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17 Sep 2001

Volume 79, Issue 12, pp. 1745-1922

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Light responsive polymer field-effect transistor

K. S. Narayan and N. Kumar

Appl. Phys. Lett. 79, 1891 (2001); http://dx.doi.org/10.1063/1.1404131 (3 pages) | Cited 94 times

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We report the effect of light incident on a polymer-based field-effect transistor and demonstrate the utility of light as an additional controlling parameter of the transistor state. The transistor exhibits large photosensitivity indicated by the sizable changes in the drain–source current at low levels of light. The response here is considerably higher than that from existing organic/polymeric planar, two-terminal photodetectors due to an additional process contributing to the enhancement. The light-responsive polymer transistor opens up a device-architecture concept for polymer-based electronics. © 2001 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.65.+h Molecular electronic devices
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.61.Ph Polymers; organic compounds

Enhanced photogeneration of carriers in a semiconductor via coupling across a nonisothermal nanoscale vacuum gap

R. S. DiMatteo, P. Greiff, S. L. Finberg, K. A. Young-Waithe, H. K. H. Choy, M. M. Masaki, and C. G. Fonstad

Appl. Phys. Lett. 79, 1894 (2001); http://dx.doi.org/10.1063/1.1400762 (3 pages) | Cited 24 times

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Enhanced generation of carriers when a thermophotovoltaic cell is placed in submicron proximity to a heated surface is demonstrated using custom-designed InAs photodiodes and special silicon-based heater chips produced using microelectromechanical system techniques. The short-circuit current of the photocells is shown to increase sharply (up to fivefold) when the spacing between the heater and photodiode surfaces is reduced, while at the same time, the heater temperature decreases, consistent with increased radiative transfer between the two surfaces. By varying the spacing sinusoidally (at up to 1 kHz), it is demonstrated that the increase in the short-circuit current occurs in phase with the decrease in separation, thereby ruling out thermal effects. It is argued that the increase in short-circuit current is due to increased evanescent coupling of blackbody radiation from the hot surface to the cold photocell, consistent with recent theoretical predictions. The demonstration of this effect is the initial step in the development of a class of energy conversion devices. © 2001 American Institute of Physics.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
85.60.-q Optoelectronic devices
85.60.Dw Photodiodes; phototransistors; photoresistors
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Scanning probe electromagnetic tweezers

Mladen Barbic, Jack J. Mock, Andrew P. Gray, and S. Schultz

Appl. Phys. Lett. 79, 1897 (2001); http://dx.doi.org/10.1063/1.1402963 (3 pages) | Cited 17 times

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We present a micromanipulation technique that utilizes integrated microcoils and magnetic microtips for localized positioning of micron-sized magnetic objects. Forces of 10 pN, and submicron positioning control are demonstrated on the 2.8 μm diameter superparamagnetic beads. The technique also implements an optical illumination scheme that provides a clear viewing of the magnetically trapped objects without including the scattering background from the magnetic manipulator tip. This simple instrument provides a noninvasive, low cost alternative to the optical trapping techniques normally used in micromanipulation. Among the possible advantages are the negligible heating of the manipulated sample, effective decoupling of the manipulation component of the experiment from the optical studies of the systems of interest, and the ability to perform studies in a variety of fluids. © 2001 American Institute of Physics.
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06.60.Sx Positioning and alignment; manipulating, remote handling
81.16.Ta Atom manipulation
75.50.Tt Fine-particle systems; nanocrystalline materials
07.79.-v Scanning probe microscopes and components

Investigation of spurious velocity overshoot using Monte Carlo data

T. Grasser, H. Kosina, and S. Selberherr

Appl. Phys. Lett. 79, 1900 (2001); http://dx.doi.org/10.1063/1.1405000 (3 pages) | Cited 4 times

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For the simulation of state-of-the-art devices, hydrodynamic and energy transport models account for nonlocal effects. Although these models have been available for several decades, there are still unresolved issues. One of these issues is the occurrence of spurious peaks in the velocity profile which are inherent to both Stratton’s [Phys. Rev. 126, 2002 (1962)] and Bløtekjær’s [IEEE Trans.Electron Devices 17, 38 (1970)] models. We investigate the origin of these peaks by introducing relaxation times, mobilities, and closure relations directly from a coupled Monte Carlo simulator. From these simulations, we conclude that the spurious peaks are a direct result of the truncation of the infinite moment series and the inaccuracies in the physical models. © 2001 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
72.10.Bg General formulation of transport theory

Indium–silicon co-doping of high-aluminum-content AlGaN for solar blind photodetectors

V. Adivarahan, G. Simin, G. Tamulaitis, R. Srinivasan, J. Yang, M. Asif Khan, M. S. Shur, and R. Gaska

Appl. Phys. Lett. 79, 1903 (2001); http://dx.doi.org/10.1063/1.1402159 (3 pages) | Cited 23 times

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We report on an indium–silicon co-doping approach for high-Al-content AlGaN layers. Using this approach, very smooth crack-free n-type AlGaN films as thick as 0.5 μm with Al mole fraction up to 40% were grown over sapphire substrates. The maximum electron concentration in the layers, as determined by Hall measurements, was as high as 8×1017 cm−3 and the Hall mobility was up to 40 cm2/Vs. We used this doping technique to demonstrate solar-blind transparent Schottky barrier photodetectors with the cut-off wavelength of 278 nm. © 2001 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.uj III-V and II-VI semiconductors

Dynamics of the response to microwave radiation in YBa2Cu3O7−x hot-electron bolometer mixers

Oliver Harnack, Konstantin S. Il’in, Michael Siegel, Boris S. Karasik, William R. McGrath, and Gert de Lange

Appl. Phys. Lett. 79, 1906 (2001); http://dx.doi.org/10.1063/1.1401095 (3 pages) | Cited 7 times

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We present a systematic study of the intermediate frequency (IF) bandwidth of hot-electron bolometer mixers made from YBa2Cu3O7−x high-temperature superconductive thin films fabricated on substrates with high thermal conductivity (MgO and sapphire). At a local oscillator frequency of 100 GHz, a strong dependence of the IF bandwidth on the bias point and temperature has been experimentally found. Moreover, an unexpected IF bandwidth variation has been detected in a broad range of operating frequencies (1–480 GHz). Besides conventional bolometric mixing mechanisms associated with thermalization of electrons and phonons, the contribution of direct interaction between radiation and magnetic vortices in the YBa2Cu3O7−x film may be responsible for the observed effects. © 2001 American Institute of Physics.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology

Subband electron properties of highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates

C. P. Jiang, Z. M. Huang, S. L. Guo, J. H. Chu, L. J. Cui, Y. P. Zeng, Z. P. Zhu, and B. Q. Wang

Appl. Phys. Lett. 79, 1909 (2001); http://dx.doi.org/10.1063/1.1396625 (3 pages)

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A Shubnikov–de Haas (SdH) oscillation measurement was performed on highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates at a temperature of 1.4 K. By analyzing the experimental data using fast Fourier transform, the electron densities and mobilities of more than one subband are obtained, and an obvious double-peak structure appears at high magnetic field in the Fourier spectrum. In comparing the results of SdH measurements, Hall measurements, and theoretical calculation, we found that this double-peak structure arises from spin splitting of the first-excited subband (i = 1). Very close mobilities of 5859 and 5827 cm2/V s are deduced from this double-peak structure. The sum of the carrier concentration of all the subbands in the quantum well is only 3.95×1012 cm−2 due to incomplete transfer of the electrons from the Si δ-doped layer to the well. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
85.30.Tv Field effect devices
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.43.Qt Magnetoresistance
73.20.At Surface states, band structure, electron density of states
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