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Elfving, Anders
Publications (10 of 26) Show all publications
Gomes, P. F., Cerdeira, F., Larsson, M., Elfving, A., Hansson, G., Ni, W.-X., . . . García-Cristóbal, A. (2008). Large optical emission blue shift in Ge/Si quantum dots under external biaxial strain. In: ICPS 29th International Conference on the Physics of Semiconductors,2008.
Open this publication in new window or tab >>Large optical emission blue shift in Ge/Si quantum dots under external biaxial strain
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2008 (English)In: ICPS 29th International Conference on the Physics of Semiconductors,2008, 2008Conference paper, Published paper (Refereed)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44291 (URN)76182 (Local ID)76182 (Archive number)76182 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
Gomes, P., Gomes, P., Iikawa, F., Iikawa, F., Cerdeira, F., Cerdeira, F., . . . Holtz, P.-O. (2007). Size dependent spatial direct and indirect transitions in Ge/Si QDs. In: The 6th International Conference on Low Dimensional Structures and Devices,2007.
Open this publication in new window or tab >>Size dependent spatial direct and indirect transitions in Ge/Si QDs
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2007 (English)In: The 6th International Conference on Low Dimensional Structures and Devices,2007, 2007Conference paper, Published paper (Refereed)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-39847 (URN)51521 (Local ID)51521 (Archive number)51521 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
Gomes, P., Iikawa, F., Cerdeira, F., Larsson, M., Elfving, A., Hansson, G., . . . Holtz, P.-O. (2007). Type-I optical emissions in GeSi quantum dots. Applied Physics Letters, 91(5)
Open this publication in new window or tab >>Type-I optical emissions in GeSi quantum dots
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2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 5Article in journal (Refereed) Published
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.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48911 (URN)10.1063/1.2764113 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Elfving, A., Zhao, M., Hansson, G. V. & Ni, W.-X. (2006). Asymmetric relaxation of SiGe/Si(110) investigated by high-resolution x-ray diffraction reciprocal space mapping. Applied physics letters, 89, 181901-1--181901-3
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
Karim, A., Elfving, A., Larsson, M., Ni, W.-X. & Hansson, G. V. (2006). Compositional analysis of Si/SiGe quantum dots using STEM and EDX. In: Volume 6129 - Quantum Dots, Particles, and Nanoclusters III, Proceedings of SPIE: .
Open this publication in new window or tab >>Compositional analysis of Si/SiGe quantum dots using STEM and EDX
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2006 (English)In: Volume 6129 - Quantum Dots, Particles, and Nanoclusters III, Proceedings of SPIE, 2006Conference paper, Published 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.

Keywords
SiGe, quantum dots, composition, intermixing, growth temperature
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-12572 (URN)10.1117/12.647318 (DOI)
Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2009-03-02
Larsson, M., Elfving, A., Ni, W.-X., Hansson, G. V. & Holtz, P.-O. (2006). Growth-temperature-dependent band alignment in Si/Ge quantum dots from photoluminescence spectroscopy. Physical Review B, 73(19), 195319-1--195319-7
Open this publication in new window or tab >>Growth-temperature-dependent band alignment in Si/Ge quantum dots from photoluminescence spectroscopy
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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
Elfving, A. (2006). Near-infrared photodetectors based on Si/SiGe nanostructures. (Doctoral dissertation). : Institutionen för fysik, kemi och biologi
Open this publication in new window or tab >>Near-infrared photodetectors based on Si/SiGe nanostructures
2006 (English)Doctoral 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.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1003
Keywords
SiGe, Ge dots, nanostructures, molecular beam epitaxy, photodetector
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-5909 (URN)91-85497-24-X (ISBN)
Public defence
2006-02-27, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Note
On the day of the defence date the status of article IV was Manuscript and the title was "A three-terminal Ge dot/SiGe quantum well MOSFET photodetector for near infrared light detection"; the status of article VI was Submitted and the title was "Band alignment studies in Si/Ge quantum dots based on optical and structural investigations"; the status of article VII was Manuscript and the title was "Thermal stability of SiGe/Si(110) investigated by high-resolution X-ray diffraction reciprocal space mapping".Available from: 2006-02-27 Created: 2006-02-27 Last updated: 2009-02-18
Elfving, A., Karim, A., Hansson, G. V. & Ni, W.-X. (2006). Three-terminal Ge dot/SiGe quantum-well photodetectors for near-infrared light detection. Applied Physics Letters, 89, 083510-083513
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
Larsson, M., Elfving, A., Holtz, P.-O., Hansson, G. & Ni, W.-X. (2005). Asymmetric band alignment at Si/Ge quantum dots studied by luminescence from p-i-n and n-i-p structures. In: ICPS2004,2004 (pp. 713).
Open this publication in new window or tab >>Asymmetric band alignment at Si/Ge quantum dots studied by luminescence from p-i-n and n-i-p structures
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2005 (English)In: ICPS2004,2004, 2005, p. 713-Conference paper, Published paper (Refereed)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-40702 (URN)53921 (Local ID)53921 (Archive number)53921 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
Larsson, M., Elfving, A., Holtz, P.-O., Ni, W.-X. & Hansson, G. (2005). Band alignment studies of self-organized Ge/Si quantum dots based on luminescence characterization. In: The 23rd International Conference on Defects in Semiconductors,2005.
Open this publication in new window or tab >>Band alignment studies of self-organized Ge/Si quantum dots based on luminescence characterization
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2005 (English)In: The 23rd International Conference on Defects in Semiconductors,2005, 2005Conference paper, Published paper (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-41079 (URN)55050 (Local ID)55050 (Archive number)55050 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
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