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Magneto-optical studies of dilute nitrides and II-VI diluted magnetic semiconductor quantum structures
Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis work aims at a better understanding of magneto-optical properties of dilute nitrides and II-VI diluted magnetic semiconductor quantum structures. The thesis is divided into two parts. The first part gives an introduction of the research fields, together with a brief summary of the scientific results included in the thesis. The second part consists of seven scientific articles that present the main findings of the thesis work. Below is a short summary of the thesis.

Dilute nitrides have been of great scientific interest since their development in the early 1990s, because of their unusual fundamental physical properties as well as their potential for device applications. Incorporation of a small amount of N in conventional Ga(In)As or Ga(In)P semiconductors leads to dramatic modifications in both electronic and optical properties of the materials. This makes the dilute nitrides ideally suited for novel optoelectronic devices such as light emitting devices for fiber-optic communications, highly efficient visible light emitting devices, multi-junction solar cells, etc. In addition, diluted nitrides open a window for combining Si-based electronics with III-V compounds-based optoelectronics on Si wafers, promising for novel optoelectronic integrated circuits. Full exploration and optimization of this new material system in device applications requires a detailed understanding of their physical properties.

Papers I and II report detailed studies of effects of post-growth rapid thermal annealing (RTA) and growth conditions (i.e. presence of N ions, N2 flow, growth temperature and In alloying) on the formation of grown-in defects in Ga(In)NP. High N2 flow and bombardment of impinging N ions on grown sample surface is found to facilitate formation of defects, such as Ga interstitial (Gai) related defects, revealed by optically detected magnetic resonance (ODMR). These defects act as competing carrier recombination centers, which efficiently decrease photoluminescence (PL) intensity. Incorporation of a small amount of In (e.g. 5.1%) in GaNP seems to play a minor role in the formation of the defects. In GaInNP with 45% of In, on the other hand, the defects were found to be abundant. Effect of RTA on the defects is found to depend on initial configurations of Gai related defects formed during the growth.

In Paper III, the first identification of an interfacial defect at a heterojunction between two semiconductors (i.e. GaP/GaNP) is presented. The interface nature of the defect is clearly manifested by the observation of ODMR lines originating from only two out of four equivalent <111> orientations. Based on its resolved hyperfine interaction between an unpaired electronic spin (S=1/2) and a nuclear spin (I=1/2), the defect is concluded to involve a P atom at its core with a defect/impurity partner along a <111> direction. Defect formation is shown to be facilitated by N ion bombardment.

In Paper IV, the effects of post-growth hydrogenation on the efficiency of the nonradiative (NR) recombination centers in GaNP are studied. Based on the ODMR results, incorporation of H is found to increase the efficiency of the NR recombination via defects such as Ga interstitials.

In Paper V, we report on our results from a systematic study of layered structures containing an InGaNAs/GaAs quantum well, by the optically detected cyclotron resonance (ODCR) technique. By monitoring PL emissions from various layers, the predominant ODCR peak is shown to be related to electrons in GaAs/AlAs superlattices. This demonstrates the role of the SL as an escape route for the carriers confined within the InGaNAs/GaAs single quantum well.

The last two papers are within a relatively new field of spintronics which utilizes not only the charge (as in conventional electronics) but also the quantum mechanical property of spin of the electron. Spintronics offers a pathway towards integration of information storage, processing and communications into a single technology. Spintronics also promises advantages over conventional charge-based electronics since spin can be manipulated on a much shorter time scale and at lower cost of energy. Success of semiconductor-based spintronics relies on our ability to inject spin polarized electrons or holes into semiconductors, spin transport with minimum loss and reliable spin detection.

In Papers VI and VII, we study the efficiency and mechanism for carrier/exciton and spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe quantum well into nonmagnetic CdSe quantum dots (QD’s) by means of spin-polarized magneto PL combined with tunable laser spectroscopy. By means of a detailed rate equation analysis presented in Paper VI, the injected spin polarization is deduced to be about 32%, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process. In Paper VII, we present evidence that energy transfer is the dominant mechanism for carrier/exciton injection from the DMS to the QD’s. This is based on the fact that carrier/exciton injection efficiency is independent of the width of the ZnSe tunneling barrier inserted between the DMS and QD’s. In sharp contrast, spin injection efficiency is found to be largely suppressed in the structures with wide barriers, pointing towards increasing spin loss.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 47 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1316
Keyword [en]
Dilute nitrides, DMS, defect, ODMR, optically detected magnetic resonance, spin injection, PLE, photoluminescence excitation, post-growth hydrogenation, heterojunction
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-54695ISBN: 978-91-7393-387-2 (print)OAI: oai:DiVA.org:liu-54695DiVA: diva2:308372
Public defence
2010-05-07, Hörsalen Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 14:15 (English)
Opponent
Supervisors
Available from: 2010-04-09 Created: 2010-04-06 Last updated: 2013-10-02Bibliographically approved
List of papers
1. Effect of nitrogen ion bombardment on defect formation and luminescence efficiency of GaNP epilayers grown by molecular-beam epitaxy
Open this publication in new window or tab >>Effect of nitrogen ion bombardment on defect formation and luminescence efficiency of GaNP epilayers grown by molecular-beam epitaxy
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2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 10, 101904- p.Article in journal (Refereed) Published
Abstract [en]

Radiative efficiency of GaNP epilayers grown on GaP substrates by solid-source molecular beam epitaxy is significantly improved by reduced nitrogen ion bombardment during the growth. Based on the results of temperature-dependent photoluminescence (PL) and optically detected magnetic resonance studies (ODMR), the observed improvements are attributed to reduced formation of defects, such as a Ga interstitial related defect and an unidentified defect revealed by ODMR. We demonstrate that these defects act as competing recombination centers, which promote thermal quenching of the PL intensity and result in a substantial (34×) decrease in room-temperature PL intensity. © 2006 American Institute of Physics.

National Category
Natural Sciences Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-36496 (URN)10.1063/1.2182028 (DOI)31453 (Local ID)31453 (Archive number)31453 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
2. Formation of grown-in defects in molecular beam epitaxial Ga(In)NP: effects of growth conditions and post-growth treatments
Open this publication in new window or tab >>Formation of grown-in defects in molecular beam epitaxial Ga(In)NP: effects of growth conditions and post-growth treatments
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2008 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, 063519- p.Article in journal (Refereed) Published
Abstract [en]

Effects of growth conditions and post-growth treatments, such as presence of N ions, N2 flow, growth temperature, In alloying, and postgrowth rapid thermal annealing (RTA), on formation of grown-in defects in Ga(In)NP prepared by molecular beam epitaxy are studied in detail by the optically detected magnetic resonance (ODMR) technique. Several common residual defects, such as two Ga-interstitial defects (i.e., Gai-A and Gai-B) and two unidentified defects with a g factor around 2 (denoted by S1 and S2), are closely monitored. Bombardment of impinging N ions on grown sample surface is found to facilitate formation of these defects. Higher N2 flow is shown to have an even more profound effect than a higher number of ions in introducing these defects. Incorporation of a small amount of In (e.g., 5.1%) in GaNP seems to play a minor role in the formation of the defects. In GaInNP with 45% of In; however, the defects were found to be abundant. Effect of RTA on the defects is found to depend on initial configurations of Gai-related defects formed during the growth. In the alloys where the Gai-A and Gai-B defects are absent in the as-grown samples (i.e., GaNP grown at a low temperature of 460 °C), the concentrations of the two Gai defects are found to increase after postgrowth RTA. This indicates that the defects originally introduced in the as-grown alloys have been transformed into the more thermally stable Gai-A and Gai-B during RTA. On the other hand, when the Gai-A and Gai-B are readily abundant (e.g., at higher growth temperatures (>=500 °C), RTA leads to a slight reduction of the Gai-A and Gai-B ODMR signals. The S2 defect is also shown to be thermally stable upon the RTA treatment.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44346 (URN)10.1063/1.2895379 (DOI)76370 (Local ID)76370 (Archive number)76370 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
3. Evidence for a phosphorus-related interfacial defect complex at a GaP/GaNP heterojunction
Open this publication in new window or tab >>Evidence for a phosphorus-related interfacial defect complex at a GaP/GaNP heterojunction
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, 115334- p.Article in journal (Refereed) Published
Abstract [en]

Optically detected magnetic resonance (ODMR) studies of molecular beam epitaxial GaNP/GaP structures reveal presence of a P-related complex defect, evident from its resolved hyperfine interaction between an unpaired electronic spin (S=1/2) and a nuclear spin (I = ½) of a 31P atom. The principal axis of the defect is concluded to be along a <111> crystallographic direction from angular dependence of the ODMR spectrum, restricting the P atom (either a PGa antisite or a Pi interstitial) and its partner in the complex defect to be oriented along this direction. The principal values of the electronic g-tensor and hyperfine interaction tensor are determined as: g=2.013, g=2.002, and A=130´10-4 cm-1, A=330´10-4 cm-1, respectively. The interface nature of the defect is clearly manifested by the absence of the ODMR lines originating from two out of four equivalent <111> orientations. Defect formation is shown to be facilitated by nitrogen ion bombardment under non-equilibrium growth conditions and the defect is thermally stable upon post-growth thermal annealing.

Place, publisher, year, edition, pages
The American Physical Society, 2010
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-54721 (URN)10.1103/PhysRevB.81.115334 (DOI)000276248800111 ()
Note

Original Publication: Daniel Dagnelund, I. P Vorona, L. S. Vlasenko, X. J. Wang, A. Utsumi, Y. Furukawa, A. Wakahara, H. Yonezu, I. A. Buyanova and W. M. Chen, Evidence for a phosphorus-related interfacial defect complex at a GaP/GaNP heterojunction, 2010, Physical Review B Condensed Matter, (81), , 115334. http://dx.doi.org/10.1103/PhysRevB.81.115334 Copyright: American Physical Society http://www.aps.org/

Available from: 2010-04-06 Created: 2010-04-06 Last updated: 2017-12-12
4. Activation of defects in GaNP by post-growth hydrogen treatment
Open this publication in new window or tab >>Activation of defects in GaNP by post-growth hydrogen treatment
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Effect of post-growth hydrogen treatment on defects and their role in carrier recombination in molecular beam epitaxial GaNP alloys is examined by means of photoluminescence and optically detected magnetic resonance. We present direct experimental evidence for effective activation of several different defects in carrier recombination by the hydrogen treatment. Among them, two defect complexes are identified to contain a Ga interstitial (Gai). None of the activated Gai complexes was previously observed in GaNP. Possible mechanisms for the hydrogen-induced defect activation are discussed.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-54792 (URN)
Available from: 2010-04-09 Created: 2010-04-09 Last updated: 2013-10-02Bibliographically approved
5. Optically detected cyclotron resonance studies of InxGa1-xNyAs1-y/GaAs quantum wells sandwiched between type-II AlAs/GaAs superlattices.
Open this publication in new window or tab >>Optically detected cyclotron resonance studies of InxGa1-xNyAs1-y/GaAs quantum wells sandwiched between type-II AlAs/GaAs superlattices.
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2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, 073705- p.Article in journal (Refereed) Published
Abstract [en]

  We report on our results from a systematic study of layered structures containing an InGaNAs/GaAs single quantum well (SQW) enclosed between staggered type II AlAs/GaAs superlattices (SL), by the photoluminescence (PL) and optically detected cyclotron resonance (ODCR) techniques. Besides the ODCR signal known to originate from electrons in GaAs, the predominant ODCR peak is shown to be related to carriers with a two-dimensional character and a cyclotron resonance effective mass of m*[approximate](0.51-0.56)m0. The responsible carriers are ascribed to electrons on the ellipsoidal equienergy surface at the AlAs X point of the Brillouin zone within the SL, based on results from angular and spectral dependences of the ODCR signal. No ODCR signal related to the InGaNAs SQW was detected, presumably due to low carrier mobility despite the high optical quality. Multiple absorption of photons with energy below the band gap energy of the SL and the GaAs barriers was observed, which bears implication on the efficiency of light-emitting devices based on these structures.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-38833 (URN)10.1063/1.2714776 (DOI)45826 (Local ID)45826 (Archive number)45826 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
6. Efficiency of optical spin injection and spin loss from a diluted magnetic semiconductor ZnMnSe to CdSe nonmagnetic quantum dots
Open this publication in new window or tab >>Efficiency of optical spin injection and spin loss from a diluted magnetic semiconductor ZnMnSe to CdSe nonmagnetic quantum dots
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2008 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 77, no 3, 035437- p.Article in journal (Refereed) Published
Abstract [en]

Magneto-optical spectroscopy in combination with tunable laser spectroscopy is employed to study optical spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe into nonmagnetic CdSe quantum dots (QDs). Observation of a DMS feature in the excitation spectra of the QD photoluminescence polarization provides clear evidence for optical spin-injection from the DMS to the QDs. By means of a rate equation analysis, the injected spin polarization is deduced to be about 32% at 5 T, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process including crossing the heterointerfaces and energy relaxation within the QDs. © 2008 The American Physical Society.

National Category
Natural Sciences Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-41901 (URN)10.1103/PhysRevB.77.035437 (DOI)59336 (Local ID)59336 (Archive number)59336 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
7. Carrier and Spin Injection from ZnMnSe to CdSe Quantum Dots
Open this publication in new window or tab >>Carrier and Spin Injection from ZnMnSe to CdSe Quantum Dots
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Optical carrier/exction and spin injection processes from a ZnMnSe dilute magnetic semiconductor (DMS) to CdSe quantum dots (QD’s) are studied in detail by means of spinpolarized magneto- photoluminescence (PL) and PL excitation spectroscopies. Efficiency of carrier/exciton transfer is found to be practically independent of width (Lb) of a ZnSe barrier layer inserted between the DMS and QD’s. This is tentatively explained in terms of photonexchange energy transfer. In sharp contrast, spin injection efficiency is found to be largely suppressed in the structures with large Lb, pointing towards increasing spin loss.

Keyword
Spin injection, carrier injection, quantum dots, CdSe, ZnMnSe.
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-54793 (URN)
Available from: 2010-04-09 Created: 2010-04-09 Last updated: 2013-10-02

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