liu.seSearch for publications in DiVA
Change search
ReferencesLink to record
Permanent link

Direct link
Optical properties and Zeeman spectroscopy of niobium in silicon carbide
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
Show others and affiliations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The optical signature of niobium in the low-temperature photoluminescence spectra of three common polytypes of SiC (4H, 6H and 15R) is observed  and confirms the previously suggested concept that Nb occupies preferably the Si – C divacancy at hexagonal site. Using this concept we propose a model considering Nb-bound exciton, the recombination of which is responsible for the observed luminescence. The exciton energy is estimated using firstprinciples calculation and the result is in very good agreement with the experimentally observed photon energy in 4H SiC at low temperature. The appearance of six Nb-related lines in the spectra of the hexagonal 4H and 6H polytypes at higher temperatures is explained on the ground of the proposed model and the concept that the Nb center can exist in both C1h and C3v symmetries. The Zeeman splitting of the photoluminescence lines is also recorded in two different experimental geometries and the results are compared with theory based on phenomenological Hamiltonians. Our results show that Nb occupying the divacancy at hexagonal site in the studied SiC polytypes behaves like a deep acceptor.

National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-117972OAI: oai:DiVA.org:liu-117972DiVA: diva2:812558
Available from: 2015-05-19 Created: 2015-05-19 Last updated: 2015-05-19Bibliographically approved
In thesis
1. Optical Characterization of Deep Level Defects in SiC
Open this publication in new window or tab >>Optical Characterization of Deep Level Defects in SiC
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon Carbide (SiC) has long been considered a promising semiconductor material for high power devices, and has also recently found to be one of the emergent materials for quantum computing. Important for these applications are both the quality and purity of the crystal. In order to be able to engineer components (be it power devices or components for quantum computing), it is necessary to study and understand the behavior of various defects in the crystal.

Deep level defects can greatly influence the semiconducting properties, since they can act as recombination centers by interacting with both holes from the valence band and electrons from the conduction band. Because of this, they may be used to control the charge carrier life time. Besides influencing the electric properties of the materials, deep level defects are also of interest in the field of quantum computing. In this application, the deep level defects can be used as basic units for quantum information – so called qubits.

Deep level defects may also be classified based on their origin, i.e. impurity or intrinsic. An impurity consists of one or more foreign atoms, which means neither carbon nor silicon in the case of SiC. Impurities can be incorporated in the crystal during growth, or through implantation or diffusion. A defect is intrinsic when it does not involve foreign atoms, but instead imperfections in the perfect crystal structure, for example a vacancy, an anti-site or a combinations of these. Intrinsic defects can be created during growth or artificially, using for example electron irradiation.

This thesis is focused on characterization of several deep level defects in SiC using different optical techniques. The optical transitions investigated are in the near-infrared region.

Paper 1 focuses on the possibility to control the concentration of intrinsic defects through the cooling down procedure after high temperature annealing. The temperature of 2300°C is close to the bulk crystal growth temperature. It is shown that it is possible to control the concentration of the silicon vacancy (VSi) and UD-2 (later identified as the divacancy (VCVSi)) by the cooling  sequence. Both these defects have later been shown to be promising candidates as qubits and single photon emitters.

Paper 2 gives insight into the electronic structure of the unidentified deep level defect UD-4, which is believed to be of intrinsic origin. The defect is investigated in the polytypes 4H-, 6H-, and 15R-SiC, and the number of optical centers associated with UD-4 follows neither the number of inequivalent sites nor the possible configurations for pair-defects. There are two optical centers in 4H- and 6H-SiC, and three optical centers in 15R-SiC.

Paper 3 investigates several transition metals incorporated in SiC and the formation energies for different possible configurations. This is of importance since several impurity related deep level defects cannot be explained as purely substitutional defects, based on the fact that the number of optical centers does not follow the number of inequivalent sites. This is investigated in detail, and explained using an asymmetric split vacancy (ASV) model. It was found that the formation energy for some transition metals in ASV are lower than the transition metal in a substitutional configuration. Further on, it was shown that the formation energies for transition metals in ASV configurations depend strongly on what kinds of inequivalent sites the ASV can be described by and the lowest formation energy that is found for transition metals in ASV occupying two hexagonal sites.

In paper 4, the optical identification and electronic configuration of the commonly observed deep level defect tungsten (formerly known as UD-1) are reported. The electronic levels involved in the optical transitions of tungsten are deduced and described using group theory techniques.

Paper 5 shows that the above mentioned ASV model can be used to describe the properties of niobium in SiC. In the paper, the optical identification and properties are analyzed and investigated experimentally using photoluminescence, photoluminescence excitation spectroscopy and Zeeman spectroscopy.

In paper 6 the identification of molybdenum (formerly known as I-1) is reported including its electronic configuration. Molybdenum can be well described using the ASV model, and in this paper its local vibrational modes are also investigated in detail. It is shown that using the polarization dependence of local vibration replicas and a simplified defect molecule model, the estimated position of Mo in the ASV is in agreement with the theoretically predicted position reported in paper 3. The usefulness for molybdenum in SiC as a qubit is also investigated.

In paper 7, two different intrinsic nearest pair-neighbor defects are reported: UD-2 (VCVSi) and UD-0 (tentatively assigned as the VCCSi). Their optical properties are analyzed together with their creation and annihilation properties.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 42 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1674
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-117978 (URN)978-91-7519-059-4 (print) (ISBN)
Public defence
2015-06-03, Nobel (BL32), Fysikhuset, Campus Valla, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2015-05-19 Created: 2015-05-19 Last updated: 2015-05-19Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Gällström, AndreasMagnusson, BjörnLeone, StefanoKordina, OlofSon, Nguyen T.Ivády, ViktorAbrikosov, Igor A.Janzén, ErikIvanov, Ivan G.
By organisation
Semiconductor MaterialsThe Institute of TechnologyTheoretical Physics
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 106 hits
ReferencesLink to record
Permanent link

Direct link