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Lundskog, Anders
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Palisaitis, J., Lundskog, A., Forsberg, U., Janzén, E., Birch, J., Hultman, L. & Persson, P. (2014). Characterization of InGaN/GaN quantum well growth using monochromated valence electron energy loss spectroscopy. Journal of Applied Physics, 115(3), 034302
Open this publication in new window or tab >>Characterization of InGaN/GaN quantum well growth using monochromated valence electron energy loss spectroscopy
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2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 3, p. 034302-Article in journal (Refereed) Published
Abstract [en]

The early stages of InGaN/GaN quantum wells growth for In reduced conditions have been investigated for varying thickness and composition of the wells. The structures were studied by monochromated STEM–VEELS spectrum imaging at high spatial resolution. It is found that beyond a critical well thickness and composition, quantum dots (>20 nm) are formed inside the well. These are buried by compositionally graded InGaN, which is formed as GaN is grown while residual In is incorporated into the growing structure. It is proposed that these dots may act as carrier localization centers inside the quantum wells.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85903 (URN)10.1063/1.4861179 (DOI)000330615500062 ()
Note

On the day of the defence date the status of this article was Manuscript.

Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved
Lundskog, A., Hsu, C.-W., Karlsson, K. F., Amloy, S., Nilsson, D., Forsberg, U., . . . Janzén, E. (2014). Direct generation of linearly-polarized photon emission with designated orientations from site-controlled InGaN quantum dots. Light: Science & Applications, 3, Article ID e139.
Open this publication in new window or tab >>Direct generation of linearly-polarized photon emission with designated orientations from site-controlled InGaN quantum dots
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2014 (English)In: Light: Science & Applications, ISSN 2095-5545, Vol. 3, article id e139Article in journal (Refereed) Published
Abstract [en]

Semiconductor quantum dots (QDs) have been demonstrated viable for the emission of single photons on demand during the past decade. However, the synthesis of QDs emitting photons with pre-defined and deterministic polarization vectors has proven arduous. The access of linearly-polarized photons is essential for various applications. In this report, a novel concept to directly generate linearly-polarized photons is presented. This concept is based on InGaN QDs grown on top of elongated GaN hexagonal pyramids, by which predefined orientations herald the polarization vectors of the emitted photons from the QDs. This growth scheme should allow fabrication of ultracompact arrays of photon emitters, with a controlled polarization direction for each individual QD emitter.

Place, publisher, year, edition, pages
Nature Publishing Group, 2014
Keywords
GaN; InGaN; photoluminescence; polarized emission; quantum dot
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-97417 (URN)10.1038/lsa.2014.20 (DOI)000331998400011 ()
Available from: 2013-09-12 Created: 2013-09-12 Last updated: 2017-04-11Bibliographically approved
Lundskog, A., Hsu, C.-W., Nilsson, D., Karlsson, K. F., Forsberg, U., Holtz, P.-O. & Janzén, E. (2013). Controlled growth of hexagonal GaN pyramids by hot-wall MOCVD. Journal of Crystal Growth, 363, 287-293
Open this publication in new window or tab >>Controlled growth of hexagonal GaN pyramids by hot-wall MOCVD
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2013 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 363, p. 287-293Article in journal (Refereed) Published
Abstract [en]

Hexagonal GaN pyramids have been fabricated by hot-wall metal organic chemical vapor deposition (hot-wall MOCVD) and the growth evolution have been studied. It was concluded that the pyramid growth can be divided into two regimes separated by the adsorption kinetics of the {1101} surfaces of the pyramids. In the adsorption regime, the pyramids grow simultaneously in the <1101> and [0001] -directions. In the zero-adsorption regime the pyramids grow only in the [0001] direction. Thus the pyramid growth ceases when the (0001) facet growth has been terminated. Large arrays consisting of highly uniform pyramids with apex radii of 3 nm or less were achieved in the zeroadsorption regime. The growth-regime type was concluded to have a large impact on the uniformity degradation of the pyramids, and their optical properties. The impacts of threading dislocations which enter the pyramid from underneath are also discussed.

Keywords
A3. Hot wall epitaxy A3. Metalorganic vapor phase epitaxy A3. Selective epitaxy B1. Nitrides
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-79317 (URN)10.1016/j.jcrysgro.2012.11.014 (DOI)000313205400047 ()
Available from: 2012-07-10 Created: 2012-07-10 Last updated: 2017-12-07Bibliographically approved
Holtz, P. O., Hsu, C.-W., Lundskog, A., Karlsson, K. F., Forsberg, U. & Janzén, E. (2013). Deterministic Single InGaN Quantum Dots grown on GaN Micro-Pyramid Arrays. Paper presented at 2012 International Conference on Nano Materials and Electric Devices (ICNMED 2012), 19-20 December 2012, Hong Kong. Advanced Materials Research, 646, 34-37
Open this publication in new window or tab >>Deterministic Single InGaN Quantum Dots grown on GaN Micro-Pyramid Arrays
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2013 (English)In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 646, p. 34-37Article in journal (Other academic) Published
Abstract [en]

InGaN quantum dots (QDs) formed on top of GaN pyramids have been fabricated by means of selective area growth employing hot wall MOCVD. Upon regrowth of a patterned substrate, the growth will solely occur in the holes, which evolve into epitaxially grown wurtzite based pyramids. These pyramids are subsequently overgrown by a thin optically active InGaN well. The QDs are preferably nucleating at the apices of the pyramids as evidenced by the transmission electron microscopy (TEM). The emission from these QDs have been monitored by means of microphotoluminescence (µPL), in which single emission lines have been detected with a sub-meV line width. The µPL measurements undoubtedly reveal that the QDs are located in the apexes of the pyramids, since the sharp emission peaks can only be monitored as the excitation laser is focused on the apices in the µPL. It is also demonstrated that the emission energy can be changed in a controlled way by altering the growth conditions, like the growth temperature and/or composition, for the InGaN layers. The tip of the GaN pyramid is on the nm scale and can be made sharp or slightly truncated. TEM analysis combined with µPL results strongly indicate that the Stranski-Krastanow growth modepreferably is taking place at the microscopic c-plane truncation of the GaN pyramid. Single emission lines with a high degree of polarization is a common feature observed for individual QDs. This emission remains unchanged with increasing the excitation power and sample temperature. An in-plane elongated QD forming a shallow potential with an equal number of electrons and holes is proposed to explain the observed characteristics of merely a single exciton emission with a high degree of polarization.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2013
Keywords
Quantum dots, Pyramid, Exciton, Photoluminescence
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-111502 (URN)10.4028/www.scientific.net/AMR.646.34 (DOI)
Conference
2012 International Conference on Nano Materials and Electric Devices (ICNMED 2012), 19-20 December 2012, Hong Kong
Available from: 2014-10-20 Created: 2014-10-20 Last updated: 2017-12-05Bibliographically approved
Hsu, C.-W., Moskalenko, E., Eriksson, M., Lundskog, A., Karlsson, F. K., Forsberg, U., . . . Holtz, P.-O. (2013). The charged exciton in an InGaN quantum dot on a GaN pyramid. Applied Physics Letters, 103(1)
Open this publication in new window or tab >>The charged exciton in an InGaN quantum dot on a GaN pyramid
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2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 1Article in journal (Refereed) Published
Abstract [en]

The emission of a charged exciton in an InGaN quantum dot (QD) on top of a GaN pyramid is identified experimentally. The intensity of the charged exciton exhibits the expected competition with that of the single exciton, as observed in temperature-dependent micro-photoluminescence measurements, performed with different excitation energies. The non-zero charge state of this complex is further supported by time resolved micro-photoluminescence measurements, which excludes neutral alternatives of biexciton. The potential fluctuations in the vicinity of the QD that localizes the charge carriers are proposed to be responsible for the unequal supply of electrons and holes into the QD.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-95961 (URN)10.1063/1.4812984 (DOI)000321497200036 ()
Note

Funding Agencies|NANO-N consortium||Swedish Foundation for Strategic Research (SSF)||

Available from: 2013-08-19 Created: 2013-08-12 Last updated: 2017-12-06
Lundskog, A. (2012). Controlled growth of hexagonal GaN pyramids and InGaN QDs. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Controlled growth of hexagonal GaN pyramids and InGaN QDs
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gallium-nitride (GaN) and its related alloys are direct band gap semiconductors, with a wide variety of applications. The white light emitting diode (LED) is of particular importance as it is expected to replace energy inefficient light bulb and hazardous incandescent lamps used today. However, today’s planar hetero epitaxial grown LEDs  structures contain an unavoidable number of dislocations, which serves as non-radiative recombination centers. The dislocations harm the luminous efficiency of the LEDs and generate additional heat. Pseudomorphically grown quantum dots (QDs) are expected to be dislocation free thus the injected carriers captured by the QDs essentially recombine radiatively since the dislocations remain outside the QD. Furthermore the continuous character of the density of states in bulk materials is redistributed when the size of the dot is reduced within the Bohr radius of the material. Fully discret energy levels are eventually reached, which offers additional control of the optical properties. The Coulomb interaction between the confined carriers also has influence on the emission energy of the recombining carriers, which opens up the possibility of manufacturing novel light sources such as the single photon emitter. Single photon emitters are essential building blocks for quantum cryptography and teleportation applications.

The main contribution of the present work is the investigation of growth and characterization of sitecontrolled indium-gallium-nitride QDs embedded in GaN matrixes. The goal has been to demonstrate the ability to grow site-controlled InGaN QDs at the apex of hexagonal GaN pyramids in a controlled way using hot-wall metal organic chemical vapor deposition (MOCVD). Strong emphasis was set on the controlled growth of InGaN QDs. For example the growth of a single InGaN QD located at the apex of hexagonal GaN pyramids with tunable emission energy, the QD emission energy impact on the mask design, and a novel approach for the growth of InGaN QDs with polarization deterministic photon vectors were reported. The thesis is mainly based on experimental investigations by secondary electron microscope (SEM), micro photo-luminescence (μPL), and scanning transition electron microscopy ((S)TEM) characterization techniques.

In Paper 1 and 2, we present the growth of symmetric GaN hexagonal pyramids which served as template for the InGaN QDs grown. In paper 1, it was concluded that the selective area growth (SAG) of hexagonal GaN pyramids by MOCVD through symmetric openings in a SIN mask roughly can be divided in two regimes where either the pyramid expands laterally or not. When the pyramid expanded laterally the resulting pyramid apex became (0001) truncated even after prolonged growth times. Lateral expansion also had major impact on the pyramid-to-pyramid uniformity. In paper 2, the MOCVD process parameter impact on the pyramid morphology was investigated. By tuning the growth temperature, the ammonia, and TMGa-flows a self limited pyramid structure with only {1101} facets visible was achieved. The presence of the {1101}, {1102}, and {1100} facets were discussed from surface stabilities under various growth conditions.

Paper 3 and 4 concern the growth of InGaN QDs located at the apex of hexagonal GaN pyramids. In paper 3, we showed that it is possible to grow single QDs at the apex of hexagonal pyramids with emission line widths in the Ångström range. The QD emission energy was demonstrated to be tunable by the growth temperature. Basic spectroscopy data is also presented on a single QD in paper 3. In paper 4, the growth mechanisms of the QDs presented in paper 3 are presented. We concluded that (0001) truncated GaN pyramid base initiated the growth of InGaN QDs which gave rise to narrow luminescence peaks in the μPL spectra.

In paper 5, the QD emission energy impact of the mask design was investigated. To our big surprise the QD emission energy increased with increasing pyramid pitch while the emission energy of the InGaN quantum wells located on the {1101} facets of the pyramids energetically shifted towards lower energies. The energy shift at the apex was found to be associated with the (0001) truncation diameter of the underlying GaN pyramid since no energy shift was observed for (0001) truncated pyramids with truncation diameters larger than 100 nm.

In paper 6, the symmetry of the GaN pyramids were intentionally broken through the introduction of elongated openings in the SiN mask (symmetric openings was used in the previous five papers). The emission polarization vectors of the subsequently grown InGaN QDs were deterministically linked to the in-plane orientation of the pyramid it was nucleated upon, implying that the QDs inhibit an inplane anisotropy directly inherited from the pyramid template.

Finally, paper 7 describes a hot-wall MOCVD reactor improvement by inserting insulating pyrolytic boron-nitride (PBN) stripes in the growth chamber. By doing this, we have completely eliminated the arcing problem between different susceptor parts. As a consequence, the reactor gained run-to-run reproducibility. Growth of state of the art advanced aluminum-gallium-nitride high electron mobility transistor structures on a 100 mm wafer with electron mobility above 2000 Vs/cm2 was demonstrated by the improved process.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. p. 53
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1464
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-79326 (URN)978-91-7519-842-2 (ISBN)
Public defence
2012-09-20, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-07-10 Created: 2012-07-10 Last updated: 2012-12-04Bibliographically approved
Lundskog, A., Palisaitis, J., Hsu, C.-W., Eriksson, M., Karlsson, F., Hultman, L., . . . Janzén, E. (2012). InGaN quantum dot formation mechanism on hexagonal GaN/InGaN/GaN pyramids. Nanotechnology, 23(30), 305708
Open this publication in new window or tab >>InGaN quantum dot formation mechanism on hexagonal GaN/InGaN/GaN pyramids
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2012 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 30, p. 305708-Article in journal (Refereed) Published
Abstract [en]

Growing InGaN quantum dots (QDs) at the apex of hexagonal GaN pyramids is an elegant approach to achieve a deterministic positioning of QDs. Despite similar synthesis procedures by metal–organic chemical vapor deposition, the optical properties of the QDs reported in the literature vary drastically. The QDs tend to exhibit either narrow or broad emission lines in the micro-photoluminescence spectra. By coupled microstructural and optical investigations, the QDs giving rise to narrow emission lines were concluded to nucleate in association with a (0001) facet at the apex of the GaN pyramid.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2012
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-79321 (URN)10.1088/0957-4484/23/30/305708 (DOI)000306333500030 ()
Available from: 2012-07-10 Created: 2012-07-10 Last updated: 2017-12-07Bibliographically approved
Lundskog, A., Forsberg, U., Holtz, P.-O. & Janzén, E. (2012). Morphology control of hot-wall MOCVD selective area -grown hexagonal GaN pyramids. Crystal Growth & Design, 12(11), 5491-5496
Open this publication in new window or tab >>Morphology control of hot-wall MOCVD selective area -grown hexagonal GaN pyramids
2012 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 12, no 11, p. 5491-5496Article in journal (Refereed) Published
Abstract [en]

Morphological variations of gallium polar (0001) oriented hexagonal GaN pyramids grown by hotwall metal organic chemical vapor deposition under various growth conditions are investigated. The stability of the semi-polar {1102} and non-polar {1100} facets are particularly discussed. The presence of the {1102} facets near the apex of the pyramid was found to be controllable by tuning the absolute flow rate of ammonia during the growth. Vertical non-polar {1100} facets appeared ingallium rich-conditions which automatically were created when the growth time was prolonged beyond pyramid completion. The result was attributed to a gallium passivation of the {1100} surface.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-79320 (URN)10.1021/cg301064p (DOI)000311240100041 ()
Available from: 2012-07-10 Created: 2012-07-10 Last updated: 2017-12-07Bibliographically approved
Holtz, P.-O., Hsu, C.-W., Larsson, L. A., Karlsson, K. F., Dufåker, D., Lundskog, A., . . . Pelucchi, E. (2012). Optical characterization of individual quantum dots. Physica. B, Condensed matter, 407(10), 1472-1475
Open this publication in new window or tab >>Optical characterization of individual quantum dots
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2012 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 407, no 10, p. 1472-1475Article in journal (Refereed) Published
Abstract [en]

Optical characterization of single quantum dots (QDs) by means of micro-photoluminescence (mu PL) will be reviewed. Both QDs formed in the Stranski-Krastanov mode as well as dots in the apex of pyramidal structures will be presented. For InGaAs/GaAs dots, several excitonic features with different charge states will be demonstrated. By varying the magnitude of an external electric or magnetic field and/or the temperature, it has been demonstrated that the transportation of carriers is affected and accordingly the charge state of a single QD can be tuned. In addition, we have shown that the charge state of the QD can be controlled also by pure optical means, i.e. by altering the photo excitation conditions. Based on the experience of the developed InAs/GaAs QD system, similar methods have been applied on the InGaN/GaN QD system. less thanbrgreater than less thanbrgreater thanThe coupling of LO phonons to the QD emission is experimentally examined for both charged and neutral excitons in single InGaAs/GaAs QDs in the apex of pyramidal structures. It is shown that the positively charged exciton exhibits a significantly weaker LO phonon coupling in the mu PL spectra than the neutral and negatively charged species, a fact, which is in consistency with model simulations performed.

Place, publisher, year, edition, pages
Elsevier, 2012
Keywords
Quantum dots, Pyramid, Exciton, Photoluminescence
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-77523 (URN)10.1016/j.physb.2011.09.064 (DOI)000303149600005 ()
Note

Funding Agencies|Swedish Research Council (VR)||Swedish Foundation for Strategic Research (SSF)||Nano-N consortium||Science Foundation Ireland|05/IN.1/I25|Knut and Alice Wallenberg Foundation||INSPIRE||

Available from: 2012-05-28 Created: 2012-05-22 Last updated: 2017-12-07
Hsu, H.-C., Hsu, G.-M., Lai, Y.-s., Chuan Feng, Z., Tseng, S.-Y., Lundskog, A., . . . Chen, L.-C. (2012). Polarized and diameter-dependent Raman scattering from individual aluminum nitride nanowires: The antenna and cavity effects. Applied Physics Letters, 101(12), 121902
Open this publication in new window or tab >>Polarized and diameter-dependent Raman scattering from individual aluminum nitride nanowires: The antenna and cavity effects
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2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 12, p. 121902-Article in journal (Refereed) Published
Abstract [en]

Raman scattering of individual aluminum nitride (AlN) nanowires is investigated systematically. The axial direction of single nanowire can be rapidly verified by polarized Raman scattering. The angular dependencies of E-2(high) mode show strongly anisotropic behavior in smaller nanowires, which results from optical antenna effect. Raman enhancement (RE) per unit volume of E-2(high) increases with decreasing diameter of nanowires. Compared to the thin film, similar to 200-fold increase of RE is observed in AlN nanowires having diameter less than 50 nm, which is far beyond the quantum confinement regime. Such a large RE can be attributed to the effects of resonant cavity and stimulated Raman scattering.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85091 (URN)10.1063/1.4753798 (DOI)000309425700020 ()
Note

Funding Agencies|Ministry of Education||National Science Council||Academia Sinica in Taiwan||US AFOSR-AOARD||

Available from: 2012-11-02 Created: 2012-11-02 Last updated: 2017-12-07
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