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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2352-2354 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the electric-field dependent band-gap energy and near-gap absorption coefficient of a specially designed strained-layer superlattice (SLS) employing tensile strained quantum wells and having a band-gap wavelength near 1.3 μm. The SLS was grown by molecular-beam epitaxy on an InP substrate and consists of In0.43Ga0.57As wells (4.5-nm-thick) and In0.6Al0.4As barriers (6.75-nm-thick). For applied fields from zero up to at least 2.5×105 V/cm, the band-edge absorption exhibits a single peak, which we attribute to a field-independent superpositioning of the heavy- and light-hole ground states. This result agrees with tunneling resonance calculations, which predict these hole states to have the same zero-field energy and to undergo nearly identical Stark shifts. Absorption–coefficient changes of up to 104 cm−1 were readily achieved with applied biases under 15 V, suggesting potential applications to optical modulator devices. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results from the first studies of electric-field effects on optical transitions in visible-band-gap InGaP/InAlGaP multiple-quantum-well (MQW) structures. These structures, grown at 775 °C by metalorganic vapor phase epitaxy on (100) GaAs substrates misoriented 6° towards P(111〉〈111〉A, consist of nominally undoped MQWs surrounded by doped In0.49Al0.51P cladding layers to form p-i-n diodes. The Stark shifts of various allowed and forbidden quantum-well transitions were observed in bias-dependent electroreflectance spectra of In0.49Ga0.51P/In0.49(Al0.5Ga0.5)0.51P MQW samples with 10-nm-thick layers. We find the magnitude of these shifts to depend on the details of the Mg doping profile, confirming the importance of Mg diffusion and unintentional background doping in these materials. Our results show that (InAlGa)P materials are promising for visible-wavelength electro-optic modulator applications.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results on the first all-semiconductor, vertical Fabry–Perot-cavity optical transmission modulator. This device combined mechanically stable strained and unstrained (In,Al,Ga)As multilayers to achieve operation at 1.06 μm. Transmission-mode operation allows the resonant wavelength of the cavity to be finely tuned by varying the angle of incidence, providing, for the first time, a means of compensating for small inaccuracies in growth parameters. Using the modulator in double-pass operation with a corner-cube retroreflector, we demonstrate a tunable reflectance modulator with a fractional modulation of 25% at 3-V bias, suitable for applications in free-space communication.
    Type of Medium: Electronic Resource
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  • 4
    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.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 753-755 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present calculations and data on a novel, electrically tunable reflector structure consisting of tandem Fabry–Perot resonators grown as a single epitaxial device. The device consists of three mirrors (quarter-wave stacks of AlGaAs and AlAs) separated by two cavities (one an AlGaAs alloy and the other a GaAs/AlGaAs superlattice) on a GaAs substrate. The tandem cavities produce a characteristic double-dipped reflectance spectrum which can be modulated by tunable electro-optic effects in the superlattice cavity. Our demonstration device has a modulation depth of (approximately-greater-than)10% over a 20 nm bandwidth with 〈4 V of bias swing.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a novel approach to optoelectronic devices by combining mechanically stable strained and unstrained epitaxial multilayers. We illustrate our approach with an optical reflectance modulator based on an asymmetric Fabry–Perot resonator designed to operate near 1.06 μm. The resonator is grown on a mechanically relaxed buffer of In0.11Ga0.89As deposited on a GaAs substrate. For mirrors, quarter-wave stacks of In0.11Ga0.89As and In0.1Al0.9As, lattice matched to the buffer, are used. The Fabry–Perot cavity consists of an In0.23Ga0.77As/Al0.35Ga0.65As strained-layer superlattice whose planar lattice constant also matches the buffer. Our first device operates at 1.04–1.05 μm depending on lateral position across the wafer. The insertion loss at resonance is less than 2 db and a fractional modulation of over 60% has been achieved with a 4 V bias swing.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Simultaneous measurement of both the conduction- and valence-band dispersion curves in single strained-layer structures is presented. These measurements rely on the application of recent observations regarding breaking of the usual selection rules for interband magnetoluminescence transitions in modulation-doped structures. Low-temperature magneto-luminescence data for three representative InGaAs/GaAs n-type single-strained quantum well structures are presented. For energies approaching 50 meV above the band gap, we find that the conduction band is parabolic with an effective mass of 0.071m0. Over the same energy range, the valence bands are highly nonparabolic.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 377-379 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical layer thickness for InxGa1−xAs layers in InxGa1−xAs/GaAs single strained quantum wells (SSQW's) and strained-layer superlattices (SLS's) are investigated. Photoluminescence microscopy (PLM) images and x-ray rocking curves for two series of SSQW and SLS structures corresponding to many different layer thicknesses were obtained. We find that the PLM technique, which directly images dislocations and is sensitive to low dislocation densities, is much more suitable for determining the onset of dislocation creation. The x-ray technique can detect lattice relaxation by dislocations but only at relatively high densities of dislocations. Using the former technique, we determine critical thicknesses of 190 A(ring) for SSQW's and 250 A(ring) for SLS's with x≈0.2. These results are near the theoretical predictions of J. W. Matthews, S. Mader, and T. B. Light [J. Appl. Phys. 41, 3800 (1970)] (150 and 300 A(ring), respectively) and are much lower than results obtained by x-ray or other techniques which sense lattice relaxation.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results on excitonic transitions and confinement at high electric fields from photocurrent and electroreflectance spectra of an In0.17Ga0.83As/Al0.3Ga0.7As strained quantum well structure fabricated into a Schottky barrier diode. Up to the highest field attained, 1.7×105 V/cm, we observe a well-defined exciton line at the band edge (in contrast to data on similar GaAs/Al0.3Ga0.7As structures), a feature important for potential optoelectronic applications. At low fields, "allowed'' (Δn=0) transitions dominate the photocurrent spectra, but with increasing field "forbidden'' transitions (allowed because of reduced symmetry and valence-band mixing) grow in intensity and eventually dominate the above-gap response. In the electroreflectance spectra, the forbidden transitions are relatively strong, even at low field. The allowed above-gap transitions nearly vanish at low temperature because of the small field dependence of the higher lying quantum well energy levels.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report electrical transport and optical studies of the efficiency with which an In0.2Ga0.8As/GaAs strained-layer superlattice (SLS) can filter threading dislocations generated in a thick In0.1 Ga0.9 As layer grown on GaAs. The electrical studies, the first of their kind, rely on a novel test structure which allows electrical characterization of just the top portion of the SLS, with the bottom portion acting as the dislocation filter. For optical characterization we detect dislocations directly by photoluminescence microscopy. The electrical results show that ∼3–6 periods of filtering are needed to attain high mobilities. The photoluminescence microimages show a small density of dislocations near the top of an eight-period SLS but no dislocations for 11 or more periods. Filtering with In0.2Ga0.8As/GaAs SLS's is more effective than with GaAs0.8P0.2/GaAs SLS's, possibly because of larger interlayer differences in strain and elastic constants for the former.
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