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5 May 2008

Volume 92, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 92, 182104 (2008); http://dx.doi.org/10.1063/1.2917705 (3 pages)

Jiang Chen, Yibin Hu, Ke Xia, and Zhongshui Ma
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Effects of spatial coherence distortion on terahertz time-domain spectroscopy

Francis Théberge, Marc Châteauneuf, and Jacques Dubois

Appl. Phys. Lett. 92, 183501 (2008); http://dx.doi.org/10.1063/1.2919729 (3 pages) | Cited 3 times

Online Publication Date: 5 May 2008

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This letter reports the impacts of the spatial coherence distortion on the measured absorption spectra and the identification of materials analyzed by terahertz time-domain spectroscopy. It is shown that the deformation of the terahertz beam wave front can result into the overestimation of the electromagnetic absorption and even to the generation of artificial absorption peaks. Obtaining clear absorption spectra without artifacts is crucial for applications based on terahertz spectroscopy. A simple model is presented in order to predict the outcome spectrum from a terahertz beam distorted by a nonuniform sample analyzed through terahertz time-domain spectroscopy.
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78.30.-j Infrared and Raman spectra
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources

Mid-IR focal plane array based on type-II InAs/GaSb strain layer superlattice detector with nBn design

H. S. Kim, E. Plis, J. B. Rodriguez, G. D. Bishop, Y. D. Sharma, L. R. Dawson, S. Krishna, J. Bundas, R. Cook, D. Burrows, R. Dennis, K. Patnaude, A. Reisinger, and M. Sundaram

Appl. Phys. Lett. 92, 183502 (2008); http://dx.doi.org/10.1063/1.2920764 (3 pages) | Cited 14 times

Online Publication Date: 7 May 2008

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A midwave infrared camera (λc = 4.2 μm) with a 320×256 focal plane array (FPA) based on type-II InAs/GaSb strain layer superlattice (SLs) has been demonstrated. The detectors consist of an nBn heterostructure, wherein the SL absorber and contact layers are separated by a Al0.2Ga0.8Sb barrier layer, which is designed to have a minimum valence band offset. Unlike a PN junction, the size of the device is not defined by a mesa etch but confined by the lateral diffusion length of minority carriers. At 77 K, the FPA demonstrates a temporal noise equivalent temperature difference (NETD) of 23.8 mK (Tint = 16.3 ms and Vb = 0.7 V) with a peak quantum efficiency and detectivity at 3.8 μm equal to 52% and 6.7×1011 Jones, respectively.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

High channel mobility 4H-SiC metal-oxide-semiconductor field-effect transistor with low temperature metal-organic chemical-vapor deposition grown Al2O3 gate insulator

S. Hino, T. Hatayama, J. Kato, E. Tokumitsu, N. Miura, and T. Oomori

Appl. Phys. Lett. 92, 183503 (2008); http://dx.doi.org/10.1063/1.2903103 (2 pages) | Cited 4 times

Online Publication Date: 9 May 2008

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Ultrahigh channel mobility is demonstrated for 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with Al2O3 gate insulators fabricated at low temperatures by metal-organic chemical-vapor deposition. Relatively high field effect channel mobility of 64 cm2/V s is obtained when the Al2O3 gate insulator is deposited at 190 °C. Furthermore, extremely high field effect mobility of 284 cm2/V s was obtained for a MOSFET fabricated with an ultrathin thermally grown SiOx layer inserted between the Al2O3 and SiC.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology

Static tuning band gaps of three-dimensional photonic crystals in subterahertz frequencies

Weiwu Chen, Soshu Kirihara, and Yoshinari Miyamoto

Appl. Phys. Lett. 92, 183504 (2008); http://dx.doi.org/10.1063/1.2916822 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2008

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Microscale three-dimensional photonic crystals with different dielectric volume fractions (β) were fabricated to tune the band gaps in the subterahertz frequency range. When changed β from 33% to 20% in the SiO2–Al2O3 ceramic-resin photonic crystals with a lattice constant of 500 μm, the measured first band gaps were increased from 380–450 to 450–520 GHz. After dewaxing and sintering, the lattice constant of SiO2–Al2O3 ceramic photonic crystals were shrunk to 380 μm, and the observed band gaps correspondingly appeared from 470–540 GHz to 520–600 GHz. These experimental results were further confirmed by calculation of band diagrams using the plan wave expansion method.
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42.70.Qs Photonic bandgap materials
61.66.Fn Inorganic compounds
71.20.-b Electron density of states and band structure of crystalline solids

Mechanism of flexural resonance frequency shift of a piezoelectric microcantilever sensor during humidity detection

Qing Zhu, Wan Y. Shih, and Wei-Heng Shih

Appl. Phys. Lett. 92, 183505 (2008); http://dx.doi.org/10.1063/1.2921050 (3 pages) | Cited 14 times

Online Publication Date: 9 May 2008

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We have examined the flexural resonance frequency shift of a piezoelectric microcantilever sensor (PEMS) during humidity detection and have shown that the flexural resonance frequency shift of the PEMS during detection was a result of Young’s modulus change of its piezoelectric layer. Because of the piezoelectric layer’s Young’s modulus change, the PEMS flexural resonance frequency shift was more than 300 times larger than could be accounted for by mass loading.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Vx Hygrometers; hygrometry
81.40.Jj Elasticity and anelasticity, stress-strain relations
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Electrical detection of the mechanical resonances in AlN-actuated microbridges for mass sensing applications

S. González-Castilla, J. Olivares, M. Clement, E. Iborra, J. Sangrador, J. Malo, and J. I. Izpura

Appl. Phys. Lett. 92, 183506 (2008); http://dx.doi.org/10.1063/1.2924284 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2008

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We report the fabrication and frequency characterization of mechanical resonators piezoelectrically actuated with aluminum nitride films. The resonators consist of a freestanding unimorph structure made up of a metal/AlN/metal piezoelectric stack and a Si3N4 supporting layer. We show that the electrical impedance of the one-port device can be used to assess the vibrational behavior of the resonators, provided that the modes do not exhibit specific symmetries, for which the impedance variations cancel. Frequency shifts arise when loading the resonators with small masses. As gravimetric sensors, the microbridges exhibit mass sensitivities of 0.18 fg/Hz for vibrational modes around 2 MHz.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Effects of heat dissipation on unipolar resistance switching in Pt/NiO/Pt capacitors

S. H. Chang, S. C. Chae, S. B. Lee, C. Liu, T. W. Noh, J. S. Lee, B. Kahng, J. H. Jang, M. Y. Kim, D.-W. Kim, and C. U. Jung

Appl. Phys. Lett. 92, 183507 (2008); http://dx.doi.org/10.1063/1.2924304 (3 pages) | Cited 35 times

Online Publication Date: 9 May 2008

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We fabricated Pt/NiO/Pt capacitor structures with various bottom electrode thicknesses tBE and investigated their resistance switching behaviors. The capacitors with tBE ≥ 50 nm exhibited typical unipolar resistance memory switching, while those with tBE ⩽ 30 nm showed threshold switching. This interesting phenomenon can be explained in terms of the temperature-dependent stability of conducting filaments. In particular, the thinner tBE makes dissipation of Joule heat less efficient, so the filaments will be at a higher temperature and become less stable. This study demonstrates the importance of heat dissipation in resistance random access memory.
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84.32.Tt Capacitors

Continuous wave single mode operation of GaInAsSb/GaSb quantum well lasers emitting beyond 3 μm

T. Lehnhardt, M. Hümmer, K. Rößner, M. Müller, S. Höfling, and A. Forchel

Appl. Phys. Lett. 92, 183508 (2008); http://dx.doi.org/10.1063/1.2926657 (3 pages) | Cited 24 times

Online Publication Date: 9 May 2008

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We report on room temperature continuous wave single mode GaInAsSb-GaSb quantum well lasers emitting beyond 3 μm. Quantum well strain and composition were carefully adjusted to enhance the hole confinement without increasing electron confinement in order to avoid inhomogeneous quantum well pumping. In order to realize single mode emission as prerequisite for gas sensing applications, distributed feedback lasers were fabricated. A record single mode emission cw wavelength of 3019 nm with a side mode suppression ratio of more than 30 dB has been obtained. The room temperature peak power output per facet exceeds 3 mW.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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