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27 Jun 2005

Volume 86, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 86, 263107 (2005); http://dx.doi.org/10.1063/1.1952585 (3 pages)

B. Yang, M. S. Marcus, D. G. Keppel, P. P. Zhang, Z. W. Li, B. J. Larson, D. E. Savage, J. M. Simmons, O. M. Castellini, M. A. Eriksson, and M. G. Lagally
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Simple layer-by-layer photonic crystal for the control of thermal emission

S. Enoch, J.-J. Simon, L. Escoubas, Z. Elalmy, F. Lemarquis, P. Torchio, and G. Albrand

Appl. Phys. Lett. 86, 261101 (2005); http://dx.doi.org/10.1063/1.1954881 (3 pages) | Cited 22 times

Online Publication Date: 20 June 2005

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We present a theoretical and experimental study of a simple layer-by-layer photonic crystal structure designed for the control of the thermal emission in the infrared wavelength domain. We show that a relatively simple structure made of alternated ZnSe homogenous layers and gold microstructured grids can act as a thermal source itself giving us the unique opportunity to tailor its emission spectra. Comparisons between computed and measured transmission and emissivity spectra illustrate the relevance of our approach.
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42.70.Qs Photonic bandgap materials
78.30.Hv Other nonmetallic inorganics

Laser terahertz emission system to investigate hydrogen gas sensors

Toshihiko Kiwa, Keiji Tsukada, Masato Suzuki, Masayoshi Tonouchi, Sonoko Migitaka, and Koichi Yokosawa

Appl. Phys. Lett. 86, 261102 (2005); http://dx.doi.org/10.1063/1.1954885 (3 pages) | Cited 9 times

Online Publication Date: 20 June 2005

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A laser terahertz emission system is proposed to investigate the catalytic metal/semiconductor interfaces of hydrogen sensors. Samples were fabricated by depositing a catalytic metal thin film on a semi-insulating silicon substrate. A femtosecond laser was used to radiate terahertz waves from the sample in a gas cell filled with a hydrogen and nitrogen gas mixture. The peak amplitude of the terahertz waves decreased with increasing hydrogen concentration. We also fabricated a metal-oxide-semiconductor field effect transistor hydrogen sensor, and compared its properties with the terahertz radiation properties. These results suggest that the laser terahertz emission system is a potential tool to investigate catalytic metal/semiconductor interfaces.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
85.30.Tv Field effect devices
78.47.-p Spectroscopy of solid state dynamics

Absorption cross section and signal enhancement in Er-doped Si nanocluster rib-loaded waveguides

N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato

Appl. Phys. Lett. 86, 261103 (2005); http://dx.doi.org/10.1063/1.1957112 (3 pages) | Cited 31 times

Online Publication Date: 20 June 2005

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Pump and probe experiments on Er3+ ions coupled to Si nanoclusters have been performed in rib-loaded waveguides to investigate optical amplification at 1.5 μm. Rib-loaded waveguides were obtained by photolithographic and reactive ion etching of Er-doped silica layers containing Si nanoclusters grown by reactive sputtering. Insertion losses measurements in the infrared erbium absorption region allowed to gauge an Er3+ absorption cross section of about 5×10−21 cm2 at 1534 nm. Signal transmission under optical pumping at 1310 nm shows confined carrier absorption of the Si nanoclusters. Amplification experiments at 1535 nm evidence two pump power regimes: Losses due to confined carrier absorption in the Si nanoclusters at low pump powers and signal enhancement at high pump powers. For strong optical pumping, signal enhancement of about 1.2 dB/cm was obtained.
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42.79.Gn Optical waveguides and couplers
81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Am Elemental semiconductors and insulators
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Amplified spontaneous emission from a conjugated polymer undergone a high-temperature lithography cycle

Dario Pisignano, Elisa Mele, Luana Persano, Giovanni Paladini, and Roberto Cingolani

Appl. Phys. Lett. 86, 261104 (2005); http://dx.doi.org/10.1063/1.1946189 (3 pages) | Cited 8 times

Online Publication Date: 20 June 2005

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We investigated the amplified spontaneous emission (ASE) and waveguiding properties of a conjugated polymer film after a heating cycle typical of soft lithography procedures. We found a maximum gain coefficient of 8 cm−1, with excitation density and length thresholds for ASE-induced line narrowing of 200 μJ cm−2 and 0.9 mm, respectively. Importantly, we found a loss coefficient of the organic slab as low as 5.4 cm−1, which is among the best results reported for organic waveguide amplifiers. These results are important in view of the application of polymer films as active layers for laser devices realized by patterning with high-temperature mechanical lithographies.
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78.45.+h Stimulated emission
78.66.Qn Polymers; organic compounds
42.79.Wc Optical coatings
42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
81.40.Gh Other heat and thermomechanical treatments
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Isolation effect in ferromagnetic-metal/semiconductor hybrid optical waveguide

V. Zayets and K. Ando

Appl. Phys. Lett. 86, 261105 (2005); http://dx.doi.org/10.1063/1.1953878 (3 pages) | Cited 11 times

Online Publication Date: 20 June 2005

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The isolation effect in a ferromagnetic-metal/semiconductor hybrid optical waveguide was experimentally studied. Optical transmission in a Ga1−xAlxAs waveguide covered by Co was found to depend on the magnetization of the Co. The isolation direction was different for a waveguide with a SiO2 buffer layer and for a waveguide with a Ga1−xAlxAs buffer layer used between the waveguide core layer and Co layer. The physical origin of the isolation in this isolator structure was clarified.
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42.79.Gn Optical waveguides and couplers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Fano resonance in a multimode tapered fiber coupled with a microspherical cavity

Akito Chiba, Hideki Fujiwara, Jun-ichi Hotta, Shigeki Takeuchi, and Keiji Sasaki

Appl. Phys. Lett. 86, 261106 (2005); http://dx.doi.org/10.1063/1.1951049 (3 pages) | Cited 22 times

Online Publication Date: 21 June 2005

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Fano resonance in a tapered optical fiber in contact with a high-Q microsphere is demonstrated. Multimode waves propagating in a 2.3 μm diameter taper were coupled with a single whispering gallery mode of a 220 μm sphere, and their coherent interaction resulted in Fano resonance. The asymmetric line shapes of the transmission spectra changed periodically with scanning of the coupling position along the taper. The observed 24 μm period was due to modal dispersion in the tapered fiber.
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42.81.Dp Propagation, scattering, and losses; solitons
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.81.Qb Fiber waveguides, couplers, and arrays

Monolithic Fabry-Perot resonator for the measurement of optical constants in the terahertz range

Adrian Dobroiu, René Beigang, Chiko Otani, and Kodo Kawase

Appl. Phys. Lett. 86, 261107 (2005); http://dx.doi.org/10.1063/1.1968423 (3 pages) | Cited 4 times

Online Publication Date: 21 June 2005

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A prism-shaped monolithic Fabry-Perot resonator is shown to allow absorption measurements of liquid samples in the terahertz wave range. As the radiation source a backward-wave oscillator was chosen for its tunable, highly monochromatic, continuous wave. The resonator is made of high-resistivity silicon, with two surfaces acting as partial mirrors and forming the cavity, while a third one contributes with a total internal reflection. When a liquid sample is placed on this latter surface the total reflection is attenuated and the finesse of the resonator decreases, providing absorption information about the sample. The measurement method relying on Fourier processing of the signal, as well as experimental data are presented.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.Rd Visible and ultraviolet spectrometers
42.30.Kq Fourier optics

Effect of n+-GaN subcontact layer on 4H–SiC high-power photoconductive switch

K. Zhu, S. Doğan, Y. T. Moon, J. Leach, F. Yun, D. Johnstone, H. Morkoç, G. Li, and B. Ganguly

Appl. Phys. Lett. 86, 261108 (2005); http://dx.doi.org/10.1063/1.1951056 (3 pages) | Cited 4 times

Online Publication Date: 22 June 2005

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High-power photoconductive semiconductor switching devices were fabricated on 4H–SiC. In order to prevent current crowding, reduce the contact resistance, and avoid contact degradation, a highly n-doped GaN subcontact layer was inserted between the contact metal and the high resistivity SiC bulk. This method led to a two orders of magnitude reduction in the on-state resistance and, similarly, the photocurrent efficiency was increased by two orders of magnitude with the GaN subcontact layer following the initial high current operation. Both dry etching and wet etching were used to remove the GaN subcontact layer in the channel area. Wet etching was found to be more suitable than dry etching.
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85.60.-q Optoelectronic devices
72.40.+w Photoconduction and photovoltaic effects
73.40.Cg Contact resistance, contact potential
81.65.Cf Surface cleaning, etching, patterning

Evolution of poling-assisted bleaching of metal-doped nanocomposite glass with poling conditions

Olivier Deparis, Peter G. Kazansky, Alexander Podlipensky, Amin Abdolvand, Gerhard Seifert, and Heinrich Graener

Appl. Phys. Lett. 86, 261109 (2005); http://dx.doi.org/10.1063/1.1977205 (3 pages) | Cited 7 times

Online Publication Date: 23 June 2005

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Poling-assisted bleaching was studied with respect to poling time, voltage, and temperature in glass samples having a gradient of silver nanoparticles across the depth. The optical extinction band due to the particles’ surface plasmon resonance (around 415 nm) was measured and the Maxwell–Garnett effective medium theory was used to fit extinction spectra. Fitting allowed us to determine the evolution of the thickness of the near-surface layer where the particles’ volume filling factor has dropped to zero as a result of the bleaching process. At 280 °C, bleaching started with a voltage as low as 200 V and saturated with time after about 1 h. Tight glass-electrode contact, voltage of at least 1 kV, and temperature higher than 200 °C were required in order to obtain significant and uniform bleaching in the poled area. The results were discussed in terms of the underlying electric-field-assisted dissolution of embedded metal nanoparticles.
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77.22.Ej Polarization and depolarization
64.75.-g Phase equilibria
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.68.+m Optical properties of surfaces

Voltage tunable superlattice infrared detector for mid- and long-wavelength detection

Amlan Majumdar, K. K. Choi, J. L. Reno, and D. C. Tsui

Appl. Phys. Lett. 86, 261110 (2005); http://dx.doi.org/10.1063/1.1977206 (3 pages) | Cited 6 times

Online Publication Date: 23 June 2005

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We have designed and fabricated a voltage tunable superlattice (SL) infrared photodetector where the detection wavelength switches from the 3–5 μm midwavelength infrared (MWIR) range under negative bias to the 8–12 μm long-wavelength infrared (LWIR) range under large positive bias. The structure consists of multiple periods of two different SLs that are separated by undoped blocking barriers on one side and heavily doped layers on the other side. The background-limited temperature with F/1.2 optics is 110 and 70 K for mid- and long-wavelength detection, respectively. This voltage tunable MWIR/LWIR detector has a performance comparable to those of one-color quantum-well infrared detectors designed for the respective wavelength ranges.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Strain dependence of lasing mechanisms in ZnO epilayers

H. D. Li, S. F. Yu, A. P. Abiyasa, Clement Yuen, S. P. Lau, H. Y. Yang, and Eunice S. P. Leong

Appl. Phys. Lett. 86, 261111 (2005); http://dx.doi.org/10.1063/1.1968418 (3 pages) | Cited 16 times

Online Publication Date: 23 June 2005

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The lasing characteristics of highly disordered ZnO thin films deposited on SiO2/Si substrates with and without a MgO buffer layer have been investigated. We observed that the emission spectra of the ZnO epilayers with and without a MgO buffer are associated with the radiative recombination of free-exciton ( ∼ 380 nm) and electron-hole plasma ( ∼ 395 nm), respectively. The difference in the lasing wavelength is due to the induced compressive (tensile) strain along the c axis of the ZnO epilayers as a result of the presence (absence) of the MgO buffer layer. It is demonstrated that the strain-induced variation of Mott density inside the ZnO epilayers is responsible for the observed lasing characteristics.
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81.05.Hd Other semiconductors
42.55.Px Semiconductor lasers; laser diodes
78.66.Li Other semiconductors
68.60.Bs Mechanical and acoustical properties
78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena
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