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Diamond Based Electronics and Valleytronics: An experimental study
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a promising semiconductor material for high power, high voltage, high temperature and high frequency applications due to its remarkable material properties: it has the highest thermal conductivity, it is the hardest material, chemically inert, radiation hard and has the widest transparency in the electromagnetic spectrum. It also exhibits excellent electrical properties like high breakdown field, high mobilities and a wide bandgap.  Hence, it may find applications in extreme conditions out of reach for conventional semiconductor materials, e.g. in high power density systems, high temperature conditions, automotive and aerospace industries, and space applications. 

 

With the recent progress in the growth of high purity single-crystalline CVD diamond, the realization of electronic devices is now possible. Natural and HPHT diamonds inevitably have too high a concentration of impurities and defects for electrical applications. To develop efficient electronic devices based on diamond, it is crucial to understand charge transport properties. Time-of-flight is one of the most powerful methods used to study charge transport properties like mobility, drift velocity and charge collection efficiency in highly resistive semiconductors, such as diamond. For commercial diamond devices to become a reality, it is necessary to have an effective surface passivation since the passivation determines the ability of a device to withstand high surface electric fields. Surface passivation studies on intrinsic SC-CVD diamond using materials like silicon oxide, silicon nitride and high-k materials have been conducted and observations reveal an increase in measured hole mobilities. Planar MOS capacitor structures form the basic building block of MOSFETs. Consequently, the understanding of MOS structures is crucial to make MOSFETs based on diamond. Planar MOS structures with aluminum oxide as gate dielectric were fabricated on boron doped diamond. The phenomenon of inversion was observed for the first time in diamond. In addition, low temperature hole transport in the range of 10-80 K has been investigated and the results are used to identify the type of scattering mechanisms affecting hole transport at these temperatures.

To utilize the potential of diamonds properties and with diamond being the hardest and most chemically inert material, new processing technologies are needed to produce devices for electrical, optical or mechanical applications. Etching of diamond is one of the important processing steps required to make devices. Achieving an isotropic etch with a high etch rate is a challenge. Semi-isotropic etch profiles with smooth surfaces were obtained by using anisotropic etching technique by placing diamond samples in a Faraday cage and etch rates of approximately 80 nm/min were achieved.

Valleytronics, which is a novel concept to encode information based on the valley quantum number of electrons has been investigated for the first time in diamond. Valley-polarized electrons with the longest relaxation time ever recorded in any material (300 ns) were observed. This is a first step towards demonstrating valleytronic devices.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 61 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1163
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-229948ISBN: 978-91-554-8999-1 (print)OAI: oai:DiVA.org:uu-229948DiVA: diva2:738515
Public defence
2014-09-29, Polhemsalen, Ångström laboratory, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-09-05 Created: 2014-08-18 Last updated: 2014-12-02
List of papers
1. Time-of-Flight Characterization of Single-crystalline CVD Diamond with Different Surface Passivation Layers
Open this publication in new window or tab >>Time-of-Flight Characterization of Single-crystalline CVD Diamond with Different Surface Passivation Layers
2011 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-229755 (URN)10.1557/opl.2011.311 (DOI)
Conference
MRS fall meeting 2010.
Available from: 2014-08-12 Created: 2014-08-12 Last updated: 2016-04-20
2. Silicon Oxide Passivation of Single-Crystalline CVD Diamond Evaluated by the Time-of-Flight Technique
Open this publication in new window or tab >>Silicon Oxide Passivation of Single-Crystalline CVD Diamond Evaluated by the Time-of-Flight Technique
2014 (English)In: ECS SOLID STATE LETT, ISSN 2162-8742, Vol. 3, no 5, P65-P68 p.Article in journal (Refereed) Published
Abstract [en]

The excellent material properties of diamond make it highly desirable for many extreme electronic applications that are out of reach of conventional electronic materials. For commercial diamond devices to become a reality, it is necessary to have an effective surface passivation since the passivation determines the ability of the device to withstand high surface electric fields. In this paper we present data from lateral Time-of-Flight studies on SiO2-passivated intrinsic single-crystalline CVD diamond. The SiO2 films were deposited using three different techniques. The influence of the passivation on hole transport was studied, which resulted in the increase of hole mobilities. The results from the three different passivations are compared. (C) 2014 The Electrochemical Society. All rights reserved.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-224497 (URN)10.1149/2.004405ssl (DOI)000333803500006 ()
Available from: 2014-05-14 Created: 2014-05-13 Last updated: 2014-09-08Bibliographically approved
3. A charge transport study in diamond, surface passivated by high-k dielectric oxides
Open this publication in new window or tab >>A charge transport study in diamond, surface passivated by high-k dielectric oxides
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 20, 202102- p.Article in journal (Refereed) Published
Abstract [en]

The recent progress in the growth of high-quality single-crystalline diamond films has sparked interest in the realization of efficient diamond power electronic devices. However, finding a suitable passivation is essential to improve the reliability and electrical performance of devices. In the current work, high-k dielectric materials such as aluminum oxide and hafnium oxide were deposited by atomic layer deposition on intrinsic diamond as a surface passivation layer. The hole transport properties in the diamond films were evaluated and compared to unpassivated films using the lateral time-of-flight technique. An enhancement of the near surface hole mobility in diamond films of up to 27% is observed when using aluminum oxide passivation.

National Category
Physical Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-229768 (URN)10.1063/1.4901961 (DOI)000345513300030 ()
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2017-12-05Bibliographically approved
4. Low Temperature Hole Transport in Single Crystal Synthetic Diamond
Open this publication in new window or tab >>Low Temperature Hole Transport in Single Crystal Synthetic Diamond
2012 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Article in journal (Refereed) Published
Abstract [en]

Hole transport properties of boron-doped single-crystalline (SC) CVD diamond, growth in the<100> crystallographic direction, has been investigated. The measurement was carried out in thetemperature range 10  T  80 K. A Time-of-Flight (ToF) measurement, using a 213 nm, pulsedultraviolet laser for excitation was performed on high-purity SC diamonds to study hole driftmobility in the low-injection regime and the scattering mechanisms involved in the process. Asaturation of the hole mobility was observed. This indicates that impurity scattering is thedominating scattering process at these low temperatures.

Keyword
ToF, time-of-flight, scattering, drift velocity, CVD diamond, single crystal diamond
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-173598 (URN)
Available from: 2012-05-02 Created: 2012-05-01 Last updated: 2017-12-07Bibliographically approved
5. MOS capacitor based on SC-CVD diamond
Open this publication in new window or tab >>MOS capacitor based on SC-CVD diamond
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-229769 (URN)
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2014-09-08
6. Generation, transport and detection of valley-polarized electrons in diamond
Open this publication in new window or tab >>Generation, transport and detection of valley-polarized electrons in diamond
Show others...
2013 (English)In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 12, no 8, 760-764 p.Article in journal (Refereed) Published
Abstract [en]

Standard electronic devices encode bits of information by controlling the amount of electric charge in the circuits. Alternatively, it is possible to make devices that rely on other properties of electrons than their charge. For example, spintronic devices make use of the electron spin angular momentum as a carrier of information. A new concept is valleytronics in which information is encoded by the valley quantum number of the electron. The analogy between the valley and spin degrees of freedom also implies the possibility of valley-based quantum computing. In this Article, we demonstrate for the first time generation, transport ( across macroscopic distances) and detection of valley-polarized electrons in bulk diamond with a relaxation time of 300 ns at 77 K. We anticipate that these results will form the basis for the development of integrated valleytronic devices.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-207029 (URN)10.1038/NMAT3694 (DOI)000322119100024 ()
Available from: 2013-09-10 Created: 2013-09-09 Last updated: 2017-12-06Bibliographically approved
7. Stability of polarized states for diamond valleytronics
Open this publication in new window or tab >>Stability of polarized states for diamond valleytronics
Show others...
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 23, 232105- p.Article in journal (Refereed) Published
Abstract [en]

The stability of valley polarized electron states is crucial for the development of valleytronics. A long relaxation time of the valley polarization is required to enable operations to be performed on the polarized states. Here, we investigate the stability of valley polarized states in diamond, expressed as relaxation time. We have found that the stability of the states can be extremely long when we consider the electron-phonon scattering processes allowed by symmetry considerations. We determine electron-phonon coupling constants by Time-of-Flight measurements and Monte Carlo simulations and use these data to map out the relaxation time temperature dependency. The relaxation time for diamond can be microseconds or longer below 100 K and 100 V/cm due to the strong covalent bond, which is highly encouraging for future use in valleytronic applications. (C) 2014 AIP Publishing LLC.

National Category
Engineering and Technology Physical Sciences
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-229299 (URN)10.1063/1.4882649 (DOI)000337891200043 ()
Available from: 2014-08-06 Created: 2014-08-05 Last updated: 2017-12-05Bibliographically approved
8. Etching of diamond in a Faraday cage
Open this publication in new window or tab >>Etching of diamond in a Faraday cage
(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Materials Engineering
Identifiers
urn:nbn:se:uu:diva-229770 (URN)
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2014-09-08

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