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30 May 2011

Volume 98, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 223101 (2011); http://dx.doi.org/10.1063/1.3595266 (3 pages)

Takahiro Ohori, Yasuhide Ohno, Kenzo Maehashi, Koichi Inoue, Yutaka Hayashi, and Kazuhiko Matsumoto
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Bragg polariton luminescence from a GaN membrane embedded in all dielectric microcavity

E. Trichas, N. T. Pelekanos, E. Iliopoulos, E. Monroy, K. Tsagaraki, A. Kostopoulos, and P. G. Savvidis

Appl. Phys. Lett. 98, 221101 (2011); http://dx.doi.org/10.1063/1.3595481 (3 pages) | Cited 1 time

Online Publication Date: 31 May 2011

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We report on the development of a band gap-selective photochemical etching technique capable of producing 200 nm thick optical quality freestanding GaN membranes. The use of low electrolyte concentration combined with intense excitation by a laser source are shown to yield highly anisotropic etch profile with optical quality etched surfaces. Using this technique, high quality GaN microcavity is fabricated by embedding the GaN membrane inside an all-dielectric mirror cavity. In these structures, Bragg polariton photoluminescence is observed at room temperature.
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78.55.Cr III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
82.45.Mp Thin layers, films, monolayers, membranes
71.20.Nr Semiconductor compounds
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Highly catalytic counter electrodes for organic redox couple of thiolate/disulfide in dye-sensitized solar cells

Liang Wang, Mingxing Wu, Yurong Gao, and Tingli Ma

Appl. Phys. Lett. 98, 221102 (2011); http://dx.doi.org/10.1063/1.3595684 (3 pages) | Cited 10 times

Online Publication Date: 31 May 2011

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We synthesized a low-cost, highly catalytic tungsten carbide that was embedded in ordered mesoporous carbon (WC-OMC). This was used as a counter electrode (CE) in dye-sensitized solar cells (DSCs). For comparison, we also evaluated the catalytic activity of bare WC, and several normal carbon materials for the organic redox couple of thiolate/disulfide (T−/T2). The DSCs showed highly photovoltaic conversion efficiencies, ranging from 4.75% to 5.34%. The efficiency of the DSC composed of WC-OMC was 45% higher than that of Pt. Based on kinetic studies, the increased efficiency was caused by the increased exchange current density and decreased charge transfer resistance.
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81.05.U- Carbon/carbon-based materials
88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics
81.05.Rm Porous materials; granular materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Optical dissolved oxygen sensor utilizing molybdenum chloride cluster phosphorescence

Ruby N. Ghosh, Per A. Askeland, Sage Kramer, and Reza Loloee

Appl. Phys. Lett. 98, 221103 (2011); http://dx.doi.org/10.1063/1.3595483 (3 pages) | Cited 3 times

Online Publication Date: 1 June 2011

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We report on an optical oxygen sensor for aqueous media. The phosphorescent signal from the indicator, K2Mo6Cl14, immobilized in a polymer matrix, is quenched by ground state 3O2. Continuous measurements (Δt = 10 s) over 36 h in oxygen atmospheres (0%–21%) were obtained with a signal to noise ratio better than 150. Photobleaching was not observed over ∼ 13 000 measurements. The senor response at 10, 22, and 37 °C water is governed by bimolecular collisional quenching, as evidenced by a linear fit to the Stern–Volmer equation for dissolved oxygen in the range 0<[O2]<3×10−4.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

A InGaN/GaN quantum dot green (λ = 524 nm) laser

Meng Zhang, Animesh Banerjee, Chi-Sen Lee, John M. Hinckley, and Pallab Bhattacharya

Appl. Phys. Lett. 98, 221104 (2011); http://dx.doi.org/10.1063/1.3596436 (3 pages) | Cited 8 times

Online Publication Date: 1 June 2011

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The characteristics of self-organized InGaN/GaN quantum dot lasers are reported. The laser heterostructures were grown on c-plane GaN substrates by plasma-assisted molecular beam epitaxy and the laser facets were formed by focused ion beam etching with gallium. Emission above threshold is characterized by a peak at 524 nm (green) and linewidth of 0.7 nm. The lowest measured threshold current density is 1.2 kA/cm2 at 278 K. The slope and wall plug efficiencies are 0.74 W/A and ∼ 1.1%, respectively, at 1.3 kA/cm2. The value of T0 = 233 K in the temperature range of 260–300 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Generalized scattering control using cut-wire-based metamaterials

Hiroki Wakatsuchi and Christos Christopoulos

Appl. Phys. Lett. 98, 221105 (2011); http://dx.doi.org/10.1063/1.3597628 (3 pages) | Cited 1 time

Online Publication Date: 2 June 2011

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We numerically show how multiple band scattering parameters for arbitrary polarization can be easily designed by using cut-wire-based (CW-based) metamaterials, which enable us to control six fundamental scattering properties, i.e., reflection, transmission, absorption, and polarization independence, dependence and change. The structure shown here is composed of three-independent metamaterial designs, each of which has a different scattering profile. The use of the simple CW-based metamaterials is expected to facilitate complex scattering parameter design, which potentially contributes to the development of more complex and multiple band metamaterial applications.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Experimental investigation on line width compression of stimulated Brillouin scattering in water

Lei Zhang, Dong Zhang, Zhuo Yang, Jinwei Shi, Dahe Liu, Wenping Gong, and Edward S. Fry

Appl. Phys. Lett. 98, 221106 (2011); http://dx.doi.org/10.1063/1.3595338 (3 pages) | Cited 3 times

Online Publication Date: 3 June 2011

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Line width compression of stimulated Brillouin scattering (SBS) in water was investigated experimentally. The results show that, when the water temperature is low, the compressing effect is obvious. However, when the temperature is higher than 25 °C, the line width is almost not compressed in water. Also, the pulse duration compression of SBS was measured simultaneously, and appeared an inherent relation to line width compression. It reveals that the line width can be simply measured by measuring the compressed pulse duration of SBS.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
78.35.+c Brillouin and Rayleigh scattering; other light scattering

High-efficiency silicon-compatible photodetectors based on Ge quantum dots

S. Cosentino, Pei Liu, Son T. Le, S. Lee, D. Paine, A. Zaslavsky, D. Pacifici, S. Mirabella, M. Miritello, I. Crupi, and A. Terrasi

Appl. Phys. Lett. 98, 221107 (2011); http://dx.doi.org/10.1063/1.3597360 (3 pages) | Cited 6 times

Online Publication Date: 3 June 2011

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We report on high responsivity, broadband metal/insulator/semiconductor photodetectors with amorphous Ge quantum dots (a-Ge QDs) as the active absorbers embedded in a silicon dioxide matrix. Spectral responsivities between 1–4 A/W are achieved in the 500–900 nm wavelength range with internal quantum efficiencies (IQEs) as high as ∼ 700%. We investigate the role of a-Ge QDs in the photocurrent generation and explain the high IQE as a result of transport mechanisms via photoexcited QDs. These results suggest that a-Ge QDs are promising for high-performance integrated optoelectronic devices that are fully compatible with silicon technology in terms of fabrication and thermal budget.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Scattering suppression in plasmonic optics using a simple two-layer dielectric structure

E. A. Bezus, L. L. Doskolovich, and N. L. Kazanskiy

Appl. Phys. Lett. 98, 221108 (2011); http://dx.doi.org/10.1063/1.3597620 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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We demonstrate that a planar structure consisting of two isotropic dielectric layers can be used to minimize parasitic scattering in plasmonic elements. It is shown using rigorous electromagnetic simulations that the utilization of the proposed structure allows reducing the scattering losses by an order-of-magnitude (1%–2%). The proposed approach can be used for the design of various plasmonic elements such as lenses, reflectors, and plasmonic crystals.
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42.25.Fx Diffraction and scattering

Microfluidic refractive-index sensors based on small-hole microstructured optical fiber Bragg gratings

A. Ping Zhang, Guofeng Yan, Shaorui Gao, Sailing He, Bongkyun Kim, Jooeun Im, and Youngjoo Chung

Appl. Phys. Lett. 98, 221109 (2011); http://dx.doi.org/10.1063/1.3597623 (3 pages) | Cited 6 times

Online Publication Date: 3 June 2011

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A microstructured optical fiber (MOF) Bragg grating is presented for microfluidic sensing applications. The MOF is specially designed to be with a large amount of microholes for developing ultrasensitive sensors based on inner coating and surface effects. With the fabrication of fiber Bragg grating (FBG), such an MOF sensor has been demonstrated for monitoring the fluid flowing through microholes. Experimental results reveal that the sensitivity of the sensor depends on both the refractive-index range of measurement and the order of fiber modes. The temperature dependency of the sensor has also been measured and compared with that of conventional FBGs.
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42.81.Pa Sensors, gyros
42.81.Wg Other fiber-optical devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
07.10.Cm Micromechanical devices and systems
42.15.Eq Optical system design
42.79.Dj Gratings

Two-dimensional carrier density distribution inside a high power tapered laser diode

R. Pagano, M. Ziegler, J. W. Tomm, I. Esquivias, J. M. G. Tijero, J. R. O’Callaghan, N. Michel, M. Krakowski, and B. Corbett

Appl. Phys. Lett. 98, 221110 (2011); http://dx.doi.org/10.1063/1.3596445 (3 pages)

Online Publication Date: 3 June 2011

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The spontaneous emission of a GaAs-based tapered laser diode emitting at λ = 1060 nm was measured through a window in the transparent substrate in order to study the carrier density distribution inside the device. It is shown that the tapered geometry is responsible for nonuniform amplification of the spontaneous/stimulated emission which in turn influences the spatial distribution of the carriers starting from below threshold. The carrier density does not clamp at the lasing threshold and above it the device shows lateral spatial hole-burning caused by high stimulated emission along the cavity center.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems

Terahertz spectroscopy of Ni–Ti alloy thin films

A. D. Jameson, J. W. Kevek, J. L. Tomaino, M. Hemphill-Johnston, M. J. Paul, M. Koretsky, E. D. Minot, and Yun-Shik Lee

Appl. Phys. Lett. 98, 221111 (2011); http://dx.doi.org/10.1063/1.3596456 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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We investigate the carrier dynamics in nickel–titanium (Ni–Ti) alloy thin films using terahertz transmission spectroscopy. Analyzing the power transmission data and the transmitted waveforms, we obtained the alloy resistivity as a function of Ti concentration. Sharp changes in the resistivity were observed at the Ti fractions of 22%, 44%, and 62%, indicating that structural disorder is greatly enhanced when the alloy undergoes a phase transition.
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78.70.Gq Microwave and radio-frequency interactions
64.70.K- Solid-solid transitions
73.61.At Metal and metallic alloys

MgZnO-based metal-semiconductor-metal solar-blind photodetectors on ZnO substrates

Qinghong Zheng, Feng Huang, Kai Ding, Jin Huang, Dagui Chen, Zhibing Zhan, and Zhang Lin

Appl. Phys. Lett. 98, 221112 (2011); http://dx.doi.org/10.1063/1.3596479 (3 pages) | Cited 5 times

Online Publication Date: 3 June 2011

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Using lattice matched ZnO substrates, wurtzite single crystalline Mg0.49Zn0.51O films were obtained by reactive magnetron cosputtering method, and the heterostructures of MgZnO/ZnO were fabricated into metal-semiconductor-metal solar-blind photodetectors (SBPDs). Calculated and experimental results demonstrate that the response of the ZnO substrate can be suppressed by adopting a thick MgZnO epilayer. The SBPD with a 2 μm thick MgZnO epilayer shows a peak responsivity of 304 mA/W at 260 nm under 10 V bias, which is comparable to the highest value ever reported in MgZnO-based SBPDs. A rejection ratio (R260 nm/R365 nm) over 5×102 is also observed, indicating fully suppression of the signal from ZnO substrate.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
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