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13 Dec 2004

Volume 85, Issue 24, pp. 5819-6053

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 5968 (2004); http://dx.doi.org/10.1063/1.1830083 (3 pages)

A. Urbieta, P. Fernández, and J. Piqueras
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Resistive limitations to spatially inhomogeneous electronic losses in solar cells

U. Rau, P. O. Grabitz, and J. H. Werner

Appl. Phys. Lett. 85, 6010 (2004); http://dx.doi.org/10.1063/1.1835536 (3 pages) | Cited 21 times

Online Publication Date: 9 December 2004

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Spatial variations of the electronic properties of solar cells are simulated with the help of a multi-diode model. Increasing the local series resistance limits the degradation of the overall performance by reducing losses of the open circuit voltage originating from cell areas with minor electronic quality. At the same time, the fill factor of the device decreases such that an optimum local series resistance for maximum power conversion efficiency is found. The value of the optimum series resistance depends on the degree of electronic inhomogeneity. Thus, optimization rules for spatially uniform solar cells are different from those for nonuniform cells.
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84.60.Jt Photoelectric conversion
73.40.Cg Contact resistance, contact potential
85.30.De Semiconductor-device characterization, design, and modeling

Micron-sized planar transformer for electromagnetic flux guidance and confinement

C. Kerner, W. Magnus, D. S. Golubović, C. Van Haesendonck, and V. V. Moshchalkov

Appl. Phys. Lett. 85, 6013 (2004); http://dx.doi.org/10.1063/1.1830688 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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We have studied electromagnetic flux guidance and confinement effects in NiFe cores, interconnecting three Al rings, to form a mesoscopic transformer-like device. Applying ac signals (of low amplitude and kHz frequency) to the contact pads of a semiclosed ring induced time-varying magnetic fields, which could be transferred to a nearby, closed ring, via the aid of a NiFe core. Similarly, a second core carried the fields of this ring, resulting from the induced signals, over to a third, semiclosed ring where readouts were performed over an applied load, using a lock-in amplifier. Highly linear curves of output versus input signal at stable phase were obtained with effective mutual inductance in the μH regime, giving an improvement of the order of 106 on the free field.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
85.70.-w Magnetic devices
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

High quality light guide plates that can control the illumination angle based on microprism structures

Di Feng, Guofan Jin, Yingbai Yan, and Shoushan Fan

Appl. Phys. Lett. 85, 6016 (2004); http://dx.doi.org/10.1063/1.1835548 (3 pages) | Cited 19 times

Online Publication Date: 9 December 2004

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In order to make the backlight system thinner and brighter, we propose a high quality poly(methylmethacrylate) light guide plate (LGP) based on microprism structures, which can be designed to control the illumination angle, and to get enough uniformity of intensity, so the backlight system will be simplified to use only one LGP and requires no other optical sheets. Design results reveal that our LGP can achieve a uniformity of intensity better than 86%, and get an illumination angle between ±25°, without using any optical sheets.
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42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics

Low-frequency noise mechanisms in Si and pseudomorphic SiGe p-channel field-effect transistors

M. J. Prest, A. R. Bacon, D. J. F. Fulgoni, T. J. Grasby, E. H. C. Parker, T. E. Whall, and A. M. Waite

Appl. Phys. Lett. 85, 6019 (2004); http://dx.doi.org/10.1063/1.1836001 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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Measurements of low frequency noise in Si and Si0.64Ge0.36 p-channel metal oxide semiconductor field effect transistors are compared with a model of carrier number fluctuations due to tunneling into an energy independent density of oxide trap states (Nox) and associated mobility fluctuations. The failure of the model to explain the data leads us to suggest that reduced noise in the SiGe device as compared to Si is primarily associated with an energy dependence of Nox and a displacement of the Fermi level at the SiO2 interface in the heterostructure relative to the Si control.
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85.30.Tv Field effect devices
72.70.+m Noise processes and phenomena
73.20.At Surface states, band structure, electron density of states
72.20.Fr Low-field transport and mobility; piezoresistance

Zigzag-shaped magnetic sensors

F. C. S. da Silva, W. C. Uhlig, A. B. Kos, S. Schima, J. Aumentado, J. Unguris, and D. P. Pappas

Appl. Phys. Lett. 85, 6022 (2004); http://dx.doi.org/10.1063/1.1834732 (3 pages) | Cited 6 times

Online Publication Date: 9 December 2004

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Magnetism in zigzag-shaped thin-film elements is investigated using scanning electron microscopy with polarization analysis, magnetotransport measurements, and micromagnetic simulations. We find that the angle of magnetization alternates along the length of the element, and is strongly correlated to the corrugated edges. We show that this simple and unique geometry can be used as a single-axis magnetic field sensor. In this configuration, the sensors are primarily sensitive to fields parallel to the applied current. Our results can be interpreted in terms of a coherent rotation model of the magnetization. These devices are scalable to nanometer dimensions.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.55.-w Magnetic instruments and components
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Localized field reduction and rate limitation in visible light photon counters

A. Bross, J. Estrada, P. Rubinov, C. Garcia, and B. Hoeneisen

Appl. Phys. Lett. 85, 6025 (2004); http://dx.doi.org/10.1063/1.1835558 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2004

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We observe the effect of localized field reduction (LFR) in visible light photon counters (VLPCs) by measuring the bias current of the device after a light pulse, and find it consistent with being produced by avalanches that have an average transverse dimension of ≈12 μm2. The characteristic recovery time for the device after an avalanche is measured to be ≈3.5 ms, and is a function of bias voltage and temperature. A simple model is presented to describe the performance drop of the VLPCs with rate as a consequence of LFR.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Surface potential measurements of AlGaN∕GaN high-electron-mobility transistors by Kelvin probe force microscopy

Kohei Nakagami, Yutaka Ohno, Shigeru Kishimoto, Koichi Maezawa, and Takashi Mizutani

Appl. Phys. Lett. 85, 6028 (2004); http://dx.doi.org/10.1063/1.1835551 (2 pages) | Cited 6 times

Online Publication Date: 9 December 2004

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Surface potential of the AlGaN∕GaN high-electron-mobility transistors was measured by Kelvin probe force microscopy to study the mechanism of the drain current collapse. The potential after the gate bias stress increased due to the emission of trapped electrons from the surface states. The time constant of the potential increase (75 s) was comparable to the time constant of the drain current recovery from the collapsed level.
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85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.37.Ps Atomic force microscopy (AFM)

Near-ideal Schottky contact on quaternary AlInGaN epilayer lattice-matched with GaN

Y. Liu, T. Egawa, H. Jiang, B. Zhang, H. Ishikawa, and M. Hao

Appl. Phys. Lett. 85, 6030 (2004); http://dx.doi.org/10.1063/1.1834729 (3 pages) | Cited 5 times

Online Publication Date: 9 December 2004

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Pd∕Ti∕Au and Ni∕Au Schottky barrier diodes (SBDs) were demonstrated on quaternary AlInGaN. Current–voltage properties indicated that near-ideal and high-performance SBDs had been realized with ideality factor of 1.05, 1.07 and barrier height of 1.32, 0.98 eV for Pd and Ni SBDs, respectively. Capacitance–voltage measurement revealed that the high-density two-dimensional electron gas (2DEG) located at the AlInGaN∕GaN interface. Ruling out the possible contribution from piezoelectric polarization and conduction band offset, we believe that the formation of 2DEG is due to the existence of large spontaneous polarization in AlInGaN layer, which experimentally verifies the feasible application of quaternary AlInGaN in the high-electron-mobility transistor.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
77.22.Ej Polarization and depolarization
73.20.At Surface states, band structure, electron density of states

Characterization of bulk and surface currents in strain-balanced InGaAs quantum-well mesa diodes

C. Kelleher, R. Ginige, B. Corbett, and G. Clarke

Appl. Phys. Lett. 85, 6033 (2004); http://dx.doi.org/10.1063/1.1835537 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2004

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We compare the electrical and optical characteristics of mesa diodes based on In0.62Ga0.38As∕In0.45Ga0.55As strain-balanced multiple-quantum wells (SB-MQW) with lattice-matched (LM) In0.53Ga0.47As diodes. The dark current density of the SB-MQW devices is at least an order of magnitude lower than the LM devices for voltages >0.4 V. Sidewall recombination current is only measured on SB-MQW diodes when exposed to a damaging plasma. While radiative recombination current dominates in the SB-MQW diodes, it is less than the diffusive current in the LM diodes for the same applied voltage.
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85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Dw Photodiodes; phototransistors; photoresistors
84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Highly sensitive detector for submillimeter wavelength range

H. Hashiba, V. Antonov, L. Kulik, S. Komiyama, and C. Stanley

Appl. Phys. Lett. 85, 6036 (2004); http://dx.doi.org/10.1063/1.1834716 (3 pages) | Cited 12 times

Online Publication Date: 9 December 2004

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A highly sensitive detector of submillimeter wavelength radiation is reported. The detector consists of a semiconductor quantum dot (QD) and a metallic single-electron transistor (SET). The SET detects change in the potential distribution induced by photon absorption within the QD. We have fabricated and studied this detector at wavelengths longer than 200 μm. High sensitivity, ∼10−20 W∕math in terms of noise equivalent power, is found. Further optimization of the detector design is suggested.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Gv Single electron devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Light-induced switching in back-gated organic transistors with built-in conduction channel

V. Podzorov, V. M. Pudalov, and M. E. Gershenson

Appl. Phys. Lett. 85, 6039 (2004); http://dx.doi.org/10.1063/1.1836877 (3 pages) | Cited 27 times

Online Publication Date: 9 December 2004

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We report an observation of light-induced switching of conductance in back-gated organic field-effect transistors (OFETs) with a built-in conduction channel. In the studied devices, the built-in channel is formed owing to the self-sensitized photo-oxidation of the rubrene surface. In the dark, the back gate controls charge injection from metal contacts into the built-in channel: The high-current ON state corresponds to zero or negative back gate voltage; the low-current OFF state—to a positive back gate voltage that blocks the Schottky contacts. Illumination of an OFET in the OFF state with a short pulse of light switches the device to the ON state, which persists in the dark for days. The OFF state can be restored by cycling the back-gate voltage. The observed effect can be explained by screening the back-gate electric field with the charges photogenerated in the bulk of organic semiconductor.
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85.30.Tv Field effect devices
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Mq Oxidation
73.50.-h Electronic transport phenomena in thin films
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