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13 Jun 2005

Volume 86, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 241913 (2005); http://dx.doi.org/10.1063/1.1946181 (3 pages)

E. Placidi, F. Arciprete, V. Sessi, M. Fanfoni, F. Patella, and A. Balzarotti
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Highly efficient in-plane channel drop filter in a two-dimensional heterophotonic crystal

Hitomichi Takano, Bong-Shik Song, Takashi Asano, and Susumu Noda

Appl. Phys. Lett. 86, 241101 (2005); http://dx.doi.org/10.1063/1.1941458 (3 pages) | Cited 14 times

Online Publication Date: 6 June 2005

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Improvements in the channel drop efficiency of an in-plane drop filter in a two-dimensional photonic crystal slab are presented, using a device consisting of two photonic crystal slabs with different lattice constants. It is theoretically shown that drop efficiencies much higher than the maximum of 25% for a conventional configuration are achievable when utilizing reflections at the photonic crystal heterostructure interface. Additionally, the higher drop efficiency is found to be less sensitive to structural fluctuations. Drop operations with efficiencies of more than 80% are experimentally demonstrated by the fabricated devices.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials

Fabrication of large area two- and three-dimensional polymer photonic crystals using single refracting prism holographic lithography

Lijun Wu, Yongchun Zhong, Che Ting Chan, Kam Sing Wong, and Guo Ping Wang

Appl. Phys. Lett. 86, 241102 (2005); http://dx.doi.org/10.1063/1.1947369 (3 pages) | Cited 57 times

Online Publication Date: 7 June 2005

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We demonstrate an approach for easy fabrication of two-dimensional (2D) hexagonal and three-dimensional (3D) face-centered-cubic (fcc)-type photonic crystal (PhC) microstructures in a photosensitive polymer by applying a simple single refracting prism. This prism enables the splitting and recombining of a single incoming laser beam to form multiple-beam interference pattern simultaneously. Thus, antivibration equipment and complicated optical alignment system are not required, leading to a much more simple optical setup than previously reported laser holographic lithography techniques. Large-scale (over 1 cm2) 2D hexagonal and 3D fcc-type PhCs have been produced. Reflection/transmission measurements performed on the fabricated 3D fcc-type PhC structures agree well with the corresponding band structure calculation.
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42.86.+b Optical workshop techniques
42.70.Qs Photonic bandgap materials
42.40.My Applications
42.70.Jk Polymers and organics

Silicon waveguide-integrated optical power monitor with enhanced sensitivity at 1550 nm

J. D. B. Bradley, P. E. Jessop, and A. P. Knights

Appl. Phys. Lett. 86, 241103 (2005); http://dx.doi.org/10.1063/1.1947379 (3 pages) | Cited 26 times

Online Publication Date: 7 June 2005

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We describe the fabrication and operation of an optical power monitor, monolithically integrated with a silicon-on-insulator rib waveguide. The device consists of a p+‐v‐n+ structure with a detection volume coincident with the single-mode supporting waveguide. Detection of optical signals at wavelengths around 1550 nm is significantly enhanced by the introduction of midband-gap generation centers, which provide partial absorption of the infrared light. The most efficient device extracted 19% of optical power from the waveguide and showed a responsivity of 3 mA/W. These devices are fabricated using current standard processing technology and are fully compatible with silicon waveguide technology and integrated operational amplifier circuits.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer

Nanocrystal-based microcavity light-emitting devices operating in the telecommunication wavelength range

J. Roither, M. V. Kovalenko, S. Pichler, T. Schwarzl, and W. Heiss

Appl. Phys. Lett. 86, 241104 (2005); http://dx.doi.org/10.1063/1.1947888 (3 pages) | Cited 7 times

Online Publication Date: 7 June 2005

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Highly luminescent colloidally prepared HgTe nanocrystals (NCs) are used to fabricate microcavity light-emitting devices operating around 1.5 μm. They consist of a Bragg interference mirror from standard optical materials deposited on glass substrates, an active layer embedding the nanocrystals, and a metallic top mirror. These devices give highly directional narrow single-mode emission with a beam divergence below 3° and a spectral width smaller by a factor of 8 than that of a NC reference sample. The emission wavelength can be tuned between 1.4 and 1.75 μm by changing the cavity length and thus, the cavity finesse. The influence of the latter on output power and beam divergence is discussed. Furthermore, operation up to 75 °C is demonstrated without degradation of the NCs, which is promising for potential applications.
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85.60.Jb Light-emitting devices
42.79.Bh Lenses, prisms and mirrors

Optical properties of a transparent CaF2:Er3+ fluoropolymer nanocomposite

G. A. Kumar, C. W. Chen, R. Riman, S. Chen, D. Smith, and J. Ballato

Appl. Phys. Lett. 86, 241105 (2005); http://dx.doi.org/10.1063/1.1947891 (3 pages) | Cited 20 times

Online Publication Date: 7 June 2005

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We report the observation of Er3+ fluorescence in an optically transparent CaF2:Er3+ perfluorocyclobutyl-based fluoropolymer composite. Under 980 nm excitation, fluorescence was observed at 1560 nm with a bandwidth of 93 nm. A quantitative analysis of the radiative properties yielded a radiative quantum efficiency of 29% corresponding to a measured lifetime of 4 ms and theoretical radiative decay time of 13.8 ms. Further, the estimated stimulated emission cross section was calculated to be 3×10−20 cm2, and the maximum optical gain from the composite was estimated to be 1.78 dB∕cm with a pump threshold of 1.1 mW. This estimate demonstrates that it is possible to use polymer nanocomposites for active optical devices.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.60.-b Other luminescence and radiative recombination
78.45.+h Stimulated emission
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

High-electric-field quantum yield roll-off in efficient europium chelates-based light-emitting diodes

J. Kalinowski, W. Stampor, M. Cocchi, D. Virgili, and V. Fattori

Appl. Phys. Lett. 86, 241106 (2005); http://dx.doi.org/10.1063/1.1948512 (3 pages) | Cited 15 times

Online Publication Date: 7 June 2005

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The europium chelates-based light-emitting-diodes (LEDs) have been fabricated showing the maximum electroluminescence (EL) quantum efficiency (QE) up to 5% photons/carrier at electric fields slightly below F = 1 MV/cm and current density j ≅  0.01 mA/cm2. Their line-like emission QE drops, however, rapidly within the high drive voltage range. This roll-off effect, exceeding one order of magnitude at F ≅ 1.6 MV/cm (j ≅ 15 mA/cm2), is shown to be underlain by the electric field-assisted dissociation of electron-hole pair precursors of europium ion-localized emissive states. The high field dependence of EL QE fits the Onsager model of geminate recombination well. This is at variance with triplet-triplet annihilation mechanism assumed previously to reduce QE in such LEDs.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence

Surface acoustic wave-induced electroluminescence intensity oscillation in planar light-emitting devices

Marco Cecchini, Vincenzo Piazza, Fabio Beltram, D. G. Gevaux, M. B. Ward, A. J. Shields, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 86, 241107 (2005); http://dx.doi.org/10.1063/1.1948520 (3 pages) | Cited 9 times

Online Publication Date: 7 June 2005

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Electroluminescence emission from surface acoustic wave-driven light-emitting diodes (SAWLEDs) is studied by means of time-resolved techniques. We show that the intensity of the SAW-induced electroluminescence is modulated at the SAW frequency ( ∼ 1 GHz), demonstrating electron injection into the p-type region synchronous with the SAW wave fronts.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.47.-p Spectroscopy of solid state dynamics

Photoresponse of n-ZnO/p-SiC heterojunction diodes grown by plasma-assisted molecular-beam epitaxy

Ya. I. Alivov, Ü. Özgür, S. Doğan, D. Johnstone, V. Avrutin, N. Onojima, C. Liu, J. Xie, Q. Fan, and H. Morkoç

Appl. Phys. Lett. 86, 241108 (2005); http://dx.doi.org/10.1063/1.1949730 (3 pages) | Cited 44 times

Online Publication Date: 8 June 2005

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High quality n-ZnO films on commercial p-type 6H–SiC substrates have been grown by plasma-assisted molecular-beam epitaxy, and n-ZnO/p-SiC heterojunction mesa structures have been fabricated. Current-voltage characteristics of the structures had a very good rectifying diode-like behavior with a leakage current less than 2×10−4 A/cm2 at −10 V, a breakdown voltage greater than 20 V, a forward turn on voltage of ∼ 5 V, and a forward current of ∼ 2 A/cm2 at 8 V. Photosensitivity of the diodes was studied at room temperature and a photoresponsivity of as high as 0.045 A/W at −7.5 V reverse bias was observed for photon energies higher than 3.0 eV.
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85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling

Absence of the enhanced intra-4f transition cross section at 1.5 μm of Er3+ in Si-rich SiO2

H. Mertens, A. Polman, I. M. P. Aarts, W. M. M. Kessels, and M. C. M. van de Sanden

Appl. Phys. Lett. 86, 241109 (2005); http://dx.doi.org/10.1063/1.1949720 (3 pages) | Cited 15 times

Online Publication Date: 8 June 2005

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We present measurements of the optical absorption cross section of the math→math transition at 1.5 μm of Er3+ ions embedded in SiO2 and Si-rich oxide, using cavity ringdown spectroscopy on thin films. The peak absorption cross section for Er3+ embedded in Si-rich oxide (10 at. % excess Si) was found to be (8±2)×10−21 cm2 at 1536 nm, similar to typical values for Er embedded in SiO2. The data imply that the silicon nanoclusters incorporated in Si-rich oxide do not enhance the peak cross section of the Er3+ math−math transition by 1-2 orders of magnitude, contrary to what has been reported in earlier work.
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81.07.Bc Nanocrystalline materials
78.30.Hv Other nonmetallic inorganics
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Nk Insulators

Unidirectional laser emission from polymer-based spiral microdisks

T. Ben-Messaoud and J. Zyss

Appl. Phys. Lett. 86, 241110 (2005); http://dx.doi.org/10.1063/1.1949708 (3 pages) | Cited 37 times

Online Publication Date: 8 June 2005

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Lasing emission has been observed in optically pumped DCM-poly(methyl methacrylate)-based spiral-shaped micropillar cavities. By transverse ring shaping of the pump beam, unidirectional laser emission is being clearly favored. The resulting improved far-field directionality evidenced by our imaging technique is shown to originate from the notch of the spiral microcavities.
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42.70.Jk Polymers and organics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Fabrication of n-ZnO:Al/p-SiC(4H) heterojunction light-emitting diodes by filtered cathodic vacuum arc technique

Clement Yuen, S. F. Yu, S. P. Lau, Rusli, and T. P. Chen

Appl. Phys. Lett. 86, 241111 (2005); http://dx.doi.org/10.1063/1.1947889 (3 pages) | Cited 52 times

Online Publication Date: 8 June 2005

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We report the low-temperature ( ∼ 150 °C) fabrication of n-ZnO:Al/p-SiC(4H) heterojunction light-emitting diodes by filtered cathodic vacuum arc technique. Diodelike rectifying current-voltage characteristics, with turn-on voltage of ∼ 3.8 V and low reverse leakage current of <10−2 μA, were measured at room temperature. In addition, ultraviolet emission with peak wavelength of ∼ 385 nm and full width at half maximum of ∼ 20 nm are observed at a forward biased voltage of ∼ 7.4 V. The ultraviolet electroluminescence from the heterojunction is originated from the exciton-exciton scattering inside the n-ZnO:Al film.
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85.60.Jb Light-emitting devices

2.8 and 1.55 μm emission from diode-pumped Er3+-doped and Yb3+ co-doped lead lanthanum zirconate titanate transparent ferroelectric ceramic

A. S. S. de Camargo, É. R. Botero, É. R. M. Andreeta, D. Garcia, J. A. Eiras, and L. A. O. Nunes

Appl. Phys. Lett. 86, 241112 (2005); http://dx.doi.org/10.1063/1.1944905 (3 pages) | Cited 14 times

Online Publication Date: 8 June 2005

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This work reports the observation of intense emissions at 2.8 and 1.55 μm from optical quality diode-pumped Er3+-doped lead lanthanum zirconate titanate (PLZT) transparent ferroelectric ceramic. Radiative properties were calculated using the Judd Ofelt theory, and the respective values of η = 0.09 and η = 0.94 were obtained. The effect of ytterbium co-doping the PLZT: Er3+ samples was investigated in an attempt to increase intensities. It was found that Yb3+→Er3+ energy transfer processes, that favor Er3+ upconversion, are detrimental to the efficiency of midinfrared emissions. Even so, the advantageous spectroscopic characteristics of PLZT: Er3+ associated with its excellent thermal and mechanical properties, indicate it is a potential cost-effective laser active media.
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78.45.+h Stimulated emission
42.70.Hj Laser materials
78.30.Hv Other nonmetallic inorganics
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Broadband efficient nonlinear difference generation in a counterpropagating configuration

Jordi Martorell

Appl. Phys. Lett. 86, 241113 (2005); http://dx.doi.org/10.1063/1.1941459 (3 pages) | Cited 3 times

Online Publication Date: 8 June 2005

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A counterpropagating parametric nonlinear interaction is considered in the framework of a short one-dimensional photonic crystal. This interaction, otherwise highly inefficient, is shown to be efficient in the framework of such one-dimensional photonic crystal. The large momentum mismatch of this counterpropagating interaction is shown to be compensated for a broad range of frequencies when difference generation is considered. The numerical results presented indicate that such nonlinear photonic crystals are a very good material to consider the observation of backward parametric oscillation without mirror feedback.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials

Optical properties of single droplet of photonic crystal assembled by ink-jet printing

Dake Wang, Minseo Park, Jungho Park, and Jooho Moon

Appl. Phys. Lett. 86, 241114 (2005); http://dx.doi.org/10.1063/1.1949279 (3 pages) | Cited 3 times

Online Publication Date: 8 June 2005

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An array of droplets of photonic crystal with polystyrene colloidal particles was assembled on silicon using ink-jet printing. A microreflectance spectrum from a single droplet was collected using an optical microscope and a spectrometer. It was observed that the photonic band gap of these droplets shifts as a function of the size of the colloidal particle. The reflectance peak position predicted from the model based on Bruggeman and Maxwell–Garnett effective medium approximations agrees well with those of the experimentally observed peak.
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42.70.Qs Photonic bandgap materials
82.70.Dd Colloids

Temperature sensitivity of a long-period waveguide grating in a channel waveguide

Qing Liu, K. S. Chiang, K. P. Lor, and C. K. Chow

Appl. Phys. Lett. 86, 241115 (2005); http://dx.doi.org/10.1063/1.1944226 (3 pages) | Cited 11 times

Online Publication Date: 9 June 2005

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We present a simulation of the temperature sensitivity of the resonance wavelength of a long-period waveguide grating (LPWG). We find that the temperature sensitivity of an LPWG in a channel waveguide is proportional to a modal dispersion factor that depends sensitively on the size of the core of the waveguide. Measurements with experimental polymer LPWGs agree well with the simulation results. The dimension of the waveguide core is an effective parameter for the control of the thermal characteristics of an LPWG in a channel waveguide.
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42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.81.Dp Propagation, scattering, and losses; solitons

Detection and identification of explosives using terahertz pulsed spectroscopic imaging

Y. C. Shen, T. Lo, P. F. Taday, B. E. Cole, W. R. Tribe, and M. C. Kemp

Appl. Phys. Lett. 86, 241116 (2005); http://dx.doi.org/10.1063/1.1946192 (3 pages) | Cited 86 times

Online Publication Date: 9 June 2005

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The absorption spectrum of the explosive 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulsed spectroscopy. Seven absorption features in the spectral range of 5–120 cm−1 have been observed and identified as the fingerprint of RDX. Furthermore, the spatial distribution of individual chemical substances including RDX, has been mapped out using reflection terahertz spectroscopic imaging in combination with component spatial pattern analysis. This is the terahertz spectroscopy and chemical mapping of explosives obtained using reflection terahertz measurement, and represents a significant advance toward developing a terahertz pulsed imaging system for security screening of explosives.
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82.80.-d Chemical analysis and related physical methods of analysis
82.33.Vx Reactions in flames, combustion, and explosions
78.30.Jw Organic compounds, polymers

Multiple-band-edge quantum-well intermixing in the InGaAs/InGaAsP/InGaP material system

Erik J. Skogen, Larry A. Coldren, James W. Raring, and Steven P. DenBaars

Appl. Phys. Lett. 86, 241117 (2005); http://dx.doi.org/10.1063/1.1946903 (3 pages) | Cited 9 times

Online Publication Date: 9 June 2005

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The development of photonic integrated circuits lattice matched to GaAs are desirable for the manufacture of high-power, high-efficiency optical components. In this letter we investigate and describe a process technique based on quantum-well intermixing to achieve multiple band edges in the Al-free 980 nm InGaAs/InGaAsP/InGaP material system.
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68.65.Fg Quantum wells
81.07.St Quantum wells
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.82.-m Integrated optics
85.60.-q Optoelectronic devices
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