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23 Nov 2009

Volume 95, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 95, 213501 (2009); http://dx.doi.org/10.1063/1.3265958 (3 pages)

S. Cibella, M. Ortolani, R. Leoni, G. Torrioli, L. Mahler, Ji-Hua Xu, A. Tredicucci, H. E. Beere, and D. A. Ritchie
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Wide dynamic range terahertz detector pixel for active spectroscopic imaging with quantum cascade lasers

S. Cibella, M. Ortolani, R. Leoni, G. Torrioli, L. Mahler, Ji-Hua Xu, A. Tredicucci, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 95, 213501 (2009); http://dx.doi.org/10.1063/1.3265958 (3 pages) | Cited 4 times

Online Publication Date: 23 November 2009

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A superconducting bolometer with an on-chip lithographic terahertz antenna has been illuminated by two quantum cascade lasers operating at 2.5 and 4.4 THz. The detector displays a 1.2 μs time constant, a noise equivalent power of 20 fW/Hz1/2 and a 60 dB dynamic range. We fabricated a monolithic prototype detector array of five elements. This scalable detector is a suitable candidate for terahertz spectroscopic imaging systems, as it can measure both full illuminator power and strongly attenuated or diffuse reflected signals in subsequent frames.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.60.By Design of specific laser systems
85.25.-j Superconducting devices

Recombination mechanisms in highly efficient thin film Zn(S,O)/Cu(In,Ga)S2 based solar cells

S. Merdes, R. Sáez-Araoz, A. Ennaoui, J. Klaer, M. Ch. Lux-Steiner, and R. Klenk

Appl. Phys. Lett. 95, 213502 (2009); http://dx.doi.org/10.1063/1.3266829 (3 pages) | Cited 10 times

Online Publication Date: 24 November 2009

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Progress in fabricating Cu(In,Ga)S2 based solar cells with Zn(S,O) buffer is presented. An efficiency of 12.9% was achieved. Using spectral response, current-voltage and temperature dependent current-voltage measurements, current transport in this junction was studied and compared to that of a highly efficient CdS/Cu(In,Ga)S2 solar cell with a special focus on recombination mechanisms. Independently of the buffer type and despite the difference in band alignment of the two junctions, interface recombination is found to be the main recombination channel in both cases. This was unexpected since it is generally assumed that a cliff facilitates interface recombination while a spike suppresses it.
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88.40.hj Efficiency and performance of solar cells
88.40.jn Thin film Cu-based I-III-VI2 solar cells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.25.+i Surface conductivity and carrier phenomena

Analog memory capacitor based on field-configurable ion-doped polymers

Qianxi Lai, Lei Zhang, Zhiyong Li, William F. Stickle, R. Stanley Williams, and Yong Chen

Appl. Phys. Lett. 95, 213503 (2009); http://dx.doi.org/10.1063/1.3268433 (3 pages) | Cited 3 times

Online Publication Date: 25 November 2009

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A memory capacitor based on a field-configurable ion-doped polymer is reported. The device can be dynamically and reversibly programed to analog capacitances with low-voltage (<5 V) pulses. After the device is programed to a specific value, its capacitance remains nonvolatile. The field-configurable capacitance is attributed to the modification of ionic dopant concentrations in the polymer. The memory capacitors might be used for analog memory, nonlinear analog, and neuromorphic circuits.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.61.Ph Polymers; organic compounds

Suppression of ambipolar behavior in metallic source/drain metal-oxide-semiconductor field-effect transistors

H. Ghoneim, J. Knoch, H. Riel, D. Webb, M. T. Björk, S. Karg, E. Lörtscher, H. Schmid, and W. Riess

Appl. Phys. Lett. 95, 213504 (2009); http://dx.doi.org/10.1063/1.3266526 (3 pages) | Cited 1 time

Online Publication Date: 25 November 2009

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We present a study on suppressing the ambipolar behavior of Schottky barrier metal-oxide-semiconductor field-effect transistors (MOSFET). Inserting a silicon nitride layer of appropriate thickness between the metallic source/drain electrodes and the silicon yields a low Schottky-barrier and simultaneously tunes the properties of the contact from metal-semiconductor-like to the behavior of a doped contact. Moreover, device characteristics of pseudo-MOSFETs reveal an efficient suppression of ambipolar behavior. Comparison with an alternative way of achieving low Schottky-barrier contacts, i.e., by inserting a strong dipole layer such as LiF between the metal and the silicon, reveals that the suppression is not a result of shifting the Fermi level closer to the conduction band but is caused by a reduction of metal-induced gap states. The trade-off between suppression of the ambipolar behavior, contact length and on-state current is investigated with simulations.
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85.30.Tv Field effect devices
89.20.Kk Engineering

Thermal flying-height control sliders in hard disk drives filled with air-helium gas mixtures

Nan Liu, Jinglin Zheng, and David B. Bogy

Appl. Phys. Lett. 95, 213505 (2009); http://dx.doi.org/10.1063/1.3268468 (3 pages) | Cited 1 time

Online Publication Date: 25 November 2009

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This letter employs established approaches to calculate the physical properties of the air-helium gas mixtures and investigates the thermal flying-height control slider’s flying performance in these environments. It is found that at a fixed heater power, the slider’s flying height first increases and then decreases with the fraction of helium in the gas mixture due to the combined effects of changes in the mean free path, viscosity, and thermal conductivity of the gas mixture with helium content. These findings, together with the proposed approach, are useful for future designs of sliders in air-helium mixtures.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
89.20.Kk Engineering

Improved performance of poly(3-hexylthiophene)/zinc oxide hybrid photovoltaics modified with interfacial nanocrystalline cadmium sulfide

Erik D. Spoerke, Matthew T. Lloyd, Erica M. McCready, Dana C. Olson, Yun-Ju Lee, and Julia W. P. Hsu

Appl. Phys. Lett. 95, 213506 (2009); http://dx.doi.org/10.1063/1.3232231 (3 pages) | Cited 24 times

Online Publication Date: 25 November 2009

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To improve zinc oxide/poly(3-hexylthiophene) (ZnO/P3HT) hybrid solar cell performance, we introduce a nanocrystalline cadmium sulfide (CdS) film at the ZnO/P3HT heterojunction, creating a cascading energy band structure. Current-voltage characteristics under AM1.5 illumination show that, compared to unmodified ZnO/P3HT devices, CdS modification leads to an approximate doubling of the open-circuit voltage and a mild increase in fill factor, without sacrificing any short-circuit current. These characteristics double the power conversion efficiency for devices with an interfacial CdS layer. External quantum efficiency spectra reveal definite photocurrent contributions from the CdS layer, confirming the cascading band structure. The mechanisms behind open-circuit voltage increase are discussed.
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84.60.Jt Photoelectric conversion
73.20.At Surface states, band structure, electron density of states
72.40.+w Photoconduction and photovoltaic effects
81.05.Dz II-VI semiconductors
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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