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29 Sep 2008

Volume 93, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 93, 132101 (2008); http://dx.doi.org/10.1063/1.2988720 (3 pages)

Yueh-Nan Chen and Lukas Gilz
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Dark carrier recombination in organic solar cell

Ying-Xuan Wang, Shin-Rong Tseng, Hsin-Fei Meng, Kuan-Chen Lee, Chiou-Hua Liu, and Sheng-Fu Horng

Appl. Phys. Lett. 93, 133501 (2008); http://dx.doi.org/10.1063/1.2972115 (3 pages) | Cited 15 times

Online Publication Date: 29 September 2008

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The carrier recombination in organic solar cells is investigated by numerical modeling to understand the weak dependence of the open-circuit voltage on the workfunction of the electrodes. In Ohmic contact structures, photocarriers recombine predominantly with dark carriers diffused from the electrode into the semiconductor. Such dark carrier recombination becomes the main limit of power conversion efficiency and open-circuit voltage. For a given semiconductor decreasing the workfunction difference of the electrodes reduces simultaneously the dark carrier recombination and the flat band voltage. The balance between these two opposite factors gives a nearly constant open-circuit voltage. In an ideal bilayer structure there is no dark carrier recombination and the efficiency is demonstrated to be 60% higher than single layer blend.
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84.60.Jt Photoelectric conversion
73.30.+y Surface double layers, Schottky barriers, and work functions

6:1 aspect ratio silicon pillar based thermal neutron detector filled with 10B

R. J. Nikolić, A. M. Conway, C. E. Reinhardt, R. T. Graff, T. F. Wang, N. Deo, and C. L. Cheung

Appl. Phys. Lett. 93, 133502 (2008); http://dx.doi.org/10.1063/1.2985817 (3 pages) | Cited 18 times

Online Publication Date: 29 September 2008

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Current helium-3 tube based thermal neutron detectors have shortcomings in achieving simultaneously high efficiency and low voltage while maintaining adequate fieldability performance. By using a three-dimensional silicon p-i-n diode pillar array filled with boron-10 these constraints can be overcome. The fabricated pillar structured detector reported here is composed of 2 μm diameter silicon pillars with a 4 μm pitch and height of 12 μm. A thermal neutron detection efficiency of 7.3+/−0.6% and a neutron-to-gamma discrimination of 105 at 2 V reverse bias were measured for this detector. When scaled to larger aspect ratio, a high efficiency device is possible.
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29.40.Wk Solid-state detectors
85.30.Kk Junction diodes

Microvortices and recirculating flow generated by an oscillatory microplate for microfluidic applications

Cheng Ming Lin, Yu Shang Lai, Hsin Ping Liu, and Andrew M. Wo

Appl. Phys. Lett. 93, 133503 (2008); http://dx.doi.org/10.1063/1.2991444 (3 pages) | Cited 3 times

Online Publication Date: 29 September 2008

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Circulatory flow structures can be useful in a microfluidic device but often are difficult to generate mechanically in microscale. This paper presents generation of such flow via an in-plane resonating microplate (100×100×1.2 μm3) actuated by Lorentz law. Results show either one of two nonlinear time-mean flow structures is feasible for the finite plate: (1) two-dimensional (2D) small-scale, counter-rotating microvortices or (2) three-dimensional, large-scale, recirculating flow. Sharpness of microplate’s edge is found to be the decisive factor for 2D microvortices to form. Both flow structures are robust and controllable. Potential applications include trapping and mixing of bioparticles in microfluidic devices.
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47.32.cb Vortex interactions
47.32.Ef Rotating and swirling flows
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Structure and interface bonding of GeO2/Ge/In0.15Ga0.85As heterostructures

Alessandro Molle, Sabina Spiga, Andrea Andreozzi, Marco Fanciulli, Guy Brammertz, and Marc Meuris

Appl. Phys. Lett. 93, 133504 (2008); http://dx.doi.org/10.1063/1.2992560 (3 pages) | Cited 4 times

Online Publication Date: 30 September 2008

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The structural and chemical details of GeO2/Ge layers grown on In0.15Ga0.85As substrates by molecular beam deposition were studied in situ by diffraction and spectroscopic techniques. The formation of semiconductor-oxygen bonds at the Ge/In0.15Ga0.85As interface, which may play a decisive role in dictating the quality of the Ge passivation, was assessed after using two different surface preparations, namely Ar sputtering and atomic hydrogen cleaning.
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68.35.Ct Interface structure and roughness
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

n-InGaN/p-GaN single heterostructure light emitting diode with p-side down

M. L. Reed, E. D. Readinger, H. Shen, M. Wraback, A. Syrkin, A. Usikov, O. V. Kovalenkov, and V. A. Dmitriev

Appl. Phys. Lett. 93, 133505 (2008); http://dx.doi.org/10.1063/1.2992582 (3 pages) | Cited 5 times

Online Publication Date: 30 September 2008

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The effects of negative polarization charge at the n-InGaN/p-GaN interface on the performance of hydride vapor phase-epitaxy deposited single heterostructure n-InGaN/p-GaN LEDs with p-side down are investigated. The strong peak emission wavelength blueshift and concomitant superlinear increase in light output as the injection current increases below 25 A/cm2 are characteristic of radiative tunneling. We show that the combination of two-dimensional hole gas formation on the n-InGaN side of the heterointerface and enhancement of the electron barrier to transport across this interface results in only ∼ 10% efficiency droop up to 500 A/cm2 without implementation of an AlGaN electron-blocking layer or a second heterointerface.
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85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Fd III-V semiconductors

Mechanism of flatband voltage roll-off studied with Al2O3 film deposited on terraced oxide

Kisik Choi, Huang-Chun Wen, Gennadi Bersuker, Rusty Harris, and Byoung Hun Lee

Appl. Phys. Lett. 93, 133506 (2008); http://dx.doi.org/10.1063/1.2993335 (3 pages) | Cited 13 times

Online Publication Date: 1 October 2008

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The mechanism of flatband voltage roll-off (FVRO) has been investigated with capacitors fabricated on terraced oxide with various thicknesses of Al2O3 film deposited by atomic layer deposition. It is found that the FVRO is mainly controlled by the thickness of the bottom interfacial layer and is independent of Al2O3 thickness. This indicates that the dipole at the SiO2/Al2O3 interface is mainly responsible for the FVRO phenomenon rather than the charges. Electrostatic analysis suggests that the disruption of the interface dipole by oxygen vacancy generated in thinner bottom interfacial layer is a potential cause of the FVRO.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
84.32.Tt Capacitors
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Three dimensional characterization of dopant distribution in polycrystalline silicon by laser-assisted atom probe

K. Inoue, F. Yano, A. Nishida, T. Tsunomura, T. Toyama, Y. Nagai, and M. Hasegawa

Appl. Phys. Lett. 93, 133507 (2008); http://dx.doi.org/10.1063/1.2995864 (3 pages) | Cited 9 times

Online Publication Date: 3 October 2008

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Dopant distribution in polycrystalline Si of n-type metal-oxide-semiconductor field effect transistor was measured by laser-assisted three dimensional atom probe. Segregation of As and P atoms to grain boundaries and at the interface between gate and gate oxide, resulting from different mechanisms, i.e., volume diffusion in the bulk and grain boundary diffusion at the interface, was clearly observed. Concentration profiles that show such clear segregation were directly obtained by atomic-resolution measurement.
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85.30.Tv Field effect devices
61.72.Mm Grain and twin boundaries
61.72.uf Ge and Si
66.30.Ny Chemical interdiffusion; diffusion barriers
81.30.Mh Solid-phase precipitation
66.30.J- Diffusion of impurities
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