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  • 1.
    Berrier, Audrey
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Shi, Yaocheng
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Siegert, Jörg
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Accumulated sidewall damage in dry etched photonic crystals2009In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 27, no 4, p. 1969-1975Article in journal (Refereed)
    Abstract [en]

    Evidence for accumulated damage is provided by investigating the effect of etch duration on the carrier lifetime of an InGaAsP quantum well (QW) inside the InP-based photonic crystal (PhC) structures. It is found that once the quantum well is etched through, additional etching reduces the carrier lifetimes from 800 to 70 ps. The surface recombination velocity (SRV) at the exposed hole sidewalls is determined from the measured carrier lifetimes of the PhC fields with different lattice parameters. The observed variation in the SRV with etch duration also confirms the presence of accumulated sidewall damage. It increases from 6x10(3) to 1.2x10(5) cm s(-1) as the etching time increases from 3 to 50 min. A geometric model based on sputtering theory and on the evolution of the hole shape is developed to explain the accumulation of sidewall damage. The model is used to estimate the number of impact events from sputtered species reaching the QW sidewalls, and the variation in the accumulated impact events with etch duration is shown to be qualitatively consistent with the experimental observations. Finally, the results suggest a new method for tailoring the carrier lifetimes in PhC membrane structures.

  • 2.
    Berrier, Audrey
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Shi, Yaocheng
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Siegert, Jörg
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Evidence for accumulated sidewall damage in dry etched photonic crystals2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Article in journal (Other academic)
  • 3.
    Berrier, Audrey
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Shi, Yaocheng
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Siegert, Jörg
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Srinivasan, Anand
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Impact of dry-etching induced damage in InP-based photonic crystals2008In: PHOTONIC CRYSTAL MATERIALS AND DEVICES VIII, 2008, Vol. 6989, p. U9890-U9890Conference paper (Refereed)
    Abstract [en]

    In this work variations of the carrier lifetime in a GaInAsP/InP quantum well in two-dimensional PhC structures etched by Ar/Cl-2 chemically assisted ion beam etching as a function of the processing parameters is investigated. It is shown that the deposition conditions of the SiO2 mask material and its coverage as well as other process steps such as annealing affect the carrier lifetimes. However the impact of patterning the semiconductor on the carrier lifetime is dominant, showing over an order of magnitude reduction. For given PhC lattice parameters, the sidewall damage is shown to be directly related to the measured carrier lifetimes. A simple qualitative model based on sputtering theory and assuming a conical hole-shape development during etching is used to explain the experimental results.

  • 4. Leon, Rosa
    et al.
    Chaparro, S.
    Johnson, S.R.
    Navarro, C.
    Jin, X.
    Zhang, Y.H.
    Siegert, Jörg
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Marcinkevicius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Dislocation-induced spatial ordering of InAs quantum dots:  Effects on optical properties2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 9, p. 5826-5830Article in journal (Refereed)
    Abstract [en]

    Misfit dislocations were used to modify the surface morphology and to attain spatial ordering of quantum dots (QDs) by molecular beam epitaxy. Effects of anneal time and temperature on strain-relaxed InxGa1-xAs/GaAs layers and subsequent spatial ordering of InAs QDs were investigated. Photoluminescence (PL) and time-resolved PL was used to study the effects of increased QD positional ordering, increased QD uniformity, and their proximity to dislocation arrays on their optical properties. Narrower inhomogeneous PL broadening from the QDs ordered on dislocation arrays were observed, and differences in PL dynamics were found.

  • 5.
    Marcinkevicius, Saulius
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Siegert, Jörg
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Zhao, Qing Xiang
    Carrier spin dynamics in modulation-doped InAs/GaAs quantum dots2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 5, p. 054310-Article in journal (Refereed)
    Abstract [en]

    Photoexcited electron and hole spin relaxation was studied in modulation-doped and undoped InAs/GaAs quantum dots by means of time-resolved photoluminescence. After excitation into the barriers or the wetting layer, the electron spin polarization is preserved during the capture and relaxation in the dots, especially in the p-doped structures, and decays with a characteristic time of about 100 ps. Spin state admixture in combination with electron interaction with acoustic phonons is suggested as the spin relaxation mechanism. Rapid spin polarization decay during carrier relaxation in undoped quantum dots is attributed to electron-optical phonon interaction. For carrier excitation directly into the dots, no significant spin polarization was observed, which points to the mixed nature of hole levels in quantum dots. The hole spin polarization randomizes on a much shorter time scale and is not detected in the experiment.

  • 6.
    Marcinkevičius, Saulius
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Siegert, Jörg
    KTH, School of Engineering Sciences (SCI), Physics.
    Carrier capture and relaxation in modulation doped InAs quantum dots2005Conference paper (Refereed)
    Abstract [en]

    Carrier dynamics in n and p-doped and undoped InAs/GaAs quantum dots were studied by time-resolved photoluminescence with selective excitation. Ultrafast carrier relaxation in doped dots is attributed to efficient carrier-carrier scattering.

  • 7.
    Marcinkevičius, Saulius
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Siegert, Jörg
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Leon, Rosa
    Čechavičius, Bronislovas
    Magness, B.
    Taylor, W.
    Lobo, C.
    Changes in luminescence intensities and carrier dynamics induced by proton irradiation in In_xGa_1-xAs/GaAs quantum dots2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 23, p. 235314-Article in journal (Refereed)
    Abstract [en]

    The effects of proton irradiation (1.5 MeV) on photoluminescence intensities and carrier dynamics were compared between InGaAs/GaAs quantum dots and similar quantum well structures. A significant enhancement in radiation tolerance is seen with three-dimensional quantum confinement. Measurements were carried out in different quantum dot structures varying in dot surface density (4x10(8)-3x10(10) cm(-2)) and substrate orientation [(100) and (311)B]. Similar trends were observed for all quantum dot samples. A slight increase in photoluminescence emission intensity after low to intermediate proton doses is observed in InGaAs/GaAs (100) quantum dot structures. The latter is explained in terms of more efficient carrier transfer from the wetting layer via radiation-induced defects.

  • 8.
    Siegert, Jörg
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Carrier dynamics in semiconductor quantum dots2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis presents results of time-resolved photoluminescence experiments conducted on several different self-assembled InGaAs/GaAs and InAs/GaAs semiconductor quantum dot (QD) structures. Depending on the application in mind, different structural, electronic or optical properties have a different weight of importance.

    Fast carrier capture and relaxation is critical for QD based lasers, for example. In this thesis, the influence of surplus carriers, introduced through modulation-doping, is studied. It is shown that carrier capture is essentially unaffected whereas the intradot relaxation mechanisms, at least at low carrier concentrations, are fundamentally different. The phonon mediated cascade relaxation found in the undoped reference sample is replaced by efficient scattering with the built-in carriers in the case of the doped structures.

    Moreover, spin relaxation also depends on presence of extra carriers. During energy relaxation via carrier-carrier scattering, the spin polarization is preserved whereas in the undoped sample the strong interaction of relaxing carriers with LO phonons causes spin relaxation. The decay of the ground state spin polarization proceeds at the same rate for doped and undoped structures and is shown to be caused by acoustic phonons, even up to 300 K. While optimizing QD growth for specific applications, it is imperative to evaluate the influence of nonradiative recombination, which is most often detrimental.

    While misfit dislocations, deliberately introduced in the substrate, lead to the formation of laterally ordered, uniform dots, these samples are found to suffer from strong nonradiative recombination. Structures with different barrier thicknesses and numerical simulations indicate defects in the vicinity of the QDs as main origin of fast carrier trapping.

    On the other hand, it is shown that direct dot doping, compared to barrier doping or undoped structures, causes only minor degradation of the optical properties. Directly doped dots even exhibit a significantly weaker photoluminescence quenching with temperature, making them prospective for devices operating at room temperature.

    Finally, the superior proton radiation hardness of QD structures compared to quantum wells is demonstrated, which is due to the three-dimensional confinement. The increase of photoluminescence intensity at low to moderate doses is interpreted as an enhanced carrier transfer into the dots via the defects introduced into the material by the protons.

  • 9.
    Siegert, Jörg
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Semiconductor Quantum Dots Studied by Time-Resolved Luminescence Techniques2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis time-resolved photoluminescence spectroscopyis presented as a powerful tool to study the carrier dynamicsin various self-assembled quantum dot (QD) structures, whichare potentially attractive for device applications.

    The experiments reveal the impact of proton irradiation onInGaAs QDs and comparable quantum wells. Nonradiativerecombination at defects–an important material parameterand“measure”of the structure optical quality–is found to play a much less important role for the QD samples.The superior radiation hardness can be explained as a result ofthe three-dimensional carrier confinement in QDs. Comparisonsbetween the structures show a decrease of photoluminescenceintensity for quantum wells but a slight increase for QDsirradiated at low to intermediate doses. This somewhatunexpected characteristic is described by an enhanced carriertransfer into the dots via the defects introduced in thematerial by the protons.

    In a different structure carrier dynamics in spatiallyaligned of InAs QDs are investigated. Alignment along lines isachieved by misfit dislocations deliberately introduced in thesubstrate. Photoluminescence spectra of the dots exhibit muchsmaller inhomogeneous broadening than for the reference sampleas a result of an improved QD uniformity. Samples with varyingbuffer layer thicknesses were grown to study the influence ofdislocation related traps on the observed fastphotoluminescence decay. It is found that the fast carriertrapping is predominantly caused by point defects close to theQDs or at the QD/barrier interfaces.

    Additional numerical simulations confirm the roles of thetwo independently acting traps in nonradiativerecombination.

  • 10.
    Siegert, Jörg
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Gaarder, Andreas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Marcinkevičius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Leon, Rosa
    Chaparro, S.
    Johnson, S.R.
    Sadofyev, Y.
    Zhang, Y.H.
    Photoexcited carrier dynamics in aligned InAs/GaAs quantum dots grown on strain-relaxed InGaAs layers2003In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 18, no 4, p. 541-Article in journal (Refereed)
    Abstract [en]

    Carrier dynamics in aligned InAs/GaAs quantum dots (QDs) grown on cross-batched patterns induced by metastable InxGa1-xAs layers have been studied by time-resolved photoluminescence. The low-temperature carrier lifetimes were found to be of the order of 100-200 ps and determined by carrier trapping and nonradiative recombination. Comparisons with control "nonaligned" InAs QDs show remarkable differences in dependence of peak PL intensities on excitation power, and in PL decay times dependences on both temperature and excitation intensities. Possible origin of traps, which determine the carrier lifetimes, is discussed.

  • 11.
    Siegert, Jörg
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Marcinkevičius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Fu, Lan
    Jagadish, C.
    Recombination properties of Si-doped InGaAs/GaAs quantum dots2006In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 17, no 21, p. 5373-5377Article in journal (Refereed)
    Abstract [en]

    The recombination properties of directly doped InGaAs/GaAs quantum dots (QDs) for application in quantum dot infrared photodetectors (QDIPs) have been investigated by time-resolved photoluminescence. Compared with undoped and barrier-doped samples, the overall effect of direct dot doping is found to be small, resulting in only slight deterioration of dot homogeneity. Low-temperature photoluminescence decay times decrease very little, indicating that direct doping does not cause a significant increase of nonradiative recombination. In addition, directly doped quantum dots show a significantly weaker quenching of the photoluminescence intensity with temperature. At the same time, barrier doping causes the formation of more and smaller dots, which results in high photoluminescence intensity at low temperatures but an early onset of thermal carrier emission from the dots. The results suggest that direct QD doping is more prospective for realizing room-temperature operation in QDIPs.

  • 12.
    Siegert, Jörg
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Marcinkevičius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Gaarder, Andreas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Leon, Rosa
    Chaparro, S.
    Johnson, S.R.
    Sadofyev, Y.
    Zhang, Y.H.
    Carrier recombination in aligned InAs/GaAs quantum dots grown in strain-relaxed InGaAs layers2003In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 0, no 4, p. 1213-Article in journal (Refereed)
    Abstract [en]

    Alignment of InAs quantum dots was achieved by introducing misfit dislocations in a metastable InGaAs layer and subsequent annealing. Photoexcited carrier dynamics were studied using time-resolved photoluminescence. Comparison with control “non-aligned” InAs quantum dots show remarkable differences in integrated photoluminescence intensities with excitation power and photoluminescence decay time dependences on excitation intensities. Low-temperature carrier lifetimes were found to be below one hundred picoseconds for the aligned quantum dots and to be determined by non-radiative recombination processes. Samples with different barrier thicknesses between the InGaAs and the quantum dot layer allow the discussion of possible influences of carrier traps at InGaAs/GaAs interface and in the dot layer.

  • 13.
    Siegert, Jörg
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Marcinkevičius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Zhao, Qing Xiang
    Carrier dynamics in modulation-doped InAs/GaAs quantum dots2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 8, p. 085316-Article in journal (Refereed)
    Abstract [en]

    Photoexcited carrier dynamics was studied in n and p modulation-doped self-assembled InAs/GaAs quantum dots by means of time-resolved photoluminescence with excitation and detection energies varied through barrier, wetting layer, and quantum dot states. Carrier transfer to the ground state of the dots was found to occur within 5 to 6 and 12 ps for the doped and undoped samples, respectively. The experiments suggest that in all samples the carrier capture into the highest quantum dot levels proceeds by phonon emission. The significant difference in the transfer times is attributed to different relaxation mechanisms for the subsequent process of intradot carrier relaxation. For the doped samples, the presence of built-in carriers in the dots leads to efficient electron-hole scattering, while in the undoped structure scattering by phonons is identified as the main relaxation channel. Additionally, experimental results show decreased carrier lifetimes in the doped structures, which is attributed to nonradiative recombination at doping-induced recombination centers in the vicinity of the quantum dot layers.

1 - 13 of 13
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