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13 May 2002

Volume 80, Issue 19, pp. 3467-3650

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Carbon reactivation kinetics in the base of heterojunction GaInP–GaAs bipolar transistors

J. Mimila-Arroyo, S. W. Bland, and J. Chevallier

Appl. Phys. Lett. 80, 3632 (2002); http://dx.doi.org/10.1063/1.1478156 (3 pages) | Cited 6 times

Online Publication Date: 7 May 2002

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The reactivation kinetics of carbon acceptors in the base region of GaInP/GaAs heterojunction bipolar transistors was studied. The reactivation was achieved by ex situ thermal annealing, through a multistage annealing experiment where the carrier concentration was monitored at each stage. Results indicate that carbon reactivation follows a first-order kinetics process in which the activation energy appears to be the sum of the energy needed to debond the hydrogen from the carbon–hydrogen complex, and the energy necessary to overcome the electrostatic junction barrier. The reactivation constant is thermally activated with an activation energy of 2.83 eV and an attempt frequency of 1.2×1013 s−1. © 2002 American Institute of Physics.
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85.30.Pq Bipolar transistors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors

Controllable alignment of nematic liquid crystals around microscopic posts: Stabilization of multiple states

Stephen Kitson and Adrian Geisow

Appl. Phys. Lett. 80, 3635 (2002); http://dx.doi.org/10.1063/1.1478778 (3 pages) | Cited 39 times

Online Publication Date: 7 May 2002

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Nematic liquid crystal materials are rod-like molecules that align in a locally common direction called the director. This gives rise to anisotropic properties that are used in electro-optical devices such as displays, which usually consist of a sandwich of material between two substrates. The behavior of the director at the substrate surfaces is a critical design consideration, and a wide variety of surface treatments has been reported. Most are dominated by molecular interactions, e.g., high surface energy materials that give homogeneous alignment (the director parallel to substrate). The elastic properties of nematics can also be used to influence alignment by shaping the surface on the micron scale. The potential that this offers to engineer device properties is relatively unexplored; to date, the majority of results reported concentrate on essentially two-dimensional effects. Here we show that the three-dimensional configuration of nematics around microscopic posts results in multiple stable director orientations, and can be used in particular to implement bistable displays with a broad range of control over the optical and switching properties. © 2002 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Simple phase bias for superconducting circuits

J. B. Majer, J. R. Butcher, and J. E. Mooij

Appl. Phys. Lett. 80, 3638 (2002); http://dx.doi.org/10.1063/1.1478150 (3 pages) | Cited 30 times

Online Publication Date: 7 May 2002

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A superconducting phase-bias tool, based on a trapped fluxoid in a ring, is proposed and demonstrated. It can provide arbitrary phase values and is simple to fabricate. The phase bias has been realized in two superconducting quantum interference devices, where the critical current versus magnetic flux is shown to be shifted by π/2 and π. © 2002 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Improved efficiency by a graded emissive region in organic light-emitting diodes

Dongge Ma, C. S. Lee, S. T. Lee, and L. S. Hung

Appl. Phys. Lett. 80, 3641 (2002); http://dx.doi.org/10.1063/1.1479450 (3 pages) | Cited 46 times

Online Publication Date: 7 May 2002

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Electrical and optical properties of organic light-emitting diodes (OLEDs) with a stepwise graded bipolar transport emissive layer for a better control of charge transport and recombination are presented. The graded bipolar transport layer was formed by co-evaporating a hole-transporting material N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB) and an electron-transporting/emissive material tris-(8-hydroxyquinoline) aluminum (Alq3) in steps, where each step has a different concentration ratio of NPB to Alq3. Compared to a conventional heterojunction OLED, electroluminescence efficiency was enhanced by a factor of more than 1.5, whereas the turn-on voltage remained unchanged in the graded structure. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
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