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6 Oct 2008

Volume 93, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 93, 141901 (2008); http://dx.doi.org/10.1063/1.2990662 (3 pages)

J. H. Han, K. B. Kim, S. Yi, J. M. Park, S. W. Sohn, T. E. Kim, D. H. Kim, J. Das, and J. Eckert
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Enhancement of light trapping in thin-film hydrogenated microcrystalline Si solar cells using back reflectors with self-ordered dimple pattern

Hitoshi Sai, Hiroyuki Fujiwara, Michio Kondo, and Yoshiaki Kanamori

Appl. Phys. Lett. 93, 143501 (2008); http://dx.doi.org/10.1063/1.2993351 (3 pages) | Cited 30 times

Online Publication Date: 8 October 2008

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In this article, the light-trapping effect of textured back surface reflectors in thin-film Si solar cells is investigated. A unique substrate with a periodic dimple pattern has been developed by utilizing anodic oxidation of Al as a self-ordering process. n-i-p hydrogenated microcrystalline Si (μc-Si:H) cells fabricated on the Al substrate with a period of 0.9 μm show an improved infrared response compared to those fabricated on randomly textured substrates. A high short circuit current density of 24.3 mA/cm2 has been achieved in a 1-μm-thick μc-Si:H cell by adopting the patterned Al substrate.
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84.60.Jt Photoelectric conversion
81.65.Mq Oxidation
64.75.Yz Self-assembly

High quantum efficiency InGaN/GaN solar cells with 2.95 eV band gap

Carl J. Neufeld, Nikholas G. Toledo, Samantha C. Cruz, Michael Iza, Steven P. DenBaars, and Umesh K. Mishra

Appl. Phys. Lett. 93, 143502 (2008); http://dx.doi.org/10.1063/1.2988894 (3 pages) | Cited 126 times

Online Publication Date: 8 October 2008

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We report on III-nitride photovoltaic cells with external quantum efficiency as high as 63%. InxGa1−xN/GaN p-i-n double heterojunction solar cells are grown by metal-organic chemical vapor deposition on (0001) sapphire substrates with xIn = 12%. A reciprocal space map of the epitaxial structure showed that the InGaN was coherently strained to the GaN buffer. The solar cells have a fill factor of 75%, short circuit current density of 4.2 mA/cm2, and open circuit voltage of 1.81 V under concentrated AM0 illumination. It was observed that the external quantum efficiency can be improved by optimizing the top contact grid.
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84.60.Jt Photoelectric conversion
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Common-emitter and common-base small-signal operation of the transistor laser

B. Faraji, W. Shi, D. L. Pulfrey, and L. Chrostowski

Appl. Phys. Lett. 93, 143503 (2008); http://dx.doi.org/10.1063/1.2998267 (3 pages) | Cited 5 times

Online Publication Date: 9 October 2008

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We derive analytic expressions for the transistor laser in the common-emitter and common-base configuration and compare the performance of the transistor in these two modes of operation. We show that the common-base operation results in a wide-band, small-signal modulation response. This effect is due to reduced carrier lifetime in the base. The bandwidth equalization and the suppression of the relaxation oscillation frequency are shown. A bandwidth of 48 GHz is predicted for a vertical cavity laser biased at 10Ith.
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42.55.-f Lasers
42.60.Fc Modulation, tuning, and mode locking
85.30.Tv Field effect devices

Effect of laminar velocity profile variation on mixing in microfluidic devices: The sigma micromixer

Ehsan Yakhshi Tafti, Ranganathan Kumar, and Hyoung J. Cho

Appl. Phys. Lett. 93, 143504 (2008); http://dx.doi.org/10.1063/1.2996564 (3 pages) | Cited 4 times

Online Publication Date: 10 October 2008

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The effect of the laminar velocity profile and its variation on mixing phenomena at the reduced scale is studied. It is shown that the diffusive mass flux between two miscible streams, flowing laminar in a microchannel, is enhanced if the velocity at their diffusion interface is increased. Based on this idea, an in-plane passive micromixing concept is proposed and implemented in a working device (sigma micromixer). This mixer shows considerable mixing performance by periodically varying the flow velocity profile, such that the maximum of the profile coincides with the transversely progressing diffusion fronts repeatedly throughout the mixing channel.
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47.15.-x Laminar flows
47.51.+a Mixing
47.60.Dx Flows in ducts and channels
47.61.Ne Micromixing

Current perpendicular to the plane spin-valves with CoFeGe magnetic layers

S. Maat, M. J. Carey, and J. R. Childress

Appl. Phys. Lett. 93, 143505 (2008); http://dx.doi.org/10.1063/1.2993213 (3 pages) | Cited 9 times

Online Publication Date: 10 October 2008

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The magnetotransport properties of current perpendicular to the plane giant magnetoresistive spin-valves utilizing (CoFe)100−xGex alloys are investigated. The composition range of 21 ≤ x ≤ 32 at. % is determined to be the alloy composition that maximizes magnetoresistance. ΔRA values of 2.6 mΩ–μm2 are measured for spin-valves with CoFeGe in the free and reference layer resulting in magnetoresistance values of greater than 6%, which is almost twice the value of similar spin-valves with CoFeAl alloys. An analysis of the physical properties of the CoFeGe thin films in the range of interest is also presented.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Optically reconfigurable patterning for control of the propagation characteristics of a planar waveguide

Y. Wang, A. Klittnick, N. A. Clark, and P. Keller

Appl. Phys. Lett. 93, 143506 (2008); http://dx.doi.org/10.1063/1.2998304 (3 pages) | Cited 2 times

Online Publication Date: 10 October 2008

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We demonstrate an easily fabricated all-optical and freely reconfigurable method of controlling the propagating characteristics of the optic path within a planar waveguide with low insertion losses by employing the optical patterning of the refractive index of an erasable and rewriteable photosensitive liquid crystal polymer cladding layer.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
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