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8 May 2000

Volume 76, Issue 19, pp. 2647-2800

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High-frequency electrical pulse generation using optical rectification in bulk GaAs

S. Graf, H. Sigg, and W. Bächtold

Appl. Phys. Lett. 76, 2647 (2000); http://dx.doi.org/10.1063/1.126432 (3 pages) | Cited 3 times

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We present the realization of a traveling-wave electrical pulse generator using pure nonresonant instantaneous optical rectification in bulk GaAs. The optical excitation was achieved by far-infrared pulses of 1–6 ps duration in the wavelength range from 8 to 15 μm, generated by a free-electron laser. The coupling of the optical rectification polarization into the fundamental mode of the microstrip transmission line is verified by angle-resolved measurements. Since optical femtosecond pulses are now becoming readily available, this alternative technique, which gains in efficiency at shorter pulses, may find growing importance for ultrafast pulse generation. © 2000 American Institute of Physics.
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42.79.-e Optical elements, devices, and systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
85.60.-q Optoelectronic devices

Efficient photon harvesting at high optical intensities in ultrathin organic double-heterostructure photovoltaic diodes

P. Peumans, V. Bulović, and S. R. Forrest

Appl. Phys. Lett. 76, 2650 (2000); http://dx.doi.org/10.1063/1.126433 (3 pages) | Cited 266 times

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We demonstrate a method for efficient photon harvesting in organic thin films, thereby increasing the efficiency of organic photovoltaic cells. By incorporating an exciton-blocking layer (EBL) inserted between the photoactive organic layers and the metal cathode, we achieved an external power conversion efficiency of 2.4%±0.3% in vacuum-deposited ultrathin organic bilayer photovoltaic (PV) cells employed in a simple light trapping geometry. Ultrathin (∼100 Å) cells incorporating the transparent, conductive EBL have an internal quantum efficiency as high as 33%±4% over a spectral region matched to the solar spectrum. The very thin organic layers have a low series resistance, allowing for efficient power conversion in organic PV cells under intense (>15 suns) AM1.5 illumination. This device structure demonstrates that control of exciton diffusion in solid-state organic devices leads to a significant increase in the photon-to-carrier conversion efficiency. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.At Surface states, band structure, electron density of states

Effect of band gap renormalization on threshold current and efficiency of a distributed Bragg reflector laser

H. Wenzel, A. Klehr, G. Erbert, J. Sebastian, G. Tränkle, and M. F. Pereira

Appl. Phys. Lett. 76, 2653 (2000); http://dx.doi.org/10.1063/1.126434 (3 pages) | Cited 3 times

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The threshold current and the external efficiency of a three-section distributed Bragg reflector laser are investigated as a function of a forward electrical bias applied to the passive sections. Within a well-determined range, the threshold current increases and the external efficiency decreases with increasing bias. This effect is attributed to band gap renormalization. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Three-dimensional microfabrication by use of single-photon-absorbed polymerization

Shoji Maruo and Koji Ikuta

Appl. Phys. Lett. 76, 2656 (2000); http://dx.doi.org/10.1063/1.126742 (3 pages) | Cited 36 times

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We developed a promising method to fabricate three-dimensional microstructures by using single-photon-absorbed polymerization confined to the vicinity of a tightly focused spot. This localized polymerization is based on the nonlinear response of the photopolymerizable resin to optical intensity with sufficiently low exposure. The nonlinear response was verified by measuring polymerization exotherm at different light intensities. The proposed method enables us to make even movable microstructures without any of the supporting parts or sacrificial layers normally required with conventional micromachining. In the experiment reported here, we fabricated a microgear with an external diameter of 47 μm and an attached shaft. © 2000 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
07.10.Cm Micromechanical devices and systems
81.20.Wk Machining, milling
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
82.60.Cx Enthalpies of combustion, reaction, and formation

Temperature dependence of intrinsic recombination coefficients in 1.3 μm InAsP/InP quantum-well semiconductor lasers

J. M. Pikal, C. S. Menoni, P. Thiagarajan, G. Y. Robinson, and H. Temkin

Appl. Phys. Lett. 76, 2659 (2000); http://dx.doi.org/10.1063/1.126435 (3 pages) | Cited 7 times

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In this letter, we report on the temperature dependence of the intrinsic recombination coefficients in long-wavelength quantum-well lasers. Unlike previous studies, we obtain the intrinsic recombination coefficients from carrier lifetime measurements with a correction for the carrier population in the barrier and separate confinement heterostructure region. Our results show that this carrier population not only affects the value of the recombination coefficients obtained but also their temperature dependence. We measure a significant increase in the intrinsic Auger coefficient with temperature indicating that the frequently reported temperature insensitivity of this coefficient is likely due to carriers spilling out of the wells at elevated temperatures and not an intrinsic property of the Auger process. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Temporal evolution of resonant Raman-scattering in ZnCdSe quantum dots

A. Kaschner, M. Strassburg, A. Hoffmann, C. Thomsen, M. Bartels, K. Lischka, and D. Schikora

Appl. Phys. Lett. 76, 2662 (2000); http://dx.doi.org/10.1063/1.126436 (3 pages) | Cited 3 times

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We investigated ZnCdSe/ZnSe quantum-dot structures which include planar and coherently strained three-dimensional islands with different sizes. Optical excitation of these islands well below the ZnSe band gap leads to a resonant enhancement of the Zn0.7Cd0.3Se longitudinal-optical (LO) phonon-scattering efficiency and makes the 2LO and 3LO multiphonon emission observable. Resonant excitation with a power density of about 1.3 MW/cm2 using a micro-Raman setup results in an exponential decrease of the 1LO, 2LO, and 3LO intensity with irradiation time. This decay behavior is not observed for pure ZnSe crystals and can be avoided for the ZnCdSe/ZnSe structures using much lower excitation densities. The decrease in intensity is accompanied by a shift of the LO mode to higher frequencies resulting from a lower cadmium concentration in the alloy. From these experimental findings, we conclude that resonant excitation at a certain power density leads to cadmium out-diffusion from the planar quantum dots, which shifts the resonance away from the excitation energy. © 2000 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

On the strong influence of the photoelastic effect in the collinear mirage deflection

A. Salazar, M. Gateshki, and A. Sánchez-Lavega

Appl. Phys. Lett. 76, 2665 (2000); http://dx.doi.org/10.1063/1.126437 (3 pages) | Cited 1 time

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We report in this letter on the strong influence of the polarization state of the probe beam in the amplitude and phase of the collinear mirage deflection. A model of the collinear mirage deflection that takes into account the photoelastic effect in the sample has been developed. The agreement between the model predictions and the experimental results is excellent. © 2000 American Institute of Physics.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.30.-d Imaging and optical processing
42.25.Ja Polarization

Photofabrication of three-dimensional photonic crystals by multibeam laser interference into a photopolymerizable resin

Satoru Shoji and Satoshi Kawata

Appl. Phys. Lett. 76, 2668 (2000); http://dx.doi.org/10.1063/1.126438 (3 pages) | Cited 93 times

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Three-dimensional (3D) photonic crystal structures can be fabricated into photopolymerizable resins by using laser beam interference with high precision. Three laser beams interfere into a glass cell filled with a liquid photopolymerizable resin to form a hexagonal periodic structure. Rods are formed in a hexagonal arrangement after being photopolymerzed according to the 3D periodic light distribution which results from the laser’s interference. Two beams of another laser also interfere to form layers which cross perpendicular to the rod array. After photofabrication, the nonsolidified resin is removed by ethanol. The lattice constant can be selected by tuning the angles of the incident beams and the laser wavelength. We have fabricated a 500 μm×500 μm×150 μm photonic crystal structure, the lattice constant of which is 1 μm and contains 150 lateral layers. © 2000 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry

Measurement of the linear electro-optic coefficients of sol-gel derived strontium barium niobate thin films using a two-beam polarization interferometer

Junmo Koo, Changho Lee, Jae Hyeok Jang, Kwangsoo No, and Byeong-Soo Bae

Appl. Phys. Lett. 76, 2671 (2000); http://dx.doi.org/10.1063/1.126439 (3 pages) | Cited 6 times

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A two-beam polarization interferometer in a reflection configuration is used to measure the electro-optic coefficients of highly oriented strontium barium niobate thin films prepared by a sol-gel method. The technique enables the determination of the electro-optic coefficients of films using a strong Fabry–Perot effect with automatic adjustment and maintenance of the operation point of the interferometer. The linear electro-optic coefficients increase with increasing Sr content in the films. © 2000 American Institute of Physics.
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78.20.Jq Electro-optical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
07.60.Ly Interferometers
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
78.66.Li Other semiconductors
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