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4 Jun 2007

Volume 90, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages)

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan
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Space charge induced gating by a leaky gate

D. Spanheimer, L. Worschech, C. R. Müller, and A. Forchel

Appl. Phys. Lett. 90, 232101 (2007); http://dx.doi.org/10.1063/1.2746065 (3 pages)

Online Publication Date: 4 June 2007

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The authors studied the role of gate leakage on the drain current in a monolithic, unipolar GaAs/AlGaAs heterostructure based on three contacts leaky coupled to each other. Two in-plane barriers, each defined by a row of etched holes in a two-dimensional electron gas, separate the leaky gate from the central drain and the drain from the source. A pronounced decrease of the drain current sets in when the gate starts to leak associated with the space charge injected from the leaky gate.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
77.22.Jp Dielectric breakdown and space-charge effects

Temperature dependent study of InAlAs–InP/GaAsSb/InP double heterojunction bipolar transistors

Che-ming Wang, Yue-Ming Hsin, Haijun Zhu, J. M. Kuo, and Y. C. Kao

Appl. Phys. Lett. 90, 232102 (2007); http://dx.doi.org/10.1063/1.2746073 (3 pages)

Online Publication Date: 4 June 2007

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InAlAs–InP/GaAsSb/InP double heterojunction bipolar transistors (HBTs) with InAlAs–InP composite emitter have been grown, fabricated, and characterized at various temperatures from 77 to 400 K. The InAlAs–InP composite emitter structure effectively reduces electron pileup in the InP/GaAsSb base-emitter junction and hence increases current gain, especially in the low-base-current region. The turn-on voltage shows a slightly different temperature dependence (−1.66 mV/K) from conventional InGaAs based HBTs due to the composite emitter. The activation energy study for the base (0.74 eV) and collector currents (0.98 eV) indicates the high quality of the base layer and the effect of InAlAs–InP composite emitter.
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85.30.Pq Bipolar transistors

Room temperature deposited indium zinc oxide thin film transistors

Yu-Lin Wang, F. Ren, Wantae Lim, D. P. Norton, S. J. Pearton, I. I. Kravchenko, and J. M. Zavada

Appl. Phys. Lett. 90, 232103 (2007); http://dx.doi.org/10.1063/1.2746084 (3 pages) | Cited 51 times

Online Publication Date: 4 June 2007

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Depletion-mode indium zinc oxide (IZO) channel thin film transistors were fabricated on glass substrates from layers deposited at room temperature using rf magnetron sputtering. The threshold voltage was in the range from −5.5 to −6.5 V depending on gate dielectric (SiO2) thickness and the drain current on-to-off ratio was ∼ 105. The maximum field effect mobility in the channel was ∼ 4.5 cm2 V−1 s−1, lower than the Hall mobility of ∼ 17 cm2 V−1 s−1 in the same layers, suggesting a strong influence of scattering due to trapped charges at the SiO2-IZO interface. The low deposition and processing temperatures make these devices suitable for applications requiring flexible substrates.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering

Dresselhaus spin-orbit coupling effect on the shot noise in resonant double-barrier structures

Rui Zhu and Yong Guo

Appl. Phys. Lett. 90, 232104 (2007); http://dx.doi.org/10.1063/1.2745199 (3 pages) | Cited 9 times

Online Publication Date: 4 June 2007

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The authors have investigated the zero-frequency shot noise of current through resonant double-barrier structures. Taking into account the spin-orbit coupling (SOC) effect, general expressions for the shot noise in fully phase-coherent mesoscopic conductors are derived based on the scattering approach. It is found that the Dresselhaus SOC can greatly affect the average current I, shot noise S, and Fano factor of resonant diode structures. A large shot noise suppression with the Fano factor below 0.5 observed experimentally can be illustrated by the influence of the Dresselhaus SOC effect.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.75.Mm Spin polarized resonant tunnel junctions
85.30.De Semiconductor-device characterization, design, and modeling

Parallel preparation of highly spin-polarized electrons in single InAs/GaAs quantum dots

W. Löffler, M. Hetterich, C. Mauser, S. Li, T. Passow, and H. Kalt

Appl. Phys. Lett. 90, 232105 (2007); http://dx.doi.org/10.1063/1.2746405 (3 pages) | Cited 9 times

Online Publication Date: 5 June 2007

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Initialization of electron spins in semiconductor quantum dots (QDs) is a major prerequisite for a successful implementation of such QDs in quantum information applications. It is essential that the initialization is achieved for many individually separable dots in parallel. Here the authors show that exactly this can be accomplished with near-unity fidelity by electrical spin injection from the diluted magnetic semiconductor ZnMnSe into InAs/GaAs quantum dots. The deviation from unity is smaller than 0.13, more precise determination is limited by the signal-to-noise ratio of their setup. They demonstrate the robust concurrent initialization of several quantum dots with the same high fidelity.
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73.63.Kv Quantum dots
72.25.Dc Spin polarized transport in semiconductors

InAsSb/GaSb heterostructure based mid-wavelength-infrared detector for high temperature operation

Y. Sharabani, Y. Paltiel, A. Sher, A. Raizman, and A. Zussman

Appl. Phys. Lett. 90, 232106 (2007); http://dx.doi.org/10.1063/1.2746951 (3 pages) | Cited 10 times

Online Publication Date: 5 June 2007

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The properties of a midinfrared photodetector, based on a lattice matched n-N InAs0.91Sb0.09/GaSb type-II heterostructure, were investigated. The relatively simple two layer structure shows very promising characteristics for sensitive and dual color infrared detection. I-V characteristics and spectral response were measured at the temperature range of 10–300 K. High zero-bias resistance area product R0A of 2.5 Ω cm2 was obtained at room temperature. The measured background limited infrared photodetection temperature was 180 K corresponding to 4.1 μm cutoff. Shot and Johnson noise limited detectivities corresponding to InAsSb absorption were measured to be 1.3×1010 and 4.9×109 cm Hz1/2 W−1 at 180 and 300 K, respectively. An enhanced optical response with gain larger than unity was observed below 120 K. Bias tunable dual color detection was demonstrated at all measured temperatures.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.60.Dq Photometers, radiometers, and colorimeters

Thermoelectric properties and electronic structure of Zintl compound BaZn2Sb2

Xiao-Jun Wang, Mei-Bo Tang, Jing-Tai Zhao, Hao-Hong Chen, and Xin-Xin Yang

Appl. Phys. Lett. 90, 232107 (2007); http://dx.doi.org/10.1063/1.2746408 (3 pages) | Cited 24 times

Online Publication Date: 6 June 2007

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Polycrystalline sample of the title compound was prepared and its thermoelectric properties from 2 to 675 K were investigated. This Zintl compound shows rather low thermal conductivity, 1.6 W m−1 K−1, at room temperature. The value of its thermoelectric figure of merit ZT reaches 0.31 at 675 K. Its electronic structure, calculated by ab initio methods, suggests that the electrical transport are mainly ascribe to [Zn2Sb2] framework for p-type BaZn2Sb2. The heat capacity curve at low temperature was fitted lineally to obtain Debye temperature (about 208 K). It provides the authors with a host lattice for modification and optimization the thermoelectric properties through substitution and/or doping.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.20.Nr Semiconductor compounds
72.80.Jc Other crystalline inorganic semiconductors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.40.Ba Heat capacity
71.15.-m Methods of electronic structure calculations

Solution deposited liquid crystalline semiconductors on a photoalignment layer for organic thin-film transistors

Takenori Fujiwara, Jason Locklin, and Zhenan Bao

Appl. Phys. Lett. 90, 232108 (2007); http://dx.doi.org/10.1063/1.2746937 (3 pages) | Cited 21 times

Online Publication Date: 6 June 2007

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Highly ordered liquid crystalline semiconductors on a light induced alignment layer results in an anisotropic electrical characteristic and an enhanced mobility of solution processed thin-film transistors. In the case of poly-9,9′-dioctyl-fluorene-co-bithiophene, a mobility as high as 0.02 cm2 V−1 s−1 has been achieved by aligning a polymer chain parallel to the charge transport direction. Using an oligomeric semiconductor, 5,5′-bis(4-octyloxyphenyl)bithiophene, an enhanced mobility of 0.05 cm2 V−1 s−1 was obtained by the alignment of the π-π intermolecular packing direction parallel to the charge transport direction.
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85.30.Tv Field effect devices

Intra- and intertube tunneling transport in ropes of single-walled carbon nanotubes

K. M. Seemann, J. Ebbecke, A. L. Hörner, and A. Wixforth

Appl. Phys. Lett. 90, 232109 (2007); http://dx.doi.org/10.1063/1.2746963 (3 pages)

Online Publication Date: 6 June 2007

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The authors report on intra- and intertube tunneling induced current oscillations in an individual rope of single-walled carbon nanotubes. Defects within single tubes and tube-tube contacts provide tunneling barriers of different transparencies and heights, respectively, and the formation of quantum dots in between. As a function of the bias voltage, the authors observe a transition from an intratube to an intertube tunneling dominated transport. The samples were fabricated on prepatterned silicon substrates employing surface acoustic wave induced streaming leading to an alignment of the ropes with respect to the contacts.
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73.40.Gk Tunneling
73.63.Fg Nanotubes
73.63.Kv Quantum dots

Enhancement of quantum efficiency of organic light emitting devices by doping magnetic nanoparticles

Cheng-Jun Sun, Yue Wu, Zhihua Xu, Bin Hu, Jianmin Bai, Jian-Ping Wang, and Jian Shen

Appl. Phys. Lett. 90, 232110 (2007); http://dx.doi.org/10.1063/1.2746415 (3 pages) | Cited 6 times

Online Publication Date: 6 June 2007

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Magnetic nanoparticles of CoFe are used as dopants to enhance the quantum efficiency of electroluminance in a single layer organic light emitting device (OLED). The enhancement of quantum efficiency increases with both increasing density of CoFe nanoparticles and external magnetic field. For a given OLED with 0.1 wt % doping, the enhancement of the quantum efficiency reaches ∼ 27% and ∼ 32% without and with a magnetic field, respectively. The origin of these improvements could be attributed to the simultaneous increases of the portion of excitons among total charge carriers and the fraction of singlets among the total excitons
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85.60.Jb Light-emitting devices

Linear electric molten zone in semiconductors

António M. Vallêra, Jorge Maia Alves, João M. Serra, Miguel C. Brito, and Roberto M. Gamboa

Appl. Phys. Lett. 90, 232111 (2007); http://dx.doi.org/10.1063/1.2747181 (3 pages) | Cited 2 times

Online Publication Date: 7 June 2007

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This letter describes how the temperature dependence of the electrical conductivity in semiconductors may be used to produce a linear floating molten zone which is intrinsically stable and uniform along its length. An analytical model and an experimental demonstration of such electric molten zone are both presented. This effect may be of particular interest for crystal growth and semiconductor recrystallization.
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81.05.Cy Elemental semiconductors
81.10.Fq Growth from melts; zone melting and refining
72.80.Cw Elemental semiconductors

Study of the thermal stress in a Pb-free half-bump solder joint under current stressing

B. Y. Wu, Y. C. Chan, H. W. Zhong, M. O. Alam, and J. K. L. Lai

Appl. Phys. Lett. 90, 232112 (2007); http://dx.doi.org/10.1063/1.2747183 (3 pages) | Cited 5 times

Online Publication Date: 7 June 2007

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The thermal stress in a Sn3.5Ag1Cu half-bump solder joint under a 3.82×108 A/m2 current stressing was analyzed using a coupled-field simulation. Substantial thermal stress accumulated around the Al-to-solder interface, especially in the Ni+(Ni,Cu)3Sn4 layer, where a maximal stress of 138 MPa was identified. The stress gradient in the Ni layer was about 1.67×1013 Pa/m, resulting in a stress migration force of 1.82×10−16 N, which is comparable to the electromigration force, 2.82×10−16 N. Dissolution of the Ni+(Ni,Cu)3Sn4 layer, void formation with cracks at the anode side, and extrusions at the cathode side were observed.
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81.05.Bx Metals, semimetals, and alloys
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
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