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Charge Transport Phenomena Unique to 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.
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2014 (English)In: MRS Online Proceedings Library, Vol. 1591, p. null-nullArticle in journal (Refereed) Published
Abstract [en]

ABSTRACT Diamond is a unique material in many respects. One of the most well-known extreme properties of diamond is its ultrahardness. This property of diamond actually turns out to have interesting consequences for charge transport, in particular at low temperatures. In fact, the strong covalent bonds that give rise to the ultrahardness results in a lack of short wavelength lattice vibrations which has a strong impact on both electron and hole scattering. In some sense diamond behaves more like a vacuum than other semiconductor materials. In this paper we describe some interesting charge transport properties of diamond and discuss possible novel electronic applications.

Place, publisher, year, edition, pages
Cambridge Journals Online , 2014. Vol. 1591, p. null-null
Keyword [en]
diamond, electrical properties, electron-phonon interactions
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-237485DOI: 10.1557/opl.2014.295ISBN: null OAI: oai:DiVA.org:uu-237485DiVA, id: diva2:768082
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2018-04-15
In thesis
1. Valley-Polarized Charge Transport in Diamond
Open this publication in new window or tab >>Valley-Polarized Charge Transport in Diamond
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a wide bandgap semiconductor with extreme properties such as high thermal conductivity, high breakdown field and high carrier mobilities. These properties together with the possibility to synthesize high purity Single-Crystalline (SC) diamond by Chemical Vapor Deposition (CVD), makes it a really interesting material for electronic devices. The low impurity concentration achieved when fabricating diamonds by CVD allows for a detailed study of the intrinsic electronic properties of diamond, especially at low temperatures when the carrier scattering rate is low.

During the last few years, our group has presented two new phenomena discovered in SC-CVD diamond at temperatures below 150 K. For the very first time, Negative Differential Mobility (NDM) and valley polarization have been observed in diamond. NDM occurs at a temperature range of 110 to 140 K and at an electric field range of 300 to 600 V/cm and has been explained by electron repopulation between different valleys. At temperatures below 100 K, stable valley polarization has been observed due to the low phonon scattering rate in diamond that enable electrons to reside in one valley.

This licentiate thesis will give a short review on electronic properties and charge transport in diamond. It will also present the two discovered phenomena and the methods used to observe them. There will be further discussions of how these discoveries can be used for making future devices, such as the Transferred-Electron Oscillator (TEO) and valleytronic devices.      

Place, publisher, year, edition, pages
Uppsala: Institutionen för teknikvetenskaper, 2015. p. 51
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352
Keyword
CVD diamond, valleytronics, Negative Differential Mobility, NDM, electron polarization, Time-of-Flight, ToF, magnetotransport, carrier transport, drift velocity
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-261009 (URN)
Presentation
(English)
Supervisors
Available from: 2015-09-07 Created: 2015-08-28 Last updated: 2015-09-15Bibliographically approved
2. 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
Keyword
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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Kovi, Kiran KumarSuntornwipat, NattakarnMajdi, SamanGabrysch, MarkusHammersberg, JohanIsberg, Jan

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