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30 Apr 2007

Volume 90, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 182501 (2007); http://dx.doi.org/10.1063/1.2734874 (3 pages)

A. V. Silhanek, W. Gillijns, V. V. Moshchalkov, V. Metlushko, F. Gozzini, B. Ilic, W. C. Uhlig, and J. Unguris
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Highly transparent and low-resistant ZnNi/indium tin oxide Ohmic contact on p-type GaN

S. W. Chae, K. C. Kim, D. H. Kim, T. G. Kim, S. K. Yoon, B. W. Oh, D. S. Kim, H. K. Kim, and Y. M. Sung

Appl. Phys. Lett. 90, 181101 (2007); http://dx.doi.org/10.1063/1.2731672 (3 pages) | Cited 6 times

Online Publication Date: 30 April 2007

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The authors report the improvement of GaN light-emitting diodes (LEDs) by applying a ZnNi/indium tin oxide (ITO) (5 nm/380 nm) electrode with high transparency and low resistance to p-GaN. The Pt/ITO (5 nm/380 nm), Ni/Au/ITO (2.5 nm/5nm/380 nm), and Ni/Au (2.5 nm/5 nm) electrodes were prepared and annealed at 400, 500, and 600 °C for 1 min in air. The ZnNi/ITO contacts showed the lowest specific contact resistance of ∼ 1.27×10−4 Ω cm2 and the highest transmittance of ∼ 90% at 460 nm. LEDs fabricated with ZnNi/ITO p electrodes showed the best performance with a forward voltage of 3.28 V and a typical brightness of 11. 7 mcd at 20 mA.
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61.72.Cc Kinetics of defect formation and annealing
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Nanoscale surface plasmon based resonator using rectangular geometry

Amir Hosseini and Yehia Massoud

Appl. Phys. Lett. 90, 181102 (2007); http://dx.doi.org/10.1063/1.2734380 (3 pages) | Cited 63 times

Online Publication Date: 30 April 2007

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The authors present an optical range resonator based on single mode metal-insulator-metal plasmonic gap waveguides. Complete transmission at 90° bends would enable the design of rectangular structures with cross-section area less than 500 nm2, which consequently leads to easing the fabrication process. The resonator exhibits a free spectral range of 270 nm. We show that a small bridge between the resonator and the input waveguide can be used to tune the resonance frequency. In addition, ultracompact add/drop directional couplers are realizable using the presented ring resonator structure.
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42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
42.15.Eq Optical system design

Upconversion with ultrabroad excitation band: Simultaneous use of two sensitizers

S. Baluschev, V. Yakutkin, G. Wegner, T. Miteva, G. Nelles, A. Yasuda, S. Chernov, S. Aleshchenkov, and A. Cheprakov

Appl. Phys. Lett. 90, 181103 (2007); http://dx.doi.org/10.1063/1.2734475 (3 pages) | Cited 26 times

Online Publication Date: 30 April 2007

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The authors demonstrate the ability to combine sensitizers effectively working with single emitter in order to increase the excitation window for noncoherent upconversion. They show effective upconversion of the red part of the sun spectrum realized by ultralow excitation intensity (as low as 1 W cm−2) and ultrabroad excitation spectrum (Δλ ∼ 80 nm).
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33.50.Dq Fluorescence and phosphorescence spectra

Heat flow in AlGaInP/GaAs light-emitting diodes

N. C. Chen, Y. K. Yang, Y. N. Wang, and Y. C. Huang

Appl. Phys. Lett. 90, 181104 (2007); http://dx.doi.org/10.1063/1.2734494 (3 pages) | Cited 6 times

Online Publication Date: 30 April 2007

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The differential equations of heat flow with boundary conditions suited to light-emitting diodes (LEDs) were analytically solved. An AlGaInP/GaAs LED is considered as an example. The agreement between the theoretical and experimental evolutions of the junction temperature demonstrates the accuracy of this analytical solution. Additionally, since the increase of the junction temperature depends on the thermal properties of the substrate, the measured junction temperature together with the analytical solution yield the thermal properties of the substrate.
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85.60.Jb Light-emitting devices

Role of surface plasmon in second harmonic generation from gold nanorods

C. Hubert, L. Billot, P.-M. Adam, R. Bachelot, P. Royer, J. Grand, D. Gindre, K. D. Dorkenoo, and A. Fort

Appl. Phys. Lett. 90, 181105 (2007); http://dx.doi.org/10.1063/1.2734503 (3 pages) | Cited 18 times

Online Publication Date: 30 April 2007

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The role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength. In addition to photoluminescence, a peak of second harmonic is observed and is found to depend on the polarization and wavelength of the fundamental frequency laser beam. In particular, the authors found similarities between extinction spectra of the nanoparticles and spectra of emmitted second harmonic. This behavior can be explained by resonant excitation of localized surface plasmon resonances.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.47.-p Spectroscopy of solid state dynamics
78.55.Hx Other solid inorganic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Three-dimensional photonic crystal by holographic contact lithography using a single diffraction mask

Guangya Zhou and Fook Siong Chau

Appl. Phys. Lett. 90, 181106 (2007); http://dx.doi.org/10.1063/1.2734473 (3 pages) | Cited 1 time

Online Publication Date: 30 April 2007

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The authors present an approach for fabrication of three-dimensional (3D) periodic micro-nanoscale structures through holographic contact lithography using a single diffraction mask. The mask functions to split an incoming laser beam into four diffracted beams in an umbrella configuration to produce a 3D periodic interference pattern immediately behind it. The recording photoresist can thus be placed in direct contact with or in close proximity to the mask. The proposed approach was investigated using 3D finite-difference time-domain method. Simulation results confirmed the feasibility of the method.
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42.70.Qs Photonic bandgap materials
42.40.My Applications
81.16.Nd Micro- and nanolithography

Degeneracy breaking of optical resonance modes in rolled-up spiral microtubes

M. Hosoda and T. Shigaki

Appl. Phys. Lett. 90, 181107 (2007); http://dx.doi.org/10.1063/1.2734878 (3 pages) | Cited 21 times

Online Publication Date: 1 May 2007

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The authors investigate the optical resonance modes (ORMs) generated in semiconductor microtubes of spiral symmetry by using finite-difference time-domain methods. Even though the tube-wall thickness is much smaller than the light wavelength, modes having an electric field parallel to the tube wall can loop around the tube periphery as ORMs. In addition, the degenerated ORMs present in conventional cylindrical cavities such as whispering gallery modes are broken and separated into two modes due to the spiral asymmetry of the rolled-up microtubes.
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42.79.-e Optical elements, devices, and systems

Two-photon absorption based optical limiting and stabilization by using a CdTe quantum dot solution excited at optical communication wavelength of ∼ 1300 nm

Guang S. He, Qingdong Zheng, Ken-Tye Yong, Aleksandr I. Ryasnyanskiy, Paras N. Prasad, and Augustine Urbas

Appl. Phys. Lett. 90, 181108 (2007); http://dx.doi.org/10.1063/1.2734904 (3 pages) | Cited 12 times

Online Publication Date: 1 May 2007

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This letter presents the results of two-photon study of CdTe quantum dots (QDs) in chloroform. The measured two-photon absorption (2PA) spectrum shows that 2PA coefficient at ∼ 1300 nm is ∼ 0.02 cm/GW. Based on a 1 cm path-length CdTe QD solution sample of 8 mg/ml concentration, irradiated by a focused ∼ 1300 nm laser beam of ∼ 160 fs duration, the nonlinear transmission could be changed from ∼ 100% to ∼ 20% when the input pulse energy was varied from ∼ 50 nJ to  ∼ 10 μJ, demonstrating a superior optical limiting performance. The input laser fluctuation was significantly reduced after passing through the sample, indicating a remarkable optical stabilization behavior.
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78.67.Hc Quantum dots
78.66.Hf II-VI semiconductors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Direct writing three-dimensional Ba2TiSi2O8 crystalline pattern in glass with ultrashort pulse laser

Ye Dai, Bin Zhu, Jianrong Qiu, Hongliang Ma, Bo Lu, Shixun Cao, and Binkung Yu

Appl. Phys. Lett. 90, 181109 (2007); http://dx.doi.org/10.1063/1.2734919 (3 pages) | Cited 25 times

Online Publication Date: 1 May 2007

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The nonlinear optical crystal Ba2TiSi2O8 is induced three-dimensionally inside a glass by a femtosecond pulse laser with 800 nm, 250 kHz, and 150 fs. Micro-Raman and photoluminescence spectra confirm that crystals can grow in the focal point of the laser beam. Continuous crystalline lines were written through moving the focal point of the laser beam inside the glass. The results demonstrate a convenient method to engrave three-dimensional patterns of crystals with nonlinear optical properties for integrated optical devices.
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42.70.Mp Nonlinear optical crystals
42.62.-b Laser applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
42.82.Gw Other integrated-optical elements and systems

Second order optical nonlinearity of ZnO/ZnO:Al bilayers deposited on glass by low temperature radio frequency sputtering

F. Michelotti, R. Canali, L. Dominici, A. Belardini, F. Menchini, G. Schoer, and J. Mueller

Appl. Phys. Lett. 90, 181110 (2007); http://dx.doi.org/10.1063/1.2735283 (3 pages) | Cited 1 time

Online Publication Date: 1 May 2007

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The authors report on the measurement of the second order nonlinear optical properties of ZnO films deposited by low temperature radio frequency sputtering on ZnO:Al coated glass substrates. They show that ZnO:Al plays a crucial role as a buffer layer for the successive growth of ZnO. The effect of aluminum doping on the relaxation of the stresses acts as a template for crystallization of ZnO, allowing us to obtain partially oriented ZnO films with relatively large nonlinear coefficients. The measurements of the second harmonic tensor by the Maker fringes method are in good agreement with results for the electro-optic coefficient obtained by nonlinear ellipsometry.
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78.66.Hf II-VI semiconductors
42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
78.20.Jq Electro-optical effects

High resolution x-ray microscope

C. K. Gary, H. Park, L. W. Lombardo, M. A. Piestrup, J. T. Cremer, R. H. Pantell, and Y. I. Dudchik

Appl. Phys. Lett. 90, 181111 (2007); http://dx.doi.org/10.1063/1.2734895 (3 pages) | Cited 2 times

Online Publication Date: 1 May 2007

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The authors present x-ray images of grid meshes and biological material obtained using a microspot x-ray tube with a multilayer optic and a 92-element parabolic compound refractive lens (CRL) made of a plastic containing only hydrogen and carbon. Images obtained using this apparatus are compared with those using an area source with a spherical lens and a spherical lens with multilayer condenser. The authors found the best image quality using the multilayer condenser with a parabolic lens, compared to images with a spherical lens and without the multilayer optics. The resolution was measured using a 155-element parabolic CRL and a multilayer condenser with the microspot tube. The experiment demonstrates about 1.1 μm resolution.
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07.85.Tt X-ray microscopes
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics

Broadband surface plasmon resonance spectroscopy for determination of refractive-index dispersion of dielectric thin films

Zhi-mei Qi, Mingdeng Wei, Hirofumi Matsuda, Itaru Honma, and Haoshen Zhou

Appl. Phys. Lett. 90, 181112 (2007); http://dx.doi.org/10.1063/1.2734898 (3 pages) | Cited 3 times

Online Publication Date: 1 May 2007

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Here the authors report the spectral surface plasmon resonance (SPR) behavior of thin gold films covered with dielectric layers. With the SPR sensor angular dependence of the resonant wavelength and refractive-index (RI) sensitivity at a specific angle were measured by broadband absorption spectroscopy. By fitting the calculated SPR absorption spectrum to the experimental result, RI dispersion of a TiO2-nanoparticle/polymer composite layer was obtained, which was compared with the ellipsometry data. The phase spectra of the sensor were calculated, and a large response of the phase to the solution RI was observed around the resonant wavelength.
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78.68.+m Optical properties of surfaces
77.55.-g Dielectric thin films
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)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.40.Kc Metals, semimetals, and alloys

Opposite temperature effects of quantum-dot laser under dual-wavelength operation

Hsueh-Shih Fan, Yi-Shin Su, Fei-Hung Chu, Fu-Yu Chang, Hao-Hsiung Lin, and Ching-Fuh Lin

Appl. Phys. Lett. 90, 181113 (2007); http://dx.doi.org/10.1063/1.2735543 (3 pages)

Online Publication Date: 1 May 2007

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The authors discover opposite temperature effects when the quantum-dot (QD) laser is controlled to simultaneously oscillate at two modes in the external cavity. The two modes correspond to the ground state and the first excited state of the QDs. Experiments show that the power of one mode increases, while the power of the other mode decreases as the temperature increases. The power variation between these two modes is similar to the situation of competition and anticompetition of laser modes. The physical reason is discussed in detail.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Photon number resolving detector based on a quantum dot field effect transistor

B. E. Kardynał, S. S. Hees, A. J. Shields, C. Nicoll, I. Farrer, and D. A. Ritchie

Appl. Phys. Lett. 90, 181114 (2007); http://dx.doi.org/10.1063/1.2735281 (3 pages) | Cited 19 times

Online Publication Date: 1 May 2007

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The authors show that the change in current flowing through the channel of a quantum dot field effect transistor is proportional to the number (N) of photons absorbed from an incident pulse. Distinct features due to photon number state up to N = 3 are resolved. With improvement of external quantum efficiency the device may form a useful photon number resolving detector.
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85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)

Photonic crystal effect on light emission from InGaN/GaN multi-quantum-well structures

Keunjoo Kim, Jaeho Choi, Sang Cheol Jeon, Jin Soo Kim, and Hee Mok Lee

Appl. Phys. Lett. 90, 181115 (2007); http://dx.doi.org/10.1063/1.2735927 (3 pages) | Cited 11 times

Online Publication Date: 2 May 2007

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Triangular hole arrays with nanoscaled lattice constants of 230 and 460 nm were fabricated on a p-type GaN epitaxial layer grown on an InGaN/GaN multi-quantum-well light emitting diode structure by metal-organic chemical vapor deposition. The hole geometries of dry-etched thin slabs for triangular lattice constants of 230 and 460 nm possessed diameters of 223 and 218 nm at the surface, and 108 and 76 nm at the bottom, with depths of 31 and 27 nm, respectively. The hole array with a lattice constant of 230 nm enhances photoluminescence intensity at wavelengths of 364 and 406 nm, but reduces light extraction at a wavelength of 450 nm, which indicates destructive surface diffraction correlated with light scattering in the photonic crystal structure.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
42.70.Qs Photonic bandgap materials
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.16.Nd Micro- and nanolithography

Mechanism of all-optical spin-dependent polarization switching in Bragg-spaced quantum wells

D. T. Nguyen, N. H. Kwong, Z. S. Yang, R. Binder, and Arthur L. Smirl

Appl. Phys. Lett. 90, 181116 (2007); http://dx.doi.org/10.1063/1.2735673 (3 pages) | Cited 1 time

Online Publication Date: 2 May 2007

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The authors outline a microscopic theory of pump-induced anisotropy in the optical response of Bragg-spaced quantum wells (BSQWs). Their theory explains the manipulation of the band structure of the BSQWs by the pump through the microscopic interactions between excitons in the quantum wells. They apply their theory to understand the mechanism of an all-optical polarization switch implemented on a BSQW structure. They trace the relation between the strongly spin-dependent exciton-exciton interactions and the switching signal. Reasonably good agreement is found between their theoretical results and experimental data.
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78.67.De Quantum wells
71.35.-y Excitons and related phenomena
42.70.Qs Photonic bandgap materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Optical thermometry through infrared excited green upconversion emissions in Er3+–Yb3+ codoped Al2O3

B. Dong, D. P. Liu, X. J. Wang, T. Yang, S. M. Miao, and C. R. Li

Appl. Phys. Lett. 90, 181117 (2007); http://dx.doi.org/10.1063/1.2735955 (3 pages) | Cited 41 times

Online Publication Date: 2 May 2007

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Fluorescence intensity ratio (FIR) variation of green upconversion emissions at 523 and 545 nm in the Er3+–Yb3+ codoped Al2O3 has been studied as a function of temperature using a 978 nm semiconductor laser diode as an excitation source. In the temperature range of 295–973 K, the maximum sensitivity and the temperature revolution derived from the FIR technique are approximately 0.0051 K−1 and 0.3 K, respectively. The Er3+–Yb3+ codoped Al2O3 material with the highest operating temperature up to 973 K, the higher temperature revolution, and the fluorescence efficiency indicated that it is promising for applications in optical high temperature sensor.
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07.20.Dt Thermometers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.55.Hx Other solid inorganic materials

Quantitative phase retrieval in transmission hard x-ray microscope

Gung-Chian Yin, Fu-Rong Chen, Yeukuang Hwu, Han-Ping D. Shieh, and Keng S. Liang

Appl. Phys. Lett. 90, 181118 (2007); http://dx.doi.org/10.1063/1.2724066 (3 pages) | Cited 3 times

Online Publication Date: 3 May 2007

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Quantitative phase retrieval with a sub-100-nm resolution is achieved from micrographs of a zone plate based transmission x-ray microscope. A plastic zone plate containing objects of sizes from micrometers down to tens of nanometers is used as a test sample to quantify the retrieved phase. Utilizing the focal serial images in the image plane, the phase information is retrieved quantitatively across the entire range of sizes by combining the transport intensity equation and self-consistent wave propagation methods in this partial coherence system. The study demonstrates a solution to overcome the deficiency encountered in the two phase retrieval approaches.
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07.85.Tt X-ray microscopes
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.30.-d Imaging and optical processing

Femtosecond filamentation and supercontinuum generation in silver-nanoparticle-doped water

Chen Wang, Yuxi Fu, Zenghui Zhou, Ya Cheng, and Zhizhan Xu

Appl. Phys. Lett. 90, 181119 (2007); http://dx.doi.org/10.1063/1.2736212 (3 pages) | Cited 13 times

Online Publication Date: 3 May 2007

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The authors report the investigation of filament and supercontinuum generation by focusing a femtosecond laser beam into water doped with silver nanoparticles. The silver nanoparticles enhance the nonlinear optical response of water, leading to broadening of supercontinuum spectra in self-focused femtosecond filaments. During the propagation of the supercontinuum light in the filament, the silver nanoparticles preferentially scatter the short-wavelength light near the plasmon resonant wavelength peak, followed by the scattering of the long-wavelength light. Thus, a side view of the filament shows a full-color spectrum in the visible range, which is herein called “rainbow filament.”
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

High-temperature interband cascade lasers emitting at λ = 3.6–4.3 μm

C. L. Canedy, W. W. Bewley, M. Kim, C. S. Kim, J. A. Nolde, D. C. Larrabee, J. R. Lindle, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 90, 181120 (2007); http://dx.doi.org/10.1063/1.2736272 (3 pages) | Cited 12 times

Online Publication Date: 3 May 2007

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The authors report the operating characteristics of ten-stage interband cascade lasers from two wafers with room-temperature wavelengths of 4.1 and 4.3 μm. For 150-μm-wide stripes, the threshold current densities are as low as 4.8 A/cm2 at 78 K (cw) and 1.15 kA/cm2 at room temperature (pulsed). At 78 K, the cw wall-plug efficiency for an 11-μm-wide ridge with 0.5-mm-long cavity and coated facets is 27%, while a 3-mm-long cavity emits a maximum cw power of 200 mW. Devices from the two wafers have maximum cw operating temperatures of 261 K (λ ≈ 4.0 μm) and 243 K (λ ≈ 4.2 μm).
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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

Switchable two-color electroluminescence based on a Si metal-oxide-semiconductor structure doped with Eu

S. Prucnal, J. M. Sun, W. Skorupa, and M. Helm

Appl. Phys. Lett. 90, 181121 (2007); http://dx.doi.org/10.1063/1.2735285 (3 pages) | Cited 23 times

Online Publication Date: 3 May 2007

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A Si metal-oxide-semiconductor electroluminescent device structure is reported which emits two colors, while being doped with a single rare-earth element. Thermally grown SiO2 oxide layers were implanted with Eu and subseqently annealed. Depending on the electrical excitation current, the luminescence is red or blue, which can be ascribed to electronic transitions in tri- and divalent europium (Eu3+ and Eu2+), respectively.
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78.60.Fi Electroluminescence
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing

Optical characteristics of a-plane InGaN/GaN multiple quantum wells with different well widths

T. S. Ko, T. C. Lu, T. C. Wang, M. H. Lo, J. R. Chen, R. C. Gao, H. C. Kuo, S. C. Wang, and J. L. Shen

Appl. Phys. Lett. 90, 181122 (2007); http://dx.doi.org/10.1063/1.2735935 (3 pages) | Cited 5 times

Online Publication Date: 3 May 2007

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a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm were grown on r-plane sapphire by metal organic chemical vapor deposition for investigation. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL study shows that the sample with 3-nm-thick wells has a better optical property with a fast exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify the more uniform and stronger luminescence intensity distribution observed for the samples of thinner quantum wells, indicating that the important growth parameters for a-plane InGaN/GaN multiple quantum wells could be dominated by the In fluctuation and crystal quality during the epitaxial growth.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.67.De Quantum wells

Photorefractive star-shaped molecular glassy materials containing tricyanopyrroline-based chromophore

Kyung Moon Jung, Min Ju Cho, Jung-Il Jin, and Dong Hoon Choi

Appl. Phys. Lett. 90, 181123 (2007); http://dx.doi.org/10.1063/1.2736301 (3 pages) | Cited 1 time

Online Publication Date: 3 May 2007

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The authors report the near-IR sensitive star-shaped molecule [D-(CBz-TCP)3] containing bifunctional chromophores. A nonlinear optical active tricyanopyrroline-based plasticizer was also synthesized and introduced into the prepared molecular glass so as to control the glass transi-tion temperature of the photorefractive matrix. In a doped glass, they observed significantly enhanced photorefractive performances with regard to the asymmetric energy transfer and the diffraction efficiency at 830 nm. In the presence of a small amount of (2,4,7-trinitro-9- fluorenylidene)malononitrile, they could demonstrate a very large net two beam coupling gain higher than 300 cm−1 and a diffraction efficiency of 58%.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials
42.70.Jk Polymers and organics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Linearly polarized dual-wavelength vertical-external-cavity surface-emitting laser

Li Fan, Mahmoud Fallahi, Jörg Hader, Aramais R. Zakharian, Jerome V. Moloney, Wolfgang Stolz, Stephan W. Koch, Robert Bedford, and James T. Murray

Appl. Phys. Lett. 90, 181124 (2007); http://dx.doi.org/10.1063/1.2735554 (3 pages) | Cited 13 times

Online Publication Date: 3 May 2007

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The authors demonstrate the multiwatt linearly polarized dual-wavelength operation in an optically pumped vertical-external-cavity surface-emitting laser by means of an intracavity tilted Fabry-Perot etalon and a Brewster window. The sum frequency generation from the lithium triborate crystal pumped by this laser confirms that these two wavelengths oscillate simultaneously. Over 30 dB side-mode suppression can be achieved at dual wavelengths with a spectral spacing of 2.1 nm. The output power is slightly reduced by the intracavity Fabry-Perot etalon and Brewster window.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
07.60.Ly Interferometers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Effects of strained InGaN interlayer on contact resistance between p-GaN and indium tin oxide

Chi-Ling Lee and Wei-I Lee

Appl. Phys. Lett. 90, 181125 (2007); http://dx.doi.org/10.1063/1.2737122 (3 pages) | Cited 6 times

Online Publication Date: 4 May 2007

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Indium tin oxide (ITO), with its transparency and strong adhesion to GaN, has been used as a replacement for Ni/Au as a contact on p-GaN. However, ITO suffers from high contact resistance on p-GaN. In this work, low contact resistance between ITO and the p-GaN layer was consistently achieved using various strained InGaN layers as the interface layers between ITO and p-GaN layer. The doping of InGaN, whether n type or p type, has a relatively weak effect on the contact resistance as long as the thickness of the InGaN layer is adequately controlled. The secondary-ion-mass spectroscopy depth profile reveals that the n-type InGaN strained contact layer was also heavily doped with Mg. Results of this study demonstrate that the piezoelectric field between InGaN and p-GaN is important in reducing the barrier height of Ohmic contact.
Show PACS
85.60.Jb Light-emitting devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
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