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Magnetotransport study of valley-polarized electrons in synthetic diamond
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Harwell Oxford, Element Innovat 6, Fermi Ave, Didcot OX11 0QR, Oxon, England..
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2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 3, article id 035408Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

We demonstrate that the highly stable valley-polarized electron states in ultrapure single-crystalline diamond allow for investigation of charge transport, magnetoresistivity, and determination of the dominant scattering mechanism. The Hall effect gives rise to nonisotropic contributions in the mobility tensor that were measured at a temperature of 70 K in a time-of-flight setup with an added magnetic field. The observations of the magnetotransport of valley-polarized electrons in diamond are compared with both Monte Carlo simulations and an analytical model based on the Boltzmann transport equation. We establish that acoustic phonon scattering is the dominant electron scattering mechanism at 70 K for each of the valley polarizations in the investigated samples.

Place, publisher, year, edition, pages
2016. Vol. 94, no 3, article id 035408
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-300466DOI: 10.1103/PhysRevB.94.035408ISI: 000379717700005OAI: oai:DiVA.org:uu-300466DiVA, id: diva2:951449
Funder
Swedish Research Council, 621-2014-6026ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 15-288Swedish National Infrastructure for Computing (SNIC), SNIC2014-3-65Available from: 2016-08-09 Created: 2016-08-09 Last updated: 2018-04-15Bibliographically approved
In thesis
1. Diamond Devices Based on Valley Polarization
Open this publication in new window or tab >>Diamond Devices Based on Valley Polarization
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a wide bandgap semiconductor with extreme properties such as high thermal conductivity, high breakdown field, high carrier mobilities and chemical inertness. These properties together with the possibility to synthesize high purity Single-Crystalline (SC) diamond by Chemical Vapor Deposition (CVD), make it a very interesting material and a candidate for use in power electronics and in hazardous environments. The low impurity concentration achieved when fabricating diamond by CVD allows for a detailed study of the intrinsic electronic properties.

Diamond has six equivalent conduction band valleys oriented along the {100} axes with a uniquely low scattering rate between them. At low temperatures, the intervalley phonon scattering rate in diamond becomes negligible, which leads to a stable valley polarization state. We have observed non-equilibrium valley populations (valley-polarized electron ensembles), which in turn have been found to result in a Negative Differential Mobility (NDM).

NDM is commonly only observed in direct bandgap materials such as GaAs, InP and CdTe but our group has also observed NDM in diamond at a temperature range of 100 to 150 K. The occurrence of this phenomenon can be explained by electron repopulation, which is the scattering of electrons between different valleys. If NDM is pronounced enough, electric current instabilities build up and give rise to oscillations. By exploiting this phenomenon, a Transferred-Electron Oscillator (TEO) can be constructed for microwave applications.

Further investigations into the valley-polarized electrons seen in diamond could bring it forward as an alternative material for use in electronic devices. This use, called valleytronics, is similar to spintronics but instead of using the electron spin, the polarization in the conduction band valleys is used to transfer information. Digital electronic circuits use the presence or absence of charge to encode information which relies on a rapid redistribution of mobile charge carriers. This requires energy which results in losses and thus sets a theoretical limit to the maximum switching frequency. This is one of the main issues of electronic devices and can be mitigated by using alternative technologies such as spintronics or valleytronics.

In order to get a better understanding of the electron valley repopulation effects, the focus of this doctoral thesis is the study of electron charge transport in SC-CVD diamond at low temperatures. The thesis also aims at using valley-polarized states as a foundation for the creation of electronic devices such as TEOs or valley-transistors, out of diamond.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 88
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1670
Keywords
CVD diamond, valleytronics, Negative Differential Mobility, NDM, electron polarization, Time-of-Flight, magnetotransport, carrier transport, drift velocity, valley-transistor, Transferred-Electron Oscillator, TEO, TED, Gunn diode
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-348551 (URN)978-91-513-0335-2 (ISBN)
Public defence
2018-06-08, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Supervisors
Available from: 2018-05-15 Created: 2018-04-15 Last updated: 2018-05-15Bibliographically approved

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Suntornwipat, NattakarnGabrysch, MarkusMajdi, SamanIsberg, Jan

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