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9 Jul 2001

Volume 79, Issue 2, pp. 145-277

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Destructive interference of freely propagating terahertz pulses and its potential for high-resolution spectroscopy and optical computing

V. Grebenev, E. Knoesel, and L. Bartels

Appl. Phys. Lett. 79, 145 (2001); http://dx.doi.org/10.1063/1.1381419 (3 pages) | Cited 1 time

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Freely propagating terahertz pulses have been superimposed on a detection crystal leading to their mutual annihilation. An extinction ratio as good as 10:1 is found. The interference pattern represents the sum of the pulses, as measured individually, with high fidelity. Its application for high-resolution spectroscopy and optical computing are discussed. © 2001 American Institute of Physics.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
41.20.Jb Electromagnetic wave propagation; radiowave propagation
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Effect of saturable response to two-photon absorption on the readout signal level of three-dimensional bit optical data storage in a photochromic polymer

Min Gu, Jose Omar Amistoso, Akiko Toriumi, Masahiro Irie, and Satoshi Kawata

Appl. Phys. Lett. 79, 148 (2001); http://dx.doi.org/10.1063/1.1383999 (3 pages) | Cited 6 times

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We observe a saturable change in the refractive index induced by two-photon absorption in a photochromic polymer, while the erasable nature of the polymer is maintained. As a result, the support region of spatial frequencies of the recorded data bits caused by the refractive index change in the polymer is enlarged. This feature leads to the significant enhancement of the signal level in a reflection confocal microscope readout system for three-dimensional photochromic bit optical data storage. © 2001 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
07.60.Pb Conventional optical microscopes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Near-transform-limited picosecond pulses from a gain-switched InGaAs diode laser with fiber Bragg gratings

D. J. L. Birkin, E. U. Rafailov, W. Sibbett, L. Zhang, Y. Liu, and I. Bennion

Appl. Phys. Lett. 79, 151 (2001); http://dx.doi.org/10.1063/1.1381412 (2 pages) | Cited 6 times

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We have generated near-transform-limited picosecond pulses (ΔτΔν ≈ 0.45) from a gain-switched diode laser using periodic and chirped fiber Bragg gratings. This configuration reduced the spectral bandwidth from 11 to 0.08 nm and the pulse duration was reduced, from 30 to <18 ps. Average and peak powers of 27 and 770 mW, respectively, were obtained. © 2001 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Dj Gratings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.81.Wg Other fiber-optical devices

Quantum dots in glass spherical microcavity

Rui Jia, De-Sheng Jiang, Ping-Heng Tan, and Bao-Quan Sun

Appl. Phys. Lett. 79, 153 (2001); http://dx.doi.org/10.1063/1.1380732 (3 pages) | Cited 16 times

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Glass spherical microcavities containing CdSexS1−x semiconductor quantum dots (QDs) are fabricated. The coupling between the optical emission of embedded CdSexS1−x QDs and spherical cavity modes is realized. When the luminescence of QDs is excited by a laser beam, the strong whispering gallery mode resonance with high Q factors is achieved in the photoluminescence spectra. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.07.Ta Quantum dots

Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer

Masamichi Ikai, Shizuo Tokito, Youichi Sakamoto, Toshiyasu Suzuki, and Yasunori Taga

Appl. Phys. Lett. 79, 156 (2001); http://dx.doi.org/10.1063/1.1385182 (3 pages) | Cited 413 times

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One of the keys to highly efficient phosphorescent emission in organic light-emitting devices is to confine triplet excitons generated within the emitting layer. We employ “starburst” perfluorinated phenylenes (C60F42) as a both hole- and exciton-block layer, and a hole-transport material 4,4′,4″-tri(N-carbazolyl) triphenylamine as a host for the phosphorescent dopant dye in the emitting layer. A maximum external quantum efficiency reaches to 19.2%, and keeps over 15% even at high current densities of 10–20 mA/cm2, providing several times the brightness of fluorescent tubes for lighting. The onset voltage of the electroluminescence is as low as 2.4 V and the peak power efficiency is 70–72 lm/W, promising for low-power display devices. © 2001 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Etching of crystalline Si in Cl2 atmosphere by means of an optical fiber tip

G. Wysocki, S. T. Dai, T. Brandstetter, J. Heitz, and D. Bäuerle

Appl. Phys. Lett. 79, 159 (2001); http://dx.doi.org/10.1063/1.1369415 (3 pages) | Cited 7 times

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We report experiments on laser-induced chemical etching of silicon in chlorine atmosphere using a near-field optical configuration. Crystalline (100) Si surfaces were locally illuminated in 300 mbar Cl2 through a tapered fiber tip. In most of the experiments, we used UV argon ion laser lines around 350 nm for illumination. The etched samples were analyzed by means of atomic force microscopy. Patterns with a width of 140 nm at full width half maximum and a vertical etch rate of the order of 15 nm/s have been achieved. Comparison of etching with a visible wavelength at intensities that cannot cause surface melting shows that the etching is primarily a photophysical process. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning

Optical characterization of 4H-SiC by far ultraviolet spectroscopic ellipsometry

Seung-Gu Lim, Thomas N. Jackson, W. C. Mitchel, R. Bertke, and J. L. Freeouf

Appl. Phys. Lett. 79, 162 (2001); http://dx.doi.org/10.1063/1.1384895 (3 pages) | Cited 1 time

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We have developed a far UV spectroscopic ellipsometer system working up to 9 eV, and applied it to the characterization of three 4H-SiC samples with different surface conditions [i.e., as-received and chemical mechanical processing (CMP) processed 4H-SiC bulk substrates and a 4H-SiC epi sample]. Pseudodielectric functions ε1 and ε2 clearly demonstrate the excellent surface sensitivity of the far UV ellipsometry system as it distinguishes the improvements provided by CMP process. Simulation results of ellipsometer data indicate the existence of a damaged subsurface layer in the as-received 4H-SiC bulk substrate. The investigation of sample surfaces using atomic force microscopy confirms the results of ellipsometry measurements. © 2001 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
07.60.Fs Polarimeters and ellipsometers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.65.Ps Polishing, grinding, surface finishing
81.05.Hd Other semiconductors

Coherent nonlinear propagation of ultrafast electric field transients through intersubband resonances

F. Eickemeyer, M. Woerner, A. M. Weiner, T. Elsaesser, R. Hey, and K. H. Ploog

Appl. Phys. Lett. 79, 165 (2001); http://dx.doi.org/10.1063/1.1384898 (3 pages) | Cited 9 times

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Amplitude and phase-controlled midinfrared field transients at a wavelength of 12.5 μm induce resonant intersubband excitations in n-type modulation-doped GaAs/AlGaAs quantum wells. The transmitted electric field transients are directly measured by ultrafast electro-optic sampling. Coherent control of intersubband excitations is demonstrated by applying two phase-locked pulses with variable relative phase. A coherent nonlinear response corresponding to partial Rabi flops of up to 60° in the Bloch sphere is observed with excitation pulses of only 1 pJ energy. © 2001 American Institute of Physics.
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78.67.De Quantum wells
73.21.Fg Quantum wells
78.47.-p Spectroscopy of solid state dynamics
78.20.Jq Electro-optical effects
78.30.Fs III-V and II-VI semiconductors
42.65.-k Nonlinear optics

Study of the thermo-optic effect in hydrogenated amorphous silicon and hydrogenated amorphous silicon carbide between 300 and 500 K at 1.55 μm

Francesco G. Della Corte, Maurizio Esposito Montefusco, Luigi Moretti, Ivo Rendina, and Alfredo Rubino

Appl. Phys. Lett. 79, 168 (2001); http://dx.doi.org/10.1063/1.1383056 (3 pages) | Cited 13 times

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The thermo-optic coefficients of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H)two of the main amorphous semiconductors in optoelectronics—have been measured and critically analyzed in the practical device operation temperature range 300–500 K, at the communication wavelength of 1.55 μm. The experimental data have been fitted using a single-oscillator model that takes into account the shape of the ϵ2 spectrum of the amorphous materials. In particular, for a-Si:H, the extracted parameters significantly extend, and are consistent with, the few data reported in the literature; an interesting analogy with crystalline silicon is also found and discussed. Complete results for a-SiC:H are finally reported. © 2001 American Institute of Physics.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
85.60.-q Optoelectronic devices
78.66.Db Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses

Enhanced performance of pulse driven small area polyfluorene light emitting diodes

C. I. Wilkinson, D. G. Lidzey, L. C. Palilis, R. B. Fletcher, S. J. Martin, X. H. Wang, and D. D. C. Bradley

Appl. Phys. Lett. 79, 171 (2001); http://dx.doi.org/10.1063/1.1383799 (3 pages) | Cited 33 times

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We have investigated the performance of conjugated polymer light emitting diodes (LEDs) as their active areas are reduced to dimensions typical for pixellated displays. We find that by reducing the active diameter of the device from our standard size (1.5×3 mm) to 50 μm, the current density that can be sustained before LED failure increases by a factor of 9. This increase in current density is mirrored by similar increases in maximum LED brightness. We propose that such effects occur due to improved thermal management in small area devices. Using pulsed driving schemes, devices with a diameter of 50 μm sustained current densities of 5.1 MA m−2, and have emitted electroluminescence with a brightness of 6.5 Mcd m−2. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
78.60.Fi Electroluminescence

Efficient electron injection in blue-emitting polymer light-emitting diodes with LiF/Ca/Al cathodes

T. M. Brown, R. H. Friend, I. S. Millard, D. J. Lacey, J. H. Burroughes, and F. Cacialli

Appl. Phys. Lett. 79, 174 (2001); http://dx.doi.org/10.1063/1.1383800 (3 pages) | Cited 85 times

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We report electroabsorption and electroluminescence investigations of polymer light-emitting diodes featuring a LiF/Ca/Al cathode, for efficient electron injection into the electroluminescent polymer layer. Our measurement of the built-in potential gives direct evidence of a sizeable reduction of the cathodic barrier height not only with respect to Ca, but also versus LiF/Al or CsF/Al bilayer cathodes, currently amongst the most efficient electron injectors for low electron affinity polymers. In blue-emitting (∼2.7 at peak) polyfluorene-based LEDs, with poly(ethylenedioxythiophene)/poly(styrene sulphonic acid) anodes and LiF/Ca/Al cathodes, we measure a built-in potential of 2.7 V, a luminance of ∼1600 cd/m2 (the highest among the devices studied here) at a driving voltage of 5 V, and efficiencies as high as ∼3 lm/W. We also find that the turn-on voltage essentially coincides with the built-in potential within the experimental error. © 2001 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.20.Jq Electro-optical effects
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