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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Picosecond photoinduced absorption measurements have been performed on four different (AlxGa1−x)0.5In0.5P fractal quantum well heterostructures. The results of these measurements reveal that, at early times following pulsed excitation, the carriers remain near the surface layer in which they were photogenerated, and populate the higher lying branches of the V-shaped fractal structure. With increasing time, the carrier population relaxes toward the lowest energy, central wall. The rate at which the relaxation occurs is governed by the characteristic layer of widths of the fractal structure.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have experimentally studied two-dimensional photonic lattices, honeycomb nanostructures, fabricated by electron beam lithography with (Al,Ga)As materials. Surface normal optical properties were investigated by measuring reflectance to determine the effective index of refraction and lattice stability against degradation. Also, continuous wave and time-resolved luminescence spectroscopy was used to assess electron-hole recombination. Finally, light scattering was employed to study photon coupling and propagation through the lattice. These measurements show that the structures are stable, that nonradiative surface recombination is present, and that resonant coupling of light into/out of the lattice occurs at selected wavelengths satisfying a Bragg condition.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated large, two-dimensional (2D) arrays of optically pumped, phase-locked vertical cavity surface-emitting lasers that emit more than 50% of their light in a central on-axis lobe. The emission of the arrays was modified from the usual four-lobed far-field of 2D coupled arrays by incorporation of a binary phase-shift mask on the surface of the array. The array consists of Fabry–Perot resonators comprising GaAs/AlGaAs quantum wells surrounded by AlAs/AlGaAs quarterwave mirrors with a multiple order AlGaAs phase-delay layer on the top mirror stack. The phase-shift layer was etched away on alternating elements of the array. The resulting on-axis emission had an angular width of 2° for an array of approximately 100 elements.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2410-2412 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new tool, a lasing phase diagram, for understanding semiconductor surface-emitting injection lasers has been synthesized. The diagram shows how to design laser resonators which have the lowest possible threshold currents and highest operating efficiencies. To create this diagram, the rate equations describing the photon and electron-hole densities in the laser are solved for the steady-state conditions. The solutions are compactly summarized on a single lasing phase diagram which shows the lasing threshold current and power efficiency contours as functions of two structural parameters (mirror loss and number of quantum wells) in a two-dimensional plane. The plane is separated into three regions corresponding to lasing, marginal lasing, and nonlasing structures. The diagram predicts that, in the high reflectance limit, the threshold current is independent of mirror loss and scales directly with the number of quantum wells in the active region. The phase diagram has been successfully used to understand the lasing characteristics of many different laser structures recently reported.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 599-601 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report microscopic photoluminescence images and corresponding spectra of epitaxial GaAs on Si substrates, prepared by molecular beam epitaxy. High magnification (3000×) images directly reveal dislocations present in the epilayer. Several substrate orientations are investigated including nominal (001) tilted 4° toward 〈110〉. The GaAs samples include structures grown with and without superlattice buffer layers. Some samples were annealed at several temperatures from 650 to 850 °C. The dislocation density versus depth is studied by varying the optical probe wavelength and by studying samples that had been beveled and etched. In addition, the images and spectra are studied over a wide temperature range.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1395-1397 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report studies of bleaching action in an epitaxial Fabry–Perot resonator grown by molecular beam epitaxy. These new structures hold exciting potential for surface-emitting lasers, optical switches, and optical modulators. The structure consisted of a multiple quantum well of AlGaAs and GaAs surrounded by two quarter-wave high reflectors with alternating layers of AlAs and AlGaAs. The spectral and temporal transmittances under intense optical pulses are reported here. The spectral data provide simultaneous information on nonlinear changes in both real and imaginary parts of the refractive index. The temporal data show that the transmittance can be switched up to three orders of magnitude in less than the experimental resolution of 300 ps, and provide evidence for time compression of optical pulses.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1004-1006 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report accurate determination of the critical layer thickness (CLT) for single strained-layer epitaxy in the InGaAs/GaAs system. Our samples were molecular beam epitaxially grown, selectively doped, single quantum well structures comprising a strained In0.2Ga0.8As layer imbedded in GaAs. We determined the CLT by two sensitive techniques: Hall-effect measurements at 77 K and photoluminescence microscopy. Both techniques indicate a CLT of about 20 nm. This value is close to that determined previously (∼15 nm) for comparable strained-layer superlattices, but considerably less than the value of ∼45 nm suggested by recent x-ray rocking-curve measurements. We show by a simple calculation that photoluminescence microscopy is more than two orders of magnitude more sensitive to dislocations than x-ray diffraction. Our results re-emphasize the necessity of using high-sensitivity techniques for accurate determination of critical layer thicknesses.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate lasing action in a novel microcavity laser device based on vertical cavity surface-emitting laser technology. This laser can be used for intracavity spectroscopy, high contrast imaging of small (10 μm) structures, and is well suited for use in micro-optical mechanical systems for analysis of particles or fluids. Here, we investigate spectra of intracavity polystyrene spheres. Lasing threshold, single-mode operation, and multimode operation are all studied. Transverse mode separation in the multimode regime is found to be effective for sizing of the spheres.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2714-2716 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed multiple optical Bloch waves in a semiconductor photonic lattice. This photonic lattice comprises epitaxial quarter-wave periodic layers surrounding a periodic quantum-well region. After growth, the layers are structured laterally into periodic square unit cells by reactive-ion-beam etching. When photoexcited, the lattice emits a complex angular distribution of photons that reflects its periodic structure. Scattered light is distributed according to the Laue conditions in analogy with x-ray diffraction from a bulk crystal. Optical Bloch waves photostimulated in the lattice are analogous to electron Bloch waves in an atomic lattice. These optical Bloch waves exhibit long-range translational symmetry and local symmetry due to the shape of the unit cell. Interestingly, the far-field pattern of stimulated emission gives a direct mapping of the allowed Bloch wave vectors in the Brillouin zone. The mapping exhibits a wave-vector gap at the Bragg condition and may be associated with a photonic energy gap. In addition to measuring the intensity distribution of these Bloch waves, we directly measure the phase of the wave by polarization shearing interferometry.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2057-2059 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have demonstrated continuous-wave, room-temperature, photopumped operation of a vertical-cavity surface-emitting laser having a 0.8% lattice mismatch with its GaAs substrate. Such mismatch provides flexibility in designing resonators with new lasing wavelengths. The laser resonator comprises lattice-matched In0.12Ga0.88As and In0.10Al0.90As quarter-wave layers for mirrors and a strained-layer superlattice of In0.23Ga0.77As/Al0.35Ga0.65As for an active region. The structure lases in the range 1.05–1.10 μm under continuous-wave photoexcitation in the wavelength range 900–950 nm. The differential power efficiency is as high as 68% and the threshold is 2 kW/cm2 (1.8 kA/cm2 injection current-density equivalent). Dislocation line densities observed by photoluminescence microscopy are about 6×102/cm in both the active region and the uppermost mirror layers. The lines predominate along one 〈110〉 direction along which the laser light is preferentially polarized. These observations suggest a way of polarizing surface-emitting lasers by intentional patterning of grating lines on the wafer surface.
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