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15 May 2006

Volume 88, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 88, 203101 (2006); http://dx.doi.org/10.1063/1.2203932 (3 pages)

Andrea Ponzoni, Elisabetta Comini, Giorgio Sberveglieri, Jun Zhou, Shao Zhi Deng, Ning Sheng Xu, Yong Ding, and Zhong Lin Wang
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Copper phthalocyanine based hybrid p-type permeable-base transistor in vertical architecture

Chengang Feng, Mingdong Yi, Shunyang Yu, Dongge Ma, Chengang Feng, Tong Zhang, Michelle S. Meruvia, and Ivo A. Hümmelgen

Appl. Phys. Lett. 88, 203501 (2006); http://dx.doi.org/10.1063/1.2204653 (3 pages) | Cited 4 times

Online Publication Date: 16 May 2006

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We demonstrate the production of copper phthalocyanine (CuPc) based p-type hybrid permeable-base transistors, which operate at low voltages having high common-base current gains. These transistors are prepared by evaporating a thin metal layer (Ag or Al) that acts as base on top of a Si substrate that acts as collector. In the sequence CuPc and Au are thermally sublimated to produce the emitter, constituting a quite simple device production procedure with the additional advantage of allowing higher integration due to its vertical architecture.
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85.30.Pq Bipolar transistors

Highly efficient organic electroluminescent device with modified cathode

Stelios A. Choulis, Mathew K. Mathai, Vi-En Choong, and Franky So

Appl. Phys. Lett. 88, 203502 (2006); http://dx.doi.org/10.1063/1.2204840 (3 pages) | Cited 12 times

Online Publication Date: 17 May 2006

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One of the key parameters for high efficiency organic electrophosphorescent light emitting diodes is charge injection into the phosphorescence compound. By introducing a hybrid device architecture, and incorporating electron and hole interfacial layers with lowest unoccupied molecular orbital and highest occupied molecular orbital levels similar to that of the phosphorescence compound, on the cathode and the anode side of the device, respectively, charge injection properties were improved. A green electrophosphorescence device with luminous efficacy of 50 lm/W at luminance efficiency reaching 55 cd/A was demonstrated.
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85.60.Jb Light-emitting devices

Terahertz imaging with a direct detector based on superconducting tunnel junctions

S. Ariyoshi, C. Otani, A. Dobroiu, H. Sato, K. Kawase, H. M. Shimizu, T. Taino, and H. Matsuo

Appl. Phys. Lett. 88, 203503 (2006); http://dx.doi.org/10.1063/1.2204842 (3 pages) | Cited 21 times

Online Publication Date: 17 May 2006

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We demonstrated terahertz imaging using a direct detector based on niobium superconducting tunnel junctions (STJs). The detector is composed of linearly distributed junctions placed on a superconducting microstrip line and is integrated on two wings of a log-periodic antenna. We succeeded nondestructive imaging for an integrated-circuit card and dry material using the detector around its sensitivity peak ( ∼ 0.66 THz). The dynamic range was measured to be higher than 4×107 (76 dB). Thus, the STJ detector is applicable to high-sensitivity and high-speed terahertz imaging for various nondestructive inspection applications.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

High charge carrier densities and conductance maxima in single-crystal organic field-effect transistors with a polymer electrolyte gate dielectric

Matthew J. Panzer and C. Daniel Frisbie

Appl. Phys. Lett. 88, 203504 (2006); http://dx.doi.org/10.1063/1.2204846 (3 pages) | Cited 43 times

Online Publication Date: 17 May 2006

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High charge carrier densities have been realized in organic field-effect transistors based on single crystals of the organic semiconductors rubrene and tetracene using a high capacitance polymer electrolyte gate dielectric. The source-drain current was modulated by five orders of magnitude in a rubrene single-crystal organic field-effect transistor (SC-OFET) with gate voltages ranging from 0 to −3 V. A peak in the field-effect conductance was also observed in SC-OFETs at induced carrier densities of ∼ 1015 charges/cm2. Key to successful device fabrication was the introduction of a thin, insulating spacer layer between the organic single crystal (OSC) and the polymer electrolyte gate dielectric. Further improvement of the device fabrication procedure may eliminate suspected solvent-related degradation effects and raise mobility values in these SC-OFETs, opening the door to a wide spectrum of experiments on OSCs at high charge carrier densities.
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85.30.Tv Field effect devices

Polarization-insensitive liquid crystal Fresnel lens of dynamic focusing in an orthogonal binary configuration

Dong-Woo Kim, Chang-Jae Yu, Hak-Rin Kim, Sung-Jin Kim, and Sin-Doo Lee

Appl. Phys. Lett. 88, 203505 (2006); http://dx.doi.org/10.1063/1.2205158 (3 pages) | Cited 15 times

Online Publication Date: 17 May 2006

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We report on a polarization-insensitive liquid crystal (LC) Fresnel lens with the centrosymmetry of dynamic focusing in an orthogonally alternating hybrid configuration. The polarization-insensitive Fresnel lens having such successive orthogonal hybrid alignment in two adjacent zones was fabricated using a single-masking process through two-step exposure of a linearly polarized ultraviolet light. It was found that the dynamic focusing property of the LC Fresnel lens is electrically controllable and entirely centrosymmetrical irrespective of the polarization state of an incident light.
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42.79.Bh Lenses, prisms and mirrors
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals

Radio-frequency point-contact electrometer

Hua Qin and David A. Williams

Appl. Phys. Lett. 88, 203506 (2006); http://dx.doi.org/10.1063/1.2205159 (3 pages) | Cited 7 times

Online Publication Date: 17 May 2006

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We fabricate and characterize a radio-frequency semiconductor point-contact (rf-PC) electrometer analogous to radio-frequency single-electron transistors (rf-SETs) [ see Schoelkopf et al., Science 280, 1238 (1998) ]. The point contact is formed by surface Schottky gates in a two-dimensional electron gas in an AlGaAs/GaAs heterostructure. In the present setup, the PC is operating as a simple voltage-controlled resistor rather than a quantum point contact and demonstrates a charge sensitivity of about 2×10−1e/math at a bandwidth of 30 kHz without the use of a cryogenic rf preamplifier. Since the impedance of a typical point-contact device is much lower than the impedance of the typical SET, a semiconductor-based rf-PC, equipped with practical cryogenic rf preamplifiers, could realize an ultrafast and ultrasensitive electrometer.
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07.68.+m Photography, photographic instruments; xerography

Brillouin scattering spectroscopy for a laser heated diamond anvil cell

Fangfei Li, Qiliang Cui, Zhi He, Tian Cui, Chunxiao Gao, Qiang Zhou, and Guangtian Zou

Appl. Phys. Lett. 88, 203507 (2006); http://dx.doi.org/10.1063/1.2205164 (3 pages) | Cited 2 times

Online Publication Date: 17 May 2006

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An in situ Brillouin scattering system is developed to study the elastic properties of materials under high pressure-temperature conditions in deep interior of the Earth and planets. This system integrates confocal Brillouin scattering system with a double-sided laser heated system. Furthermore, the magnetic sputter film deposition technique and photolithographic shaping method are used to grow heat insulated layer and internal heat absorber on the surface of diamond anvil for heating sample easily and uniformly. To study the elastic properties of “hot ice,” the Brillouin scattering of liquid water was performed up to 21.8 GPa and 1170 K in this paper.
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93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
91.60.Ba Elasticity, fracture, and flow
91.35.Gf Structure of the crust and upper mantle

Planar GaN p-i-n photodiodes with n+-conductive channel formed by Si implantation

M. C. Chen, J. K. Sheu, M. L. Lee, C. J. Kao, and G. C. Chi

Appl. Phys. Lett. 88, 203508 (2006); http://dx.doi.org/10.1063/1.2206687 (3 pages) | Cited 1 time

Online Publication Date: 18 May 2006

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In this study, planar GaN p-i-n photodiodes (PDs) were fabricated by Si implantation into GaN-based p-i-n structure grown by metal organic vapor-phase epitaxy. Triple silicon implantation was performed to form a selective n+ channel through the multilayer p-i-n structure. As a result of n+-channel formation, a planar GaN p-i-n detector could be obtained. With the reverse bias below 2 V, the dark current density was well below 50 pA. The dark current increased significantly with an increase of reverse bias, which may be attributed to the incomplete damage (from implantation) removal and thereby result in the higher leakage current. The typical peak responsivity and the cutoff wavelength for the Si-implanted planar p-i-n PDs were around 0.13 A/W and 365 nm, respectively. In addition, the visible (450 nm)-to-UV (365 nm) rejection ratio of around three to four orders could be extracted from the spectra response. Furthermore, the transient response measurements revealed that the full width at half maximum (FWHM) of impulse response was as low as 1.12 ns.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Piezoelectric waves near an imperfectly bonded interface between two half-spaces

Hui Fan, Jiashi Yang, and Limei Xu

Appl. Phys. Lett. 88, 203509 (2006); http://dx.doi.org/10.1063/1.2206702 (3 pages) | Cited 19 times

Online Publication Date: 18 May 2006

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We show the existence of certain waves propagating near an imperfectly bonded interface between two half-spaces of different piezoelectric ceramics. Some of the waves reduce to known waves when perfect bonding is assumed. There are also waves that rely on the imperfection of the interface bonding and they do not remain as interface waves when the bonding is perfect. In particular, it is shown that interface imperfection causes dispersion in general, although there does not explicitly exist a geometric characteristic length of the two-half-space structure. The theoretical results obtained can also be used to design experiments for measuring interface properties.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.35.Gy Mechanical properties; surface strains
62.65.+k Acoustical properties of solids

Bias induced strain in AlGaN/GaN heterojunction field effect transistors and its implications

A. F. M. Anwar, Richard T. Webster, and Kurt V. Smith

Appl. Phys. Lett. 88, 203510 (2006); http://dx.doi.org/10.1063/1.2203739 (3 pages) | Cited 9 times

Online Publication Date: 19 May 2006

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We report gate bias dependence of the charge due to piezoelectric polarization obtained by using a fully coupled formulation based upon the piezoelectric constitutive equations for stress and electric displacement. This formulation is significant because it fully accounts for electromechanical coupling under the constraint of global charge control. The coupled formulation results in lower charge due to piezoelectric polarization as compared to the uncoupled formulation for a given Al mole fraction. With increasing two dimensional electron gas concentration, that is, for gate biases greater than threshold, the compressive strain along the c axis in the barrier AlGaN layer increases with a concomitant increase of in-plane stress. Current collapse is correlated to the increase in source and drain resistances through their dependence upon surface charge. An alternate explanation of current collapse using local charge neutrality is also presented.
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85.30.Tv Field effect devices
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