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28 Mar 2005

Volume 86, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 131114 (2005); http://dx.doi.org/10.1063/1.1889243 (3 pages)

R. Chan, M. Feng, N. Holonyak, and G. Walter
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Pyroelectric effect of a p–n junction in a nonpolar solid

V. Sandomirsky, Y. Schlesinger, and Z. Dashevsky

Appl. Phys. Lett. 86, 133501 (2005); http://dx.doi.org/10.1063/1.1896101 (3 pages) | Cited 3 times

Online Publication Date: 21 March 2005

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We discuss the possibility of a pyroelectric effect in a nonpolar solid. The built-in electrical field of a p–n junction barrier creates a polar axis in the solid. The electric dipole moment, due to the charge separation at the junction, depends on temperature mainly via the temperature dependence of the dielectric constant, giving rise to the pyroelectric effect. Illustrative estimates have been calculated for two quantum paraelectrics, PbTe and SrTiO3.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.70.+a Pyroelectric and electrocaloric effects
77.22.Ch Permittivity (dielectric function)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Are spin junction transistors suitable for signal processing?

S. Bandyopadhyay and M. Cahay

Appl. Phys. Lett. 86, 133502 (2005); http://dx.doi.org/10.1063/1.1883722 (3 pages) | Cited 4 times

Online Publication Date: 21 March 2005

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A number of spintronic analogs of bipolar junction transistors have been proposed for signal processing applications. Here, we show that some of these transistors unfortunately may not have sufficient voltage and current gains for signal processing. They may also have poor isolation between input and output terminals which hinders unidirectional propagation of logic signal from the driver stage to the output. Therefore, these devices may not improve state-of-the-art signal processing capability, although they may provide some additional functionality by offering nonvolatile storage. They may also have niche applications in nonlinear circuits.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.Pq Bipolar transistors
85.70.Ay Magnetic device characterization, design, and modeling
07.68.+m Photography, photographic instruments; xerography

Low-resistance Al-based reflectors for high-power GaN-based flip-chip light-emitting diodes

June-O Song, Woong-Ki Hong, Y. Park, J. S. Kwak, and Tae-Yeon Seong

Appl. Phys. Lett. 86, 133503 (2005); http://dx.doi.org/10.1063/1.1894614 (3 pages) | Cited 9 times

Online Publication Date: 21 March 2005

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We report on the formation of high-quality p-type Al-based ohmic reflectors using Ag (3 nm)/indium tin oxide (ITO)(100 nm) interlayers for use in high-power flip-chip light-emitting diodes (LEDs). The Ag∕ITO interlayers are first annealed at temperatures of 530 and 630 °C for 1 min in air, after which Al reflectors (200 nm thick) are deposited and subsequently annealed at 330 °C for 5 min in a vacuum. It is shown that the annealed Ag∕ITO∕Al contacts give specific contact resistances as low as ∼ 10−5 Ω cm−2 and reflectance of ∼ 85% at a wavelength of 460 nm, which are much better than those of oxidized Ni/Au schemes. LEDs fabricated with the annealed Ag∕ITO∕Al p-type electrodes give forward-bias voltages of 3.29–3.37 V at injection current of 20 mA.
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85.60.Jb Light-emitting devices
61.72.Cc Kinetics of defect formation and annealing
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Enhancement of hole injection using iridium-oxide-coated indium tin oxide anodes in organic light-emitting diodes

Soo Young Kim, Jong-Lam Lee, Ki-Beom Kim, and Yoon-Heung Tak

Appl. Phys. Lett. 86, 133504 (2005); http://dx.doi.org/10.1063/1.1894605 (3 pages) | Cited 18 times

Online Publication Date: 21 March 2005

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We report the enhancement of hole injection using an IrOx layer between indium tin oxide anodes and 4,4’-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light-emitting diodes (OLEDs). The turn-on voltage of OLEDs decreased from 7 V to 4 V and the maximum luminescence value increased from 1200 cd/m2 to 1800 cd/m2 as the Ir layer changed to IrOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.6 eV as the Ir layer transformed into IrOx. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.
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85.60.Jb Light-emitting devices
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
81.65.-b Surface treatments
78.55.Kz Solid organic materials
73.50.Dn Low-field transport and mobility; piezoresistance
73.30.+y Surface double layers, Schottky barriers, and work functions

Carrier trapping and efficient recombination of electrophosphorescent device with stepwise doping profile

Byung Doo Chin, Min Chul Suh, Mu-Hyun Kim, Seong Taek Lee, Hye Dong Kim, and Ho Kyoon Chung

Appl. Phys. Lett. 86, 133505 (2005); http://dx.doi.org/10.1063/1.1894596 (3 pages) | Cited 41 times

Online Publication Date: 22 March 2005

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We have presented a physical concept for enhancing efficiency and lifetime of doped electrophosphorescent organic light-emitting devices. In order to provide a control parameter for higher device performance, a stepwise doping concentration profile at the emission layer was prepared. A more than 30% improvement of power efficiency was obtained for green electrophosphorescent device with a higher doping ratio at the emission layer-hole transport layer interface. We explained the carrier trapping and transport mechanism with direct recombination of an exciton in an iridium-based dopant system. When compared to green device, phosphorescent red devices showed a more significant charge trapping effect at low doping concentration, which is responsible for shifting the recombination zone far from the emission layer-hole transport layer interface. Therefore, charge trapping by doping control in an emission layer could be utilized for a charge-balancing technique for the confinement of a triplet exciton.
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85.60.Jb Light-emitting devices
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.72.S- Impurities in crystals
78.55.Kz Solid organic materials

The Ebers–Moll model for magnetic bipolar transistors

Jaroslav Fabian and Igor Žutić

Appl. Phys. Lett. 86, 133506 (2005); http://dx.doi.org/10.1063/1.1886251 (3 pages) | Cited 6 times

Online Publication Date: 23 March 2005

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The equivalent electrical circuit of the Ebers–Moll-type is introduced for magnetic bipolar transistors. In addition to conventional diodes and current sources, the new circuit comprises two novel elements due to spin-charge coupling. A classification scheme of the operating modes of magnetic bipolar transistors in the low bias regime is presented.
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85.30.Pq Bipolar transistors
85.30.De Semiconductor-device characterization, design, and modeling
85.70.Ay Magnetic device characterization, design, and modeling
72.25.Dc Spin polarized transport in semiconductors

Spin on dopants for high-performance single-crystal silicon transistors on flexible plastic substrates

Z.-T. Zhu, E. Menard, K. Hurley, R. G. Nuzzo, and J. A. Rogers

Appl. Phys. Lett. 86, 133507 (2005); http://dx.doi.org/10.1063/1.1894611 (3 pages) | Cited 34 times

Online Publication Date: 23 March 2005

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Free-standing micro/nanoelements of single-crystal silicon with integrated doped regions for contacts provide a type of material that can be printed onto low-temperature device substrates, such as plastic, for high-performance mechanically flexible thin-film transistors (TFTs). We present simple approaches for fabricating collections of these elements, which we refer to as microstructured silicon (μs-Si), and for using spin-on dopants to introduce doped regions in them. Electrical and mechanical measurements of TFTs formed on plastic substrates with this doped μs-Si indicate excellent performance. These and other characteristics make the material potentially useful for emerging large area, flexible ‘macroelectronic’ devices.
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85.30.Tv Field effect devices
61.72.uf Ge and Si
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Low-temperature processable inherently photosensitive polyimide as a gate insulator for organic thin-film transistors

Seungmoon Pyo, Hyunsam Son, Kil-Yeong Choi, Mi Hye Yi, and Sung Kwon Hong

Appl. Phys. Lett. 86, 133508 (2005); http://dx.doi.org/10.1063/1.1894587 (3 pages) | Cited 21 times

Online Publication Date: 24 March 2005

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We have fabricated organic thin-film transistors (OTFTs) on polyethersulfone substrate using low-temperature processable, inherently photosensitive polyimide as the gate insulator and pentacene as the active material. The polyimide was prepared through two-step reaction. The polyimide precursor, poly(amic acid), was prepared from a dianhydride and aromatic diamine through a polycondensation reaction, and subsequently converted to its corresponding polyimide by a chemical imidization. Photolithographic properties of the polyimide are investigated. The pattern resolution of the cured polyimide was about 50 μm. The pentacene OTFTs with the patterned polyimide were obtained with a carrier mobility of 0.1 cm2/V s and ION/IOFF of 5×105. The OTFT characteristics are discussed in more detail with respect to the electrical properties of the photosensitive polyimide thin film. This low-temperature photopatternable polyimide paves the way for the easy and low-cost fabrication of OTFT arrays without expensive and complicated photolithography and dry etching processes.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
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