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22 Jan 2001

Volume 78, Issue 4, pp. 393-559

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Stimulated emission depletion microscopy with an offset depleting beam

T. A. Klar, M. Dyba, and S. W. Hell

Appl. Phys. Lett. 78, 393 (2001); http://dx.doi.org/10.1063/1.1338491 (3 pages) | Cited 10 times

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We demonstrate that an offset stimulated emission depletion (STED) beam breaks the diffraction barrier of fluorescence microscopy in both the lateral and the axial directions. A 2.5-fold axial reduction of the focal spot is accomplished through the ear-shaped lobes of the diffraction maximum of the STED beam. The effect of the minima and side maxima of the STED beam on the lateral and axial resolution is shown to be in remarkable agreement with theory. Conditions are given for which a regular STED beam reduces the axial extent of a confocal spot from 490±36 to 175±18 nm, and simultaneously from 183±12 to 70±8 nm along the direction of the offset. The latter establishes the lowest reported value in far-field fluorescence microscopy. © 2001 American Institute of Physics.
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07.60.Pb Conventional optical microscopes
42.30.Va Image forming and processing
07.05.Pj Image processing

High-temperature operation of distributed feedback quantum-cascade lasers at 5.3 μm

Daniel Hofstetter, Mattias Beck, Thierry Aellen, and Jérôme Faist

Appl. Phys. Lett. 78, 396 (2001); http://dx.doi.org/10.1063/1.1340865 (3 pages) | Cited 76 times

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High-temperature operation of a low-threshold 5.3 μm quantum-cascade distributed feedback laser is presented. The emission spectrum was single mode with more than 20 dB side mode suppression ratio for all investigated temperatures and up to thermal rollover. For 1.5% duty cycle and at 0 °C, the laser emitted 1.15 W of single mode peak power; at 120 °C, a value of 92 mW was seen. For a 3 mm long device, we observed a room-temperature threshold current density of 3.6 kA/cm2. This remarkable performance is mainly due to a 4 quantum-well active region using a double phonon resonance for the lower laser level. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Submilliwatt operation of AlGaN-based ultraviolet light-emitting diode using short-period alloy superlattice

T. Nishida, H. Saito, and N. Kobayashi

Appl. Phys. Lett. 78, 399 (2001); http://dx.doi.org/10.1063/1.1338964 (2 pages) | Cited 29 times

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Over 0.1 mW ultraviolet output was achieved by an AlGaN-based light-emitting diode. To realize a highly conductive and ultraviolet-transparent layer, a short-period alloy superlattice was introduced. The device was fabricated on SiC substrate. Low electric resistivity due to the short-period alloy superlattice and the high thermal conductivity of the SiC substrate enabled large current injection of up to 1.7 kA/cm2. The emission was monochromatic band-edge emission about 350 nm in wavelength without significant D–A and/or deep emissions. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
73.21.Cd Superlattices

SiGe/Si THz laser based on transitions between inverted mass light-hole and heavy-hole subbands

L. Friedman, G. Sun, and R. A. Soref

Appl. Phys. Lett. 78, 401 (2001); http://dx.doi.org/10.1063/1.1341221 (3 pages) | Cited 23 times

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We have investigated a SiGe/Si quantum-well laser based on transitions between the light-hole and heavy-hole subbands. The lasing occurs in the region of k space where the dispersion of ground-state light-hole subband is so nonparabolic that its effective mass is inverted. This kind of lasing mechanism makes total population inversion between the two subbands unnecessary. The laser structure can be electrically pumped through tunneling in a quantum cascade scheme. Optical gain as high as 172/cm at the wavelength of 50 μm can be achieved at the temperature of liquid nitrogen, even when the population of the upper laser subband is 15% less than that of the lower subband. © 2001 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.)
73.21.Fg Quantum wells
78.45.+h Stimulated emission

BeCdSe as a ternary alloy for blue-green optoelectronic applications

S. V. Ivanov, O. V. Nekrutkina, S. V. Sorokin, V. A. Kaygorodov, T. V. Shubina, A. A. Toropov, P. S. Kop’ev, G. Reuscher, V. Wagner, J. Geurts, A. Waag, and G. Landwehr

Appl. Phys. Lett. 78, 404 (2001); http://dx.doi.org/10.1063/1.1342202 (3 pages) | Cited 12 times

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Bulk BeCdSe layer lattice-matched to a GaAs substrate, as well as a BeCdSe/ZnSe quantum well (QW) structure have been grown using the submonolayer digital alloying mode of molecular beam epitaxy. The structures have demonstrated bright photoluminescence up to room temperature and good structural quality. Stimulated emission under optical pumping has been obtained for a 2 nm BeCdSe/ZnSe multiple QW structure at 80 K. The bowing parameter of the energy gap of this ternary alloy has been estimated as about 4.5 eV. © 2001 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
71.20.Nr Semiconductor compounds
78.67.De Quantum wells
78.45.+h Stimulated emission
68.55.-a Thin film structure and morphology
68.65.Fg Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.St Quantum wells

Ultraviolet-emitting ZnO nanowires synthesized by a physical vapor deposition approach

Y. C. Kong, D. P. Yu, B. Zhang, W. Fang, and S. Q. Feng

Appl. Phys. Lett. 78, 407 (2001); http://dx.doi.org/10.1063/1.1342050 (3 pages) | Cited 476 times

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ZnO nanowires were mass produced using a physical vapor deposition approach. The ZnO nanowire monocrystallites have an average diameter around 60 nm and length up to a few micrometers. The unidirectional growth of the ZnO nanowires was controlled by the conventional vapor-liquid-solid mechanism. Intensive UV light emission peaked around 3.27 eV was observed at room temperature, which was assigned to emission from free exciton under low excitation intensity. The observed room temperature UV emission was ascribed to the decrease in structure defects as compared to bulk ZnO materials, and in particularly to the size effect in the ZnO wires. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
73.22.Lp Collective excitations
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Very-low-operating-voltage organic light-emitting diodes using a p-doped amorphous hole injection layer

X. Zhou, M. Pfeiffer, J. Blochwitz, A. Werner, A. Nollau, T. Fritz, and K. Leo

Appl. Phys. Lett. 78, 410 (2001); http://dx.doi.org/10.1063/1.1343849 (3 pages) | Cited 152 times

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We demonstrate the use of a p-doped amorphous starburst amine, 4, 4′, 4″-tris(N, N-diphenyl- amino)triphenylamine (TDATA), doped with a very strong acceptor, tetrafluoro- tetracyano-quinodimethane by controlled coevaporation as an excellent hole injection material for organic light-emitting diodes (OLEDs). Multilayered OLEDs consisting of double hole transport layers of p-doped TDATA and triphenyl-diamine, and an emitting layer of pure 8-tris-hydroxyquinoline aluminum exhibit a very low operating voltage (3.4 V) for obtaining 100 cd/m2 even for a comparatively large (110 nm) total hole transport layer thickness. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices

Decreasing the emission wavelength of GaAs–AlGaAs quantum cascade lasers by the incorporation of ultrathin InGaAs layers

L. R. Wilson, J. W. Cockburn, M. J. Steer, D. A. Carder, M. S. Skolnick, M. Hopkinson, and G. Hill

Appl. Phys. Lett. 78, 413 (2001); http://dx.doi.org/10.1063/1.1343841 (3 pages) | Cited 11 times

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We demonstrate that the emission wavelength of GaAs–Al0.33Ga0.67As quantum cascade lasers can be decreased significantly by incorporating InGaAs layers within the active regions. InAs monolayers are deposited during growth, with segregation effects resulting in the formation of thin InGaAs layers within the GaAs active region quantum wells of the laser. The InGaAs layers are positioned close to the antinodes of the lower laser level wave function, thus decreasing its confinement energy. The small spatial overlap of the InGaAs layers with the upper laser level minimizes the perturbation of the upper state. Consequently, the energy separation between the upper and lower laser levels increases, reducing the emission wavelength. The measured operating wavelength of 7.4 μm is the shortest reported for a GaAs–AlGaAs quantum cascade laser and is approximately 2 μm less than for an identical structure without InGaAs layers in the active regions. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
68.35.Dv Composition, segregation; defects and impurities

High-performance quantum cascade lasers (λ ∼ 11 μm) operating at high temperature (T  ≥ 425 K)

A. Tahraoui, A. Matlis, S. Slivken, J. Diaz, and M. Razeghi

Appl. Phys. Lett. 78, 416 (2001); http://dx.doi.org/10.1063/1.1343848 (3 pages) | Cited 21 times

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We report record-low threshold current density and high output power for λ ∼ 11 μm Al0.48In0.52As/Ga0.47In0.53As quantum cascade lasers operating up to 425 K. The threshold current density is 1.1, 3.83, and 7.08 kA/cm2 at 80, 300, and 425 K, respectively, for 5 μs pulses at a 200 Hz repetition rate. The cavity length is 3 mm with a stripe width of 20 μm. The maximum peak output power per facet is 1 W at 80 K, 0.5 W at 300 K, and more than 75 mW at 425 K. The characteristic temperature of these lasers is 174 K between 80 and 300 K and 218 K in the range of 300–425 K. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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