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24 Jan 2005

Volume 86, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 043106 (2005); http://dx.doi.org/10.1063/1.1853514 (3 pages)

William L. Hughes and Zhong L. Wang
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Frequency beating between monolithically integrated semiconductor ring lasers

Hongjun Cao, Chiyu Liu, Hai Ling, Hui Deng, Marcita Benavidez, Vladimir A. Smagley, Robert B. Caldwell, Gregory M. Peake, Gennady A. Smolyakov, Petr G. Eliseev, and Marek Osiński

Appl. Phys. Lett. 86, 041101 (2005); http://dx.doi.org/10.1063/1.1853532 (3 pages) | Cited 8 times

Online Publication Date: 18 January 2005

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Optoelectronic integrated circuits incorporating a pair of optically independent large-cavity semiconductor ring lasers (SRLs), directional couplers, waveguides, Y-junction mixer, and photodetectors are demonstrated. Counterclockwise and clockwise output beams from the two SRLs are collected separately and mixed prior to detection. Frequency beating between modes of two SRLs is measured. The beat frequency is fine-tuned by an integrated Joule heater, designed for thermal control of the lasing wavelength. No signs of frequency lock-in in the vicinity of zero detuning are observed, which makes this structure a promising candidate for applications in ring laser gyros and optical rotation sensors.
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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
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
73.50.Pz Photoconduction and photovoltaic effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Bt Optoelectronic device characterization, design, and modeling

Quantum-transfer-efficiency excitation spectroscopy: Application to direct observation of yellow luminescent level of GaN

Tianshu Lai, Jinhui Wen, and Weizhu Lin

Appl. Phys. Lett. 86, 041102 (2005); http://dx.doi.org/10.1063/1.1854201 (3 pages)

Online Publication Date: 18 January 2005

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A quantum-transfer-efficiency excitation spectroscopy (QTEES) is developed. It measures the quantum transfer efficiency from the photoexcited level to the initial level of the luminescence measured. It is self-normalized and based on the relative measurement of photoluminescence intensity. The initial level of the luminescence detected corresponds to the position of the strongest excitation peak in a QTEES spectrum. An experiment of QTEES on an undoped GaN film is carried out, and the initial level of the yellow luminescence is obtained directly from the QTEES spectrum. The initial level measured is very close to the bottom of the conduction band, which provides direct evidence to support shallow donor–deep acceptor recombination of the yellow luminescence in the GaN film. QTEES spectra have the advantages of easy explanation and clear physical meanings. It is also found that the conventional photoluminescence excitation spectra need to be corrected by a factor of the energy of the excitation photon.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Optical properties of stoichiometric LiNbO3 waveguides formed by low-dose oxygen ion implantation

Xue-Lin Wang, Ke-Ming Wang, Feng Chen, Gang Fu, Shi-Ling Li, Hong Liu, Lei Gao, Ding-Yu Shen, Hong-Ji Ma, and Rui Nie

Appl. Phys. Lett. 86, 041103 (2005); http://dx.doi.org/10.1063/1.1854202 (3 pages) | Cited 15 times

Online Publication Date: 18 January 2005

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The planar waveguides in z-cut stoichiometric LiNbO3 crystal have been fabricated by 3.0 MeV oxygen ion implantation with the dose of 6×1014 ions/cm2 at room temperature. The modes of the waveguides were measured by the prism-coupling method with the wavelength 633 and 1539 nm, respectively. The refractive index profiles of the waveguides were reconstructed using reflectivity calculation method. The Rutherford backscattering/channeling technique was used to investigate the damage produced by the ion implantation, the minimum yield of the spectra was 4.52%. The propagation loss of waveguide was 0.61 dB/cm obtained by fiber probe technique. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such change increased after the annealing treatment at 260 °C for 60 min.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.80.Jh Ion radiation effects
61.82.Ms Insulators
81.40.Gh Other heat and thermomechanical treatments

Integrated fluorescent light source for optofluidic applications

Dmitri V. Vezenov, Brian T. Mayers, Daniel B. Wolfe, and George M. Whitesides

Appl. Phys. Lett. 86, 041104 (2005); http://dx.doi.org/10.1063/1.1850610 (3 pages) | Cited 32 times

Online Publication Date: 18 January 2005

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This letter describes a simple fluidic light source for use “on-chip” in integrated microsystems. It demonstrates the feasibility of light sources based on liquid-core, liquid-cladding (L2) microchannel waveguides, with liquid cores containing fluorescent dyes. These fluorescent light sources, using both miscible and two-phase systems, are tunable in terms of the beam size, intensity and spectral content. The observed output intensity from fluorescent L2 light sources is comparable to standard fiber optic spectrophotometer light sources. Integration of fluorescent light sources during device fabrication removes both the need for insertion and alignment of conventional, optical-fiber light sources and the constraints on channel size imposed by fiber optics, albeit at the cost of establishing a microfluidic infrastructure.
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42.82.Et Waveguides, couplers, and arrays
42.72.Bj Visible and ultraviolet sources
42.79.Gn Optical waveguides and couplers
42.81.Bm Fabrication, cladding, and splicing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.82.Bq Design and performance testing of integrated-optical systems

Mechanism of dark-spot degradation of organic light-emitting devices

P. Melpignano, A. Baron-Toaldo, V. Biondo, S. Priante, R. Zamboni, M. Murgia, S. Caria, L. Gregoratti, A. Barinov, and M. Kiskinova

Appl. Phys. Lett. 86, 041105 (2005); http://dx.doi.org/10.1063/1.1852706 (3 pages) | Cited 25 times

Online Publication Date: 18 January 2005

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Using chemically sensitive x-ray photoelectron microscopy, we investigate the mechanism of dark-spot formation and degradation of organic light-emitting devices. The morphological and chemical evolution of the Al cathode surface under operation conditions reveals the formation of “domelike” structures, followed by local disruptions of the cathode, exposing microareas of the underlying indium tin oxide anode. The chemical maps and microspot spectra identify a release of volatile In-, Sn-, and C-containing species, including metallic In, which is clear evidence that the degradation is driven by local decomposition of the anode∕organic interface.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.45.Fk Electrodes

Midinfrared luminescence imaging and its application to the optimization of light-emitting diodes

F. Weik, J. W. Tomm, R. Glatthaar, U. Vetter, D. Szewczy, J. Nurnus, A. Lambrecht, L. Mechold, B. Spellenberg, M. Bassler, M. Behringer, and J. Luft

Appl. Phys. Lett. 86, 041106 (2005); http://dx.doi.org/10.1063/1.1855420 (3 pages) | Cited 2 times

Online Publication Date: 18 January 2005

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Midinfrared luminescence imaging spectroscopy is used for evaluating surface structures etched into narrow-gap PbSe films. These structures provide a luminescence enhancement by a factor of 6. On the basis of such structures an optically pumped luminescence device is realized. A maximum cw output power of 0.5 mW and a slope efficiency of 0.2 mW/A are obtained at 25 °C. The power efficiency amounts to 2.3×10−2%. The emission wavelength is 4.2 μm, with a half width of 0.8 μm (50 meV). Such devices are promising light sources for a new generation of gas detection systems.
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85.60.Jb Light-emitting devices
68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
68.35.B- Structure of clean surfaces (and surface reconstruction)

Enhanced 1.54 μm photoluminescence from Er-containing ZnO through nitrogen doping

Zhen Zhou, Toshitaka Komori, Masahito Yoshino, Masahiko Morinaga, Noriaki Matsunami, Atsushi Koizumi, and Yoshikazu Takeda

Appl. Phys. Lett. 86, 041107 (2005); http://dx.doi.org/10.1063/1.1856692 (3 pages) | Cited 24 times

Online Publication Date: 19 January 2005

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Nitrogen doping into an erbium (Er)-containing ZnO specimen through the N+ irradiation and the subsequent annealing in air was found to increase the photoluminescence (PL) intensity around 1.54 μm by about 40 times. The existence of nitrogen in the specimen was proved firmly by means of the math(d,α)math nuclear reaction analysis. Further, the Ne+ irradiation was conducted instead of the N+ irradiation, but no effect was observed in the PL spectra. So, it was concluded that the substitution of N for O could modify the local structure around Er3+, resulting in the surprisingly large enhancement of the PL intensity.
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78.55.Et II-VI semiconductors
61.82.Fk Semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects

Self-consistent theory of the gain linewidth for quantum-cascade lasers

F. Banit, S.-C. Lee, A. Knorr, and A. Wacker

Appl. Phys. Lett. 86, 041108 (2005); http://dx.doi.org/10.1063/1.1851004 (3 pages) | Cited 33 times

Online Publication Date: 20 January 2005

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The linewidth in intersubband transitions can be significantly reduced below the sum of the lifetime broadening for the involved states, if the scattering environment is similar for both states. This is studied within a nonequilibrium Green function approach here. We find that the effect is of particular relevance for a recent, relatively low doped, Terahertz quantum-cascade laser.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Room-temperature, continuous-wave, single-mode quantum-cascade lasers at λ ≃ 5.4 μm

Stéphane Blaser, Dmitri A. Yarekha, Lubos Hvozdara, Yargo Bonetti, Antoine Muller, Marcella Giovannini, and Jérôme Faist

Appl. Phys. Lett. 86, 041109 (2005); http://dx.doi.org/10.1063/1.1853511 (3 pages) | Cited 54 times

Online Publication Date: 20 January 2005

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We demonstrate room-temperature, single-mode, continuous-wave operation of a λ ≃ 5.4 μm quantum-cascade laser up to the temperature of 30 °C. Processing is done using standard lithography in a ridge waveguide mounted junction-up. The active region is based on a bound-to-continuum transition. The high performances were achieved with a low active region doping and a thick electroplated gold deposition, resulting in a characteristic temperature of T0 = 155 K in continuous-wave with a threshold current density of jth = 2.05 kA/cm2 at 300 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Strong exciton-photon coupling in a length tunable optical microcavity with J-aggregate dye heterostructures

C. E. Finlayson, G. Vijaya Prakash, and J. J. Baumberg

Appl. Phys. Lett. 86, 041110 (2005); http://dx.doi.org/10.1063/1.1850189 (3 pages) | Cited 10 times

Online Publication Date: 20 January 2005

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We report the incorporation of thin films of a cyanine dye J aggregate into a versatile, length tunable, optical microcavity. The dense J-aggregate layers give an optical response that can be modified by embedding them at specific positions within heterostructures of dielectric and metal layers. The microcavities are composed of separate gold mirrors, which can be individually nanopositioned, and give sharp resonant modes in the red/near-infrared region of the spectrum. With the dye layer favorably placed, anticrossing behavior is observed as the cavity modes are successively swept through the absorption resonance. Large Rabi splittings of up to 170 meV are achieved at room temperature, agreeing well with predictions from a transfer-matrix model. These strongly coupled microcavities pave the way for microelectromechanical systems-integrated microdevices with tailored nonlinear optical properties.
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78.66.Qn Polymers; organic compounds
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Jw Organic compounds, polymers

Beam divergence measurements of InGaN/GaN micro-array light-emitting diodes using confocal microscopy

C. Griffin, E. Gu, H. W. Choi, C. W. Jeon, J. M. Girkin, M. D. Dawson, and G. McConnell

Appl. Phys. Lett. 86, 041111 (2005); http://dx.doi.org/10.1063/1.1850599 (3 pages) | Cited 11 times

Online Publication Date: 20 January 2005

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The recent development of high-density, two-dimensional arrays of micrometer-sized InGaN/GaN light-emitting diodes (micro-LEDs) with potential applications from scientific instrumentation to microdisplays has created an urgent need for controlled manipulation of the light output from these devices. With directed light output these devices can be used in situations where collimated beams or light focused onto several thousand matrix points is desired. In order to do this effectively, the emission characteristics of the devices must be fully understood and characterized. Here we utilize confocal microscopy to directly determine the emission characteristics and angular beam divergences from the individual micro-LED elements. The technique is applied to both top (into air) and bottom (through substrate) emission in arrays of green (540 nm), blue (470 nm), and UV (370 nm) micro-LED devices, at distances of up to 50 μm from the emission plane. The results are consistent with simple optical modeling of the expected beam profiles.
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85.60.Jb Light-emitting devices
78.55.Cr III-V semiconductors

Photonic molecule laser composed of GaInAsP microdisks

Atsuo Nakagawa, Satoru Ishii, and Toshihiko Baba

Appl. Phys. Lett. 86, 041112 (2005); http://dx.doi.org/10.1063/1.1855388 (3 pages) | Cited 33 times

Online Publication Date: 20 January 2005

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We fabricated a photonic molecule consisting of GaInAsP microdisks, and obtained the lasing operation by photopumping. We also observed mode splits arising from the optical coupling, which was confirmed by an anticrossing characteristic against the disk diameter detuning and a miniband being dependent on the number of disks, their arrangement and coupling strength. The coupling characteristics were explained by considering bonding and antibonding states of modes, and by finite-difference time-domain calculation. Such a laser is expected to be some functional devices, and the concept of the photonic molecule will be helpful for the understanding of complex coupled modes.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Fc Modulation, tuning, and mode locking

Coupling of Er ions to surface plasmons on Ag

J. Kalkman, L. Kuipers, A. Polman, and H. Gersen

Appl. Phys. Lett. 86, 041113 (2005); http://dx.doi.org/10.1063/1.1856133 (3 pages) | Cited 30 times

Online Publication Date: 21 January 2005

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Er3+ ions located 100 nm beneath the surface of silica glass show an enhanced photoluminescence decay rate when the glass is covered with Ag. Correcting for concentration quenching effects, the decay rate is enhanced by 70%, compared to the case without Ag. The data are in agreement with a model that takes into account variations in local density of states and excitation of surface plasmons and lossy surface waves, resulting in direct evidence for the efficient generation of surface plasmons by excited Er3+ ions. Using the model, optimum conditions for coupling to surface plasmons are derived, which can be used to enhance the emission rate and quantum efficiency of a wide range of Er-doped materials.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.20.At Surface states, band structure, electron density of states
71.55.Jv Disordered structures; amorphous and glassy solids
61.72.S- Impurities in crystals
78.55.Hx Other solid inorganic materials
78.68.+m Optical properties of surfaces

Subpicosecond shifting of the photonic band gap in a three-dimensional photonic crystal

Dmitry A. Mazurenko, Robert Kerst, Jaap I. Dijkhuis, Andrey V. Akimov, Valery G. Golubev, Alexander A. Kaplyanskii, Dmitry A. Kurdyukov, and Alexander B. Pevtsov

Appl. Phys. Lett. 86, 041114 (2005); http://dx.doi.org/10.1063/1.1856687 (3 pages) | Cited 20 times

Online Publication Date: 21 January 2005

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We demonstrate spectral shifting of the photonic band gap in a three-dimensional photonic crystal within a time of less than 350 fs. Single 120 fs high-power optical pulses are capable to induce the transition from the semiconductor to the metallic phase of VO2 in the pores of our artificial silica opal. The phase transition produces a substantial decrease of the real part of the effective refractive index of the photonic crystal and shifts the spectral position of the photonic band gap.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics
72.60.+g Mixed conductivity and conductivity transitions

A polarization insensitive 2×2 optical switch fabricated by liquid crystal–polymer composite

Y. J. Liu, X. W. Sun, J. H. Liu, H. T. Dai, and K. S. Xu

Appl. Phys. Lett. 86, 041115 (2005); http://dx.doi.org/10.1063/1.1857092 (3 pages) | Cited 22 times

Online Publication Date: 21 January 2005

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A polarization insensitive 2×2 optical switch was fabricated with liquid crystal–polymer composite by means of holography. The highest diffraction efficiency achieved was 85.7%. The rise time and the decay time measured were 36 and 160 μs, respectively, at an applied electric field of 18.2 V/μm. The polarization-dependent loss was 0.03 dB measured for s- and p-polarized light at the wavelength of 632.8 nm.
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42.70.Df Liquid crystals
42.70.Jk Polymers and organics
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.86.+b Optical workshop techniques
42.40.Eq Holographic optical elements; holographic gratings
42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
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