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  • 1990-1994  (24)
  • 1
    Electronic Resource
    Electronic Resource
    Optical properties of two-dimensional photonic lattices fabricated as honeycomb nanostructures in compound semiconductors (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 687-689 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.111034
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  • 2
    Electronic Resource
    Electronic Resource
    Transmission electron microscopy study of CdTe(111) grown on GaAs(100) by molecular-beam epitaxy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4114-4117 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used transmission electron microscopy to investigate CdTe(111) grown on GaAs(100) by molecular-beam epitaxy. The loop structure previously observed by photoluminescence microscopy has been identified as the boundary between twinned microcrystallites that extend from the CdTe/GaAs interface to the CdTe surface. When viewed along the growth axis, these boundaries between the columnar twins appear as loops and segments. Surface roughness of the GaAs substrate contributes to the initial growth of twinned material. This leads to competitive growth between the twins and the creation of the observed columnar twins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344971
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  • 3
    Electronic Resource
    Electronic Resource
    Coherent beams from high efficiency two-dimensional surface-emitting semiconductor laser arrays (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 890-892 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated and operated large two-dimensional (2D) arrays of phase-locked surface-emitting semiconductor lasers. The arrays were fabricated by reactive ion beam etching of epitaxial Fabry–Perot resonators comprising GaAs/AlGaAs quantum wells surrounded by AlAs-AlGaAs quarter-wave mirrors. Different arrays corresponding to different pixel size (2–5 μm) and spacing (1–2 μm) were produced to investigate evanescent coupling between pixels. The arrays were photopumped so that the array size could be conveniently varied from 1×1, 2×2,... up to 20×20. Except for the 1×1 which emits a circular pattern, all arrays exhibit a well-defined four-lobed far-field pattern in agreement with our theoretical analysis of the optical modes which predicts domination by the 2D out-of-phase eigenmode. As a consequence this pattern can be understood with simple Fraunhofer diffraction theory. The angular spread of the lobes, determined by the periodicity of the array elements, is 10° for the array with element size/spacing of 4/1 μm. The widths of the lobes are 6.7° for the 2×2 and narrow to 3.2° with increasing number of pixels in the array. The array exhibits a sharp onset for lasing, operation on a single longitudinal mode, and a linewidth which narrows to ∼1 A(ring) with increasing array size. The differential power efficiency is as high as 70%. These observations provide further impetus and guidance for the development of 2D laser diode arrays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104468
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  • 4
    Electronic Resource
    Electronic Resource
    Gain characteristics of strained quantum well lasers (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 10-12 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InGaAs/AlGaAs laser diode arrays fabricated with differing amounts of In in the quantum well active layer are characterized by threshold currents of 115 A/cm2, transparency currents of 50 A/cm2, optical losses of 3 cm−1, and wavelengths to 960 nm for In compositions of 20%. Gain coefficient measurements indicate an increase from 0.0535 to 0.0691 cm μm/A for quantum well lasers with 0% InAs and 10–20% InAs, respectively. The maximum output power achieved for a device with a 100 μm aperture is 3 W cw.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102647
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  • 5
    Electronic Resource
    Electronic Resource
    Role of substrate threading dislocation density in relaxation of highly strained InGaAs/GaAs quantum well structures (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1350-1352 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Structures with highly strained InGaAs/GaAs single quantum wells have been grown on GaAs substrates with KOH etch pit densities from ∼1000 to ∼45 000 cm−2. These structures were characterized by photoluminescence microscopy and 77 K Hall measurements to determine the extent to which the substrate threading dislocation density affects the misfit dislocation density at the quantum well interfaces. For well thicknesses near or below the Matthews–Blakeslee critical thickness, similar results are obtained for substrates of different dislocation density. However, for metastable structures significantly above the critical thickness, the misfit dislocation density is a sensitive function of the substrate quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102511
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  • 6
    Electronic Resource
    Electronic Resource
    Optical properties of fractal quantum wells (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 1736-1738 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the growth of new fractal quantum-well structures and the first studies of their optical properties. In these (Al,Ga)As structures the composition is varied in a fractal sequence between layers to create a highly branched, self-similar distribution of quantum wells. Experimentally, we studied optical absorption, luminescence and excitation spectra, and electron-hole recombination dynamics. We computed the electron and hole wave functions and transition energies and found good agreement with experiment. The optical and transport properties are strikingly different from those in single or periodic quantum wells. First, the band-edge absorption slope (change in optical density per unit energy) can be controlled over wide limits simply by modifying the sequence. Second, the transport of carriers across the quantum-well layers can be adjusted to control the carrier relaxation rate and energy distribution within the quantum wells. These results suggest possible applications of these new materials for several new devices including broadband emitters, solar cells, electro-optical, and nonlinear optical devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109590
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  • 7
    Electronic Resource
    Electronic Resource
    Lasing phase diagram for semiconductor surface-emitting lasers (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2410-2412 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.103861
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  • 8
    Electronic Resource
    Electronic Resource
    Optical Bloch waves in a semiconductor photonic lattice (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2714-2716 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.106853
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  • 9
    Electronic Resource
    Electronic Resource
    Epitaxial surface-emitting laser on a lattice-mismatched substrate (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2057-2059 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107088
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  • 10
    Electronic Resource
    Electronic Resource
    Optical scatter in epitaxial semiconductor multilayers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1360-1362 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements of optical scatter in epitaxial semiconductor multilayer structures. The structures comprise quarter-wave layers of Al0.2Ga0.8As/AlAs and GaAs/AlAs grown by molecular beam epitaxy and Al0.2Ga0.8As/AlAs grown by metalorganic chemical vapor deposition to assess differences due to growth technique and layer composition. The bidirectional reflective distribution function (BRDF) is measured at a wavelength of 835 nm corresponding closely to the Bragg reflection condition of the multilayer. The BRDF measurement yields calculated values for the total integrated scatter and effective surface roughness. The former is in the range 7×10−4–5×10−3 while the latter is typically 3–16 A(ring) over the spatial frequency range 3×10 −2–1 μm−1. Both growth techniques yield comparable scatter loss on average, but there are significant differences in microscopic surface morphology, uniformity of scatter across the wafer, and lower limits of scatter. The measurements have significant implications for applications such as surface-emitting laser technology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104308
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