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10 Jan 2005

Volume 86, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 86, 021101 (2005); http://dx.doi.org/10.1063/1.1849439 (3 pages)

H. W. Choi, C. W. Jeon, C. Liu, I. M. Watson, M. D. Dawson, P. R. Edwards, R. W. Martin, S. Tripathy, and S. J. Chua
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Enhancement of the electroabsorption in multiple quantum well structures containing a nipi delta-doping superlattice

C. V-B. Tribuzy, M. C. L. Areiza, S. M. Landi, M. Borgstrom, M. P. Pires, and P. L. Souza

Appl. Phys. Lett. 86, 023501 (2005); http://dx.doi.org/10.1063/1.1849421 (3 pages) | Cited 1 time

Online Publication Date: 3 January 2005

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Transmission measurements as a function of applied reverse voltage, together with a fit procedure, demonstrate that the introduction of a nipi delta-doping superlattice in a GaAs∕AlGaAs multiple-quantum-well structure, for application in amplitude modulation, enhances the change in absorption with applied electric field, leading to an improvement of the device performance.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.20.Jq Electro-optical effects
73.63.Hs Quantum wells
68.65.Cd Superlattices
72.40.+w Photoconduction and photovoltaic effects

Electrically commanded surfaces for nematic liquid crystal displays

Lachezar Komitov, Bertil Helgee, Johan Felix, and Avtar Matharu

Appl. Phys. Lett. 86, 023502 (2005); http://dx.doi.org/10.1063/1.1849844 (3 pages) | Cited 15 times

Online Publication Date: 4 January 2005

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Electrically commanded surfaces (ECS) is a liquid crystal display concept whereby the switching of the alignment layer, which is driven by an electric field applied across the layer, is further transferred to the bulk liquid crystal material via elastic forces. This work presents the electro-optic response of a sandwich cell with alignment layer made of siloxane-based ferroelectric liquid crystal polymer, representing the ECS. The bulk liquid crystal material of choice was an in-house nematic mixture comprising fluorinated liquid crystalline compounds with negative dielectric anisotropy (Δε<0). We report a distinct linear electro-optic response, arising from the field-induced in-plane switching of the nematic which in turn is mediated by the ECS.
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77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
61.30.Vx Polymer liquid crystals
78.20.Jq Electro-optical effects
42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
64.70.M- Transitions in liquid crystals

Observation of trapping defects in 4H–silicon carbide metal-oxide-semiconductor field-effect transistors by spin-dependent recombination

David J. Meyer, Patrick M. Lenahan, and Aivars J. Lelis

Appl. Phys. Lett. 86, 023503 (2005); http://dx.doi.org/10.1063/1.1851592 (3 pages) | Cited 4 times

Online Publication Date: 4 January 2005

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We utilize a highly sensitive electron spin resonance technique called spin-dependent recombination to observe deep level dangling bond centers at and very near the SiC/SiO2 interface in fully processed n-channel 4H–SiC lateral metal-oxide-semiconductor field-effect transistors. The axially symmetric g tensor of the largest signal strongly suggests that the responsible defect is a dangling bond center with the dangling bond orbital pointing along the crystalline c axis.
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85.30.Tv Field effect devices
76.30.Mi Color centers and other defects
71.55.-i Impurity and defect levels

Direct observation of self-heating in intrinsic Josephson junction array with a nanoelectrode in the middle

H. B. Wang, T. Hatano, T. Yamashita, P. H. Wu, and P. Müller

Appl. Phys. Lett. 86, 023504 (2005); http://dx.doi.org/10.1063/1.1852077 (3 pages) | Cited 16 times

Online Publication Date: 4 January 2005

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Modifying the double-sided fabrication method we invented a few years ago, a new type of Bi2Sr2CaCu2O8 intrinsic Josephson junction (IJJs) array is explored in which, in addition to the indispensable top and bottom electrodes, there is an electrode only 100 nm thick fabricated in the middle of the array. This electrode provides easy access to the inside of the IJJs, enabling us to understand the device physics better than was possible before. As the first application of such a new device, we have clearly shown how “hot” a junction stack can be under various bias conditions.
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74.81.Fa Josephson junction arrays and wire networks
85.25.Cp Josephson devices
74.25.Sv Critical currents
74.72.-h Cuprate superconductors

Near-field enhanced imaging by a magnetized ferrite slab

R. Marqués, F. Mesa, and F. Medina

Appl. Phys. Lett. 86, 023505 (2005); http://dx.doi.org/10.1063/1.1852091 (3 pages) | Cited 6 times

Online Publication Date: 4 January 2005

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This letter demonstrates the near-field imaging enhancement at microwave frequencies of two-dimensional sources by a ferrite slab magnetized to saturation. It is shown that this effect is based on the nonreciprocal amplification of magnetostatic surface waves (MSSW) across the ferrite slab. The inclusion of losses in our analysis has also made it possible to prove this effect for realistic yttrium iron garnet ferrite samples. For ferrite slabs of width d, the resolution at the image plane (at a distance 2d from the source) is better than the resolution in air at a distance d of the source, which leads to an equivalent air length of the ferrite slab less than zero. Since the constitutive parameters of saturated ferrites depend on the external magnetizing field, the operation frequency of the proposed imaging devices can be tuned by varying this biasing field.
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75.50.Gg Ferrimagnetics
75.30.Ds Spin waves
75.70.Rf Surface magnetism
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High-voltage operation with high current gain of pnp AlGaN/GaN heterojunction bipolar transistors with thin n-type GaN base

Kazuhide Kumakura and Toshiki Makimoto

Appl. Phys. Lett. 86, 023506 (2005); http://dx.doi.org/10.1063/1.1851608 (3 pages) | Cited 6 times

Online Publication Date: 5 January 2005

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A pnp AlGaN/GaN heterojunction bipolar transistor (HBT) with a thin n-GaN base shows high-voltage operation with high current gain in the common-emitter configuration at room temperature. The device structure was grown by metalorganic vapor phase epitaxy on a sapphire substrate. The emitter area is 30 μm×50 μm. The HBT can operate at high voltage of 70 V with the maximum current gain of 40 at the collector current of 10 mA. The maximum output power density is 172 kW/cm2. Transport characteristics in the HBT were also investigated. At small collector current, the current gain is dominated by the recombination current at the emitter-base heterojunction. At moderate collector current, the calculated minority hole diffusion length well agreed with that determined from electron beam induced current measurements, indicating the current gain is dominated by the minority carrier diffusion. At large collector current, a high injection effect was observed in the current gain characteristics.
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85.30.Pq Bipolar transistors
73.63.-b Electronic transport in nanoscale materials and structures
66.30.J- Diffusion of impurities
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Low-force contact heating and softening using micromechanical switches in diffusive-ballistic electron-transport transition

Brian D. Jensen, Kuangwei Huang, Linda L.-W. Chow, and Katsuo Kurabayashi

Appl. Phys. Lett. 86, 023507 (2005); http://dx.doi.org/10.1063/1.1850191 (3 pages) | Cited 7 times

Online Publication Date: 5 January 2005

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We demonstrate softening of the gold-to-gold contact in surface micromachined microelectromechanical switches under electrostatic force near 30 μN, which results from the heating of contact asperities sustaining electron transport. A bias potential that causes the switch contacts to soften is measured for initial contact resistance varying between 0.5 and 300 Ω. The asperity sizes in this range are comparable to the electron mean-free path at room temperature. We show that contact spots smaller than the mean-free path require larger bias for softening. Our results can be explained using a model accounting for ballistic electron transport in the contact.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
73.40.Jn Metal-to-metal contacts
73.40.Cg Contact resistance, contact potential
72.15.Lh Relaxation times and mean free paths
73.23.Ad Ballistic transport

Microfluidic devices with tunable microtopographies

Chia-Hsien Hsu and Albert Folch

Appl. Phys. Lett. 86, 023508 (2005); http://dx.doi.org/10.1063/1.1850593 (3 pages) | Cited 14 times

Online Publication Date: 5 January 2005

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Microfluidic devices are critical components of many biomedical and bioanalytical instruments and allow for probing chemical and physical phenomena at the micron scale. Most current microfluidic devices, however, have the inherent functional limitation that the cross-sectional channel geometry, which determines the fluid flow patterns, is essentially constant at any given point in the channel. We present microfluidic channels that contain topographical features whose size can be tuned by the user in real time. We demonstrate that the topographical changes can be used to alter the laminar flow patterns in microfluidic mixers and to physically trap small fluid volumes.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Va Micromachining
87.16.D- Membranes, bilayers, and vesicles
87.15.Vv Diffusion
47.85.Np Fluidics

Magnetic suppression of secondary electrons in plasma immersion ion implantation

Ing Hwie Tan, Mario Ueda, Renato S. Dallaqua, and Jose O. Rossi

Appl. Phys. Lett. 86, 023509 (2005); http://dx.doi.org/10.1063/1.1852704 (3 pages) | Cited 1 time

Online Publication Date: 6 January 2005

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In this work, magnetic suppression of secondary electrons in plasma immersion ion implantation is demonstrated experimentally in a vacuum arc system. Secondary electrons emitted normally to a copper sample surface were detected by a Faraday cup, whose signal exhibited large negative spikes coincident with high voltage pulses when aluminum ions of an unmagnetized plasma were implanted. When a 12.5 mT magnetic field parallel to the sample’s surface is applied, these spikes are not seen, showing that secondary electrons were magnetically suppressed. Another cup, oriented to detect electrons that flow along the field lines, does not exhibit such negative spikes in either unmagnetized or magnetized plasmas, indicating that a virtual cathode was formed by the trapped secondary electrons.
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52.77.Dq Plasma-based ion implantation and deposition
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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