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19 Dec 2011

Volume 99, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 253701 (2011); http://dx.doi.org/10.1063/1.3666819 (3 pages)

Jun Huang, Hui Li, Wei Chen, Guo-Hua Lv, Xing-Quan Wang, Guo-Ping Zhang, Kostya Ostrikov, Peng-Ye Wang, and Si-Ze Yang
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Tunable and collimated terahertz radiation generation by femtosecond laser pulses

Hitendra K. Malik and Anil K. Malik

Appl. Phys. Lett. 99, 251101 (2011); http://dx.doi.org/10.1063/1.3666855 (3 pages) | Cited 1 time

Online Publication Date: 19 December 2011

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A mechanism is proposed for the generation of tunable terahertz (THz) radiation under the application of two femtosecond laser pulses and an external magnetic field, where quick tunnel ionization is achieved that leads to higher plasma density evolution and large residual current for the efficient THz radiation generation. With the optimization of magnetic field, phase difference, and amplitudes of lasers’ fields, a THz source can be obtained with tunable frequency and power along with a control on the direction of radiation emission.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
84.40.-x Radiowave and microwave (including millimeter wave) technology
52.80.-s Electric discharges
52.25.-b Plasma properties
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

An ultraviolet photo-detector based on TiO2/water solid-liquid heterojunction

Wen-Jen Lee and Min-Hsiung Hon

Appl. Phys. Lett. 99, 251102 (2011); http://dx.doi.org/10.1063/1.3671076 (3 pages) | Cited 2 times

Online Publication Date: 19 December 2011

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In this study, an ultraviolet photodetector (UV-PD) based on TiO2/water solid-liquid heterojunction (SLHJ) is reported. The SLHJ UV-PD exhibits a high photosensitivity, excellent spectral selectivity, linear variations in photocurrent, and fast response. In addition, it is suggested that the spectral response can be tailored and that the performance can be improved through deliberate design of the active layer, electrolyte, and substrate of the SLHJ UV–PD. Moreover, we anticipate this work to be a starting point for more sophisticated commercial photon detection using an SLHJ device.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Optical lattices of InGaN quantum well excitons

V. V. Chaldyshev, A. S. Bolshakov, E. E. Zavarin, A. V. Sakharov, W. V. Lundin, A. F. Tsatsulnikov, M. A. Yagovkina, Taek Kim, and Youngsoo Park

Appl. Phys. Lett. 99, 251103 (2011); http://dx.doi.org/10.1063/1.3670499 (4 pages) | Cited 3 times

Online Publication Date: 20 December 2011

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We demonstrate optical Bragg lattices formed by quasi-two-dimensional excitons in periodic systems of the InGaN quantum wells separated by the GaN barriers. When the Bragg resonance and exciton-polariton resonance are tuned to each-other, the medium exhibits an exciton-mediated resonantly enhanced optical Bragg reflection. The enhancement factor appeared to be larger than 2 for the system of 60 quantum wells. Owing to a high binding energy and oscillator strength of the excitons in InGaN quantum wells, the resonant enhancement was achieved at room temperature.
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78.67.De Quantum wells
73.21.Fg Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Phase-locking regimes of photonic crystal nanocavity laser arrays

T. Suhr, P. T. Kristensen, and J. Mørk

Appl. Phys. Lett. 99, 251104 (2011); http://dx.doi.org/10.1063/1.3671151 (3 pages)

Online Publication Date: 20 December 2011

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We model and analyze the dynamical properties of coupled photonic crystal nanocavity lasers. The model includes Purcell enhancement of the spontaneous emission and intercavity coupling. The coupling strength between neighboring cavities is an essential parameter, and by performing finite-difference time-domain calculations, the typical coupling strength is extracted for realistic structures. Phase-locking regimes are identified, and their stability with respect to parameter variation is investigated. The results suggest that quantum well devices are not well suited for phase-locked nanocavity laser array devices.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials
42.60.Fc Modulation, tuning, and mode locking

Nonlinear behavior of photoluminescence from silicon particles under two-photon excitation

Xingsheng Xu and Shiyoshi Yokoyama

Appl. Phys. Lett. 99, 251105 (2011); http://dx.doi.org/10.1063/1.3665042 (3 pages)

Online Publication Date: 21 December 2011

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Two-photon excited fluorescence (TPEF) under continuous-wave excitation from silicon particles produced by a pulsed laser is investigated. Spectra and images of TPEF from silicon particles are studied under different excitation intensities and operation modes (continuous wave or pulse). It is found that the photoluminescence depends superlinearly on the excitation intensity and that the spectral shape and peaks vary with different silicon particles. The above phenomena show the nonlinear behavior of TPEF from silicon particles, and stimulated emission is a possible process.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.05.Cy Elemental semiconductors
78.45.+h Stimulated emission
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Ap Elemental semiconductors

Diamond based light-emitting diode for visible single-photon emission at room temperature

A. Lohrmann, S. Pezzagna, I. Dobrinets, P. Spinicelli, V. Jacques, J.-F. Roch, J. Meijer, and A. M. Zaitsev

Appl. Phys. Lett. 99, 251106 (2011); http://dx.doi.org/10.1063/1.3670332 (4 pages) | Cited 4 times

Online Publication Date: 21 December 2011

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Diamond-based p-i-n light-emitting diodes capable of single-photon emission in the visible spectral region at room temperature are discussed. The diodes were fabricated on a high quality single crystal diamond grown by chemical vapor deposition. Implantation of boron and phosphorus ions followed by annealing at a temperature of 1600 °C has been used for doping p-type and n-type areas, respectively. Electrical characterization of the devices demonstrates clear diode behavior. Spectra of electroluminescence generated in the i-area reveal sole emission from the neutral nitrogen-vacancy (NV) defects. Photon antibunching implies single-photon character of this emission when generated by individual NV defects.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Mid-infrared quantitative spectroscopy by comb-referencing of a quantum-cascade-laser: Application to the CO2 spectrum at 4.3 μm

A. Gambetta, D. Gatti, A. Castrillo, G. Galzerano, P. Laporta, L. Gianfrani, and M. Marangoni

Appl. Phys. Lett. 99, 251107 (2011); http://dx.doi.org/10.1063/1.3671081 (3 pages) | Cited 10 times

Online Publication Date: 21 December 2011

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A robust phase-lock of a quantum-cascade-laser to a near-infrared frequency-comb allows absorption spectra of a CO2 gas sample to be acquired at different pressures with extreme repeatability and accuracy by tuning the repetition-rate of the comb, thus ensuring an absolute frequency scale on the acquired spectra. The method proves useful to retrieve traceable spectroscopic parameters such as line-center frequencies, line intensity factors, pressure shift, and pressure broadening coefficients, with unprecedented quality from the metrological point of view.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.60.Fc Modulation, tuning, and mode locking
78.30.Hv Other nonmetallic inorganics

Hybrid magneto-optical mode converter made with a magnetic nanoparticles-doped SiO2/ZrO2 layer coated on an ion-exchanged glass waveguide

Hadi Amata, François Royer, Fadi Choueikani, Damien Jamon, François Parsy, Jean-Emmanuel Broquin, Sophie Neveu, and Jean Jacques Rousseau

Appl. Phys. Lett. 99, 251108 (2011); http://dx.doi.org/10.1063/1.3671180 (4 pages)

Online Publication Date: 21 December 2011

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This paper describes the possibility to achieve a TE-TM mode conversion in a magneto-optical hybrid waveguide operating at λ = 1550 nm. This hybrid device is made by coating a SiO2/ZrO2 layer doped with magnetic nanoparticles on an ion-exchanged glass waveguide. Soft annealing (90 °C) and UV treatment, both compatible with the ion exchange process, have been implemented to finalize the magneto-optical film. Optical characterizations that have been carried out demonstrated the efficiency of these hybrid structures in terms of lateral confinement and mode conversion. Indeed, TE to TM mode conversion has been observed when a longitudinal magnetic field is applied to the device. The amount of this conversion is discussed taking into account the distribution of light between the layer and the guide, and the modal birefringence of the structure.
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85.70.Sq Magnetooptical devices
42.79.Gn Optical waveguides and couplers

Crystal particle Raman-scattering and applications for improved solar cell performance

Ping Lee, Jason Shank, Komal Magsi, Yeona Kang, and C. M. Fortmann

Appl. Phys. Lett. 99, 251109 (2011); http://dx.doi.org/10.1063/1.3665942 (3 pages)

Online Publication Date: 21 December 2011

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Raman-based spectral modification for improved solar cell (SC) performance was investigated. While, Raman scattering is a weak phenomena commonly used for material characterization, small-sized particles embedded in a light scattering matrix have increased Raman and increased anti-Stokes energy up shift probability; because, embedding particles in a diffusive, transparent matrix vastly increases light path lengths (kilometers) and because optically generated phonons contribute to anti-Stokes probability in long phonon lifetime small particles. Increased long wavelength quantum efficiency was obtained using these layers on silicon SCs. Diffusion theory was applied to the spatial light diffusion and to Raman light energy broadening.
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88.40.H- Solar cells (photovoltaics)
02.50.Cw Probability theory

Significantly improved minority carrier lifetime observed in a long-wavelength infrared III-V type-II superlattice comprised of InAs/InAsSb

E. H. Steenbergen, B. C. Connelly, G. D. Metcalfe, H. Shen, M. Wraback, D. Lubyshev, Y. Qiu, J. M. Fastenau, A. W. K. Liu, S. Elhamri, O. O. Cellek, and Y.-H. Zhang

Appl. Phys. Lett. 99, 251110 (2011); http://dx.doi.org/10.1063/1.3671398 (3 pages) | Cited 13 times

Online Publication Date: 22 December 2011

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Time-resolved photoluminescence measurements reveal a minority carrier lifetime of >412 ns at 77 K under low excitation for a long-wavelength infrared InAs/InAs0.72Sb0.28 type-II superlattice (T2SL). This lifetime represents an order-of-magnitude increase in the minority carrier lifetime over previously reported lifetimes in long-wavelength infrared InAs/Ga1−xInxSb T2SLs. The considerably longer lifetime is attributed to a reduction of non-radiative recombination centers with the removal of Ga from the superlattice structure. This lifetime improvement may enable background limited T2SL long-wavelength infrared photodetectors at higher operating temperatures.
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81.05.Ea III-V semiconductors
78.47.jd Time resolved luminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors

Room temperature lasing with high group index in metal-coated GaN nanoring

Yow-Gwo Wang, Shu-Wei Chang, Cheng-Chang Chen, Ching-Hsueh Chiu, Ming-Yen Kuo, M. H. Shih, and Hao-Chung Kuo

Appl. Phys. Lett. 99, 251111 (2011); http://dx.doi.org/10.1063/1.3671648 (3 pages) | Cited 1 time

Online Publication Date: 22 December 2011

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The room temperature lasing action from a metal-coated GaN nanoring cavity was observed by optical pumping. The GaN nanoring is 7 μm in diameter and 400 nm in width. The quality factor of the cavity is approximately 860 with a threshold power density of 37.5 mJ/cm2. Such a device performance was attributed to the combination of metal-coated nanocavity with whispering-gallery modes. Moreover, the group index extracted from the experiment was 5.99 and was verified with calculations and analyses of the lasing modes as well as their characteristics. The study showed a promising way to further improve the performance of metal-coated nanolasers.
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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

Polarization property of deep-ultraviolet light emission from C-plane AlN/GaN short-period superlattices

Yoshitaka Taniyasu and Makoto Kasu

Appl. Phys. Lett. 99, 251112 (2011); http://dx.doi.org/10.1063/1.3671668 (4 pages) | Cited 15 times

Online Publication Date: 22 December 2011

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AlN/GaN short-period superlattices (SLs) is experimentally shown to have a different polarization property from AlGaN. As the GaN well thickness decreases from 2.5 to 0.9 monolayers, the emission wavelength decreases from 275.8 to 236.9 nm due to a quantum size effect. Because the quantized energy level for holes originates from the heavy hole band of GaN, the emission is polarized for electric field perpendicular to the c-axis (E⊥c). Consequently, the SLs show intense C-plane emission compared with AlGaN, whose emission is inherently polarized for electric field parallel to the c-axis (E||c). Using the SLs, we demonstrate a E⊥c-polarized deep-ultraviolet (UV) light-emitting diode (LED).
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68.65.Cd Superlattices
73.21.Cd Superlattices
78.40.Fy Semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization

Electroluminescence from Si nanocrystal/c-Si heterojunction light-emitting diodes

Dawei Di, Ivan Perez-Wurfl, Lingfeng Wu, Yidan Huang, Alessandro Marconi, Andrea Tengattini, Aleksei Anopchenko, Lorenzo Pavesi, and Gavin Conibeer

Appl. Phys. Lett. 99, 251113 (2011); http://dx.doi.org/10.1063/1.3671671 (4 pages) | Cited 4 times

Online Publication Date: 22 December 2011

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Silicon nanocrystals have shown attractive properties for photonic and photovoltaic applications. We demonstrate all-Si light-emitting diodes based on boron-doped Si nanocrystal/c-Si p-n heterojunction structure, which show electroluminescence in the visible/infrared regions. The electroluminescence spectra of these diodes can be modified by changing the quantum confining barriers from SiO2 to Si3N4. Our results are an important demonstration of electroluminescence from boron-doped Si nanocrystals—a wide band gap absorber material for third generation photovoltaics.
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85.60.Jb Light-emitting devices

Quantum efficiency control of InGaN/GaN multi-quantum-well structures using Ag/SiO2 core-shell nanoparticles

Lee-Woon Jang, Trilochan Sahoo, Dae-Woo Jeon, Myoung Kim, Ju-Won Jeon, Dong-Seob Jo, Min-Kyu Kim, Yeon-Tae Yu, Alexander Y. Polyakov, and In-Hwan Lee

Appl. Phys. Lett. 99, 251114 (2011); http://dx.doi.org/10.1063/1.3671394 (3 pages) | Cited 5 times

Online Publication Date: 23 December 2011

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Photoluminescence (PL) efficiency increase up to 2.8 times was observed for GaN/InGaN multi-quantum-well (MQW) structures as a result of deposition of a thin layer of about 40-nm-diameter Ag nanoparticles (NPs) surrounded by SiO2 shell. These Ag/SiO2 NPs were prepared by sol-gel method. The amount of PL intensity enhancement decreased with increasing the SiO2 shell thickness. PL intensity increase was accompanied by corresponding decrease of PL decay time and is ascribed to a strong coupling of MQW region to localized surface plasmons (LSPs) associated with Ag/SiO2 NPs.
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73.21.Fg Quantum wells
73.22.-f Electronic structure of nanoscale materials and related systems
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Asymmetry of carrier transport leading to efficiency droop in GaInN based light-emitting diodes

David S. Meyaard, Guan-Bo Lin, Qifeng Shan, Jaehee Cho, E. Fred Schubert, Hyunwook Shim, Min-Ho Kim, and Cheolsoo Sone

Appl. Phys. Lett. 99, 251115 (2011); http://dx.doi.org/10.1063/1.3671395 (3 pages) | Cited 9 times

Online Publication Date: 23 December 2011

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The effect of the asymmetry in carrier concentration and mobility is studied in GaInN pn-junction light-emitting diodes (LEDs). We propose and present experimental evidence that the asymmetry in carrier concentration and mobility, and associated high-level injection phenomena, cause efficiency droop in GaInN LEDs. Low temperatures exacerbate the degree of asymmetry of the junction by reducing acceptor ionization, and shift high-injection-phenomena to lower currents. Accordingly, at temperatures near 80 K, we measure a greater droop compared to room temperature. The analysis of temperature-dependent I–V curves shows an excellent correlation between the onset of high-level injection and the onset of droop.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Detecting surface acoustic wave gyroscopic signal by acousto-optic coupling

Shuxiang Lu, Shufen Chen, Honglang Li, Lei Fu, Zhengfeng Zou, and Yanbin Meng

Appl. Phys. Lett. 99, 251116 (2011); http://dx.doi.org/10.1063/1.3671616 (3 pages)

Online Publication Date: 23 December 2011

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A technique for surface acoustic wave (SAW) gyroscopic signal detection by acousto-optic coupling is presented in this article. The principles of the technique and the detection structure were analyzed, and experiments were conducted using the gyroscope. The static results show that the maximum coupling efficiency obtained using this technique is 80.02% when the acousto-optic interaction length is maintained at 15 mm, the SAW electrical power is 99 mW, and the SAW frequency is 168.201 MHz. When the gyroscope was rotating, a linear voltage-rotation response curve was obtained and the sensitivity was approximately 1.2 mV/deg/s.
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07.10.-h Mechanical instruments and equipment
42.79.Jq Acousto-optical devices
68.35.Iv Acoustical properties
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
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