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29 Aug 2011

Volume 99, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 99, 094101 (2011); http://dx.doi.org/10.1063/1.3629783 (3 pages)

Tomasz Szymborski, Piotr M. Korczyk, Robert Hołyst, and Piotr Garstecki
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A hybrid surface passivation on HgCdTe long wave infrared detector with in-situ CdTe deposition and high-density hydrogen plasma modification

W. D. Hu, X. S. Chen, Z. H. Ye, and W. Lu

Appl. Phys. Lett. 99, 091101 (2011); http://dx.doi.org/10.1063/1.3633103 (3 pages) | Cited 6 times

Online Publication Date: 29 August 2011

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A hybrid surface passivation, in-situ CdTe passivation and high-density hydrogen plasma modification, is used to improve the surface quality of typical n+-on-p HgCdTe long wave infrared photodiode detectors. Three types of surface-passivated pixels, conventional, in-situ CdTe, and hybrid surface passivation, are fabricated in one chip for better comparison. The maximum dynamic resistances of the hybrid-surface-passivation device are increased to 1∼2 times greater than that in the conventional surface passivation technique. Theoretical modeling shows that the hybrid passivation can significantly suppress the trap-assisted tunneling current. Shallow traps close to the Fermi level under reverse voltage, which are the main source of the trap-assisted tunneling current for conventional surface passivation processing, are reduced by the hybrid passivation treatment.
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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)
85.60.Dw Photodiodes; phototransistors; photoresistors

A quasi-droplet optofluidic ring resonator laser using a micro-bubble

Wonsuk Lee, Yuze Sun, Hao Li, Karthik Reddy, Misha Sumetsky, and Xudong Fan

Appl. Phys. Lett. 99, 091102 (2011); http://dx.doi.org/10.1063/1.3629814 (3 pages) | Cited 6 times

Online Publication Date: 29 August 2011

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Optofluidic ring resonator lasers based on micro-bubbles filled with liquid gain medium are demonstrated. Due to the sub-micron wall thickness of the micro-bubble, significant amount of the electric field resides inside the liquid. Consequently, micro-bubbles mimic the droplets in air that have 3-dimensional optical confinement, extremely high Q-factors, and versatility in handling liquids of different refractive index. Furthermore, they enable repetitive interrogation and easy directional laser emission out-coupling without evaporation or size/shape variations. The laser using Rhodamine 6G in methanol is achieved with a threshold of 300 nJ/mm2 and 5.3 μJ/mm2 for 1 mM and 10 μM in concentration, respectively.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.55.Mv Dye lasers

Doping of GaAs by laser ablated ZnTe

B. Ullrich and G. J. Brown

Appl. Phys. Lett. 99, 091103 (2011); http://dx.doi.org/10.1063/1.3630033 (3 pages)

Online Publication Date: 29 August 2011

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The exposure of GaAs to laser ablated ZnTe causes the formation of donor (Te)-acceptor (Zn) pair states. The photonically transferred dopants resulted in a distinct transition at 1.378 eV (FWHM ≤ 30 meV), visualized by room temperature photocurrent spectroscopy. The presence of impurity absorption in the GaAs was confirmed by transmission measurements. Notably, from the standpoint of technological applications, flipping the applied bias (±1.0 V) to the ZnTe/GaAs heterostructure switches the spectral photocurrent response between the fundamental GaAs absorption and the donor-acceptor transition peak. The results further reveal the influence of the ablating laser line on the optoelectronic device properties.
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61.72.uj III-V and II-VI semiconductors
79.20.Eb Laser ablation
72.40.+w Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.-b Surface treatments

Efficiency droop in InGaN/GaN multiple-quantum-well blue light-emitting diodes grown on free-standing GaN substrate

Zhiqiang Liu, Tongbo Wei, Enqing Guo, Xiaoyan Yi, Liancheng Wang, Junxi Wang, Guohong Wang, Yi Shi, Ian Ferguson, and Jinmin Li

Appl. Phys. Lett. 99, 091104 (2011); http://dx.doi.org/10.1063/1.3605572 (3 pages) | Cited 9 times

Online Publication Date: 29 August 2011

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In this work, the dislocation-related efficiency droop in InGaN/GaN blue light-emitting diodes (LEDs) was investigated by comparing the external quantum efficiency (EQE) of GaN grown on c-plane sapphire and free-standing GaN substrate over a wide range of operation conditions. The values of A, B, and C coefficients had been iteratively obtained by fitting quantum efficiency in the rate equation model. Analysis revealed that threading dislocation density was strongly related to the decrease in EQE of InGaN LEDs at elevated currents by introducing a number of acceptor-like levels with the energy EA lying within the band gap.
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85.60.Jb Light-emitting devices
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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Realization of a narrowband single wavelength microring mirror

Amir Arbabi, Young Mo Kang, Ching-Ying Lu, Edmond Chow, and Lynford L. Goddard

Appl. Phys. Lett. 99, 091105 (2011); http://dx.doi.org/10.1063/1.3633111 (3 pages) | Cited 3 times

Online Publication Date: 30 August 2011

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We present a small footprint narrowband on-chip mirror made by integration of a distributed Bragg reflector (DBR) inside a microring resonator. The DBR covers half of the ring’s circumference and is only reflective at one of the ring resonances. Design, fabrication, and characterization of the proposed device are presented. A single reflection peak with maximum power reflectivity of 92.3% and full width at half maximum of 0.4 nm is demonstrated. The device has potential application as an in-line mirror for low-threshold, narrow linewidth single mode laser diodes.
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42.79.Bh Lenses, prisms and mirrors
42.82.Bq Design and performance testing of integrated-optical systems
42.82.Cr Fabrication techniques; lithography, pattern transfer

Random lasing in the composites consisting of photonic crystals and semiconductor nanowires

M. L. Lu, H. Y. Lin, T. T. Chen, and Y. F. Chen

Appl. Phys. Lett. 99, 091106 (2011); http://dx.doi.org/10.1063/1.3631673 (3 pages) | Cited 4 times

Online Publication Date: 30 August 2011

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A well designed material composed of photonic crystals (PCs) and semiconductor nanowires was proposed. To illustrate our working principle, the nanocomposites consisting of SnO2 nanowires and PCs based on Tb(OH)3/SiO2 core/shell nanospheres have been synthesized and characterized. It is found that lasing behavior can be easily achieved using this composite material. The light confined inside the PCs due to the formation of stop band can be extracted along SnO2 nanowires. The observation of random lasing behavior indicates that the composites developed here open a route for the creation of optoelectronic devices.
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42.55.Zz Random lasers
42.60.By Design of specific laser systems

Advantages of InGaN light-emitting diodes with GaN-InGaN-GaN barriers

Yen-Kuang Kuo, Tsun-Hsin Wang, Jih-Yuan Chang, and Miao-Chan Tsai

Appl. Phys. Lett. 99, 091107 (2011); http://dx.doi.org/10.1063/1.3633268 (3 pages) | Cited 10 times

Online Publication Date: 31 August 2011

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The advantages of InGaN light-emitting diodes with GaN-InGaN-GaN barriers are studied. The energy band diagrams, carrier concentrations in the quantum wells, radiative recombination rate in the active region, light-current performance curves, and internal quantum efficiency are investigated. The simulation results show that the InGaN/GaN-InGaN-GaN light-emitting diode has better performance over its conventional InGaN/GaN and InGaN/InGaN counterparts due to the appropriately modified energy band diagrams which are favorable for the injection of electrons and holes and uniform distribution of these carriers in the quantum wells.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells

Patterned polarized fluorescence from a thin film

G. Myhre, A Sayyad, S. Mataka, and S. Pau

Appl. Phys. Lett. 99, 091108 (2011); http://dx.doi.org/10.1063/1.3631670 (3 pages) | Cited 2 times

Online Publication Date: 31 August 2011

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Patterned polarized fluorescence from a thin film comprised of fluorescent dichroic dye dispersed in liquid crystalline polymer is demonstrated with features as small as 11 μm. Cooperative alignment of these fluorescent dichroic molecules in a liquid crystal polymer leads to films exhibiting polarized green, red, and yellow emission. The dichroic fluorescence emission ratios for these films are 10 to 16 depending on the type of the dye. This simple strategy could be utilized for generating large area linearly polarized light sources or electroluminescent displays.
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81.05.Qk Reinforced polymers and polymer-based composites
42.70.Df Liquid crystals
61.30.Vx Polymer liquid crystals
78.55.Bq Liquids
78.66.Qn Polymers; organic compounds

A numerical study of broadband absorbers for visible to infrared detectors

C. A. Keasler and E. Bellotti

Appl. Phys. Lett. 99, 091109 (2011); http://dx.doi.org/10.1063/1.3632110 (3 pages) | Cited 4 times

Online Publication Date: 31 August 2011

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We have studied the electromagnetic response of micro-structured surfaces realized with pillar arrays intended to provide a broadband (0.5–5.0 μm) absorption enhancement for HgCdTe photovoltaic detector arrays. We have considered both square and hexagonal lattice pillar configurations. Using a finite-difference time-domain approach we have found that the absorption enhancement is weakly dependent on the pillar lattice type, but the lattice period does have a significant impact on the enhancement. The use of these micro-structured surfaces makes it possible to eliminate the need for anti-reflection coatings on the detector back-side while maintaining negligible reflectance over a broad spectral band.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Room temperature, continuous-wave coupled-cavity InAsP/InP photonic crystal laser with enhanced far-field emission directionality

Jingqing Huang, Se-Heon Kim, Jonathan Gardner, Philippe Regreny, Christian Seassal, Pablo Aitor Postigo, and Axel Scherer

Appl. Phys. Lett. 99, 091110 (2011); http://dx.doi.org/10.1063/1.3633120 (3 pages) | Cited 3 times

Online Publication Date: 1 September 2011

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We demonstrate room temperature, continuous-wave lasing with enhanced far field emission directionality in coupled-cavity photonic crystal lasers, made with InAsP/InP quantum well material. These surface-emitting lasers can have a very low effective threshold power of 14.6 μW, with a linewidth of 60 pm, and 40% of the surface emitted power concentrated within a small divergence angle of ±30°.
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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
42.70.Qs Photonic bandgap materials

All-optical four-state magnetization reversal in (Ga,Mn)As ferromagnetic semiconductors

M. D. Kapetanakis, P. C. Lingos, C. Piermarocchi, J. Wang, and I. E. Perakis

Appl. Phys. Lett. 99, 091111 (2011); http://dx.doi.org/10.1063/1.3634031 (3 pages) | Cited 2 times

Online Publication Date: 1 September 2011

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Using density matrix equations of motion and a tight-binding band calculation, we predict all-optical switching between four metastable magnetic states of (III,Mn)As ferromagnets. This switching is initiated non-thermally within 100 fs, during nonlinear coherent photoexcitation. For a single optical pulse, magnetization reversal is completed after ∼100 ps and controlled by the coherent femtosecond photoexcitation. Our predicted switching comes from magnetic nonlinearities triggered by a femtosecond magnetization tilt that is sensitive to un-adiabatic light-induced spin interactions.
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78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Jk Magnetization reversal mechanisms
75.50.Pp Magnetic semiconductors
81.05.Ea III-V semiconductors
78.47.jh Coherent nonlinear optical spectroscopy

Magneto-photonic crystal optical sensors with sensitive covers

Neluka Dissanayake, Miguel Levy, A. Chakravarty, P. A. Heiden, N. Chen, and V. J. Fratello

Appl. Phys. Lett. 99, 091112 (2011); http://dx.doi.org/10.1063/1.3633344 (3 pages) | Cited 1 time

Online Publication Date: 2 September 2011

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We report on a magneto-photonic crystal on-chip optical sensor for specific analyte detection with polypyrrole and gold nano particles as modified photonic crystal waveguide cover layers. The reaction of the active sensor material with various analytes modifies the electronic structure of the sensor layer causing changes in its refractive index and a strong transduction signal. Magneto-photonic crystal enhanced polarization rotation sensitive to the nature of the cover layer detects the index modification upon analyte adsorption. A high degree of selectivity and sensitivity are observed for aqueous ammonia and methanol with polypyrrole and for thiolated-gold- with gold-nanoparticles covers.
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85.70.Sq Magnetooptical devices
42.70.Qs Photonic bandgap materials
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Gn Optical waveguides and couplers
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