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  • 1.
    Adnane, Bouchaib
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Elfving, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Zhao, Ming
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Larsson, Mats
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Magnuson, Bengt
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Mid/far-infrared detection using a MESFET with B-modulation doped Ge-dot/SiGe-well multiple stacks in the channel region2004Conference paper (Refereed)
    Abstract [en]

    Multiple modulation-doped Ge-dot/SiGe-QW stack structures were grown using MBE, and processed as FET devices for mid/far infrared detection. From a non-optimized device, a broadband photoresponse has been observed in the mid-infrared range of 3-15 μm. A peak responsivity was estimated to be as high as 100 mA/W at T= 20 K. This work indicates that SiGE QD/QW structures using the lateral transport geometry can be a potential candidate for photodetectors operating in far-infrared range.

  • 2.
    Adnane, Bouchaib
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Karlsson, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Zhao, Ming
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Hansson, Göran
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235XArticle in journal (Other academic)
    Abstract [en]

    A normal incidence photodetector operating at 8-14 μm is demonstrated using p-type δ-doped SiGe dot multilayer structures grown by molecular beam epitaxy on Si(001) substrates. Based on the experimental results of photoluminescence and photoluminescence excitation spectroscopies together with numerical analysis, the origin of the measured photocurrent was attributed to intersubband optical transitions between the heavy hole and light hole states of the valence band of the self-assembled SiGe dots and subsequent lateral transport of photo-excited carriers in the conduction channels formed by Ge wetting layers.

  • 3.
    Elfving, Anders
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Zhao, Ming
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Hansson, Göran V.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Asymmetric relaxation of SiGe/Si(110) investigated by high-resolution x-ray diffraction reciprocal space mapping2006In: Applied physics letters, ISSN 0003-6951, Vol. 89, p. 181901-1--181901-3Article in journal (Refereed)
    Abstract [en]

    Strain relaxation of SiGe/Si(110) has been studied by x-ray reciprocal space mapping. To get information about the in-plane lattice mismatch in different directions, two-dimensional maps around, e.g., (260) and (062) reciprocal lattice points have been obtained from Si0.8Ge0.2/Si(110) samples, which were exposed to different annealing conditions. The in-plane lattice mismatch was found to be asymmetric with the major strain relaxation observed in the lateral [001] direction. This was associated with the formation and propagation of dislocations oriented along [10]. The relaxation of as-grown structures during postannealing is thus different from relaxation during growth, which is mainly along [10].

     

     

  • 4.
    Lynch, S.A.
    et al.
    IEEE, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
    Paul, D.J.
    IEEE, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
    Townsend, P.
    IEEE, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
    Matmon, G.
    IEEE, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
    Suet, Z.
    IEEE, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
    Kelsall, R.W.
    School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
    Ikonic, Z.
    School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
    Harrison, P.
    School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
    Zhang, J.
    Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
    Norris, D.J.
    School of Electronics and Electrical Engineering, University of Sheffield, Sheffield S10 2TN, United Kingdom.
    Cullis, A.G.
    School of Electronics and Electrical Engineering, University of Sheffield, Sheffield S10 2TN, United Kingdom.
    Pidgeon, C.R.
    Department of Physics, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.
    Murzyn, P.
    Department of Physics, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.
    Murdin, B.
    School of Electronics and Physical Sciences, University of Surrey, Surrey GU2 7XH, United Kingdom.
    Bain, M.
    School of Electrical and Electronic Engineering, Queens University, Belfast BT9 5AH, United Kingdom.
    Gamble, H.S.
    School of Electrical and Electronic Engineering, Queens University, Belfast BT9 5AH, United Kingdom.
    Zhao, Ming
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Toward silicon-based lasers for terahertz sources2006In: IEEE Journal of Selected Topics in Quantum Electronics, ISSN 1077-260X, E-ISSN 1558-4542, Vol. 12, no 6, p. 1570-1577Article in journal (Refereed)
    Abstract [en]

    Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried suicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser. © 2006 IEEE.

  • 5.
    Paul, D.J.
    et al.
    University of Cambridge.
    Matmon, G.
    University of Cambridge.
    Townsend, P.
    University of Cambridge.
    Zhang, J.
    University of London Imperial College of Science, Technology and Medicine.
    Zhao, Ming
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    A Review Of Progress Towards Terahertz Si/SiGe Quantum Cascade Lasers2007In: Journal of the Institution of Electronics and Telecommunication Engineers, ISSN 0377-2063, E-ISSN 0974-780X, Vol. 53, no 3, p. 285-292Article, review/survey (Refereed)
    Abstract [en]

    [ABST].

  • 6. Pidgeon, CR
    et al.
    Phillips, PJ
    Carder, D
    Murdin, BN
    Fromherz, T
    Paul, DJ
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Zhao, Ming
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Pump-probe measurement of lifetime engineering in SiGe quantum wells below the optical phonon energy2005In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 20, no 10, p. L50-L52Article in journal (Refereed)
    Abstract [en]

    We have directly determined with pump/probe spectroscopy the light hole (LH1) excited state lifetime for the lowest heavy hole to light hole intrawell subband transition (HH1-LH1) for three prototype samples of Si/SiGe strain-symmetrized multi-quantum well structures, designed to have the final LH1 state increasingly unconfined. The transition energy is below the optical phonon energy. We find that a decay time of 20 ps for sample 1 with a well width of 5.0 nm lengthens to 40 ps for sample 3 with a well width of 3.0 nm, in good agreement with the design. In addition, we have measured the lifetime for holes excited out of the well, from which we determine the lifetime for diagonal transitions (back into the well) to be of approx. several hundred picoseconds.

  • 7.
    Rauter, P.
    et al.
    University of Linz.
    Fromherz, T.
    University of Linz.
    Vinh, N.Q.
    FOM Institute for Plasma Physics.
    Murdin, B.N.
    University of Surrey .
    Phillips, J.P.
    Heriot-Watt University.
    Pidgeon, C.R.
    Heriot-Watt University.
    Diehl, L.
    Paul Scherrer Institut.
    Dehlinger, G.
    Paul Scherrer Institut.
    Gruetzmacher, D.
    Paul Scherrer Institut.
    Zhao, Ming
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Bauer, G.
    University of Linz.
    Direct determination of ultrafast intersubband hole relaxation times in voltage biased SiGe quantum wells by a density matrix interpretation of femtosecond resolved photocurrent experiments2007In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9Article in journal (Refereed)
    Abstract [en]

    We report the quantitative and direct determination of hole intersubband relaxation times in a voltage biased SiGe heterostructure using density matrix calculations applied to a four-level system in order to interpret photocurrent (PC) pump-pump experiments. One consistent set of parameters allows the simulation of two kinds of experiments, namely pump-pump photocurrent experiments at a free electron laser (wavelength 7.9 mu m) and the laser-power dependence of the PC signal. This strongly confirms the high reliability of these parameter values, of which the most interesting in respect to Si based quantum cascade laser development is the extracted heavy-hole relaxation time. The simulations show that this relaxation time directly determines the experimentally observed decay of the pump-pump photocurrent signal as a function of the delay time. For a heavy hole intersubband spacing of 160 meV, a value of 550 fs was obtained. The experimental method was further applied to determine the LH1-HH1 relaxation time of a second sample with a transition energy below the optical phonon energy. The observed relaxation time of 16 ps is consistent with the value found for the same structure by transmission pump-probe experiments.

  • 8.
    Zhao, Ming
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Growth and Characterization of Strain-engineered Si/SiGe Heterostructures Prepared by Molecular Beam Epitaxy2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The strain introduced by lattice mismatch is a built-in characteristic in Si/SiGe heterostructures, which has significant influences on various material properties. Proper design and precise control of strain within Si/SiGe heterostructures, i.e. the so-called “strain engineering”, have become a very important way not only for substantial performance enhancement of conventional microelectronic devices, but also to allow novel device concepts to be integrated with Si chips for new functions, e.g. Si-based optoelectronics. This thesis thus describes studies on two subjects of such strain-engineered Si/SiGe heterostructures grown by molecular beam epitaxy (MBE). The first one focuses on the growth and characterizations of delicately strain-symmetrized Si/SiGe multi-quantum-well/superlattice structures on fully relaxed SiGe virtual substrates for light emission in the THz frequency range. The second one investigates the strain relaxation mechanism of thin SiGe layers during MBE growth and post-growth processes in non-conventional conditions.

    Two types of THz emitters, based on different quantum cascade (QC) intersubband transition schemes, were studied. The QC emitters using the diagonal transition between two adjacent wells were grown with Si/Si0.7Ge0.3 superlattices up to 100 periods. It was shown that nearly perfect strain symmetry in the superlattice with a high material quality was obtained. The layer parameters were precisely controlled with deviations of ≤ 2 Å in layer thickness and ≤ 1.5 at. % in Ge composition from the designed values. The fabricated emitter devices exhibited a dominating emission peak at ~13 meV (~3 THz), which was consistent with the design. An attempt to produce the first QC THz emitter based on the bound-to-continuum transition was made. The structures with a complicated design of 20 periods of active units were extremely challenging for the growth. Each unit contained 16 Si/Si0.724Ge0.276 superlattice layers, in which the thinnest one was only 8 Å. The growth parameters were carefully studied, and several samples with different boron δ-doping concentrations were grown at optimized conditions. Extensive material characterizations revealed a high crystalline quality of the grown structures with an excellent growth control, while the heavy δ-doping may introduce layer undulations as a result of the non-uniformity in the strain field. Moreover, carrier lifetime dynamics, which is crucial for the THz QC structure design, was also investigated. Strain-symmetrized Si/SiGe multi-quantum-well structures, designed for probing the carrier lifetime of intersubband transitions inside a well between heavy hole 1 (HH1) and light hole 1 (LH1) states with transition energies below the optical phonon energy, were grown on SiGe virtual substrates. The lifetime of the LH1 excited state was determined directly with pump-probe spectroscopy. The measurements indicated an increase of lifetime by a factor of ~2 due to the increasingly unconfined LH1 state, which agreed very well with the theory. It also showed a very long lifetime of several hundred picoseconds for the holes excited out of the well to transit back to the well through a diagonal process.

    Strained SiGe grown on Si (110) substrates has promising potentials for high-speed microelectronics devices due to the enhanced carrier mobility. Strain relaxation of SiGe/Si(110) subjected to different annealing treatments was studied by X-ray reciprocal space mapping. The in-plane lattice mismatch was found to be asymmetric with the major strain relaxation observed in the lateral [001] direction. It was concluded that this was associated to the formation and propagation of conventional a/2<110> dislocations oriented along [110]. This was different from the relaxation observed during growth, which was mainly along in-plane [110].

    A novel MBE growth process to fabricate thin strain-relaxed Si0.6Ge0.4 virtual substrates involving low-temperature (LT) buffer layers was investigated. At a certain LT-buffer growth temperature, a dramatic increase in the strain relaxation accompanied with a decrease of surface roughness was observed in the top SiGe, together with a cross-hatch/cross-hatch-free transition in the surface morphology. It was explained by the association with a certain onset stage of the ordered/disordered transition during the growth of the LT-SiGe buffer.

    List of papers
    1. Low-temperature molecular beam epitaxy growth of Si/SiGe THz quantum cascade structures on virtual substrates
    Open this publication in new window or tab >>Low-temperature molecular beam epitaxy growth of Si/SiGe THz quantum cascade structures on virtual substrates
    Show others...
    2006 (English)In: Thin Solid Films, ISSN 0040-6090, Vol. 508, no 1-2, p. 24-28Article in journal (Refereed) Published
    Abstract [en]

    Si/SiGe quantum cascade structures containing superlattice up to 100 periods have been grown on SiGe virtual substrates by using solid-source molecular beam epitaxy at low temperature. The surface morphology and structural properties of the grown samples were characterized using various experimental techniques. It has been concluded that the structures were completely symmetrically strained with high crystalline quality, precise layer parameters, and excellent reproducibility. Electroluminescence was observed with peaked intensity at 3 THz at both 4 and 40 K, which agrees very well with expected interwell intersubband transition according to the design.

    Keywords
    Molecular beam epitaxy (MBE); Si/SiGe; Quantum cascade; X-ray diffraction
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13273 (URN)10.1016/j.tsf.2005.07.355 (DOI)
    Available from: 2008-05-07 Created: 2008-05-07
    2. Strain-symmetrized Si/SiGe multi-quantum well structures grown by molecular beam epitaxy for intersubband engineering
    Open this publication in new window or tab >>Strain-symmetrized Si/SiGe multi-quantum well structures grown by molecular beam epitaxy for intersubband engineering
    Show others...
    2006 (English)In: Journal of luminescence, ISSN 0022-2313, Vol. 121, no 2, p. 403-408Article in journal (Refereed) Published
    Abstract [en]

    Three strain-symmetrized Si/SiGe multi-quantum well structures, designed for probing the carrier lifetime of intrawell intersubband transitions between heavy hole 1 (HH1) and light hole 1 (LH1) states with transition energies below the optical phonon energy, were grown by molecular beam epitaxy at low temperature on fully relaxed SiGe virtual substrates. The grown structures were characterized by using various experimental techniques, showing a high crystalline quality and very precise growth control. The lifetime of the LH1 excited state was determined directly with pump-probe spectroscopy. The measurements indicated an increase of the lifetime by a factor of 2 due to the increasingly unconfined LH1 state, which agreed very well with the design. It also showed a very long lifetime of several hundred picoseconds for the holes excited out of the well to transit back to the well through a diagonal process.

    Keywords
    Molecular beam epitaxy (MBE); Si/SiGe; Pump-probe spectroscopy; Intersubband transition; Lifetime
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13274 (URN)10.1016/j.jlumin.2006.08.080 (DOI)
    Available from: 2008-05-07 Created: 2008-05-07
    3. Molecular beam epitaxy growth of Si/SiGe bound-to-continuum quantum cascade structures for THz emission
    Open this publication in new window or tab >>Molecular beam epitaxy growth of Si/SiGe bound-to-continuum quantum cascade structures for THz emission
    Show others...
    2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 1, p. 34-37Article in journal (Refereed) Published
    Abstract [en]

    A Si/SiGe bound-to-continuum quantum cascade design for THz emission was grown using solid-source molecular beam epitaxy on Si0.8Ge0.2 virtual substrates. The growth parameters were carefully studied and several samples with different boron doping concentrations were grown at optimized conditions. Extensive material characterizations revealed a high crystalline quality of the grown structures with an excellent growth control. Layer undulations resulting from a nonuniform strain field, introduced by high doping concentration, were observed. The device characterizations suggested that a modification on the design was needed in order to enhance the THz emission.

    Keywords
    Molecular beam epitaxy (MBE), Si/SiGe, Quantum cascade, X-ray diffraction, Transmission electron microscopy (TEM)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-16177 (URN)10.1016/j.tsf.2008.08.091 (DOI)
    Available from: 2009-01-09 Created: 2009-01-09 Last updated: 2017-12-14
    4. Asymmetric relaxation of SiGe/Si(110) investigated by high-resolution x-ray diffraction reciprocal space mapping
    Open this publication in new window or tab >>Asymmetric relaxation of SiGe/Si(110) investigated by high-resolution x-ray diffraction reciprocal space mapping
    2006 (English)In: Applied physics letters, ISSN 0003-6951, Vol. 89, p. 181901-1--181901-3Article in journal (Refereed) Published
    Abstract [en]

    Strain relaxation of SiGe/Si(110) has been studied by x-ray reciprocal space mapping. To get information about the in-plane lattice mismatch in different directions, two-dimensional maps around, e.g., (260) and (062) reciprocal lattice points have been obtained from Si0.8Ge0.2/Si(110) samples, which were exposed to different annealing conditions. The in-plane lattice mismatch was found to be asymmetric with the major strain relaxation observed in the lateral [001] direction. This was associated with the formation and propagation of dislocations oriented along [10]. The relaxation of as-grown structures during postannealing is thus different from relaxation during growth, which is mainly along [10].

     

     

    Keywords
    Ge-Si alloys, silicon, semiconductor materials, elemental semiconductors, X-ray diffraction, annealing, dislocations, stress relaxation
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13276 (URN)10.1063/1.2364861 (DOI)
    Available from: 2008-05-07 Created: 2008-05-07 Last updated: 2009-05-11
    5. Strain relaxation of thin Si0.6Ge0.4 grown with low-temperature buffers by molecular beam epitaxy
    Open this publication in new window or tab >>Strain relaxation of thin Si0.6Ge0.4 grown with low-temperature buffers by molecular beam epitaxy
    Manuscript (Other academic)
    Identifiers
    urn:nbn:se:liu:diva-13277 (URN)
    Available from: 2008-05-07 Created: 2008-05-07 Last updated: 2010-01-13
  • 9.
    Zhao, Ming
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Hansson, Göran
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Ni , Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Strain relaxation of thin Si0.6Ge0.4 grown with low-temperature buffers by molecular beam epitaxy2009In: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979 , Vol. 105, no 6, p. 063502-Article in journal (Refereed)
    Abstract [en]

    A double-low-temperature-buffer variable-temperature growth scheme was studied for fabrication of strain-relaxed thin Si0.6Ge0.4 layer on Si(001) by using molecular beam epitaxy (MBE), with particular focuses on the influence of growth temperature of individual low-temperature-buffer layers on the relaxation process and final structural qualities. The low-temperature buffers consisted of a 40 nm Si layer grown at an optimized temperature of similar to 400 degrees C, followed by a 20 nm Si0.6Ge0.4 layer grown at temperatures ranging from 50 to 550 degrees C. A significant relaxation increase together with a surface roughness decrease both by a factor of similar to 2, accompanied with the cross-hatch/cross-hatch-free surface morphology transition, took place for the sample containing a low-temperature Si0.6Ge0.4 layer that was grown at similar to 200 degrees C. This dramatic change was explained by the association with a certain onset stage of the ordered/disordered growth transition during the low-temperature MBE, where the high density of misfit dislocation segments generated near surface cusps largely facilitated the strain relaxation of the top Si0.6Ge0.4 layer.

  • 10.
    Zhao, Ming
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Karim, Amir
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Townsend, P
    University of Cambridge.
    Lynch, S A
    University of Cambridge.
    Paul , D J
    University of Cambridge.
    Molecular beam epitaxy growth of Si/SiGe bound-to-continuum quantum cascade structures for THz emission2008In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 1, p. 34-37Article in journal (Refereed)
    Abstract [en]

    A Si/SiGe bound-to-continuum quantum cascade design for THz emission was grown using solid-source molecular beam epitaxy on Si0.8Ge0.2 virtual substrates. The growth parameters were carefully studied and several samples with different boron doping concentrations were grown at optimized conditions. Extensive material characterizations revealed a high crystalline quality of the grown structures with an excellent growth control. Layer undulations resulting from a nonuniform strain field, introduced by high doping concentration, were observed. The device characterizations suggested that a modification on the design was needed in order to enhance the THz emission.

  • 11.
    Zhao, Ming
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Karim, Amir
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Pidgeon, C. R.
    Department of Physics, Heriot-Watt University, Riccarton, Edinburgh, UK.
    Phillips, P. J.
    Department of Physics, Heriot-Watt University, Riccarton, Edinburgh, UK.
    Carder, D.
    Department of Physics, Heriot-Watt University, Riccarton, Edinburgh, UK.
    Murdin, B. N.
    Department of Physics, University of Surrey, UK.
    Fromherz, T.
    Institut für Halbleiter- und Festkörperphysik, Johannes Kepler Universität, Linz, Austria.
    Paul, D. J.
    Cavendish Laboratory, University of Cambridge, UK.
    Strain-symmetrized Si/SiGe multi-quantum well structures grown by molecular beam epitaxy for intersubband engineering2006In: Journal of luminescence, ISSN 0022-2313, Vol. 121, no 2, p. 403-408Article in journal (Refereed)
    Abstract [en]

    Three strain-symmetrized Si/SiGe multi-quantum well structures, designed for probing the carrier lifetime of intrawell intersubband transitions between heavy hole 1 (HH1) and light hole 1 (LH1) states with transition energies below the optical phonon energy, were grown by molecular beam epitaxy at low temperature on fully relaxed SiGe virtual substrates. The grown structures were characterized by using various experimental techniques, showing a high crystalline quality and very precise growth control. The lifetime of the LH1 excited state was determined directly with pump-probe spectroscopy. The measurements indicated an increase of the lifetime by a factor of 2 due to the increasingly unconfined LH1 state, which agreed very well with the design. It also showed a very long lifetime of several hundred picoseconds for the holes excited out of the well to transit back to the well through a diagonal process.

  • 12.
    Zhao, Ming
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Ni, Wei- Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Townsend, P
    Cavendish Laboratory, University of Cambridge, Cambridge, UK.
    Lynch, S. A.
    Cavendish Laboratory, University of Cambridge, Cambridge, UK.
    Paul, D. J.
    Cavendish Laboratory, University of Cambridge, Cambridge, UK.
    Chang, M. N.
    National Nano Device Laboratories, Taiwan.
    Hsu, C. C.
    National Nano Device Laboratories, Taiwan.
    Low-temperature molecular beam epitaxy growth of Si/SiGe THz quantum cascade structures on virtual substrates2006In: Thin Solid Films, ISSN 0040-6090, Vol. 508, no 1-2, p. 24-28Article in journal (Refereed)
    Abstract [en]

    Si/SiGe quantum cascade structures containing superlattice up to 100 periods have been grown on SiGe virtual substrates by using solid-source molecular beam epitaxy at low temperature. The surface morphology and structural properties of the grown samples were characterized using various experimental techniques. It has been concluded that the structures were completely symmetrically strained with high crystalline quality, precise layer parameters, and excellent reproducibility. Electroluminescence was observed with peaked intensity at 3 THz at both 4 and 40 K, which agrees very well with expected interwell intersubband transition according to the design.

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