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5 Jan 2009

Volume 94, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 94, 013102 (2009); http://dx.doi.org/10.1063/1.3062938 (3 pages)

Hao-Chih Yuan, Jonghyun Shin, Guoxuan Qin, Lei Sun, Pallab Bhattacharya, Max G. Lagally, George K. Celler, and Zhenqiang Ma
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Degenerate and nondegenerate lateral-mode patterns in quantum cascade lasers

Nikolai Stelmakh, Michael Vasilyev, Fatima Toor, and Claire Gmachl

Appl. Phys. Lett. 94, 013501 (2009); http://dx.doi.org/10.1063/1.3058768 (3 pages) | Cited 4 times

Online Publication Date: 5 January 2009

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We experimentally investigate near-field lateral-mode patterns of 10–25-μm-wide quantum cascade wide-ridge lasers with few lateral modes using a 1-GHz-resolution spatially resolving midinfrared spectrometer. The results supported by simple box-model theory demonstrate that, depending on the laser geometry, one can either obtain lateral-mode frequency degeneracy or find the high-order lateral modes to be blueshifted or redshifted from the fundamental. We show that, with proper laser geometry, all longitudinal and lateral modes can be frequency nondegenerate and, therefore, be easily suited for spatiospectral mode combining to increase brightness.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Photopatternable self-assembled monolayers as micron scale templates for polymer based field effect transistors

Eran Avnon, Yaron Paz, and Nir Tessler

Appl. Phys. Lett. 94, 013502 (2009); http://dx.doi.org/10.1063/1.3064158 (3 pages) | Cited 5 times

Online Publication Date: 6 January 2009

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We study the use of photopatternable self-assembled monolayers (SAMs) as a template for self-localizing patterns of conducting-polymer based transistors. To allow the use of standard SAMs, we studied and optimized the photocatalytic effect of TiO2, so that it can render the SAMs photopatternable by direct UV light imaging down to micron scale resolution. The resulting template produces high resolution patterns of conducting polymer without resorting to high resolution inkjet printing. This process is used to demonstrate 2 μm channel length organic field effect transistors.
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85.30.Tv Field effect devices

Deep ultraviolet and near infrared photodiode based on n-ZnO/p-silicon nanowire heterojunction fabricated at low temperature

Hai Zhou, Guojia Fang, Longyan Yuan, Chong Wang, Xiaoxia Yang, Huihui Huang, Conghua Zhou, and Xingzhong Zhao

Appl. Phys. Lett. 94, 013503 (2009); http://dx.doi.org/10.1063/1.3064161 (3 pages) | Cited 13 times

Online Publication Date: 6 January 2009

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n-ZnO/p-silicon nanowire (SiNW) photodiodes were prepared by radio frequency reactive magnetron sputtering of n-type zinc oxide at room temperature on photoresist filled p-SiNWs, which were fabricated by electroless metal deposition method at 323 K. Our n-ZnO/p-SiNW photodiodes showed good temperature- and light-intensity dependence. They exhibited strong responsivities of 19.2 and 2.5 A/W for 254 and 1000 nm photons, respectively, under a reverse bias of 2 V with a strong peak of responsivity near 390 nm, the wavelength corresponding to the band gap of ZnO. These results present potential applications of n-ZnO/p-SiNW photodetectors in deep ultraviolet and near infrared regions.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Reverse biased Pt/nanostructured MoO3/SiC Schottky diode based hydrogen gas sensors

J. Yu, S. J. Ippolito, M. Shafiei, D. Dhawan, W. Wlodarski, and K. Kalantar-zadeh

Appl. Phys. Lett. 94, 013504 (2009); http://dx.doi.org/10.1063/1.3054164 (3 pages) | Cited 11 times

Online Publication Date: 7 January 2009

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Pt/nanostructured molybdenum oxide (MoO3)/SiC Schottky diode based gas sensors were fabricated for hydrogen (H2) gas sensing. Due to the enhanced performance, which is ascribed to the application of MoO3 nanostructures, these devices were used in reversed bias. MoO3 characterization by scanning electron microscopy showed morphology of randomly orientated nanoplatelets with thicknesses between 50 and 500 nm. An α-β mixed phase crystallographic structure of MoO3 was characterized by x-ray diffraction. At 180 °C, 1.343 V voltage shift in the reverse I-V curve and a Pt/MoO3 barrier height change of 20 meV were obtained after exposure to 1% H2 gas in synthetic air.
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85.30.Kk Junction diodes
61.46.Hk Nanocrystals
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices

Electrically induced deflective amplification for adaptive sensing of chemicals

Ruhai Tian, Liyuan Ma, and Ming Su

Appl. Phys. Lett. 94, 013505 (2009); http://dx.doi.org/10.1063/1.2999582 (3 pages)

Online Publication Date: 7 January 2009

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An adaptive strategy for sensitive detection of chemicals is proved in electrically induced deflections of an optical fiber. The surface of the fiber, close to one end, is modified by a sensing polymer film. Upon contact with solutions, the adsorption of ions onto the polymer changes the surface charge and bends the fiber in an electric field. The concept has been confirmed in several systems including detections of pH and metal ion, nanoparticles, and self-assembled monolayers. The dependence of the sensitivity on the strength of electric field provides an adaptive approach with adjustable sensitivity for chemical sensing.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Organic thin film transistors using 6,13-bis(tri-isopropylsilylethynyl)pentacene embedded into polymer binders

Jae-Hong Kwon, Sang-Il Shin, Kyung-Hwan Kim, Min Ju Cho, Kyu Nam Kim, Dong Hoon Choi, and Byeong-Kwon Ju

Appl. Phys. Lett. 94, 013506 (2009); http://dx.doi.org/10.1063/1.3063123 (3 pages) | Cited 20 times

Online Publication Date: 8 January 2009

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The active channel material of an organic thin film transistor (OTFT), 6,13-bis(tri-isopropylsilylethynyl)pentacene (TIPS pentacene), is a functionalized pentacene designed to enhance both the solubility and solid-state packing of the pentacene. In this work, in order to improve device performance, three types of polymer binders—poly(α-methylstyrene) (PAMS), poly(4-vinylbiphenyl) (PVBP), and poly(triarylamine) (PTAA)—were employed to fabricate OTFT devices with organic soluble TIPS pentacene. These binders improved film formation in a large area uniformly and helped the TIPS pentacene to form a stronger binding between source/drain electrodes onto dielectric layer. Thus, device performance was highly improved due to improvement of interfacial contact and an increase in the charge transfer in the active channel. OTFTs using TIPS pentacene with PAMS, PVBP, and PTAA for field effect mobilities in the saturation regime have 5×10−3, 8×10−3, and 2.7×10−2 cm2/V s, respectively.
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85.30.Tv Field effect devices
64.75.Bc Solubility
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

Field and polarity dependence of time-to-resistance increase in Fe–O films studied by constant voltage stress method

Koji Eriguchi, Zhiqiang Wei, Takeshi Takagi, Hiroaki Ohta, and Kouichi Ono

Appl. Phys. Lett. 94, 013507 (2009); http://dx.doi.org/10.1063/1.3064127 (3 pages) | Cited 4 times

Online Publication Date: 8 January 2009

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Constant voltage stress (CVS) was applied to Fe–O films prepared by a sputtering process to investigate a stress-induced resistance increase leading to a fundamental mechanism for switching behaviors. Under the CVS, an abrupt resistance increase was found for both stress polarities. A conduction mechanism after the resistance increase exhibited non-Ohmic transport. The time-to-resistance increase (tr) under the CVS was revealed to strongly depend on stress voltage as well as the polarity. From a polarity-dependent resistance increase determined by a time-zero measurement, the voltage and polarity-dependent tr were discussed on the basis of field- and structure-enhanced thermochemical reaction mechanisms.
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73.61.Ng Insulators
68.55.J- Morphology of films
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments

Ellipsometric study of vertically aligned nematic liquid crystals

A. Marino, E. Santamato, N. Bennis, X. Quintana, J. M. Otón, V. Tkachenko, and G. Abbate

Appl. Phys. Lett. 94, 013508 (2009); http://dx.doi.org/10.1063/1.3064131 (3 pages) | Cited 3 times

Online Publication Date: 8 January 2009

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The director tilt angle distribution in vertically aligned nematic liquid crystal displays has been investigated by means of variable angle spectroscopic ellipsometry. Liquid crystal vertical alignment has been realized by thermal evaporation of SiOx. By changing the deposition angle, it is possible to control the pretilt angle. The director profile inside the sample was inferred by reflection and transmission ellipsometric measurements. The tilt angle distribution inside the cell versus the applied voltage is reported and eventually, comparing it with the simulations from the elastic theory, the anchoring energy has been obtained.
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42.79.Kr Display devices, liquid-crystal devices

Bandwidth extension by trade-off of electrical and optical gain in a transistor laser: Three-terminal control

H. W. Then, M. Feng, and N. Holonyak, Jr.

Appl. Phys. Lett. 94, 013509 (2009); http://dx.doi.org/10.1063/1.3068489 (3 pages) | Cited 3 times

Online Publication Date: 9 January 2009

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We present data and describe analytically the “trade-off” between collector current gain and the differential optical gain of a heterojunction bipolar transistor laser (TL). The electrical-optical gain relationship shows that a reduction in the transistor current gain is accompanied by an increase in the differential optical gain of the TL and, as a consequence, results in a larger optical modulation bandwidth. Third-terminal electrical control can be used to enhance the optical bandwidth of a TL beyond the “gain-clamped” cutoff limitation of the carrier-photon (population) resonance characteristic of a diode laser.
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42.55.Px Semiconductor lasers; laser diodes
85.30.Pq Bipolar transistors
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Efficient microfluidic particle separation arrays

David W. Inglis

Appl. Phys. Lett. 94, 013510 (2009); http://dx.doi.org/10.1063/1.3068750 (3 pages) | Cited 15 times

Online Publication Date: 9 January 2009

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Microfluidic particle separation arrays are capable of passive sorting of microparticles or cells by size while avoiding blockage. Despite the usefulness of boundaries for concentration and parallel integration of arrays, separation efficiency is severely degraded in the areas adjacent to the boundaries due to the aberrant fluid flow found there. This letter shows how to eliminate this problem by modifying the boundary interface. At each row the boundary is moved by a specific amount to ensure a linear change in flux from row to row, which leads to uniform flow patterns and improved separation characteristics throughout the array.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.61.-k Micro- and nano- scale flow phenomena
47.85.Np Fluidics

A high performance In0.53Ga0.47As metal-oxide-semiconductor field effect transistor with silicon interface passivation layer

Feng Zhu, Han Zhao, I. Ok, H. S. Kim, J. Yum, Jack C. Lee, Niti Goel, W. Tsai, C. K. Gaspe, and M. B. Santos

Appl. Phys. Lett. 94, 013511 (2009); http://dx.doi.org/10.1063/1.3068752 (3 pages) | Cited 6 times

Online Publication Date: 9 January 2009

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In this letter, we demonstrate a high performance In0.53Ga0.47As channel n-type metal-oxide-semiconductor field effect transistor with silicon interface passivation layer (IPL) and HfO2 gate oxide. Owing to the effectiveness of Si IPL on improving the interface quality, good device characteristics have been obtained, including the peak transconductance of 7.7 mS/mm (Lg = 5 μm and Vd = 50 mV), drive current of 158 mA/mm (Lg = 5 μm, Vgs = Vth+2 V, and Vd = 2.5 V), and the peak effective channel mobility of 1034 cm2/V s. As an important factor on device design, the impact of silicon IPL thickness on the transistor characteristics has been investigated.
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85.30.Tv Field effect devices

Photodetectors formed by an indium tin oxide/zinc oxide/p-type gallium nitride heterojunction with high ultraviolet-to-visible rejection ratio

M. L. Lee, Ping-Feng Chi, and J. K. Sheu

Appl. Phys. Lett. 94, 013512 (2009); http://dx.doi.org/10.1063/1.3064130 (3 pages) | Cited 6 times

Online Publication Date: 9 January 2009

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In this study, indium tin oxide (ITO) or ITO/ZnO films, which were prepared by magnetron sputtering, were deposited onto p-GaN epitaxial films to form ultraviolet photodetectors (PDs). The ITO/ZnO/p-GaN heterojunction PDs behave like the p-i-n photodiodes, which characteristically exhibit low dark current, as opposed to the ITO/p-GaN PDs, which exhibit a marked bias-dependent dark current. The zero-bias rejection ratio can be improved up to 4×105 due to a further reduction in the dark current compared to the ITO/p-GaN PDs. When the incident wavelength is 360 nm, the ITO/ZnO/p-GaN heterojunction PD exhibits a zero-bias photocurrent/dark current ratio and a responsivity of approximately 8×104 and 0.015 A/W, respectively.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Dz II-VI semiconductors
81.05.Ea III-V semiconductors

Spatial distribution of oxygen vacancies in Cr-doped SrTiO3 during an electric-field-driven insulator-to-metal transition

B. P. Andreasson, M. Janousch, U. Staub, and G. I. Meijer

Appl. Phys. Lett. 94, 013513 (2009); http://dx.doi.org/10.1063/1.3069140 (3 pages) | Cited 9 times

Online Publication Date: 9 January 2009

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Spatially resolved x-ray fluorescence maps are presented that show the introduction and the evolution of oxygen vacancies in chromium-doped strontium titanate during an electric-field-driven insulator-to-metal transition. The vacancies are introduced at the anode and diffuse through the crystal toward the cathode. The spatial distribution of vacancies is explained by a model describing the electrical breakdown as a percolation process. Strong differences in the vacancy distribution were found when the transition took place in air and in a hydrogen-enriched atmosphere. In air, the vacancies disappeared from the surface, whereas in the reducing hydrogen atmosphere, they remained at the surface.
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61.72.jd Vacancies
71.30.+h Metal-insulator transitions and other electronic transitions
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
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