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Low temperature conduction-band transport in 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. Argonne Natl Lab, Ctr Nanoscale Mat, Argonne, IL 60439 USA..
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
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2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 16, article id 162106Article in journal (Refereed) Published
Abstract [en]

By performing Time-of-Flight measurements on high-purity single-crystalline chemical vapor deposited diamond, we are able to extract the electron drift velocity of valley-polarized electrons in the low-injection regime. The aim of this study is to improve the understanding of the mechanisms involved in the conduction-band transport of valley-polarized electrons. The measurements were carried out within the temperature range of 10-80 K, and the experimental results are systematically compared with Monte Carlo charge transport simulations. We observe a rapid enhancement of the electron mobility with decreasing temperature, which reveals that inelastic effects in electron-phonon scattering become important below similar to 40 K. In addition, we obtain the momentum relaxation rate for electrons with different valley polarizations.

Place, publisher, year, edition, pages
2016. Vol. 109, no 16, article id 162106
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-310010DOI: 10.1063/1.4964720ISI: 000386933200020OAI: oai:DiVA.org:uu-310010DiVA, id: diva2:1055360
Funder
Swedish Research Council, 621-2014-6026ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 15-288Carl Tryggers foundation , 14:151 15:225Swedish National Infrastructure for Computing (SNIC), SNIC2014-3-65Available from: 2016-12-12 Created: 2016-12-09 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)
Opponent
Supervisors
Available from: 2018-05-15 Created: 2018-04-15 Last updated: 2018-05-15Bibliographically approved

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Majdi, SamanGabrysch, MarkusKumar Kovi, KiranSuntornwipat, NattakarnIsberg, Jan

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