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16 Jul 2007

Volume 91, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 033106 (2007); http://dx.doi.org/10.1063/1.2757609 (3 pages)

S. Ingole, P. Aella, Sean J. Hearne, and S. T. Picraux
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Population inversion by resonant tunneling in quantum wells

Giacomo Scalari, Romain Terazzi, Marcella Giovannini, Nicolas Hoyler, and Jérôme Faist

Appl. Phys. Lett. 91, 032103 (2007); http://dx.doi.org/10.1063/1.2759271 (3 pages) | Cited 16 times

Online Publication Date: 18 July 2007

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A terahertz quantum cascade laser based on a single quantum well active region is reported. It displays laser action at 3.74 THz with low threshold current densities around 30 A/cm2. Analysis of the optical and electrical characteristics and their comparison with a transport model based on a density matrix approach clearly demonstrate the role of resonant tunneling for both injection and extraction of the electrons from the upper and lower states of the laser transition.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

SiGe double barrier resonant tunneling diodes on bulk SiGe substrates with high peak-to-valley current ratio

S. Tsujino, N. Usami, A. Weber, G. Mussler, V. Shushunova, D. Grützmacher, Y. Azuma, and K. Nakajima

Appl. Phys. Lett. 91, 032104 (2007); http://dx.doi.org/10.1063/1.2756363 (3 pages) | Cited 3 times

Online Publication Date: 19 July 2007

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The authors present high-quality p-type SiGe double barrier resonant tunneling diodes obtained from bulk SiGe substrates grown by the multicomponent zone-melting method and by the layer deposition with molecular beam epitaxy. Devices exhibit a high peak-to-valley current ratio up to 8.8 at 4.2 K and a negative differential resistance up to 340 K. The result demonstrates that bulk SiGe substrates have a clear potential impact for fabricating high-performance SiGe heterostructure devices based on quantum transport.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
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Long range and selective coupler for superconducting flux qubits

Hayato Nakano, Kosuke Kakuyanagi, Masahito Ueda, and Kouichi Semba

Appl. Phys. Lett. 91, 032501 (2007); http://dx.doi.org/10.1063/1.2756275 (3 pages) | Cited 3 times

Online Publication Date: 16 July 2007

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The authors propose a qubit-qubit coupling scheme for superconducting flux quantum bits (qubits), where quantized Josephson junction resonator and microwave irradiation are utilized. The junction is used as a tunable inductance controlled by changing the bias current flowing through the junction, and thus the circuit works as a tunable resonator. This enables them to make any qubits interact with the resonator. Entanglement between two of many qubits whose level splittings satisfy some conditions is formed by microwave irradiation causing a two-photon Rabi oscillation. Since the size of the resonator can be as large as submillimeters and qubits interact with it via mutual inductance, their scheme makes it possible to construct a quantum gate involving remote qubits.
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03.67.Lx Quantum computation architectures and implementations
03.67.Mn Entanglement measures, witnesses, and other characterizations
85.25.Cp Josephson devices

Charge-order breaking and ferromagnetism in La0.4Ca0.6MnO3 nanoparticles

C. L. Lu, S. Dong, K. F. Wang, F. Gao, P. L. Li, L. Y. Lv, and J.-M. Liu

Appl. Phys. Lett. 91, 032502 (2007); http://dx.doi.org/10.1063/1.2753749 (3 pages) | Cited 42 times

Online Publication Date: 17 July 2007

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La0.4Ca0.6MnO3 nanoparticles of grain size as small as ∼ 20 nm are prepared and their magnetic behaviors are investigated in order to understand the size effect of the charge ordering in manganites. The highly stable charge-ordered state can be significantly suppressed upon reduction of the grain size down to nanometer scale, while the ferromagnetism is enhanced. The magnetic phase separation due to the competition between ferromagnetic state and charge-ordered state as well as the surface spin disordering is responsible for the spin-glass-like state at low temperature.
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75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.10.Nr Spin-glass and other random models
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Large remanent polarization in ferroelectric BiFeO3–PbTiO3 thin films on Pt/Si substrates

Mikael A. Khan, Tim P. Comyn, and Andrew J. Bell

Appl. Phys. Lett. 91, 032901 (2007); http://dx.doi.org/10.1063/1.2759256 (3 pages) | Cited 24 times

Online Publication Date: 18 July 2007

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Bismuth ferrite–lead titanate thin films in the region of the morphotropic phase boundary, with compositions of (1−x)BiFeO3–xPbTiO3 (0.3<x<0.5), were prepared by pulsed laser deposition on Pt/Si substrates. X-ray diffraction confirmed the formation of pure perovskite phase at a substrate temperature of 565 °C under 75 mTorr of oxygen. The films exhibit remanent polarizations with 2Pr up to 100 μC cm−2 for a field amplitude of 820 kV cm−1 and switchable polarization up to 80 μC cm−2.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Correlation between number of ferroelectric variants and coercive field of lead ziconate titanate single crystals

S. Choudhury, L. Q. Chen, and Y. L. Li

Appl. Phys. Lett. 91, 032902 (2007); http://dx.doi.org/10.1063/1.2759274 (3 pages) | Cited 7 times

Online Publication Date: 18 July 2007

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Understanding the magnitude of coercive fields, the external electric field that results in zero net polarization, has been a long-standing problem for ferroelectrics. The authors studied the switching and coercive fields using a combination of the continuum phase field approach, microelasticity, and electrostatics. While the values of coercive fields predicted from the phenomenological thermodynamic theory assuming a single ferroelectric domain or the theory of nucleation are at least one order of magnitude too high compared to those measured experimentally, the predictions incorporating structural inhomogeneities show remarkably good agreement with experimental measurements, revealing the critical role of multidomain/variants in polarization switching.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Low temperature perovskite crystallization of 70%PbMg1/3Nb2/3O3–30%PbTiO3 thin films deposited by sputtering and their electrical performance evaluation

M. Detalle, D. Rémiens, G. Wang, P. Roussel, and B. Dkhil

Appl. Phys. Lett. 91, 032903 (2007); http://dx.doi.org/10.1063/1.2749859 (3 pages) | Cited 3 times

Online Publication Date: 19 July 2007

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PbMg1/3Nb2/3O3–PbTiO3 films were deposited on silicon by sputtering, followed by an annealing treatment. The authors demonstrate the pure perovskite phase may be obtained at very low temperature (400 °C) without any pyrochlore phase. The existence of an interfacial layer of Pb2Nb2O7 structure is evidenced. They suggest that such phase serves as seed layer which promotes the apparition of the perovskite phase. The permittivity of the films annealed at 450 °C is high (600) compared to most dielectric materials obtained at this temperature. The electromechanic properties (d33 = 50 pC/m) are also suitable for microelectromechanical system applications with a thermal treatment compatible with the above integrated circuits.
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68.55.A- Nucleation and growth
73.61.-r Electrical properties of specific thin films
64.70.K- Solid-solid transitions
81.15.Cd Deposition by sputtering
77.22.Ch Permittivity (dielectric function)
81.40.Gh Other heat and thermomechanical treatments

Aging effect and large recoverable electrostrain in Mn-doped KNbO3-based ferroelectrics

Zuyong Feng and Xiaobing Ren

Appl. Phys. Lett. 91, 032904 (2007); http://dx.doi.org/10.1063/1.2756355 (3 pages) | Cited 20 times

Online Publication Date: 19 July 2007

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KNbO3-based ferroelectrics have drawn much attention in recent years owing to their good piezoelectric performance among Pb-free piezoelectrics. However, little is known about the aging effect of these materials. In the present study, the authors systematically studied the aging effect of a Mn-doped (K0.99Li0.01)(Nb0.65Ta0.35)O3 ceramic with an aim to find an aging-induced recoverable electrostrain effect based on a reversible domain switching mechanism. They found that aging in the ferroelectric state made the otherwise normal hysteresis loop into a double loop, and more interestingly the aged sample demonstrated a large recoverable electrostrain of 0.125% at 4 kV/mm in an unpoled state. Such a behavior persisted up to 140 °C and showed good recoverability. The aging-induced double hysteresis and recoverable electrostrain suggest a reversible domain switching mechanism due to a symmetry-conforming short-range ordering of point defects. The striking similarity of the aging effect between acceptor-doped A+B5+O3 and acceptor-doped A2+B4+O3 systems indicates a common physical origin of aging.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
61.72.J- Point defects and defect clusters
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Laser-induced exfoliation of amorphous carbon layer on an individual multiwall carbon nanotube

G. Singh, P. Rice, K. E. Hurst, J. H. Lehman, and R. L. Mahajan

Appl. Phys. Lett. 91, 033101 (2007); http://dx.doi.org/10.1063/1.2756357 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2007

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Pulsed laser treatment of an individual multiwall carbon nanotube induced selective exfoliation of the amorphous carbon contamination layer. The multiwall carbon nanotube (MWCNT) was exposed to a 248 nm excimer laser. After the treatment, transmission electron microscopy images show that the amorphous layer has expanded and separated from the crystalline MWCNT walls. This interesting observation has implications for laser cleaning and possible thinning of MWCNTs to reduce the radial dimensions.
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81.05.U- Carbon/carbon-based materials
81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
42.62.-b Laser applications
61.43.-j Disordered solids
61.46.Fg Nanotubes

Curvature effects on electronic properties of small radius nanotube

H. Zeng, H. F. Hu, J. W. Wei, Z. Y. Wang, L. Wang, and P. Peng

Appl. Phys. Lett. 91, 033102 (2007); http://dx.doi.org/10.1063/1.2757119 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2007

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The authors use the density functional theory associated with nonequilibrium Green function to calculate (2,2) and (3,3) single-walled nanotubes. The result of T(E) imply that π or π* band has been suppressed at certain electronic energy region result in the effect of curvature induce complex hybridization procedure. In view of the I-V characteristics of (2,2) tube, it is found that the current curve appears to have an oscillation behavior. These peculiar electronic transport properties of small diameter tube directly relate to a large curvature effect, which may be useful for the manufacture of electronic applications.
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73.63.Fg Nanotubes

Orientation-controlled molecule-by-molecule polymer wire growth by the carrier-gas-type organic chemical vapor deposition and the molecular layer deposition

Tetsuzo Yoshimura, Shinji Ito, Tomohiro Nakayama, and Kotaro Matsumoto

Appl. Phys. Lett. 91, 033103 (2007); http://dx.doi.org/10.1063/1.2754646 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2007

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The carrier-gas-type organic chemical vapor deposition (CG-OCVD) and the molecular layer deposition were developed for orientation-controlled molecule-by-molecule growth of conjugated polymer wires on a surface with self-assembled monolayer (SAM), which provides a feasible way to construct self-organized three-dimensional polymer wire networks. It was also found that, in CG-OCVD, growth saturation occurs for a substrate without SAM while no growth saturation for a substrate with SAM. The analysis of results in terms of reaction site densities on surfaces suggests vertical wire growth on a substrate with SAM and horizontal wire growth on a substrate without SAM.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Fabrication of Si1−xGex alloy nanowire field-effect transistors

Cheol-Joo Kim, Jee-Eun Yang, Hyun-Seung Lee, Hyun M. Jang, Moon-Ho Jo, Won-Hwa Park, Zee Hwan Kim, and Sunglyul Maeng

Appl. Phys. Lett. 91, 033104 (2007); http://dx.doi.org/10.1063/1.2753722 (3 pages) | Cited 16 times

Online Publication Date: 17 July 2007

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The authors present the demonstration of nanowire field-effect transistors incorporating group IV alloy nanowires, Si1−xGex. Single-crystalline Si1−xGex alloy nanowires were grown by a Au catalyst-assisted chemical vapor synthesis using SiH4 and GeH4 precursors, and the alloy composition was reproducibly controlled in the whole composition range by controlling the kinetics of catalytic decomposition of precursors. Complementary in situ doping of Si1−xGex nanowires was achieved by PH3 and B2H6 incorporation during the synthesis for n- and p-type field-effect transistors. The availability of both n- and p-type Si1−xGex nanowire circuit components suggests implications for group IV semiconductor nanowire electronics and optoelectronics.
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85.40.Sz Deposition technology
85.30.Tv Field effect devices

Resonant microwave absorption determination of characteristic magnetic length in magnetic-field-annealed Vitroperm

G. A. Basheed, S. N. Kaul, and A. Michels

Appl. Phys. Lett. 91, 033105 (2007); http://dx.doi.org/10.1063/1.2754362 (3 pages) | Cited 1 time

Online Publication Date: 17 July 2007

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The first direct resonant microwave absorption determination of the thermal renormalization of exchange stiffness, average magnetic anisotropy constant, and characteristic magnetic length in “field-annealed” Vitroperm samples with an initial magnetic permeability of μi = 20 000 and 150 000 has been presented and discussed.
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75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Directed assembly of nanowire contacts using electrodeposition

S. Ingole, P. Aella, Sean J. Hearne, and S. T. Picraux

Appl. Phys. Lett. 91, 033106 (2007); http://dx.doi.org/10.1063/1.2757609 (3 pages) | Cited 8 times

Online Publication Date: 17 July 2007

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A maskless process for the directed assembly of Ni contacts to Si nanowires on prepatterned electrodes is reported. Microarrays of thin Au/Cr electrodes were lithographically formed on oxidized Si substrates followed by electric-field assisted alignment of Si nanowires between the electrodes. The nanowire ends were then embedded in Ni by selective electrodeposition over the prepatterned electrodes. Annealing to 300 °C provided good electrical contacts for transport through the doped nanowires. This approach provides a parallel, maskless method to establish metal contacts to the nanowires without the need of high resolution electron beam lithography for electrical and mechanical applications.
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81.16.-c Methods of micro- and nanofabrication and processing
73.63.Rt Nanoscale contacts

Low-frequency charge noise in suspended aluminum single-electron transistors

T. F. Li, Yu. A. Pashkin, O. Astafiev, Y. Nakamura, J. S. Tsai, and H. Im

Appl. Phys. Lett. 91, 033107 (2007); http://dx.doi.org/10.1063/1.2759260 (3 pages) | Cited 11 times

Online Publication Date: 18 July 2007

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The authors have developed a fabrication method for suspended metallic single-electron transistors (SETs) utilizing a combination of conventional angle evaporation technique and ashing of the underlying organic polymer. The authors’ Al-based suspended devices exhibit clear Coulomb blockade effects typical for conventional SETs. The measured low-frequency charge noise is rather low but still within the range reported for conventional Al devices. We suggest that the noise level can be further reduced by decreasing the effective SET temperature.
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85.35.Gv Single electron devices
85.35.Ds Quantum interference devices

Two-dimensional slicing method to speed up the fabrication of micro-objects based on two-photon polymerization

Chao-Yaug Liao, Michel Bouriauand, Patrice L. Baldeck, Jean-Claude Léon, Cédric Masclet, and Tien-Tung Chung

Appl. Phys. Lett. 91, 033108 (2007); http://dx.doi.org/10.1063/1.2759269 (3 pages) | Cited 7 times

Online Publication Date: 18 July 2007

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Generally, a layer-by-layer method along one specific direction (two-and-half-dimensional method) is used to fabricate three-dimensional (3D) microstructures. Ultrathin layers and long processing times are necessary to obtain smooth surfaces in near flat regions of microstructures. In their approach, the authors slice these nearly flat areas along another slicing direction to produce the scanning paths of the laser beam. Several examples, including a microdragon, have been produced to validate that this real 3D method can generate micro-objects with a good balance between surface accuracy and processing efficiency.
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82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
42.62.-b Laser applications

Electrochromic properties of intercrossing nickel oxide nanoflakes synthesized by electrochemically anodic deposition

Mao-Sung Wu and Chung-Hsien Yang

Appl. Phys. Lett. 91, 033109 (2007); http://dx.doi.org/10.1063/1.2759270 (3 pages) | Cited 21 times

Online Publication Date: 18 July 2007

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Nanostructured nickel oxide film is synthesized directly onto a transparent and conducting indium tin oxide coated glass substrate by electrochemically anodic deposition from an aqueous solution. The deposited nickel oxide film has an intercrossing nanoflake and highly porous morphology. X-ray diffraction peaks of the film resemble closely to the cubic NiO structure. The deposited film oxidized/reduced electrochemically at 0.36 and 0.25 V versus a saturated Ag/AgCl electrode, respectively, which corresponds to the reversible changes in coloration and bleaching. The difference in optical response (transmittance) ΔT at wavelength of 550 nm between the colored state and bleached state can reach as high as 80%.
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82.45.Qr Electrodeposition and electrodissolution
82.45.Mp Thin layers, films, monolayers, membranes
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Nk Insulators
78.20.Jq Electro-optical effects

Three dimensional mapping of thermal and tunneling electron emission from InAs/GaAs quantum dots

O. Engström, M. Kaniewska, W. Jung, and M. Kaczmarczyk

Appl. Phys. Lett. 91, 033110 (2007); http://dx.doi.org/10.1063/1.2753543 (3 pages) | Cited 10 times

Online Publication Date: 19 July 2007

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Using a three dimensional representation of data from deep level transient spectroscopy (DLTS) in a parameter space given by temperature, applied sample voltage, and DLTS signal, a method is demonstrated for interpreting a complex set of basic properties of quantum dots. Experimental results on InAs/GaAs quantum dots are compared with theoretical calculations presented in the same parameter space. From such a comparison, different regimes dominated by charge carrier tunneling and thermal emission and mixture of these can be identified, thus resolving the complex emission data from this kind of systems into its component parts.
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78.67.Hc Quantum dots
73.63.Kv Quantum dots
73.40.Gk Tunneling
73.21.La Quantum dots

Anomalous light-induced enhancement of photoluminescence from Si nanocrystals fabricated by thermal oxidation of amorphous Si

Min Choul Kim, Sung Kim, Suk-Ho Choi, and Sangjin Park

Appl. Phys. Lett. 91, 033111 (2007); http://dx.doi.org/10.1063/1.2756110 (3 pages) | Cited 4 times

Online Publication Date: 19 July 2007

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A band of ∼ 1.6 nm diameter Si nanocrystals (NCs) has been prepared at a depth of about 5 nm within SiO2 by atomic-layer deposition of 2 nm amorphous Si on 5 nm SiO2 and subsequent thermal oxidation at 900 °C. After 4 h light exposure of 5.66 W/cm2, photoluminescence (PL) spectrum of the Si NCs is almost 60 times enhanced with its peak blueshifted by about 30 nm. The enhancement rate of the PL intensity with illumination time increases as the oxidation time increases. The PL intensity and its peak wavelength are partially recovered by annealing the samples at 440 K for 1 h, suggesting the effect is metastable. It is proposed that the anomalous light-induced effect is originated from the defect states at the Si NCs/SiO2 interfaces.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
71.55.Cn Elemental semiconductors

Evolution of InAs nanostructures grown by droplet epitaxy

C. Zhao, Y. H. Chen, B. Xu, P. Jin, and Z. G. Wang

Appl. Phys. Lett. 91, 033112 (2007); http://dx.doi.org/10.1063/1.2757151 (3 pages) | Cited 3 times

Online Publication Date: 19 July 2007

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The authors report the growth evolution of InAs dot and ring nanostructures with the indium deposition amount on GaAs (001) by droplet molecular beam epitaxy. There is a critical flux for the indium to form InAs dots even when there is no droplet. When the flux exceeds a critical value, In droplets form, which act as nucleation centers for the formation of InAs rings.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Synthesis and characterization of an n = 6 Aurivillius phase incorporating magnetically active manganese, Bi7(Mn,Ti)6O21

M. A. Zurbuchen, R. S. Freitas, M. J. Wilson, P. Schiffer, M. Roeckerath, J. Schubert, M. D. Biegalski, G. H. Mehta, D. J. Comstock, J. H. Lee, Y. Jia, and D. G. Schlom

Appl. Phys. Lett. 91, 033113 (2007); http://dx.doi.org/10.1063/1.2756163 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2007

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Epitaxial films of Bi7Mn3.75Ti2.25O21 were prepared to yield a previously unsynthesized material. The superlattice phase is produced by incorporating the magnetoelectric BiMnO3 into the perovskite substructure of the ferroelectric Bi4Ti3O12, a strategy which is hoped to yield previously undiscovered multiferroic materials. X-ray diffraction and transmission electron microscopy (TEM) confirm synthesis of an epitaxial n = 6 Aurivillius phase. Magnetization measurements show ferromagnetic behavior with a Curie point of 55 K, but electronic polarization measurements show no remanent polarization. Rutherford backscattering spectrometry indicates a channeling minimum χmin of 22%, consistent with the high density of out-of-phase domain boundaries observed by TEM.
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77.55.-g Dielectric thin films
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
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Electron detrapping characteristics in positive bias temperature stressed n-channel metal-oxide-semiconductor field-effect transistors with ultrathin HfSiON gate dielectrics

Shiyang Zhu and Anri Nakajima

Appl. Phys. Lett. 91, 033501 (2007); http://dx.doi.org/10.1063/1.2754640 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2007

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Electrons trapped in the HfSiON gate dielectrics of n-channel metal-oxide-semiconductor field-effect transistors induced by positive bias temperature stress start to decay when the stress is interrupted or an opposite (recovery) voltage is applied. The decay begins with a quick detrapping within tens of nanoseconds followed by a slow detrapping. The quick detrapping depends on the recovery voltage and the trapping history, whereas the slow detrapping obeys approximately a logarithmic dependence on time with an almost identical slope before saturation. The observed detrapping behavior can be explained by a spatial and/or energetic distribution of trapped electrons in the HfSiON film. The device degradation under various dynamic stresses is found to be almost independent of frequency ranging from 0.001 to 1 MHz, while it is slightly enhanced at 10 MHz, probably due to insufficient recovery at the recovering half cycle.
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85.30.Tv Field effect devices

Charge characterization in metal-gate/high-κ layers: Effect of post-deposition annealing and gate electrode

B. J. O’Sullivan, G. Pourtois, V. S. Kaushik, T. Schram, J. A. Kittl, L. Pantisano, S. De Gendt, and M. Heyns

Appl. Phys. Lett. 91, 033502 (2007); http://dx.doi.org/10.1063/1.2754647 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2007

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The effect of varying interfacial SiO2 and high-κ thickness on charge density within the gate stack are examined. It is demonstrated that there is a significant effect of the gate electrode on the charge density levels within the stack, with one order of magnitude lower charge in the case of Ni3Si2 electrodes, than in the case of tantalum-rich metal electrodes. The effect of post-deposition annealing on high-κ HfSixOy(Nz) stacks is less significant that that of the electrode. The reasons behind these findings are discussed.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Ns Metal-nonmetal contacts

Observation of a two dimensional electron gas formed in a polarization doped C-face 3C/4H SiC heteropolytype junction

M. V. S. Chandrashekhar, C. I. Thomas, Jie Lu, and Michael. G. Spencer

Appl. Phys. Lett. 91, 033503 (2007); http://dx.doi.org/10.1063/1.2754650 (3 pages) | Cited 5 times

Online Publication Date: 17 July 2007

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A two dimensional electron gas (2DEG) was observed in a C-face 3C/4H SiC heteropolytype junction. Sheet carrier concentrations of ∼ 3×1013 cm−2 and Hall mobility of ∼ 314 cm2/V s were measured at 77 K. The temperature dependences of mobility and carrier concentration clearly demonstrate the presence of the 2DEG. Comparison with theory indicates that the carriers originate from both spontaneous polarization and unintentional degenerate nitrogen doping of 3C-SiC, suggesting a 77 K 2DEG mobility ∼ 700 cm2/V s in parallel with bulk hopping conduction. Mobility at high temperatures was phonon limited, indicating a Debye temperature of 1600 K. Transmission line measurements yielded similar mobilities, with saturation currents of ∼ 3 A/mm, suggesting the utility of SiC heteropolytypes in microwave devices.
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73.21.Ac Multilayers
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.up Other materials
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.50.Dn Low-field transport and mobility; piezoresistance

Direct insertion of oxygen atoms into the backbonds of subsurface Si atoms using translational energies of oxygen atom beams

Masahito Tagawa, Kumiko Yokota, Shinnosuke Tsumamoto, Chie Sogo, Akitaka Yoshigoe, and Yuden Teraoka

Appl. Phys. Lett. 91, 033504 (2007); http://dx.doi.org/10.1063/1.2759262 (3 pages) | Cited 1 time

Online Publication Date: 18 July 2007

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A direct oxidation reaction of Si atoms on a Si(001) surface was studied by ellipsometry and synchrotron radiation photoemission spectroscopy. In situ ellipsometry measurements when exposed to 2.7–5.0 eV O atom beams indicated that oxide growth follows a linear relationship with an O atom fluence up to an oxide thickness of 0.6–0.7 nm. In contrast, the limit of linear growth was 0.3 nm in the case of the 1.8 eV beam. These results suggest that the backbonds of Si atoms in the first layer are directly oxidized by O atom with a translational energy between 2.7 and 5.0 eV.
Show PACS
81.65.Mq Oxidation
82.40.-g Chemical kinetics and reactions: special regimes and techniques
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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