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  • 11
    Electronic Resource
    Electronic Resource
    Intra- and interwell transitions in GaInN/GaN multiple quantum wells with built-in piezoelectric fields (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 82-84 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied optical transitions in GaInN/GaN single and multiple quantum wells using time-resolved photoluminescence spectroscopy. Our results show that the energy positions of the dominant emission lines strongly depend both on the well width and on the number of wells. In the case of multiple quantum wells, time-resolved measurements clearly distinguish multiple emission lines. These observations are consistently explained by considering the large built-in piezoelectric field in strained GaInN quantum wells. The multiple emission lines are attributed to intra- and interwell transitions between nearest and next-nearest neighbors. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122958
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  • 12
    Electronic Resource
    Electronic Resource
    Intrinsic modulation bandwidth of strained GaInP/AlGaInP quantum well lasers (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 650-652 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the intrinsic modulation response of GaxIn1-xP/AlGaInP quantum well lasers. The differential gain resulting from the measurement of the frequency response, is in good agreement with calculations based on a 6-band kp-theory and direct measurements of the optical gain. We find a maximum value of 3.8×10−16 cm2 for a strongly compressively strained sample, which is less than in InGaAs lasers according to the larger effective masses. The maximum bandwidth we observed is 9.3 GHz at −3 dB. We show that the bandwidth is limited by catastrophic optical damage and not by intrinsic mechanisms. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119818
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  • 13
    Electronic Resource
    Electronic Resource
    A mechanism for low-power all-optical switching in multiple-quantum-well structures (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 4212-4214 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate a novel type of optical switching mechanism in pin separate confinement multiple quantum well (SCMQW) structures. By introducing additional large barriers into conventional InGaAs(P)/InP SCMQW structures, the transport of photogenerated holes can be controlled in such a way that they accumulate in the intrinsic region. This positive space charge leads to a local screening of the internal field in the optical confinement layer and to an enhancement of the internal field in the MQW region. We characterize the optical nonlinearity, which is based on the quantum confined Stark effect (QCSE), experimentally and theoretically. As the nonlinearity is observed at input powers 〈1 W/cm2 in the basic nonoptimized structures presented here, we propose to use our structure especially for low-power optical switches. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116989
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  • 14
    Electronic Resource
    Electronic Resource
    Deep-level defects and n-type-carrier concentration in nitrogen implanted GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2525-2527 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyzed the intrinsic defects and the n-type-carrier concentration generated by nitrogen ion implantation in n-type GaN by deep-level-transient spectroscopy and by capacitance–voltage measurements, respectively. The samples were grown on sapphire by metalorganic vapor-phase epitaxy. Nitrogen implantation with different ion doses and postimplantation rapid-thermal annealing (RTA) were investigated. We observed a growing n-type-carrier concentration and increasing defect concentration with increasing nitrogen ion implantation doses. After RTA the concentration of free carriers and deep levels as found in the as-grown state are restored. We also address contrarily seeming results from measurements of sheet resistance after N implantation published recently. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117727
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  • 15
    Electronic Resource
    Electronic Resource
    Evaluation of the effective hole masses in pseudomorphic compressively strained GaxIn1−xAs/InP quantum wells (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 67-69 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The valance band structure of metalorganic vapor phase epitaxy (MOVPE) grown strained GaxIn1−xAs/InP single quantum well structures is experimentally verified by the determination of the effective in-plane hole masses. The masses are obtained by performing magnetotransport experiments. Mobilities up to 8700 cm2/V s for gallium content of x=0.3 were reached. The effective heavy hole masses of compressively strained GaInAs are drastically reduced compared to bulk material in excellent agreement to calculations using the k⋅p-perturbation theory, whereas the masses of the uppermost valence band of tensile strained material appear to be rather high. Consequently, no experimental determination was possible in the latter case. A precise analysis of the Shubnikov–de Haas oscillation patterns of compressively strained quantum wells shows a spin splitting of the uppermost heavy hole band, containing two different effective masses. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115509
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  • 16
    Electronic Resource
    Electronic Resource
    Valence-band splitting and band-gap reduction in ordered GaInAs/InP (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6196-6198 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the linear absorption and the nonlinear absorption due to the bleaching of the excitonic resonance have been used to determine the band-gap reduction and valence-band splitting in spontaneously ordered GaInAs/InP. Tilts of the substrate ranging from 2° to 15° towards {111}B, different growth rates and temperatures have been used to produce a series of samples containing various degrees of ordering. Best sample quality including small x-ray and photoluminescence linewidth as well as low temperature luminescence from the band edge was obtained using a substrate tilted 6° towards {111}B. The ratio between ordering induced band-gap reduction and crystal-field splitting was found to be ζ=1.8±0.4. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367493
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  • 17
    Electronic Resource
    Electronic Resource
    Self-assembled InAs/GaAs quantum dots under resonant excitation (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1631-1636 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The energy structure and the carrier relaxation in self-assembled InAs/GaAs quantum dots (SADs) is investigated by photoluminescence excitation spectroscopy (PLE) and photoluminescence (PL) at resonant excitation (below the GaAs and the wetting layer bandgap). In PLE measurements we find a clear resonance from the first excited hole state as well as resonances from a relaxation via different phonons. From a comparison of the PL-rise times in time resolved spectroscopy, we conclude on a fast electron relaxation (≤50 ps) and a slow hole relaxation with a time constant of about 400 ps. Different relaxation paths are observed in the InAs/GaAs quantum dot system and allow us to identify the hole relaxation in the SADs as multiphonon assisted tunneling. The PL-decay time in the SADs after resonant excitation (about 600 ps) is attributed to the lifetime of the quantum dot exciton. In agreement with theoretical predictions, we find a constant lifetime of about 600 ps for temperatures below 50 K and a linear increase of the lifetime between 50 and 100 K with a slope of 26 ps/K. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366876
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  • 18
    Electronic Resource
    Electronic Resource
    Implantation-induced disordering of CuPtB-ordered GaInP (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 1042-1052 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, a comprehensive treatment of the implantation-induced disordering (IID) of CuPtB-ordered GaInP with regard to microstructuring is presented. Ion implantation reduces the thermal stability of the crystal, so that disordering occurs at temperatures smaller than 800 °C for which the ordered phase normally is stable. It is shown that IID is mediated by implantation defects and can be described quantitatively by a model based on defect annealing. From the temperature dependence of the disordering process an activation energy of 2.15 eV has been evaluated, which is supposed to be the migration enthalpy of group III vacancies. Lateral order/disorder structures were achieved by masked implantation using high resolution electron beam lithography for the definition of wire and dot implantation masks down to 35 nm width. These structures were examined using photoluminescence and transmission electron microscopy. Both methods show that the spatial resolution is determined by implantation straggling, whereas defect diffusion can be neglected. This is also confirmed by extracting the defect diffusion length from the disordering model. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365869
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  • 19
    Electronic Resource
    Electronic Resource
    Optical transitions and carrier relaxation in self assembled InAs/GaAs quantum dots (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4019-4026 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present experimental results concerning optical transitions and carrier dynamics (capture and relaxation) in self assembled InAs/GaAs quantum dot structures grown by metalorganic vapor phase epitaxy. Photoluminescence (PL) measurements at high excitation level reveal optical transitions above the ground state emission. These transitions are found to originate from occupied hole states by solving the quantum dot eigenvalue problem. Time-resolved studies after non-resonant pulse excitation exhibit a relaxation ladder of the excited carriers from the GaAs barrier down to the ground state of the quantum dots. From both the continuous-wave measurements and the PL-decay curves we conclude that the carrier relaxation at non-resonant excitation is mediated by Coulomb interaction (Auger effect). PL-decay curves after resonant pulse excitation reveal a longer rise time compared to non-resonant excitation which is a clear indication of a relaxation bottleneck inside the quantum dots. We interpret the rise time (≈ 400 ps) in this case to originate from relaxation via scattering by acoustic phonons. The PL-decay time of the ground state emission ≈700 ps is interpreted as the excitonic lifetime of the quantum dot. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363361
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  • 20
    Electronic Resource
    Electronic Resource
    Single variant ordering in GaInAs/InP (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2127-2129 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spontaneously ordered Ga0.47In0.53As grown on substrates with the (001) surface tilted 4° towards {111}B are studied using spectroscopic methods as well as x-ray diffraction, transmission electron diffraction and dark-field transmission electron microscopy. The single variant ordering is proved by the absence of one class of the ordering induced 〈fraction SHAPE="CASE"〉12{111}B superlattice spots in transmission electron diffraction patterns as well as by the tilted polarization of the photoluminescence emerging from the samples cleaved edge. The temperature dependence of the luminescence peak position shows an anomalous behavior at low temperatures and a strong dependence of the peak position on the excitation power. From low temperature absorption measurements, we find a band gap reduction of 37 meV and a valence band splitting of 13.2 meV. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119357
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