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18 Jan 1999

Volume 74, Issue 3, pp. 329-478

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Improved energy transfer in electrophosphorescent devices

D. F. O’Brien, M. A. Baldo, M. E. Thompson, and S. R. Forrest

Appl. Phys. Lett. 74, 442 (1999); http://dx.doi.org/10.1063/1.123055 (3 pages) | Cited 331 times

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External quantum efficiencies of up to (5.6±0.1)% at low brightness and (2.2±0.1)% at 100 cd/m2 are obtained from a red electrophosphorescent device containing the luminescent dye 2,3,7,8, 12,13,17,18-octaethyl-21H23H-phorpine platinum(II) (PtOEP) doped in a 4,4′-N,N′-dicarbazolebiphenyl (CBP) host. Due to weak overlap between excitonic states in PtOEP and CBP, efficiency losses due to nonradiative recombination are low. However, energy transfer between the species is also poor. In compensation, a thin layer of 2,9-dimethyl-4,7 diphenyl-1,10-phenanthroline is used as a barrier to exciton diffusion in CBP, improving the energy transfer to PtOEP. This technique may be applied to improve the efficiency of other electrophosphorescent devices. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
71.35.-y Excitons and related phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Fabry–Perot cavity chemical sensors by silicon micromachining techniques

Jaeheon Han

Appl. Phys. Lett. 74, 445 (1999); http://dx.doi.org/10.1063/1.123056 (3 pages) | Cited 9 times

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Micromachined Fabry–Perot microcavity structures filled with polymeric layers composed of poly(3-dodecylthiophene) have been fabricated and studied for use as chemical sensors. The polymer-filled microcavity devices show reversible sensing behavior in response to the exposure of molecular iodine. Here, the chemical dosing results in a dramatic change in the fraction of transmitted light which passes through the microcavity structure (up to 50% at 633 nm). Importantly, the Fabry–Perot microcavity structure produces a significantly larger change in transmitted light intensity compared to a single membrane structure. © 1999 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
07.10.Cm Micromechanical devices and systems

Low resistance spin-dependent tunnel junctions deposited with a vacuum break and radio frequency plasma oxidized

J. J. Sun, V. Soares, and P. P. Freitas

Appl. Phys. Lett. 74, 448 (1999); http://dx.doi.org/10.1063/1.123057 (3 pages) | Cited 40 times

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Spin-dependent tunnel junctions with resistance-area products (RJ×A) down to 1.8 kΩ×μm2 and tunneling magnetoresistance (TMR)⩾15% were fabricated. Junction areas vary from 6 to 45 μm2. A systematic study of junction resistance and TMR versus deposited Al thickness (tAl = 7, 9, 11, and 13 Å), and oxidation time (from 4 to 90 s) is presented. The TMR is maximum (25% to 27%) for tAl = 11 Å, with 6 s oxidation time (RJ×A = 10 to 20 kΩ×μm2). At 6–10 s oxidation time, reducing the Al thickness from 11 to 7 Å reduces the resistance-area products from 10–20 kΩ×μm2 to 1–3 kΩ×μm2, while TMR decreases from 22%–27% to 13%–17%. Excess oxidation or incomplete oxidation of the Al layer leads to current–voltage curve asymmetry. © 1999 American Institute of Physics.
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73.40.Gk Tunneling
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Rw Metal-insulator-metal structures
81.65.Mq Oxidation
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.61.At Metal and metallic alloys

Piezoresistive torque magnetometry below 1 K

Christian Lupien, Brett Ellman, Peter Grütter, and Louis Taillefer

Appl. Phys. Lett. 74, 451 (1999); http://dx.doi.org/10.1063/1.123058 (3 pages) | Cited 10 times

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We have investigated the performance of piezoresistive cantilevers as magnetometers in the temperature range below 1 K. The de Haas-van Alphen effect was used to study the temperature dependence of a sample of κ-(BEDT-TTF)2Cu(NCS)2, fixed on the end of a cantilever, as a function of the excitation current through the piezoresistive device. We found that by using a small thermalizing wire connected directly to the sample, large excitations were not incompatible with sample temperatures remaining low, thereby establishing the use of these devices as sensitive magnetometers well below 1 K. A large hysteretic behavior observed at low fields (below 0.01 T) and low temperature (below ∼2 K) precludes their use in that regime. © 1999 American Institute of Physics.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Nanometer patterning of epitaxial CoSi2/Si(100) for ultrashort channel Schottky barrier metal–oxide–semiconductor field effect transistors

Q. T. Zhao, F. Klinkhammer, M. Dolle, L. Kappius, and S. Mantl

Appl. Phys. Lett. 74, 454 (1999); http://dx.doi.org/10.1063/1.123059 (3 pages) | Cited 19 times

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A nanometer patterning method, based on local oxidation of silicide layers, was used to pattern epitaxial CoSi2 layers. A feature size as small as 50 nm was obtained for 20 nm epitaxial CoSi2 layers on Si(100) after patterning by local rapid thermal oxidation in dry oxygen. A Schottky source/drain metal–oxide–semiconductor field effect transistor with epitaxial CoSi2 on p-Si(100) was fabricated using this nanopatterning method to make the 100 nm gate. The device shows good I–V characteristics at 300 K. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.30.+y Surface double layers, Schottky barriers, and work functions
85.40.Hp Lithography, masks and pattern transfer
73.61.Cw Elemental semiconductors

Analytic model for direct tunneling current in polycrystalline silicon-gate metal–oxide–semiconductor devices

Leonard F. Register, Elyse Rosenbaum, and Kevin Yang

Appl. Phys. Lett. 74, 457 (1999); http://dx.doi.org/10.1063/1.123060 (3 pages) | Cited 88 times

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An analytic model of the direct tunneling current in metal–oxide–semiconductor devices as a function of oxide field is presented. Accurate modeling of the low-field roll-off in the current results from proper modeling of the field dependencies of the sheet charge, electron impact frequency on the interface, and tunneling probability. To obtain the latter dependence, a modified WKB approximation is used. © 1999 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
73.40.Gk Tunneling
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Tv Field effect devices
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