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8 Aug 2005

Volume 87, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 87, 061103 (2005); http://dx.doi.org/10.1063/1.2008357 (3 pages)

Y. C. Zhong, S. A. Zhu, H. M. Su, H. Z. Wang, J. M. Chen, Z. H. Zeng, and Y. L. Chen
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Analytical on-state current model of polycrystalline silicon thin-film transistors including the kink effect

A. T. Hatzopoulos, D. H. Tassis, C. A. Dimitriadis, and G. Kamarinos

Appl. Phys. Lett. 87, 063501 (2005); http://dx.doi.org/10.1063/1.2007859 (3 pages) | Cited 1 time

Online Publication Date: 1 August 2005

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A simple analytical expression for the on-state current of polycrystalline silicon thin-film transistors is presented, valid in both linear and saturation regimes including the impact ionization effect. The maximum channel electric field and the avalanche multiplication factor are described in terms of an average trapped charge density at the grain boundary, varying with gate voltage due to the continuous energy distribution of the grain boundary trap states. Based on the parameters of the charge inversion voltage, effective carrier mobility and grain boundary barrier height which are extracted from the transfer characteristic at low drain voltage, the model reproduces the experimental output characteristics in devices with different gate lengths using few fitting parameters.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Effective hole injection of organic light-emitting diodes by introducing buckminsterfullerene on the indium tin oxide anode

Il-Hwa Hong, Min-Woo Lee, Young-Mo Koo, Hyein Jeong, Tae-Shick Kim, and Ok-Keun Song

Appl. Phys. Lett. 87, 063502 (2005); http://dx.doi.org/10.1063/1.2005399 (3 pages) | Cited 40 times

Online Publication Date: 1 August 2005

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We demonstrate that dramatically improved hole injection can be achieved by inserting a very thin C60 film between the indium tin oxide (ITO) electrode and N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB) layer. This result is ascribed to the formation of an interfacial dipole layer of buckminsterfullerene (C60) on the ITO electrode. The dipole layer induces the surface potential shift that contributes to improve the charge injection efficiency. The chemical shift was downward to help lower the hole injection energy barrier from the ITO electrode to the NPB layer, consistent with the moderately strong electron accepting nature of C60. The enhanced-charge injection provides a simple way of reducing the power consumption of organic electronic devices for real applications.
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85.60.Jb Light-emitting devices
73.30.+y Surface double layers, Schottky barriers, and work functions
76.60.Cq Chemical and Knight shifts
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Towards addressable organic impedance switch devices

Fredrik L. E. Jakobsson, Xavier Crispin, and Magnus Berggren

Appl. Phys. Lett. 87, 063503 (2005); http://dx.doi.org/10.1063/1.2008369 (3 pages) | Cited 18 times

Online Publication Date: 2 August 2005

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The addressability of organic impedance switch devices as the memory elements of cross-point matrices is improved by introducing nonlinear behavior in their current-voltage characteristics. This is realized by adding a semiconducting layer of copper (II) phthalocyanine (CuPc) on top of the switch layer of Rose Bengal (RB) sodium salt. Leakage currents from unaddressed cells in a matrix are reduced by a factor of 17; thus improving the signal-to-background ratio, reducing driver currents and limiting the potential drop along the addressing lines. The matrix size of RB switch devices, using organic conductors, is predicted to be increased by 32 times when using the additional CuPc layer.
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85.30.-z Semiconductor devices

Ultrasound-modulated optical speckle measurement for scattering medium in a coaxial transmission system

Masaki Hisaka

Appl. Phys. Lett. 87, 063504 (2005); http://dx.doi.org/10.1063/1.2009058 (3 pages) | Cited 2 times

Online Publication Date: 2 August 2005

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Ultrasound-modulated optical speckle measurement interfaced with a charge-coupled device camera has been developed to study the biological speckle pattern behavior modulated by a pulsed-ultrasound wave propagating through strong scattering media in a coaxial transmission system. This method reveals an absorptive object located at 5.0 mm depth within a 10.0 millimeter thick impedance-matched scattering media with submillimeter spatial resolution. Introducing a quantitative value to the speckle pattern in order to evaluate the modulated patterns, we have succeeded in obtaining a series of absorptive distribution values, and simultaneously have improved the signal to noise ratio by 3.8 times.
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87.63.D- Ultrasonography
87.63.L- Visual imaging
43.80.Qf

Organic light-emitting devices with in situ postgrowth annealed organic layers

B. J. Chen, X. W. Sun, T. K. S. Wong, X. Hu, and A. Uddin

Appl. Phys. Lett. 87, 063505 (2005); http://dx.doi.org/10.1063/1.2009831 (3 pages) | Cited 16 times

Online Publication Date: 2 August 2005

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A comparative study of in situ postgrowth annealing of organic layers before metal cathode was conducted on tris-(8-hydroxyqunoline) aluminum (Alq3)-based organic light-emitting devices (OLEDs). The devices were fabricated in the same run with a standard device without annealing for comparison, with an identical structure of indium tin oxide (ITO)/copper phthalocyanine (CuPc) (10 nm)/N,N′-di(naphthalene-l-yl)-N,N′-diphenyl-benzidine (NPB) (90 nm)/Alq3 (90 nm)/Mg:Ag (200 nm)/Ag (20 nm). The annealing temperature used was 60, 80, and 100 °C, respectively. It was found that, in situ postgrowth annealing improves the device performance, and annealing near the glass transition temperature of NPB (99.7 °C), improves device performance drastically. Power efficiency and current efficiency increase significantly with the annealing temperature, except the current efficiency for device annealed at 100 °C is slightly lower than that of the standard device. The voltage and current density for 100 cd/m2 luminance are 5.6 V and 4.4 mA/cm2, respectively, for the device annealed at 100 °C, in comparison to 9.2 V and 4.3 mA/cm2, respectively, for the standard device, the power efficiency is much improved by more than 40%. The in situ postgrowth annealed organic layers were characterized by photoluminescence and Raman spectroscopy.
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85.60.Jb Light-emitting devices
78.55.Kz Solid organic materials
78.30.Jw Organic compounds, polymers
81.40.Gh Other heat and thermomechanical treatments
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
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