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9 Dec 2002

Volume 81, Issue 24, pp. 4499-4663

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Backilluminated ultraviolet photodetector based on GaN/AlGaN multiple quantum wells

S. K. Zhang, W. B. Wang, F. Yun, L. He, H. Morkoç, X. Zhou, M. Tamargo, and R. R. Alfano

Appl. Phys. Lett. 81, 4628 (2002); http://dx.doi.org/10.1063/1.1527994 (3 pages) | Cited 11 times

Online Publication Date: 3 December 2002

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The operation of backilluminated ultraviolet (UV) photodetector based on GaN/Al0.27Ga0.73N multiple quantum wells (MQWs) is reported. The MQW structure was deposited on a 1-μm-thick Al0.35Ga0.65N buffer layer which was epitaxied on a sapphire substrate. Coplanar Ohmic contacts were made on the top side of the MQW structure. By illuminating the Ohmic contact positions from the backside of the detector, a flat and narrow band spectral response is achieved in the UV wavelength range from 297 nm to 352 nm. The electron-heavy hole absorption in the MQW region produces the sharp long-wavelength cutoff at 352 nm and the band-to-band absorption of the Al0.35Ga0.65N buffer layer introduces the sharp short-wavelength cutoff at 297 nm. The polarization-induced electric fields result in a redshift of the long-wavelength cutoff. The response time is measured to be RC limited and determined to be 5 μs at a 50 Ω load. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Thermal activation and reversal time in antiferromagnetically coupled media

D. T. Margulies, A. Moser, M. E. Schabes, and Eric. E. Fullerton

Appl. Phys. Lett. 81, 4631 (2002); http://dx.doi.org/10.1063/1.1526464 (3 pages) | Cited 7 times

Online Publication Date: 3 December 2002

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The thermally-activated magnetization reversal process of the lower layer in antiferromagnetically coupled media is investigated. The temperature dependence of the hysteresis loops is used to determine the magnetic parameters of the lower layer and to predict its reversal time. We discuss this reversal time both with and without transitions recorded in the media, and present an experimental technique that demonstrates thermally activated writing of the lower layer. © 2002 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Single-crystalline Si on insulator in confined structures fabricated by two-step metal-induced crystallization of amorphous Si

Yaocheng Liu, Michael D. Deal, Krishna C. Saraswat, and James D. Plummer

Appl. Phys. Lett. 81, 4634 (2002); http://dx.doi.org/10.1063/1.1527977 (3 pages) | Cited 2 times

Online Publication Date: 3 December 2002

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We present a technology and its mechanism to obtain single-crystalline Si pillars on SiO2 using a two-step Ni-induced crystallization process on amorphous Si pillars with confined sizes. The amorphous Si pillars with a Ni cap were first annealed at 400 °C for 15 h so that a single-crystalline NiSi2 template was formed on top of each pillar. In the second step, they were annealed at 550 °C for 2 h, during which single-crystalline Si pillars were formed by NiSi2-mediated solid-phase epitaxy. These single-crystalline Si pillars can be used for advanced vertical metal–oxide–semiconductor transistors and surround-gate structures, especially where low-temperature processing is required. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing
81.15.Np Solid phase epitaxy; growth from solid phases

Resonant detection of subterahertz and terahertz radiation by plasma waves in submicron field-effect transistors

W. Knap, Y. Deng, S. Rumyantsev, and M. S. Shur

Appl. Phys. Lett. 81, 4637 (2002); http://dx.doi.org/10.1063/1.1525851 (3 pages) | Cited 96 times

Online Publication Date: 3 December 2002

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We report on the experiments on resonant photoresponse of the gated two-dimensional electron gas to the terahertz radiation. The visible-light-induced, metastable increase of the carrier density in the transistor channel shifts the resonance position to the higher gate voltages, in agreement with plasma wave detection theory. In this way, an unambiguous proof of the origin of the observed resonant detection is provided. The visible light illumination also leads to an increase of the electron mobility and, as a result, to an increase of the resonant detection quality factor. Resonant detection of the harmonics of the Gunn diode-based emission system is demonstrated up to 1.2 THz. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices
81.05.Ea III-V semiconductors

Hole transport in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors

M. H. Choo, Jae Hoon Kim, and Seongil Im

Appl. Phys. Lett. 81, 4640 (2002); http://dx.doi.org/10.1063/1.1527993 (3 pages) | Cited 24 times

Online Publication Date: 3 December 2002

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We report on the hole transport behavior in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors. Five organic thin-film transistors (OTFTs) were fabricated by evaporating the pentacene films at rates of 1, 3, 5, and 7 Å/s at 25 °C (RT), and 7 Å/s at 60 °C. The field-effect mobility increased with the deposition rate even though the crystalline quality of the pentacene film degraded from an amorphous-crystalline-mixed phase to an amorphous phase. With our optimum deposition rate of 5 Å/s at RT, we obtained a saturation current (ID-SAT) of about 4 μA at a gate bias of −40 V, the field-effect mobility of 0.1 cm2/V s, and the on/off current ratio of 105. For the OTFT prepared with a deposition rate of 7 Å/s at 60 °C, an amorphous pentacene channel layer with a high mobility of ∼0.3 cm2/V s and the on/off current ratio of 104 were observed. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
72.20.Ee Mobility edges; hopping transport

Humidity sensors based on pentacene thin-film transistors

Zheng-Tao Zhu, Jeffrey T. Mason, Rüdiger Dieckmann, and George G. Malliaras

Appl. Phys. Lett. 81, 4643 (2002); http://dx.doi.org/10.1063/1.1527233 (3 pages) | Cited 153 times

Online Publication Date: 3 December 2002

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When a pentacene thin-film transistor is exposed to humidity, its saturation current decreases. This decrease was found to be reversible and can therefore be used to measure the amount of relative humidity in atmosphere. The sensitivity was found to depend on the thickness of the pentacene layer. The microscopic origin of the sensing mechanism is discussed. © 2002 American Institute of Physics.
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07.07.Vx Hygrometers; hygrometry
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds

Influence of carrier mobility and contact barrier height on the electrical characteristics of organic transistors

A. Bolognesi, A. Di Carlo, and P. Lugli

Appl. Phys. Lett. 81, 4646 (2002); http://dx.doi.org/10.1063/1.1527983 (3 pages) | Cited 35 times

Online Publication Date: 3 December 2002

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We have investigated the electrical properties of organic thin-film transistors by way of two-dimensional drift-diffusion simulations. The dependence of the electrical characteristics on the mobility model and on the Schottky barrier height of the contacts is analyzed. We found that both the field dependence of the carrier mobility and the barrier height of the contacts are responsible for the nonlinearity of the output characteristics in the low bias region. We have then extracted the mobility from the simulated characteristics using standard metal–oxide–semiconductor analytic relations and compared to the mobility used in the simulation. The discrepancy found between the two mobilities is mainly induced by the presence of the contact barrier. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
73.30.+y Surface double layers, Schottky barriers, and work functions

Delta-doped AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with high breakdown voltages

Z. Y. Fan, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 81, 4649 (2002); http://dx.doi.org/10.1063/1.1527984 (3 pages) | Cited 8 times

Online Publication Date: 3 December 2002

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The fabrication and dc characteristics of AlGaN/GaN-based heterostructure field-effect transistors (HFETs) by employing the δ-doped barrier and the SiO2 insulated gate are reported. The device grown on sapphire substrate has a high drain-current-driving and gate-control capabilities as well as a very high gate-drain breakdown voltage of 200 V for a gate length of 1 μm and a source-drain distance of 3 μm. The incorporation of the SiO2 insulated gate and the δ-doped barrier into HFET structures reduces the gate leakage and improves the two-dimensional channel carrier mobility, and thereby allows one to take the inherent advantage of AlGaN/GaN HFETs with relatively high Al contents—the device structure is capable to deliver higher electron density (or drain current density) yet ensures an excellent pinch-off property as well as small gate leakage current. These characteristics indicate a great potential of this structure for high-power-microwave applications. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.30.De Semiconductor-device characterization, design, and modeling
73.61.Ey III-V semiconductors

Integrated organic light-emitting device/fluorescence-based chemical sensors

V. Savvate’ev, Z. Chen-Esterlit, J. W. Aylott, B. Choudhury, C.-H. Kim, L. Zou, J. H. Friedl, R. Shinar, J. Shinar, and R. Kopelman

Appl. Phys. Lett. 81, 4652 (2002); http://dx.doi.org/10.1063/1.1518154 (3 pages) | Cited 23 times

Online Publication Date: 3 December 2002

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A fluorescent chemical sensor platform, integrating an organic light-emitting device (OLED) light-source with a fluorescent probe, is demonstrated for a subsecond-fast oxygen sensor. The integration results in strong light coupling and negligible heating of the sensor film or analyte. The potential in vivo operation of compact, stand-alone, battery-powered, OLED-based miniaturized sensor arrays for chemical and biological applications is discussed. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence

GaN metal–semiconductor–metal ultraviolet photodetector with IrO2 Schottky contact

Jong Kyu Kim, Ho Won Jang, Chang Min Jeon, and Jong-Lam Lee

Appl. Phys. Lett. 81, 4655 (2002); http://dx.doi.org/10.1063/1.1524035 (3 pages) | Cited 30 times

Online Publication Date: 3 December 2002

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Iridium oxide (IrO2) was used as the Schottky barrier materials of GaN metal–semiconductor–metal (MSM) ultraviolet photodetector. Annealing an Ir contact at 500 °C under O2 ambient, the reverse leakage current density at −5 V reduced by the four orders of magnitude, to ∼ 10−6 A/cm2. Simultaneously, Schottky barrier height and optical transmittance increased to 1.48 eV and 74.8% at 360 nm, respectively. The dramatic improvement originated from the formation of IrO2 by the annealing, resulting in the increase in the responsivity of the GaN MSM photodetector by one order of magnitude, in comparison with the photodetector with Pt Schottky contact. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Sx Metal-semiconductor-metal structures
73.30.+y Surface double layers, Schottky barriers, and work functions
81.40.Gh Other heat and thermomechanical treatments

Deep-ultraviolet emission of AlGaN/AlN quantum wells on bulk AlN

R. Gaska, C. Chen, J. Yang, E. Kuokstis, A. Khan, G. Tamulaitis, I. Yilmaz, M. S. Shur, J. C. Rojo, and L. J. Schowalter

Appl. Phys. Lett. 81, 4658 (2002); http://dx.doi.org/10.1063/1.1524034 (3 pages) | Cited 27 times

Online Publication Date: 3 December 2002

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An approach for growing high-quality AlGaN/AlN multiple quantum wells (MQW) emitting in deep UV region is proposed. The structures are deposited on bulk AlN substrates. Structural analysis by using x-ray diffraction confirms high crystalline quality of these structures. Photoluminescence dependences on excitation intensity and temperature under band-to-band excitation of AlN barrier layers and under selective excitation of the quantum wells are presented. Al0.5Ga0.5N/AlN MQW grown on bulk AlN demonstrate emission at 260 nm with high emission intensity. Stimulated emission of these structures at 258 nm was observed. The results prove great potential of growing structures with high-aluminum-content layers on bulk AlN substrates. © 2002 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.35.Ct Interface structure and roughness
78.45.+h Stimulated emission
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