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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.
    Elfving, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Near-infrared photodetectors based on Si/SiGe nanostructures2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two types of photodetectors containing Ge/Si quantum dots have been fabricated based on materials grown by molecular beam epitaxy and characterized with several experimental techniques. The aim was to study new device architectures with the implementation of Ge nanostructures, in order to obtain high detection efficiency in the near infrared range at room temperature.

    Heterojunction bipolar phototransistors were fabricated with 10 Ge dot layers in the base-collector (b-c) junction. With the illumination of near infrared radiation at 1.31 to 1.55 µm, the incident light would excite the carriers. The applied field across the b-c junction caused hole transport into the base, leading to a reduced potential barrier between the emitter-base (e-b) junction. Subsequently, this resulted in enhanced injection of electrons across the base into the collector, i.e., forming an amplified photo-induced current. We have therefore obtained significantly enhanced photo-response for the Ge-dot based phototransistors, compared to corresponding quantum dot p-i-n photodiodes. Responsivity values up to 470 mA/W were measured at 1.31 µm using waveguide geometry, and ∼2.5 A/W at 850 nm, while the dark current was as low as 0.01 mA/cm2 at –2 V.

    Metal-oxide field-effect phototransistors were also studied. These lateral detectors were processed with three terminals for source, drain and gate contacts. The Ge quantum dot layers were sandwiched between pseudomorphically grown SiGe quantum wells. The detector devices were processed using a multi-finger comb structure with an isolated gate contact on top of each finger and patterned metal contacts on the side edges for source and drain. It was found that the photo-responsivity was increased by a factor of more than 20 when a proper gate bias was applied. With VG above threshold, the measured response was 350 and >30 mA/W at 1.31 and 1.55 µm, respectively.

    Properties of Si/Si1-xGex nanostructures were examined, in order to facilitate proper design of the above mentioned transistor types of photodetectors. The carrier recombination processes were characterized by photoluminescence measurements, and the results revealed a gradual change from spatially indirect to direct transitions in type II Si1-xGex islands with increased measurement temperature. Energy dispersive X-ray spectrometry of buried Ge islands produced at different temperatures indicated a gradual decrease of the Ge concentration with temperature, which was due to the enhanced intermixing of Si and Ge atoms. At a deposition temperature of 730°C the Ge concentration was as low as around 40 %.

    Finally, the thermal stability of the Si/SiGe(110) material system, which is a promising candidate for future CMOS technology due to its high carrier mobility, was investigated by high resolution X-ray diffraction reciprocal space mapping. Anisotropic strain relaxation was observed with maximum in-plane lattice mismatch in the [001] direction.

    List of papers
    1. SiGe (Ge-dot) heterojunction phototransistors for efficient light detection at 1.3-1.55 µm
    Open this publication in new window or tab >>SiGe (Ge-dot) heterojunction phototransistors for efficient light detection at 1.3-1.55 µm
    2003 (English)In: Physica E: Low-dimensional Systems and Nanostructures, ISSN 1386-9477, Vol. 16, no 3-4, p. 528-532Article in journal (Refereed) Published
    Abstract [en]

    The aim of this work is to develop a Si/SiGe HBT-type phototransistor with several Ge dot layers incorporated in the collector, in order to obtain improved light detectivity at 1.3–1.55 μm. The MBE grown HBT detectors are of n–p–n type and based on a multilayer structure containing 10 Ge-dot layers (8 ML in each layer, separated by 60 nm Si spacer) in the base-collector junction. The transistors were processed for normal incidence or with waveguide geometry where the light is coupled through the edge of the sample. The measured breakdown voltage, BVceo, was about 6 V. Compared to a p–i–n reference photodiode with the same dot layer structure, photoconductivity measurements show that the responsivity is improved by a factor of 60 for normal incidence at 1.3 μm. When the light is coupled through the edge of the device, the detectivity is even further enhanced. The measured photo-responsivity is more than 100 and 5 mA/W at 1.3 and 1.55 μm, respectively.

    Keywords
    Si, Ge, Quantum dot, Detector, Heterojunction bipolar transistor
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13790 (URN)10.1016/S1386-9477(02)00634-3 (DOI)
    Available from: 2006-02-27 Created: 2006-02-27
    2. Efficient near infrared Si/Ge quantum dot photodetector based on a heterojunction bipolar transistor
    Open this publication in new window or tab >>Efficient near infrared Si/Ge quantum dot photodetector based on a heterojunction bipolar transistor
    Show others...
    2003 (English)In: Material Research Society Symposium Proceedings, 2003, Vol. 770Conference paper, Published paper (Refereed)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13791 (URN)
    Available from: 2006-02-27 Created: 2006-02-27 Last updated: 2009-05-11
    3. Infrared photodetectors based on a Ge-dot/SiGe-well field effect transistor structure
    Open this publication in new window or tab >>Infrared photodetectors based on a Ge-dot/SiGe-well field effect transistor structure
    2003 (English)In: Electrochemical Society Proceedings, SiGe: Materials, Processing, and Devices, 2003, Vol. 7Conference paper, Published paper (Refereed)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13792 (URN)
    Available from: 2006-02-27 Created: 2006-02-27
    4. Three-terminal Ge dot/SiGe quantum-well photodetectors for near-infrared light detection
    Open this publication in new window or tab >>Three-terminal Ge dot/SiGe quantum-well photodetectors for near-infrared light detection
    2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, p. 083510-083513Article in journal (Refereed) Published
    Abstract [en]

    A three-terminal metal-oxide-semiconductor field-effect transistor type of photodetector has been fabricated with a multiple stack of Ge dot/SiGe quantum-well heterostructures as the active region for light detection at 1.3–1.55  µm. Gate-dependent edge incidence photoconductivity measurements at room temperature revealed a strong dependence of the photoresponse on the gate voltage. At positive gate bias, the hole transport from the dots into the wells was improved, resulting in a faster response. The high photoresponsivity at negative VG, measured to be 350  mA  W–1 at 1.31  µm and 30  mA  W–1 at 1.55  µm, was ascribed to the photoconductive gain.

    Keywords
    germanium, Ge-Si alloys, elemental semiconductors, semiconductor quantum wells, photodetectors, MOSFET, photoconductivity
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-12573 (URN)10.1063/1.2337867 (DOI)
    Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2017-12-14
    5. Spatially direct and indirect transitions observed for Si/Ge quantum dots
    Open this publication in new window or tab >>Spatially direct and indirect transitions observed for Si/Ge quantum dots
    Show others...
    2003 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 26, p. 4785-4787Article in journal (Refereed) Published
    Abstract [en]

    The optical properties of Ge quantum dots embedded in Si were investigated by means of photoluminescence, with temperature and excitation power density as variable parameters. Two different types of recombination processes related to the Ge quantum dots were observed. A transfer from the spatially indirect to the spatially direct recombination in the type-II band lineup was observed with increasing temperature. A blueshift of the spatially indirect Ge quantum-dot-emission energy with increasing excitation power is ascribed to band bending at the type-II Si/Ge interface for high carrier densities. Comparative studies were performed on uncapped Ge dot structures.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13794 (URN)10.1063/1.1587259 (DOI)
    Available from: 2006-02-27 Created: 2006-02-27 Last updated: 2017-12-13
    6. Growth-temperature-dependent band alignment in Si/Ge quantum dots from photoluminescence spectroscopy
    Open this publication in new window or tab >>Growth-temperature-dependent band alignment in Si/Ge quantum dots from photoluminescence spectroscopy
    Show others...
    2006 (English)In: Physical Review B, ISSN 1098-0121, Vol. 73, no 19, p. 195319-1--195319-7Article in journal (Refereed) Published
    Abstract [en]

    The present work is a photoluminescence study of Si-embedded Stranski-Krastanov Ge quantum dots. The value of the conduction band offset is a result of the magnitude of the tensile strain in the Si surrounding the compressive strained Ge dot. Due to the increased Si/Ge intermixing and reduced strain in the Si barrier, a reduction of the conduction band offset is observed at increased growth temperatures. The optical properties as derived from photoluminescence spectroscopy are correlated with structural properties obtained as a function of the growth temperature. High growth temperatures result in large Ge dots with low density due to the pronounced surface diffusion and Si/Ge intermixing. As confirmed by photoluminescence, the band gap of the Ge dots increases with increased growth temperature due to the higher degree of Si/Ge intermixing. The band alignment is of type II in these structures, but the occurrence of both spatially indirect and spatially direct transitions are confirmed in temperature-dependent photoluminescence measurements with varied excitation power conditions. An increasing temperature results in a gradual transition from the spatially indirect to the spatially direct recombination in the type-II band lineup, due to higher oscillator strength for the spatially direct transition combined with a higher population factor at higher temperatures.

    Keywords
    germanium, silicon, elemental semiconductors, semiconductor quantum dots, semiconductor growth, photoluminescence, conduction bands, internal stresses, surface diffusion, chemical interdiffusion, electron-hole recombination, oscillator strengths
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13795 (URN)10.1103/PhysRevB.73.195319 (DOI)
    Note
    Original Publication: Mats Larsson, Anders Elfving, Wei-Xin Ni, Göran V. Hansson and Per-Olof Holtz, Growth-temperature-dependent band alignment in Si/Ge quantum dots from photoluminescence spectroscopy, 2006, Physical Review B, (73), 195319. http://dx.doi.org/10.1103/PhysRevB.73.195319 Copyright: American Physical Society http://www.aps.org/ Available from: 2009-01-15 Created: 2009-01-15 Last updated: 2009-03-04Bibliographically approved
    7. 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
  • 3.
    Elfving, Anders
    et al.
    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.
    Infrared photodetectors based on a Ge-dot/SiGe-well field effect transistor structure2003In: Electrochemical Society Proceedings, SiGe: Materials, Processing, and Devices, 2003, Vol. 7Conference paper (Refereed)
  • 4.
    Elfving, Anders
    et al.
    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.
    SiGe (Ge-dot) heterojunction phototransistors for efficient light detection at 1.3-1.55 µm2003In: Physica E: Low-dimensional Systems and Nanostructures, ISSN 1386-9477, Vol. 16, no 3-4, p. 528-532Article in journal (Refereed)
    Abstract [en]

    The aim of this work is to develop a Si/SiGe HBT-type phototransistor with several Ge dot layers incorporated in the collector, in order to obtain improved light detectivity at 1.3–1.55 μm. The MBE grown HBT detectors are of n–p–n type and based on a multilayer structure containing 10 Ge-dot layers (8 ML in each layer, separated by 60 nm Si spacer) in the base-collector junction. The transistors were processed for normal incidence or with waveguide geometry where the light is coupled through the edge of the sample. The measured breakdown voltage, BVceo, was about 6 V. Compared to a p–i–n reference photodiode with the same dot layer structure, photoconductivity measurements show that the responsivity is improved by a factor of 60 for normal incidence at 1.3 μm. When the light is coupled through the edge of the device, the detectivity is even further enhanced. The measured photo-responsivity is more than 100 and 5 mA/W at 1.3 and 1.55 μm, respectively.

  • 5.
    Elfving, Anders
    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.
    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.
    Three-terminal Ge dot/SiGe quantum-well photodetectors for near-infrared light detection2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, p. 083510-083513Article in journal (Refereed)
    Abstract [en]

    A three-terminal metal-oxide-semiconductor field-effect transistor type of photodetector has been fabricated with a multiple stack of Ge dot/SiGe quantum-well heterostructures as the active region for light detection at 1.3–1.55  µm. Gate-dependent edge incidence photoconductivity measurements at room temperature revealed a strong dependence of the photoresponse on the gate voltage. At positive gate bias, the hole transport from the dots into the wells was improved, resulting in a faster response. The high photoresponsivity at negative VG, measured to be 350  mA  W–1 at 1.31  µm and 30  mA  W–1 at 1.55  µm, was ascribed to the photoconductive gain.

  • 6.
    Elfving, Anders
    et al.
    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, Materials Science . Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . 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.
    Efficient near infrared Si/Ge quantum dot photodetector based on a heterojunction bipolar transistor2003In: Material Research Society Symposium Proceedings, 2003, Vol. 770Conference paper (Refereed)
  • 7.
    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].

     

     

  • 8. Gomes, P F
    et al.
    Cerdeira, F
    Larsson, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    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 .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Madureira, J R
    García-Cristóbal, A
    Large optical emission blue shift in Ge/Si quantum dots under external biaxial strain2008In: ICPS 29th International Conference on the Physics of Semiconductors,2008, 2008Conference paper (Refereed)
  • 9. Gomes, P.F.
    et al.
    Gomes, P.F.
    Iikawa, F.
    Iikawa, F.
    Cerdeira, F.
    Cerdeira, F.
    Larsson, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Larsson, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    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 .
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Size dependent spatial direct and indirect transitions in Ge/Si QDs2007In: The 6th International Conference on Low Dimensional Structures and Devices,2007, 2007Conference paper (Refereed)
  • 10.
    Gomes, P.F.
    et al.
    Intituto de Física Gleb Wataghin, Unicamp, CP 6165, Campinas, São Paulo 13083-970, Brazil.
    Iikawa, F.
    Intituto de Física Gleb Wataghin, Unicamp, CP 6165, Campinas, São Paulo 13083-970, Brazil.
    Cerdeira, F.
    Intituto de Física Gleb Wataghin, Unicamp, CP 6165, Campinas, São Paulo 13083-970, Brazil.
    Larsson, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    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 .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Type-I optical emissions in GeSi quantum dots2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 5Article in journal (Refereed)
    Abstract [en]

    The authors studied the optical emission of GeSi quantum dots under externally applied biaxial stress using samples grown with different temperatures varying from 430 to 700 °C. The optical emission energy of samples grown at low temperatures is rather insensitive to the applied external stress, consistent with the type-II band alignment. However, for samples grown at high temperatures we observed a large blueshift, which suggests type-I alignment. The result implies that recombination strength can be controlled by the growth temperature, which can be useful for optical device applications. © 2007 American Institute of Physics.

  • 11.
    Hansson, Göran
    et al.
    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 .
    Du, Chun-Xia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Duteil, F.
    Origin of abnormal temperature dependence of electroluminescence from Er/O-doped Si diodes2001In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 78, no 15, p. 2104-2106Article in journal (Refereed)
    Abstract [en]

    The temperature dependencies of the current-voltage characteristics and the electroluminescence (EL) intensity of molecular beam epitaxy grown Er/O-doped Si light emitting diodes at reverse bias have been studied. To minimize the scattering of electrons injected from the p-doped Si1-xGex electron emitters, an intrinsic Si layer was used in the depletion region. For many diodes, there is a temperature range where the EL intensity increases with temperature. Data are reported for a structure that shows increasing intensity up to 100°C. This is attributed to an increasing fraction of the pumping current being due to phonon-assisted tunneling, which gives a higher saturation intensity, compared to ionization-dominated breakdown at lower temperatures. © 2001 American Institute of Physics.

  • 12.
    Karim, Amir
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. 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.
    Larsson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . 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.
    Hansson, G. V.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Compositional analysis of Si/SiGe quantum dots using STEM and EDX2006In: Volume 6129 - Quantum Dots, Particles, and Nanoclusters III, Proceedings of SPIE, 2006Conference paper (Refereed)
    Abstract [en]

    Ge islands fabricated on Si(100) by molecular beam epitaxy at different growth temperatures, were studied using crosssectional scanning transmission electron microscopy and energy-dispersive X-ray spectrometry combined with electron energy loss spectrometry experiments. The island size, shape, strain, and material composition define the dot-related optical transition energies, but they are all strongly dependent on the growth temperature. We have performed quantitative investigations of the material composition of Ge/Si(001) quantum dots. The samples were grown at temperatures ranging from 430 to 730 °C, with one buried and one uncapped layer of Ge islands separated by 140 nm intrinsic Si. The measurements showed a Ge concentration very close to 100 % in the islands of samples grown at 430 °C. With a growth temperature of 530 °C, a ~20 % reduction of the Ge fraction was observed, which is due to intermixing of Si and Ge. This is consistent with our previous photoluminescence results, which revealed a significant blue shift of the Ge dot-related emission peak in this growth temperature range. The Ge concentration decreases more slowly when the growth temperature is increased above 600 °C, which can be explained by geometrical arguments. The longer distance between the interface and the core of these larger sized dome-shaped islands implies that less Si atoms reach the dot center. In general, the uncapped Ge dots have similar widths as the embedded islands, but the height is almost exclusively larger. Furthermore, the Ge concentration is slightly lower for the overgrown dots.

  • 13.
    Karim, Amir
    et al.
    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.
    Elfving, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Persson, Per O.Å
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film 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.
    Characterization of Er/O-doped Si-LEDs with low thermal quenching2005In: Material Research Society Symposium Proceedings, 2005, p. 117-124Conference paper (Refereed)
    Abstract [en]

    Electroluminescence studies of MBE-grown Er/O-doped Si-diodes at reverse bias have been done. For some devices there is much reduced thermal quenching of the emission at 1.54 µm. There are examples where the temperature dependence is abnormal in that the intensity for a constant current even increases with temperature up to e.g. 80 oC. These devices have been studied with cross-sectional transmission electron microscopy to see the microstructure of the Er/O-doped layers as well as the B-doped SiGe-layers that are used as electron emitters during reverse bias. Although there are defects in the layers there is no evidence for large thick precipitates of SiO2. While reduced thermal quenching often is attributed to having the Er-ions within SiO2 layers, this is not the case for our structures as evidenced by our TEM-studies. The origin of the abnormal temperature dependence is attributed to the two mechanisms of breakdown in the reverse-biased diodes. At low temperature the breakdown current is mainly due to avalanche resulting in low-energy electrons and holes that quenches the intensity by Auger de-excitation of the Er-ions. At higher temperature the breakdown current is mainly phonon-assisted tunnelling which results in a more efficient pumping with less de-excitation of the Er-ions. Finally at the highest temperatures the thermal quenching sets in corresponding to an activation energy of 125 meV, which is slightly lower than 150 meV that has been reported in other studies.

  • 14.
    Larsson, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    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 .
    Asymmetric band alignment at Si/Ge quantum dots studied by luminescence from p-i-n and n-i-p structures2005In: ICPS2004,2004, 2005, p. 713-Conference paper (Refereed)
  • 15.
    Larsson, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    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 .
    Luminescence study of Si/Ge quantum dots2003In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 16, no 3-4, p. 476-480Article in journal (Refereed)
    Abstract [en]

    We present a photoluminescence (PL) study of Ge quantum dots embedded in Si. Two different types of recombination processes related to the Ge quantum dots are observed in temperature-dependent PL measurements. The Ge dot-related luminescence peak near 0.80 eV is ascribed to the spatially indirect recombination in the type-II band lineup, while a high-energy peak near 0.85 eV has its origin in the spatially direct recombination. A transition from the spatially indirect to the spatially direct recombination is observed as the temperature is increased. The PL dependence of the excitation power shows an upshift of the Ge quantum dot emission energy with increasing excitation power density. The blueshift is ascribed to band bending at the type-II Si/Ge interface at high carrier densities. Comparison is made with results derived from measurements on uncapped samples. For these uncapped samples, no energy shifts due to excitation power or temperatures are observed in contrast to the capped samples.

  • 16.
    Larsson, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    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 .
    Photoluminescence study of Si/Ge quantum dots2003In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 532-535, p. 832-836Article in journal (Refereed)
    Abstract [en]

    Ge quantum dots embedded in Si are studied by means of photoluminescence (PL). The temperature dependent PL measurements show two different types of recombination processes related to the quantum dots. We ascribe a peak near 0.80 eV to the spatially indirect recombination in the type-II band lineup where the electron is located in the surrounding Si close to the interface and the hole in the Ge dot. Furthermore, a peak near 0.85 eV is attributed to the spatially direct recombination. We observe a transition from the spatially indirect to the spatially direct recombination as the temperature is increased. The measurements also show an up-shift of the Ge quantum dot emission energy with increasing excitation power density. The blueshift is primarily ascribed to an enhanced confinement of the electron associated with the increased band bending at the type-II Si/Ge interface at high carrier densities. Comparison is made with results, derived from measurements on uncapped samples. For these uncapped samples, no energy shifts due to excitation power or temperatures are observed in contrast to the capped samples. ⌐ 2003 Elsevier Science B.V. All rights reserved.

  • 17.
    Larsson, Mats
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Elfving, Anders
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hansson, Göran
    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. Linköping University, The Institute of Technology.
    Spatially direct and indirect transitions observed for Si/Ge quantum dots2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 26, p. 4785-4787Article in journal (Refereed)
    Abstract [en]

    The optical properties of Ge quantum dots embedded in Si were investigated by means of photoluminescence, with temperature and excitation power density as variable parameters. Two different types of recombination processes related to the Ge quantum dots were observed. A transfer from the spatially indirect to the spatially direct recombination in the type-II band lineup was observed with increasing temperature. A blueshift of the spatially indirect Ge quantum-dot-emission energy with increasing excitation power is ascribed to band bending at the type-II Si/Ge interface for high carrier densities. Comparative studies were performed on uncapped Ge dot structures.

  • 18.
    Larsson, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Band alignment studies of self-organized Ge/Si quantum dots based on luminescence characterization2005In: The 23rd International Conference on Defects in Semiconductors,2005, 2005Conference paper (Other academic)
  • 19.
    Larsson, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Band alignment studies of self-organized Ge/Si quantum dots based on luminescence characterization2005In: The 9th Conference on Optics and Excitons in Confined Systems,2005, 2005Conference paper (Other academic)
  • 20.
    Larsson, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hussain, M.I.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ni, Wei-Xin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Luminescence Properties of Ge Quantum Dots Produced by MBE at Different Temperatures2004In: Proc. of IEEE/LEOS 1st International Conference on Group IV Photonics,2004, 2004Conference paper (Other academic)
  • 21.
    Larsson, Mats
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Elfving, Anders
    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. Linköping University, The Institute of Technology.
    Hansson, Göran
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Band alignment studies in Si/Ge quantum dots based on optical and structural investigationsManuscript (preprint) (Other academic)
    Abstract [en]

    The present work is a photoluminescence study of Si-embedded Stranski-Krastanov Ge quantum dots. The value of the conduction band offset is a result of the magnitude of the tensile strain in the Si surrounding the compressive strained Ge dot. Due to the increased Si/Ge intermixing and reduced strain in the Si barrier, a reduction of the conduction band offset is observed at increased growth temperatures. The optical properties as derived from photoluminescence spectroscopy are correlated with structural properties obtained as a function of the growth temperature. High growth temperatures result in large Ge dots with low density due to the pronounced surface diffusion and Si/Ge intermixing. As confirmed by photoluminescence, the band gap of the Ge dots increases with increased growth temperature due to the higher degree of Si/Ge intermixing. The band alignment is of type-II in these structures, but the occurrence of both spatially indirect and spatially direct transitions are confirmed in temperature dependent photoluminescence measurements with varied excitation power conditions. An increasing temperature results in a gradual transition from the spatially indirect to the spatially direct recombination in the type-II band lineup, due to higher oscillator strength for the spatially direct transition combined with a higher population factor at higher temperatures.

  • 22.
    Larsson, Mats
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Elfving, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Hansson, Göran V.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Growth-temperature-dependent band alignment in Si/Ge quantum dots from photoluminescence spectroscopy2006In: Physical Review B, ISSN 1098-0121, Vol. 73, no 19, p. 195319-1--195319-7Article in journal (Refereed)
    Abstract [en]

    The present work is a photoluminescence study of Si-embedded Stranski-Krastanov Ge quantum dots. The value of the conduction band offset is a result of the magnitude of the tensile strain in the Si surrounding the compressive strained Ge dot. Due to the increased Si/Ge intermixing and reduced strain in the Si barrier, a reduction of the conduction band offset is observed at increased growth temperatures. The optical properties as derived from photoluminescence spectroscopy are correlated with structural properties obtained as a function of the growth temperature. High growth temperatures result in large Ge dots with low density due to the pronounced surface diffusion and Si/Ge intermixing. As confirmed by photoluminescence, the band gap of the Ge dots increases with increased growth temperature due to the higher degree of Si/Ge intermixing. The band alignment is of type II in these structures, but the occurrence of both spatially indirect and spatially direct transitions are confirmed in temperature-dependent photoluminescence measurements with varied excitation power conditions. An increasing temperature results in a gradual transition from the spatially indirect to the spatially direct recombination in the type-II band lineup, due to higher oscillator strength for the spatially direct transition combined with a higher population factor at higher temperatures.

  • 23.
    Larsson, Mats
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Elfving, Anders
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hansson, Göran
    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. Linköping University, The Institute of Technology.
    Reversed quantum-confined Stark effect and an asymmetric band alignment observed for type-II Si∕Ge quantum dots2005In: Physical Review B, ISSN 1098-0121, Vol. 71, no 11, p. 113301-Article in journal (Refereed)
    Abstract [en]

    We report on the quantum-confined Stark effect for spatially indirect transitions in Stranski-Krastanov grown type-II Si∕Ge quantum dots. A linear blueshift of the spatially indirect transition is observed at increasing electric field in contrast to the commonly observed redshift for type-I transitions. A shift of the emission-peak position and different quenching rates of the photoluminescence for p-i-n and n-i-p diodes at increased electric field and temperature indicate a deeper notch potential for electrons above the dot than below due to a strain-induced asymmetry in the band alignment.

  • 24.
    Ni, Wei-Xin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Du, Chun-Xia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Duteil, F.
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    1.54 µm light emitting devices based on Er/O-doped Si layered structures grown by molecular beam epitaxy2001In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 17, no 1-2, p. 65-69Conference paper (Other academic)
    Abstract [en]

    Two types of Si:Er light emitting devices have been processed and characterized with an aim to efficiently use hot electrons for impact excitation. One is a p+-SiGe/i-Si/n-Si:Er:O/n+-Si tunneling diode with a design favoring electron tunneling from the SiGe valence band to the Si conduction band and subsequent acceleration. Another type of Si:Er light emitters is based on a heterojunction bipolar transistor (HBT) structure containing an Er-doped active layer in the collector. In these devices, one can introduce hot electrons from the HBT emitter in a controlled way with a collector bias voltage prior to the avalanche breakdown to improve the impact excitation efficiency. Intense electroluminescence was observed at 300 K at low current (0.1 A cm-2) and low bias (3 V). An impact cross-section value of 1 × 10-14 cm2 has been estimated, which is a 100-fold increase compared with the values reported from any other type of Er-doped LEDs. © 2001 Elsevier Science B.V.

  • 25.
    Ni, Wei-Xin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Larsson, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hansson, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Si-based Photonic Transistor Devices for Integrated Optoelectronics2003In: The 3rd International Conference on SiGe Epitaxy and Heterostructures,2003, 2003, p. 231-Conference paper (Refereed)
    Abstract [en]

      

  • 26. Wu, Y.-H.
    et al.
    Wang, C.-Y.
    Elfving, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics .
    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 .
    Surface diffusion limited nucleation of Ge dots on the Si(001) surface2002Conference paper (Refereed)
    Abstract [en]

    The formation of Ge islands during MBE growth is a spontaneous process and these islands, i.e. dots, are usually randomly arranged. In order to implement these nanoscaled islands into device applications, ordering of epitaxial dots is a crucial step. We report a study on the MBE growth of Ge islands on Si(001) substrates, containing <110>-oriented square and long stripe type patterns defined by anisotropic wet etching of Si, in order to provide more understanding of how surface diffusion of Ge atoms would influence the formation of Ge islands on various types of surfaces. It has been found that there were preferential nucleation sites for Ge islands along the bottom edges of the Si ridges. The Ge islands at the edge positions were larger than those formed on the free surface and they could be regularly spaced. Due to the consumption of Ge at the bottom edges of ridge patterns, the density of Ge dots on the free surface varied between ˜ 3 × 108 and ˜ 1 × 109 cm-2 when changing the spatial separation between two adjacent Si ridges (2-100 µm). A Ge mean diffusion length of ˜ 7.5 µm has been determined for Ge growth at 700 °C. © 2002 Elsevier Science B.V. All rights reserved.

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