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9 Jul 2007

Volume 91, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages)

M. Fendrich and T. Kunstmann
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Spin-dependent resonant tunneling through 6 μm diameter double barrier resonant tunneling diode

Z. L. Fang, P. Wu, N. Kundtz, A. M. Chang, X. Y. Liu, and J. K. Furdyna

Appl. Phys. Lett. 91, 022101 (2007); http://dx.doi.org/10.1063/1.2751132 (3 pages) | Cited 2 times

Online Publication Date: 9 July 2007

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A vertical resonant tunneling diode based on the paramagnetic Zn1−x−yMnyCdxSe system has been fabricated with a pillar diameter down to ∼ 6 μm. The diode exhibits high quality resonant tunneling characteristics through the electron subband of the quantum well at a temperature of 4.2 K, where a clear phonon replica was observable in addition to the primary peak. Both peaks show a giant Zeeman splitting in an applied magnetic field. Employing a self-consistent real-time Green’s function method, the current-voltage characteristic was simulated, showing good agreement with the measured result.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Small valence band offset in (010) InS/CuI heterojunction diodes

I. Konovalov and L. Makhova

Appl. Phys. Lett. 91, 022102 (2007); http://dx.doi.org/10.1063/1.2753094 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2007

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Heterojunctions between the (010) facet of an orthorhombic InS single crystal and evaporated CuI show a remarkably small valence band offset of 0.15 eV (cliff). This minor band offset allows rather good injection conditions for holes. In accordance to this result, the current-voltage characteristics of the device are rectifying and show a large forward voltage.
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85.30.Kk Junction diodes

Room-temperature photoluminescence from ZnO/ZnMgO multiple quantum wells grown on Si(111) substrates

X. Q. Gu, L. P. Zhu, Z. Z. Ye, H. P. He, Y. Z. Zhang, F. Huang, M. X. Qiu, Y. J. Zeng, F. Liu, and W. Jaeger

Appl. Phys. Lett. 91, 022103 (2007); http://dx.doi.org/10.1063/1.2755922 (3 pages) | Cited 26 times

Online Publication Date: 9 July 2007

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A set of ten-period ZnO/Zn0.85Mg0.15O multiple quantum wells with well thickness varying from 2.5 to 5 nm has been grown on Si(111) substrates by pulsed laser deposition. A periodic structure with sharp interfaces was observed by cross-sectional transmission electron microscopy. The room-temperature photoluminescence resulting from the well regions exhibits a significant blueshift with respect to the ZnO single layer. The well layer thickness dependence of the emission energy from the well regions was investigated and compared with a simple theoretical model. The results suggest that the quantum confinement effects in the quantum wells can be observed up to room temperature.
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81.07.St Quantum wells
81.05.Dz II-VI semiconductors
78.67.De Quantum wells
78.55.Et II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.65.Fg Quantum wells

Phonon-induced shot noise enhancement in resonant tunneling structures

V. Nam Do, P. Dollfus, and V. Lien Nguyen

Appl. Phys. Lett. 91, 022104 (2007); http://dx.doi.org/10.1063/1.2756127 (3 pages) | Cited 6 times

Online Publication Date: 10 July 2007

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Using the nonequilibrium Green’s function formalism, the authors investigate the effect of the electron-phonon interaction on the current and shot noise in one dimensional resonant tunneling structures. Besides the well-known current behavior, they particularly show that the shot noise may be enhanced over the Poissonian value due to the phonon-assisted tunneling effect. The observed super-Poissonian noise is then interpreted as a result of the competition between the coherent and sequential current components.
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72.70.+m Noise processes and phenomena
73.40.Gk Tunneling
63.20.K- Phonon interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.38.-k Polarons and electron-phonon interactions
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations

Large hysteretic magnetoresistance in high-mobility semiconductor quantum wires bridged by single-domain nanomagnets

J.-U. Bae, T.-Y. Lin, Y. Yoon, S. J. Kim, J. P. Bird, A. Imre, W. Porod, and J. L. Reno

Appl. Phys. Lett. 91, 022105 (2007); http://dx.doi.org/10.1063/1.2756270 (3 pages) | Cited 9 times

Online Publication Date: 10 July 2007

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The authors discuss hysteresis in the magnetoresistance of hybrid semiconductor/ferromagnetic devices composed of high-mobility semiconductor quantum wires (QWs) bridged by single-domain Co nanomagnets (NMs). This hysteresis is shown to be consistent with the ballistic transport of electrons in the QW through the nonuniform magnetic field generated by the NM. It is also found to be strongly dependent on tilt angle, suggestive of a transition between easy- and hard-axis magnetizations.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Solidification contraction-free synthesis for the Yb0.15Co4Sb12 bulk material

H. Y. Geng, S. Ochi, and J. Q. Guo

Appl. Phys. Lett. 91, 022106 (2007); http://dx.doi.org/10.1063/1.2755926 (3 pages) | Cited 10 times

Online Publication Date: 10 July 2007

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The solidification contraction and feeding ability of Yb partially filled CoSb3 skutterudite alloys were studied in this letter. It is found that the pore formation was mainly due to the large solidification contraction during the L+CoSb→CoSb2 peritectic phase transition and the primary dendrite networks. Homogeneous and full density Yb0.15Co4Sb12 bulk material was synthesized directly from the peritectic phase transition L+CoSb2→CoSb3 by controlling the melting temperature and starting materials. The result of thermoelectric property measurement from room temperature to 500 °C shows that the thermoelectric dimensionless figure of merit reaches to the maximum of 0.7 at 400 °C.
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81.20.-n Methods of materials synthesis and materials processing
81.30.Fb Solidification
64.70.K- Solid-solid transitions
72.15.Jf Thermoelectric and thermomagnetic effects

Electric-field control of tunneling magnetoresistance effect in a Ni/InAs/Ni quantum-dot spin valve

K. Hamaya, M. Kitabatake, K. Shibata, M. Jung, M. Kawamura, K. Hirakawa, T. Machida, T. Taniyama, S. Ishida, and Y. Arakawa

Appl. Phys. Lett. 91, 022107 (2007); http://dx.doi.org/10.1063/1.2759264 (3 pages) | Cited 27 times

Online Publication Date: 10 July 2007

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The authors demonstrate an electric-field control of tunneling magnetoresistance (TMR) effect in a semiconductor quantum-dot spin-valve device. By using ferromagnetic Ni nanogap electrodes, they observe the Coulomb blockade oscillations at a small bias voltage. In the vicinity of the Coulomb blockade peak, the TMR effect is significantly modulated and even its sign is switched by changing the gate voltage, where the sign of the TMR value changes at the resonant condition.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.35.Ds Quantum interference devices

Enhancement-mode InP n-channel metal-oxide-semiconductor field-effect transistors with atomic-layer-deposited Al2O3 dielectrics

Y. Q. Wu, Y. Xuan, T. Shen, P. D. Ye, Z. Cheng, and A. Lochtefeld

Appl. Phys. Lett. 91, 022108 (2007); http://dx.doi.org/10.1063/1.2756106 (3 pages) | Cited 33 times

Online Publication Date: 11 July 2007

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Enhancement-mode (E-mode) n-channel InP metal-oxide-semiconductor field-effect transistors (MOSFETs) with 0.75–40 μm gate length fabricated on a semi-insulating substrate with atomic-layer-deposited (ALD) Al2O3 as gate dielectric are demonstrated. The ALD process on III-V compound semiconductors enables the formation of high-quality gate oxides and unpinning of Fermi level on compound semiconductors. A 0.75 μm gate length E-mode n-channel MOSFET with an Al2O3 gate oxide thickness of 30 nm shows a gate leakage current less than 10 μA/mm at the highest gate bias of 8 V, a maximum drain current of 70 mA/mm, and a transconductance of 10 mS/mm. The peak effective mobility is ∼ 650 cm2/V s and the interface trap density of Al2O3/InP is estimated to be ∼ (2–3)×1012/cm2 eV.
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85.30.Tv Field effect devices

Anisotropic electronic structure in quasi-one-dimensional K0.3MoO3: An angle-dependent x-ray absorption study

H. M. Tsai, K. Asokan, C. W. Pao, J. W. Chiou, C. H. Du, W. F. Pong, M.-H. Tsai, and L. Y. Jang

Appl. Phys. Lett. 91, 022109 (2007); http://dx.doi.org/10.1063/1.2756358 (3 pages) | Cited 1 time

Online Publication Date: 11 July 2007

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The electronic structure of quasi-one-dimensional (quasi-1D) blue bronze, K0.3MoO3, was investigated by angle-dependent x-ray absorption near-edge structure (XANES) spectroscopy at O and K K and Mo L3 edges along the quasi-1D MoO6 octahedron-chain direction, i.e., the b axis, and the octahedron-in-plane direction, i.e., the d axis, well below its Peierls phase transition temperature (180 K). The O K-edge XANES spectra indicate that the angle dependence of O 2p–Mo 4d hybridization, especially those with the π* character, is more significant along the b axis than along the d axis. Similar trend is also observed in the Mo L3-edge XANES spectra. The K K-edge XANES spectra reveal anisotropic effect of hybridization of K 4p states with O 2p states on the MoO6 octahedron.
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71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra

Schottky barrier characteristics and interfacial reactions of Ti on n-In0.52Al0.48As

Liang Wang and Ilesanmi Adesida

Appl. Phys. Lett. 91, 022110 (2007); http://dx.doi.org/10.1063/1.2756313 (3 pages)

Online Publication Date: 11 July 2007

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Schottky barrier heights (ϕB) and ideality factors (n) of Ti/Pt/Au diodes on n-InAlAs were characterized. Transmission electron microscopy (TEM) investigations were utilized to correlate the electrical performance with interfacial reactions. The enhancement of ϕB and increase in n were obtained with increasing annealing temperatures. TEM studies confirmed that amorphous layers were formed at the Ti/InAlAs interface at short annealing times, while prolonged annealing resulted in the crystallization of TiAs, defective layer formation, and Kirkendall void formation. Such aggressive reactions after prolonged annealing extended deep into the InAlAs and may affect the active region of InAlAs/InGaAs-based transistors. The activation energy for this reaction was calculated to be 1.5±0.1 eV.
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85.30.Kk Junction diodes

Extremely high oxygen sensing of individual ZnSnO3 nanowires arising from grain boundary barrier modulation

X. Y. Xue, P. Feng, Y. G. Wang, and T. H. Wang

Appl. Phys. Lett. 91, 022111 (2007); http://dx.doi.org/10.1063/1.2750543 (3 pages) | Cited 9 times

Online Publication Date: 12 July 2007

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Extremely high oxygen sensing is realized from individual ZnSnO3 nanowires with abundant grain boundaries. The current across one single ZnSnO3 nanowire increases by about six orders of magnitude, from 1.20×10−7 to 3.78×10−1 μA, as the oxygen pressure decreases from 3.7×104 to 1.0×10−4 Pa. Such a drastic sensing is ascribed to grain boundary barrier modulation. This interpretation is confirmed by the sensing experiments under UV illumination. The results demonstrate a promising approach to realize miniaturized and highly sensitive oxygen sensors.
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82.80.-d Chemical analysis and related physical methods of analysis
61.72.Mm Grain and twin boundaries
85.30.-z Semiconductor devices

Decrease in switching voltage fluctuation of Pt/NiOx/Pt structure by process control

Ranju Jung, Myoung-Jae Lee, Sunae Seo, Dong Chirl Kim, Gyeong-Su Park, Kihong Kim, Seungeon Ahn, Youngsoo Park, In-Kyeong Yoo, Jin-Soo Kim, and Bae Ho Park

Appl. Phys. Lett. 91, 022112 (2007); http://dx.doi.org/10.1063/1.2755712 (3 pages) | Cited 33 times

Online Publication Date: 12 July 2007

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Resistance change random access memory devices using NiOx films with resistance switching properties have immense potential for high-density nonvolatile memory exceeding currently used flash memory. The only critical failure of a NiOx film is to write wrong information due to large fluctuations of switching voltages during successive resistance switching operations. The authors show that failure-free NiOx film can be grown directly on Pt electrode just by process control. Intensive analyses show that the superior resistance switching behaviors of their simple Pt/NiOx/Pt structure may result from a very thin Ni–Pt layer self-formed at the bottom interface during deposition of NiOx.
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73.40.Ns Metal-nonmetal contacts
72.60.+g Mixed conductivity and conductivity transitions
68.55.A- Nucleation and growth

n+-doped-layer-free microcrystalline silicon thin film transistors fabricated with the CuMg as source/drain metal

M. C. Wang, T. C. Chang, Po-Tsun Liu, R. W. Xiao, L. F. Lin, Y. Y. Li, F. S. Yeh, and J. R. Chen

Appl. Phys. Lett. 91, 022113 (2007); http://dx.doi.org/10.1063/1.2749847 (3 pages) | Cited 2 times

Online Publication Date: 13 July 2007

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The feasibility of using CuMg as source/drain metal electrodes for n+-doped-layer-free microcrystalline silicon thin film transistors (μ-Si:H TFTs) has been investigated. The Ohmic-contact characteristic has been achieved by using the CuMg alloy as source/drain metal. Furthermore, a wet etching process of Cu alloy source/drain metal has been completed by using the ferric chloride base etchant. The proposed μ-Si:H TFT has shown similar electrical characteristic with the μ-Si:H TFT with n+-doped layer. The experimental result also showed that the CuMg alloy was suitable for the replacement of n+-doped layer in thin film transistor liquid-crystal displays.
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85.30.Tv Field effect devices

Application of weak ferromagnetic BiFeO3 films as the photoelectrode material under visible-light irradiation

X. Y. Chen, T. Yu, F. Gao, H. T. Zhang, L. F. Liu, Y. M. Wang, Z. S. Li, Z. G. Zou, and J.-M. Liu

Appl. Phys. Lett. 91, 022114 (2007); http://dx.doi.org/10.1063/1.2757132 (3 pages) | Cited 5 times

Online Publication Date: 13 July 2007

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BiFeO3 films prepared by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates were studied as photoelectrode for water splitting. Under visible-light irradiation, the photocurrent intensity of the polycrystalline BiFeO3 film was found to double that of the amorphous one in a three-electrode cell. The incident photon to current conversion efficiency for the polycrystalline BiFeO3 electrode was approximately 16% at 350 nm and 7% at 530 nm at 1.5 V (versus saturated calomel electrode). The ferromagnetism of the amorphous BiFeO3 film was an order of magnitude weaker than that of the polycrystalline one, supporting the “size effect” explanation for magnetic origin.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Kj Amorphous and quasicrystalline magnetic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
72.40.+w Photoconduction and photovoltaic effects

Bias-induced insulator-metal transition in organic electronics

J. H. Wei, S. J. Xie, L. M. Mei, and YiJing Yan

Appl. Phys. Lett. 91, 022115 (2007); http://dx.doi.org/10.1063/1.2756354 (3 pages) | Cited 4 times

Online Publication Date: 13 July 2007

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The authors investigate the bias-induced insulator-metal transition in organic electronics devices on the basis of the Su-Schrieffer-Heeger model [ W. P. Su et al., Phys. Rev. B 22, 2099 (1980) ] combined with the nonequilibrium Green’s function formalism. The insulator-metal transition is explained with the energy level crossover that eliminates the Peierls phase [ R. Peierls, Quantum Theory of Solids (Oxford University Press, Oxford, 1955) ] and delocalizes the electron states near the threshold voltage. This may account for the experimental observations on the devices that exhibit intrinsic bistable conductance switching with large on-off ratio.
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85.65.+h Molecular electronic devices
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