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  • 1
    Electronic Resource
    Electronic Resource
    Band-offset determination for GaInP-AlGaInP structures with compressively strained quantum well active layers (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 892-894 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: (AlGaIn)P-on-GaAs structures incorporating compressively strained Ga1−xInxP (x(approximately-greater-than)0.48) quantum well active layers have been studied by low-temperature photoluminescence excitation spectroscopy. The splitting between the lowest energy heavy- and light-hole excitonic transitions is observed to be only weakly dependent on well width over the range 25–300 A(ring), for sample sets with x=0.56 and x=0.59. Envelope function approximation fitting, based on bulk valence band dispersion calculations which include the strain-induced interaction with the spin split-off band, shows this splitting behavior to be a sensitive function of the heterojunction band offset. Conduction band discontinuities, ΔEc, of 0.67ΔEg (x=0.56) and 0.85ΔEg (x=0.59) provide the best fit to these and all higher lying transitions for the full range of structures examined, indicating that poor hole confinement is a limiting factor in practical compressive strain (AlGaIn)P laser device performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110987
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  • 2
    Electronic Resource
    Electronic Resource
    Optical measurements of electronic bandstructure in AlGaInP alloys grown by gas source molecular beam epitaxy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3412-3415 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of bulk (AlyGa1−y)0.52In0.48P epilayers, covering the full range of compositions from y=0 to y=1, have been grown lattice matched on GaAs substrates by gas source molecular beam epitaxy. Double crystal x-ray diffraction, and low temperature photoluminescence (PL) and photoluminescence excitation (PLE) optical spectroscopy have been used to characterize the structures. PL and PLE data indicate the direct-to-indirect energy gap crossover composition to be near y∼0.55 for this alloy system. From PLE, the y dependence of the (5 K) lowest energy direct gap, EΓ–Γ, has been found to be 2.014+0.499y+0.16y2 eV. EΓ–Γ (5 K) for the indirect-gap ternary end-member Al0.52In0.48P is directly determined to be 2.685 eV. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358631
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  • 3
    Electronic Resource
    Electronic Resource
    Ambipolar diffusion and carrier lifetime measurements in all-binary (InAs)2(GaAs)5 strained quantum wells grown on GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1868-1873 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The in-well ambipolar diffusion coefficients and carrier lifetimes in ordered all-binary quantum wells, composed of (InAs)2(GaAs)5 short-period strained-layer superlattices (SPSLSs) grown on [001]-oriented GaAs substrates, are measured using picosecond optically induced transient grating and pump-probe techniques. Quantum wells containing SPSLSs may be expected to exhibit higher in-plane hole mobilities compared to InGaAs ternary alloy quantum wells because of a larger average indium content and reduced disorder scattering in the SPSLS structures. The results obtained in the SPSLSs are compared to those obtained in InGaAs alloy quantum wells of comparable well width and confinement energies. This indicates that, for a given SPSLS and its equivalent alloy, the ambipolar diffusion coefficients are comparable while the carrier lifetimes in the SPSLSs are longer. The longer carrier lifetimes in the SPSLSs suggest that these binary structures possess fewer nonradiative recombination centers than the alloys. The absence of a dramatic improvement in the transport properties, however, may indicate that imperfect interfaces in the SPSLSs may be offsetting their possible advantages, in spite of the fact that optical measurements in the SPSLSs indicate high quality and x-ray and transmission electron microscopic measurements demonstrate the binary nature of these structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355301
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  • 4
    Electronic Resource
    Electronic Resource
    Picosecond optical nonlinearities in a strained InAs/GaAs hetero n-i-p-i structure (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 929-932 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear optical properties of a n-i-p-i structure containing strained superlattice quantum wells in the intrinsic regions are studied using picosecond pump and probe pulses of the same photon energy. For pump fluences as low as 1.1 μJ/cm2, a blue shift of the excitonic resonance, caused by the screening of the built-in space-charge field and the accompanying reduction in the quantum-confined Stark effect, is clearly observed. At higher fluences, the onset of bleaching of the excitonic absorption is observed. The nonlinearities associated with the quantum confined Stark effect in the hetero n-i-p-i are directly compared to those arising from excitonic bleaching in identical strained superlattice quantum wells under flatband conditions. The picosecond time resolution allows a more accurate estimation of the carrier density in the hetero n-i-p-i by ignoring the density-dependent recombination and a quantitative comparison between the strength of the nonlinearities in the two structures. Although such comparisons depend on the optical fluence and structure of the hetero n-i-p-i, we find that the magnitudes of the nonlinearities in these two specific structures are comparable on a per carrier basis, although their spectral signatures are quite distinct.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351315
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  • 5
    Electronic Resource
    Electronic Resource
    Optical nonlinearities and ultrafast charge transport in all-binary InAs/GaAs strained hetero n-i-p-i's (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6891-6897 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use picosecond differential spectroscopy to temporally and spectrally resolve the formation and decay of nonlinearities and space-charge fields in a hetero n-i-p-i that contains quantum wells in the intrinsic regions that are composed of all-binary InAs/GaAs short-period strained-layer superlattices. The evolution of the optical response is determined by competition between excitonic bleaching and the excitonic shift caused by screening of the built-in electric field of the n-i-p-i. The relative contributions of the two resulting optical nonlinearities are complicated functions of fluence, time, and wavelength, with the detailed dynamics determined by thermionic emission from the wells, picosecond charge transport over nanometer dimensions, screening, and recombination. At low fluences, excitonic bleaching is the source of an ultrafast nonlinear response that can be turned on and off in 〈10 ps. This initial excitonic bleaching gives way to a blue shift of the exciton as the carriers escape the wells in ∼3 ps and drift to screen the built-in field in 〈10 ps. The blue shift persists until the carriers recombine nonexponentially on microsecond time scales. At higher fluences, excitonic bleaching and the blue shift are observed simultaneously, since only a fraction of the carriers are required to screen the field and the wells remain partially occupied. On the time scale of ∼10 ns, the bleaching contribution disappears as the carriers within the wells recombine, leaving only the persistent blue shift.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349813
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  • 6
    Electronic Resource
    Electronic Resource
    Room-temperature optical nonlinearities in strained (InAs)2(GaAs)5 superlattice quantum wells (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3243-3248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report room-temperature measurements of the nonlinear absorption cross section, σeh, and the nonlinear refraction coefficient, neh, associated with saturation of excitonic absorption and bandfilling, for high-quality multiple quantum well (MQW) structures in which each well consists of a highly strained, all binary (InAs)2(GaAs)5 short-period superlattice. The three samples studied, which have effective well thicknesses of 10.7, 14.8, and 18.8 nm, respectively, each display clearly resolved excitonic resonances at room temperature. Picosecond nonlinear transmission and transient grating measurements were performed on each sample in the spectral vicinity of the n = 1 heavy-hole excitonic resonance. The peak values of neh and σeh extracted from these measurements are comparable to those measured in high-quality GaAs/AlGaAs and unstrained InGaAs/InP MQWs. We determine the dependence of σeh and neh on the width of the quantum wells, and we discuss the fluence dependence of the nonlinearities. Consistency between the differential transmission and transient grating diffraction efficiency is demonstrated via a Kramers–Kronig analysis of the differential transmission spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348544
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  • 7
    Electronic Resource
    Electronic Resource
    Linear optical properties of quantum wells composed of all-binary InAs/GaAs short-period strained-layer superlattices (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 937-939 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear optical properties of a variety of (InAs/GaAs)-GaAs multiple quantum well structures, where each well consists of a highly strained InAs/GaAs short-period superlattice, have been investigated in detail. The results attest to the improvement in material quality over previously reported structures of this type. Clearly resolved excitonic absorption peaks have been observed at room temperature in all samples. Photoluminescence and excitonic absorption linewidths at 15 K are less than 10 meV in each case, with the photoluminescence Stokes shifted by less than 1 meV. Temporally resolved photoluminescence measurements at 15 K indicate carrier lifetimes of 1.4–1.8 ns. Dramatic strain-related differences are observed when compared to random alloy InGaAs/GaAs quantum wells with an equivalent average indium mole fraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104483
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  • 8
    Electronic Resource
    Electronic Resource
    Uniform and efficient GaAs/AlGaAs quantum dots (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1382-1384 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Uniform arrays of approximately 57 nm diam free-standing quantum dots have been produced from GaAs/AlGaAs single quantum well material by electron-beam lithography and low damage electron cyclotron resonance plasma etching. Low-temperature (5 K) photoluminescence and photoluminescence excitation spectroscopy were used to characterize the material before and after processing into quantum dots. Clear free-exciton features of linewidth comparable to that obtained from the unprocessed material have been observed in the excitation spectra of the quantum dots. As expected for this size of dot, no significant shift in the wavelength of the luminescence was observed, however, there is an apparent enhancement of the external luminescence efficiency when the geometric fill factor is taken into account. The results also show that luminescence efficiency measurements seeking to identify and elucidate intrinsic 0D effects (i.e., those due to quantum confinement in the active region) should be performed with photoexcitation directly into the active region energy states. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113208
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  • 9
    Electronic Resource
    Electronic Resource
    Room-temperature short-period transient grating measurement of perpendicular transport in GaAs/AlGaAs multiple quantum wells (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 219-221 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A short-period transient grating technique with 100 fs resolution is used to study room-temperature perpendicular transport over nanometer dimensions in GaAs/Al0.3Ga0.7As multiple quantum wells (MQWs) whose barrier widths range from 1.4 to 15 nm. With decreasing barrier width, a transition from transport dominated by thermal over-barrier hopping to that dominated by tunneling is observed. For the thinnest barriers, measurements are in good quantitative agreement with simple rate equations describing tunneling, and the measured grating decay rates are related to the microscopic tunneling rates. By comparison, for MQWs with thick barriers, the transport shows no barrier width dependence, and a room-temperature over-barrier hopping rate is extracted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105971
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