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18 Oct 2004

Volume 85, Issue 16, pp. 3343-3639

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3570 (2004); http://dx.doi.org/10.1063/1.1807953 (2 pages)

X. N. Zhang, C. R. Li, Z. Zhang, and Z. X. Cao
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Triple quantum dot charging rectifier

A. Vidan, R. M. Westervelt, M. Stopa, M. Hanson, and A. C. Gossard

Appl. Phys. Lett. 85, 3602 (2004); http://dx.doi.org/10.1063/1.1807030 (3 pages) | Cited 58 times

Online Publication Date: 22 October 2004

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Three tunnel-coupled quantum dots in the Coulomb blockade regime act as a molecular rectifier. We have realized this device in a GaAs∕Al0.3Ga0.7As heterostructure containing a two-dimensional electron gas using lithographically patterned gates. The current through two tunnel-coupled dots in series is recorded versus applied voltage. Ratchet behavior is created by a third dot, with one lead, tunnel-coupled to one of the two dots. An electron enters the third dot where it is trapped, producing a jamming effect where no other electron may enter the device. The current–voltage characteristics show rectification and negative resistance arising from charging of the third dot.
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85.35.Ds Quantum interference devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.La Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Kv Quantum dots
73.40.Ei Rectification
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Modeling and performance of vanadium–oxide transition edge microbolometers

L. A. L. de Almeida, G. S. Deep, A. M. N. Lima, I. A. Khrebtov, V. G. Malyarov, and H. Neff

Appl. Phys. Lett. 85, 3605 (2004); http://dx.doi.org/10.1063/1.1808890 (3 pages) | Cited 19 times

Online Publication Date: 22 October 2004

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The performance of a VO2 thin-film microbolometer has been investigated. The device is operated within 35 °C<T<60 °C, in the hysteretic metal-insulator transition region. An algebraic hysteresis model has been used to model the resistance-temperature characteristic of the sensor. It accurately describes the resistance versus temperature characteristics of the material. Employing this model, and in conjunction with established bolometer theory, the responsivity of a VO2 film is calculated and compared with experimental data. Superior performance of the device is achievable under conditions of single pulse incident radiation where the operating point remains on the major hysteresis loop. This results in a pronounced responsivity peak within the center of the metal-insulator transition. Continuous periodic excitation, in contrast, leads to a steadily decreasing and much lower sensitivity at higher temperature, due to the formation of minor hysteresis loops and the loop accommodation process.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
71.30.+h Metal-insulator transitions and other electronic transitions

Schottky diode characteristics of electrodeposited Au∕n-Si(111) nanocontacts

M. Hugelmann and W. Schindler

Appl. Phys. Lett. 85, 3608 (2004); http://dx.doi.org/10.1063/1.1808871 (3 pages) | Cited 21 times

Online Publication Date: 22 October 2004

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Au∕n-Si(111) contacts with interface areas in the range of 10−12 cm2 have been fabricated at the solid/liquid interface by electrochemical Au nucleation onto n-Si(111):H substrates. The contacts show a Schottky diode behavior with current densities much higher than expected from thermionic emission theory. The applied sophisticated in situ measurement technique allows, in general, in situ studies of electronic properties at any (semi-) conducting nanostructure at solid/liquid interfaces under well-defined conditions.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Ns Metal-nonmetal contacts
73.63.Rt Nanoscale contacts

Self-consistent determination of the generation rate from photoconductance measurements

T. Trupke and R. A. Bardos

Appl. Phys. Lett. 85, 3611 (2004); http://dx.doi.org/10.1063/1.1807961 (3 pages) | Cited 9 times

Online Publication Date: 22 October 2004

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The determination of effective excess carrier lifetimes from photoconductance measurements generally requires knowledge of the absolute generation rate within a sample. Measurements of the generation rate typically involve measurement of the sample absorption spectrum and of the incident light intensity. This letter presents an experimental and analytical method by which both the effective lifetime and the generation rate can be self-consistently determined. The method involves only relative measurements of the generation rate, greatly simplifying the experimental requirements. Good agreement is found experimentally between the results achieved using this method and results from transient photoconductance measurements.
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72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Two-photon-absorption-induced nonlinear photoresponse in GaAs∕AlGaAs quantum-well infrared photodetectors

J. Jiang, Y. Fu, Ning Li, X. S. Chen, H. L. Zhen, W. Lu, M. K. Wang, X. P. Yang, G. Wu, Y. H. Fan, and Y. G. Li

Appl. Phys. Lett. 85, 3614 (2004); http://dx.doi.org/10.1063/1.1781732 (3 pages) | Cited 2 times

Online Publication Date: 22 October 2004

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Using a free-electron laser(FEL) source, we have studied the two-photon-absorption (TPA) effect in GaAs∕AlGaAs quantum-well infrared photodetector (QWIP). The TPA-induced photoresponse in QWIPs has been measured under different FEL excitation power by the photoconductivity method. The effective-mass approximation theory is used for the QWIP structure to explain the photoresponse behavior. It is demonstrated that the TPA-induced photocarrier density is proportional to the square of the excitation power. Based on the experimental results, the TPA coefficients of QWIPs were obtained to be 0.0045, 0.0030, 0.0103, and 0.0061 cm∕MW for the excitation lines of 10.6, 10.7, 11.9 and 13.2 μm, respectively. The dependence the TPA coefficients on the excitation wavelength is explained by our theoretical model.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
71.20.Ps Other inorganic compounds
73.50.Pz Photoconduction and photovoltaic effects
73.21.Fg Quantum wells
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Reach-through band bending in semiconductor thin films

Y. Roussillon, D. M. Giolando, V. G. Karpov, Diana Shvydka, and A. D. Compaan

Appl. Phys. Lett. 85, 3617 (2004); http://dx.doi.org/10.1063/1.1803950 (3 pages) | Cited 7 times

Online Publication Date: 22 October 2004

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We describe a phenomenon of reach-through band bending in thin film semiconductors. It occurs through generation of defects that change the semiconductor work function. This translates the effect of the metal presence through the semiconductor film and induces a Schottky barrier in another semiconductor tangent to the film on the opposite side (reach-through band bending). We have found experimental evidence of this effect in CdTe photovoltaics.
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81.05.Dz II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors

Organic field-effect transistors with electroplated platinum contacts

L. A. Majewski, R. Schroeder, and M. Grell

Appl. Phys. Lett. 85, 3620 (2004); http://dx.doi.org/10.1063/1.1797540 (3 pages) | Cited 8 times

Online Publication Date: 22 October 2004

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Recent developments in organic transistor semiconductors and engineering have led to a situation where the performance of state-of-the-art organic transistors (organic field-effect transistors) often is limited by the resistance at the metal/semiconductor contacts, rather than the semiconductor channel. This letter shows that organic transistor contacts can be improved by the most important industrial process for the deposition of noble metals, electroplating. The advantages of electroplating over vacuum-based techniques such as evaporating and sputtering, in particular for the deposition of platinum (Pt), are discussed.
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85.30.Tv Field effect devices
81.15.Pq Electrodeposition, electroplating
73.40.Ns Metal-nonmetal contacts
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