom, Douglas Allen, and Lieber, Charles M. Nanowire Radial Heterostructures as High Electron Mobility Transistors. United States: N. p., 2006. Web. doi:10.1021/nl060849z.
Li, Yat, Xiang, Jie, Qian, Fang, Gradecak, Silvija, Wu, Yue, Yan, Hao, Blom, Douglas Allen, & Lieber, Charles M. Nanowire Radial Heterostructures as High Electron Mobility Transistors. United States. doi:10.1021/nl060849z.
Li, Yat, Xiang, Jie, Qian, Fang, Gradecak, Silvija, Wu, Yue, Yan, Hao, Blom, Douglas Allen, and Lieber, Charles M. Sun . "Nanowire Radial Heterostructures as High Electron Mobility Transistors". United States. doi:10.1021/nl060849z.
@article{osti_1003393,
title = {Nanowire Radial Heterostructures as High Electron Mobility Transistors},
author = {Li, Yat and Xiang, Jie and Qian, Fang and Gradecak, Silvija and Wu, Yue and Yan, Hao and Blom, Douglas Allen and Lieber, Charles M.},
abstractNote = {We report the rational synthesis of dopant-free GaN/AlN/AlGaN radial nanowire heterostructures and their implementation as high electron mobility transistors (HEMTs). The radial nanowire heterostructures were prepared by sequential shell growth immediately following nanowire elongation using metal-organic chemical vapor deposition (MOCVD). Transmission electron microscopy (TEM) studies reveal that the GaN/AlN/AlGaN radial nanowire heterostructures are dislocation-free single crystals. In addition, the thicknesses and compositions of the individual AlN and AlGaN shells were unambiguously identified using cross-sectional high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM). Transport measurements carried out on GaN/AlN/AlGaN and GaN nanowires prepared using similar conditions demonstrate the existence of electron gas in the undoped GaN/AlN/AlGaN nanowire heterostructures and also yield an intrinsic electron mobility of 3100 cm{sup 2}/Vs and 21,000 cm{sup 2}/Vs at room temperature and 5 K, respectively, for the heterostructure. Field-effect transistors fabricated with ZrO{sub 2} dielectrics and metal top gates showed excellent gate coupling with near ideal subthreshold slopes of 68 mV/dec, an on/off current ratio of 10{sup 7}, and scaled on-current and transconductance values of 500 mA/mm and 420 mS/mm. The ability to control synthetically the electronic properties of nanowires using band structure design in III-nitride radial nanowire heterostructures opens up new opportunities for nanoelectronics and provides a new platform to study the physics of low-dimensional electron gases.},
doi = {10.1021/nl060849z},
journal = {Nano Letters},
number = 7,
volume = 6,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3μm)/ AlN(100nm)/Al{sub 2}O{sub 3} high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPEmore » reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.« less
  • This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98–2.56) × 10{sup 12 }cm{sup −2} eV{sup −1} is located at E{sub T} inmore » a range of (0.37–0.44) eV in the thin sample, while the trap state density of (2.3–2.92) × 10{sup 12 }cm{sup −2} eV{sup −1} is located at E{sub T} in a range of (0.33–0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.« less
  • This paper presents strain-effect transistors (SETs) based on flexible III-nitride high-electron-mobility transistors (HEMTs) through theoretical calculations. We show that the electronic band structures of InAlGaN/GaN thin-film heterostructures on flexible substrates can be modified by external bending with a high degree of freedom using polarization properties of the polar semiconductor materials. Transfer characteristics of the HEMT devices, including threshold voltage and transconductance, are controlled by varied external strain. Equilibrium 2-dimensional electron gas (2DEG) is enhanced with applied tensile strain by bending the flexible structure with the concave-side down (bend-down condition). 2DEG density is reduced and eventually depleted with increasing compressive strainmore » in bend-up conditions. The operation mode of different HEMT structures changes from depletion- to enchantment-mode or vice versa depending on the type and magnitude of external strain. The results suggest that the operation modes and transfer characteristics of HEMTs can be engineered with an optimum external bending strain applied in the device structure, which is expected to be beneficial for both radio frequency and switching applications. In addition, we show that drain currents of transistors based on flexible InAlGaN/GaN can be modulated only by external strain without applying electric field in the gate. The channel conductivity modulation that is obtained by only external strain proposes an extended functional device, gate-free SETs, which can be used in electro-mechanical applications.« less
  • A gate length of 0.2 μm InAlN/GaN high electron mobility transistor on SiC substrate is obtained with a maximum current gain cutoff frequency (f{sub T}) of 65.8 GHz and a maximum power gain cutoff frequency (f{sub max}) of 143.6 GHz. Lombardi model, which takes interface roughness scattering into consideration, has been introduced to model the transconductance (g{sub m}) degradation. The simulated g{sub m} and f{sub T} with Lombardi model are 69% and 58% lower than the ones without considering interface roughness scattering, respectively. Further analysis show experimental g{sub m}, gate capacitance (C{sub g}), and f{sub T} are consistent with results based on Lombardimore » model.« less
  • We have stressed AlGaN/GaN HEMTs (High Electron Mobility Transistors) under high-power and high-temperature DC conditions that resulted in various levels of device degradation. Following electrical stress, we conducted a well-established three-step wet etching process to remove passivation, gate and ohmic contacts so that the device surface can be examined by SEM and AFM. We have found prominent pits and trenches that have formed under the gate edge on the drain side of the device. The width and depth of the pits under the gate edge correlate with the degree of drain current degradation. In addition, we also found visible erosionmore » under the full extent of the gate. The depth of the eroded region averaged along the gate width under the gate correlated with channel resistance degradation. Both electrical and structural analysis results indicate that device degradation under high-power DC conditions is of a similar nature as in better understood high-voltage OFF-state conditions. The recognition of a unified degradation mechanism provides impetus to the development of a degradation model with lifetime predictive capabilities for a broad range of operating conditions spanning from OFF-state to ON-state.« less