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9 Jul 2007

Volume 91, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages)

M. Fendrich and T. Kunstmann
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Temperature induced stress phase transition in CdTe quantum dots observed by dielectric constant and thermal diffusivity measurements

S. G. C. Moreira, E. C. da Silva, A. M. Mansanares, L. C. Barbosa, and C. L. Cesar

Appl. Phys. Lett. 91, 021101 (2007); http://dx.doi.org/10.1063/1.2751128 (3 pages) | Cited 3 times

Online Publication Date: 9 July 2007

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The authors measured the dielectric constant by capacitance method and the thermal diffusivity by thermal lens technique in the temperature range from 20 to 300 K for CdTe quantum dot doped borosilicate glass samples. Results show a huge difference between the thermal behavior of the pure glass matrix, without quantum dots, and of the doped glass, especially around 90 and 250 K. The authors attributed this difference to the phase transition experienced by the CdTe nanocrystals due to the high pressure exerted by the glass matrix over the CdTe quantum dots. The temperature induced stress is caused by the thermal expansion coefficient mismatch between the quantum dot and the glass matrix.
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64.70.K- Solid-solid transitions
68.65.Hb Quantum dots (patterned in quantum wells)
62.50.-p High-pressure effects in solids and liquids
77.22.Ch Permittivity (dielectric function)
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Optical transitions in type-II InAs/GaAs quantum dots covered by a GaAsSb strain-reducing layer

C. Y. Jin, H. Y. Liu, S. Y. Zhang, Q. Jiang, S. L. Liew, M. Hopkinson, T. J. Badcock, E. Nabavi, and D. J. Mowbray

Appl. Phys. Lett. 91, 021102 (2007); http://dx.doi.org/10.1063/1.2752778 (3 pages) | Cited 29 times

Online Publication Date: 9 July 2007

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The excitation power dependence of the ground and excited state transitions in type-II InAs-GaAs0.78Sb0.22 quantum dot structure has been studied. Both transitions exhibit a strong blueshift with increasing excitation power but their separation remains constant. This behavior indicates a carrier-induced electric field oriented predominantly along the growth axis, which requires the holes to be localized in the GaAsSb above quantum dots. An accelerated blueshift of the ground state emission is observed once the excited state in the dots starts to populate. This behavior can be explained by a smaller spontaneous recombination coefficient for the excited state transition.
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78.67.Hc Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Plasmonic very-small-aperture lasers

Baoshan Guo, Guofeng Song, and Lianghui Chen

Appl. Phys. Lett. 91, 021103 (2007); http://dx.doi.org/10.1063/1.2755784 (3 pages) | Cited 12 times

Online Publication Date: 9 July 2007

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The fabrication of plasmonic very-small-aperture lasers is demonstrated in this letter. It is an integration of the surface plasmon structures and very-small-aperture lasers (VSAL). The experimental and numerical results demonstrate that the transmission field can be confined to a spot with subwavelength width in the far field, and the power output can be enhanced 140% of the normal VSAL. Such a device can be useful in the application of a high resolution far-field scanning optical microscope.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.82.Gw Other integrated-optical elements and systems

Laser oscillations of whispering gallery modes in thiophene/phenylene co-oligomer microrings

Seiji Fujiwara, Kazuki Bando, Yasuaki Masumoto, Fumio Sasaki, Shunsuke Kobayashi, Satoshi Haraichi, and Shu Hotta

Appl. Phys. Lett. 91, 021104 (2007); http://dx.doi.org/10.1063/1.2755925 (3 pages) | Cited 11 times

Online Publication Date: 9 July 2007

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Laser oscillation of whispering gallery modes was observed in microring structures of semiconducting thiophene/phenylene co-oligomer (TPCO) crystals at room temperature. Microring structures were formed by dry etching from thin film crystals of TPCO. The thresholds for the laser oscillation of a microring and a thin film crystal are 200 and 1400 μJ/cm2 for picosecond excitation, respectively. Therefore, the threshold for the microring was reduced to 1/7 of that for the thin film crystal. The dramatic reduction of threshold clearly demonstrates the importance of microcavity in making efficient organic semiconductor lasers.
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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
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Electrophotoluminescence of ZnO film

Xiangyang Ma, Peiliang Chen, Dongsheng Li, Yuanyuan Zhang, and Deren Yang

Appl. Phys. Lett. 91, 021105 (2007); http://dx.doi.org/10.1063/1.2753760 (3 pages) | Cited 18 times

Online Publication Date: 10 July 2007

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The electric-field-controlled photoluminescence (PL), i.e., electrophotoluminescence (EPL) of ZnO film has been investigated via a ZnO-based metal-insulator-semiconductor (MIS) structure on a silicon substrate applied with different biases. Compared with the PL of ZnO film in the case where there is no bias on the MIS structure, the positive bias with negative voltage applied on silicon substrate significantly enhances the near-band-edge ultraviolet emission while suppressing the deep-level-related visible emissions, whereas the negative bias hardly changes the PL of ZnO film. The mechanism for EPL of ZnO film is proposed in terms of the electric-field effect on the bending of energy bands of ZnO.
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78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors

Near-infrared photoluminescence of erbium tris(8-hydroxyquinoline) spin-coated thin films induced by low coherence light sources

S. Penna, A. Reale, R. Pizzoferrato, G. M. Tosi Beleffi, D. Musella, and W. P. Gillin

Appl. Phys. Lett. 91, 021106 (2007); http://dx.doi.org/10.1063/1.2755933 (3 pages) | Cited 3 times

Online Publication Date: 10 July 2007

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The authors present the characterization of spin-coated erbium tris(8-hydroxyquinoline) (ErQ3) solution on glass substrates under high temperature conditions. Absorption and infrared photoluminescence, induced by laser and light emitting diode sources, were measured and compared to cast and evaporated ErQ3 samples. A broad absorption band and 1.52 μm luminescence were observed, suggesting spin coating as a valid deposition technique for processing of organic infrared emitting diodes.
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78.55.Kz Solid organic materials
78.30.Jw Organic compounds, polymers
78.66.Qn Polymers; organic compounds

Germanium near infrared detector in silicon on insulator

L. Colace, V. Sorianello, M. Balbi, and G. Assanto

Appl. Phys. Lett. 91, 021107 (2007); http://dx.doi.org/10.1063/1.2757123 (3 pages) | Cited 5 times

Online Publication Date: 11 July 2007

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The authors demonstrate near infrared photodetectors in evaporated germanium on silicon-on-insulator waveguides. The authors achieve peak responsivities as high as 1 A/W and dark current densities as low as 40 nA at a reverse bias of 1 V. Owing to the low deposition temperature, this technology allows for simple and low cost monolithic integration with silicon.
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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)

Demonstrations of the diffraction and dispersion phenomena of part Fresnel phase zone plates

Binzhi Zhang, Daomu Zhao, and Shaomin Wang

Appl. Phys. Lett. 91, 021108 (2007); http://dx.doi.org/10.1063/1.2757126 (3 pages) | Cited 4 times

Online Publication Date: 11 July 2007

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The authors report on experimental demonstrations of the diffraction and dispersion phenomena of part Fresnel phase zone plates (FPZPs) by employing a He–Ne laser beam and a white point source. The experimental results have shown that a part square FPZP can behave like a complete circular FPZP, and a part circular FPZP has a focus at 1/3 f and f with a shift. Some numerical simulations are performed. The simulations and the experiments have shown that the diffraction and dispersion properties of part FPZPs can be well explained by the different diffraction orders.
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42.79.Ci Filters, zone plates, and polarizers
42.87.-d Optical testing techniques

Metal and dielectric duality for an aligned Al nanorod array

Yi-Jun Jen and Ching-Wei Yu

Appl. Phys. Lett. 91, 021109 (2007); http://dx.doi.org/10.1063/1.2757133 (3 pages) | Cited 1 time

Online Publication Date: 11 July 2007

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In this letter, aluminum (Al) is used to make a narrow rod array (NRA) by oblique angle deposition method. The Al NRA film exhibits both metallic and dielectric optical characteristics. Like metal films, the Al NRA film only weakly disperses visible wavelength of normally incident light. However, strong interference causes the obliquely incident s-polarized and p-polarized lights to resonate in the Al NRA film. Even though the optical constant of the Al NRA film is dielectriclike, the surface plasmon wave excited and propagating on the surface of Al NRA is demonstrated to be responsible for the p-polarized resonance.
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78.66.Bz Metals and metallic alloys
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Single point defect photonic crystal nanocavity with ultrahigh quality factor achieved by using hexapole mode

Takasumi Tanabe, Akihiko Shinya, Eiichi Kuramochi, Shingo Kondo, Hideaki Taniyama, and Masaya Notomi

Appl. Phys. Lett. 91, 021110 (2007); http://dx.doi.org/10.1063/1.2757099 (3 pages) | Cited 15 times

Online Publication Date: 11 July 2007

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Photonic crystal (PhC) nanocavities with an extremely high quality factor (Q) based on a point defect are fabricated and their properties are studied. Their confinement of light is based on rotational symmetry, which forms a hexapole mode with a Q of 3.2×105. It demonstrates that this nanocavity is an alternative candidate for achieving an ultrahigh Q. In addition, we observed bistable behavior based on the thermo-optic effect at a threshold power of a few 100 μW. We also investigated the dynamic properties of this cavity, where we observed that the cavity exhibits a smaller Q at a higher input power.
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42.82.Gw Other integrated-optical elements and systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Dispersion of silicon nonlinearities in the near infrared region

Q. Lin, J. Zhang, G. Piredda, R. W. Boyd, P. M. Fauchet, and G. P. Agrawal

Appl. Phys. Lett. 91, 021111 (2007); http://dx.doi.org/10.1063/1.2750523 (3 pages) | Cited 43 times

Online Publication Date: 12 July 2007

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The authors present the detailed characterization of the wavelength dependence of two-photon absorption and the Kerr nonlinearity in silicon over a spectral range extending from 1.2 to 2.4 μm. They show that silicon exhibits a significant increase in its nonlinear figure of merit with increasing wavelengths beyond the two telecommunication bands. They expect their results to provide guidance for extending nonlinear silicon photonics into new spectral regimes.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.Db Elemental semiconductors and insulators

Tunable surface plasmon mediated emission from semiconductors by using metal alloys

D. Y. Lei, J. Li, and H. C. Ong

Appl. Phys. Lett. 91, 021112 (2007); http://dx.doi.org/10.1063/1.2752770 (3 pages) | Cited 19 times

Online Publication Date: 12 July 2007

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The authors have explored the possibility of using binary metal alloys on surface plasmon mediated emission from semiconductor. By adjusting the alloy composition, they have found that the surface plasmon resonance energy can be tuned to match with the emission energy of semiconductor so that the energy transfer process between the semiconductor and surface plasmons can be optimized. They have calculated the plasmonic density of states and Purcell factor for ZnO and ZnTe at different alloy compositions and the results support the argument. Experimentally, they have prepared AlxAg1−x/ZnO films at different compositions and have measured their photoluminescence. The band-edge emission from Al0.8Ag0.2/ZnO is found to be ∼ 60 times stronger than that of bare ZnO, which is consistent with the theoretical prediction. As a result, metal alloys can be considered as a simple and effective means in optimizing the surface plasmon mediated emission.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.-w Optical properties of specific thin films
78.55.-m Photoluminescence, properties and materials

Direct measurement of increased light intensity in optical waveguides coupled to a surface plasmon spectroscopy setup

M. Dürr, B. Menges, W. Knoll, A. Yasuda, and G. Nelles

Appl. Phys. Lett. 91, 021113 (2007); http://dx.doi.org/10.1063/1.2753757 (3 pages) | Cited 5 times

Online Publication Date: 13 July 2007

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The local increase of light intensity in waveguide structures was monitored by a combination of conventional surface plasmon spectroscopy and a dye-sensitized solar cell (DSSC). The sensitized nanoporous TiO2 layer of the DSSC served both as waveguide structure and light absorber in the DSSC. If the conditions for the excitation of guided modes in the TiO2 waveguide structure were fulfilled, increased light intensity in the porous layer was monitored by an increase of short circuit current in the DSSC. Comparison with direct illumination yields an increase of intensity by a factor of 19±6, in good agreement with transfer matrix calculations.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Defect reduction of GaAs epitaxy on Si (001) using selective aspect ratio trapping

J. Z. Li, J. Bai, J.-S. Park, B. Adekore, K. Fox, M. Carroll, A. Lochtefeld, and Z. Shellenbarger

Appl. Phys. Lett. 91, 021114 (2007); http://dx.doi.org/10.1063/1.2756165 (3 pages) | Cited 23 times

Online Publication Date: 13 July 2007

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Metal-organic chemical vapor deposition growth of GaAs on Si was studied using the selective aspect ratio trapping method. Vertical propagation of threading dislocations generated at the GaAs/Si interface was suppressed within an initial thin GaAs layer inside SiO2 trenches with aspect ratio >1, leading to defect-free GaAs regions up to 300 nm in width. Cross-sectional and plan-view transmission electron microscopies were used to characterize the defect reduction. Material quality was confirmed by room temperature photoluminescence measurements. This approach shows great promise for the fabrication of optoelectronic integrated circuits on Si substrates.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
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