Electronic and structural characterizations of unreconstructed SiC(0001) surfaces and the growth of graphene overlayers [Elektronische Ressource] / vorgelegt von Konstantin Emtsev

Konstantin Georgievich Mostras

Sujets

• Physik

Informations

• Publié par: friedrich-alexander-universitat_erlangen-nurnberg
• Publié le: 01 janvier 2009
• Nombre de lectures: 50
• Langue: English
• Poids de l'ouvrage: 14 Mo

Extrait

Electronic and structural characterizations of
unreconstructed SiC{0001} surfaces and the
growth of graphene overlayers



Der Naturwissenschaftlichen Fakultät
der Friedrich-Alexander-Universität Erlangen-Nürnberg
zur
Erlangung des Doktorgrades











vorgelegt von
Konstantin Emtsev
aus St.-Petersburg













Als Dissertation genehmigt von der
Naturwissenschaftlichen Fakultät der Universität Erlangen-Nürnberg
















Tag der mündlichen Prüfung: 03.06.2009

Vorsitzender der
Promotionskommission: Prof. Dr. Eberhard Bänsch

Erstberichterstatter: Prof. Dr. Lothar Ley

Zweitberichterstatter: Prof. Dr. Klaus Heinz
Contents 1


Contents

Introduction........................................................................................................................3

1. Basics..............................................................................................................................7
1.1 Silicon Carbide........................................................................................................7
1.1.1 Atomic and electronic structure of SiC .........................................................7
1.1.2 Unreconstructed SiC{0001} surfaces..........................................................10
1.1.3 Reconstructed SiC{0001} surfaces .............................................................12
1.2 Graphene ...............................................................................................................15

2. Experimental methods................................................................................................21
2.1 Photoelectron spectroscopy...................................................................................21
2.1.1 Principle of photoelectron spectroscopy .....................................................21
2.1.2 Angle resolved photoelectron spectroscopy................................................24
2.1.3 Core level photoelectron spectroscopy........................................................27
2.2 Experimental details..............................................................................................32

3. Samples and sample preparations.............................................................................35
3.1 Samples ..................................................................................................................35
3.2 Wet chemical cleaning ...........................................................................................36
3.3 Sample preparation in vacuum (in situ) .................................................................36
3.4 Ex-situ sample preparation.....................................................................................36
3.4.1 Hydrogen terminated SiC surfaces...............................................................36
3.4.2 High temperature hydrogen etching of SiC..................................................37
3.4.3 Graphitization of SiC....................................................................................37

4. Electronic properties of the unreconstructed 6H-SiC {0001} surfaces..................39
4.1 Introduction - Mott-Hubbard metal insulator transition on SiC surfaces .............39
4.2 Preparation of unreconstructed SiC surfaces ........................................................41
4.3 The SiC(0001) surface ..........................................................................................42
4.3.1 The Si-rich (√3×√3)R30° surface reconstruction........................................46
4.4 The SiC(0001) surface47
4.5 Discussion .............................................................................................................52

5. Graphene-SiC interface formation on {0001} surfaces ...........................................57
5.1 Introduction ...........................................................................................................57
2 Contents
5.2 The 6H-SiC(0001) surface .................................................................................. 61
5.2.1 Initial stages of graphitization – overview................................................. 61
5.2.2 The 6√3 reconstructed surface and graphene ............................................ 63
5.2.3 Few layer graphene on SiC(0001) ............................................................. 70
5.2.3.1 Core level data............................................................................... 70 5.2.3.2 ARPES data................................................................................... 72
5.2.4 STM characterization of FLG films on SiC(0001) surface ...................... 76
5.2.5 Discussion - Interface between FLG and the SiC(0001) surface ............. 79
5.3 The 6H-SiC(0001) surface .................................................................................. 83
5.3.1 ARPES data ............................................................................................... 83
5.3.2 Core level data ........................................................................................... 86
5.3.3. Discussion - Interface between FLG and the SiC(0001) surface ............. 93
5.4 Discussion - Bonding and ordering of graphene on SiC{0001} surfaces........... 94

6. Morphology of epitaxial graphene films on SiC{0001} surfaces............................ 97
6.1 Morphology of epitaxial graphene synthesized in vacuum................................. 98
6.2 Ex situ preparation of epitaxial graphene .......................................................... 100
6.2.1 Graphene on the SiC(0001) surface 101
6.2.2 Graphene on the SiC(0001) surface ......................................................... 106
6.3 Initial stages of graphene formation on SiC{0001} prepared ex situ................ 108
6.3.1 Graphene on the SiC(0001) surface 108
6.3.2 Graphene on the SiC(0001) surface 112
6.4 Discussion.......................................................................................................... 113

7. Summary ................................................................................................................... 117

8. Zusammenfassung.................................................................................................... 121

Appendix A. Morphology and composition of the SiC{0001} surfaces after high
temperature hydrogen etching..................................................................................... 125

Appendix B. Determination of the graphene film thickness .................................... 130

References ...................................................................................................................... 133


Introduction 3






Introduction


Silicon carbide (SiC) is a semiconductor material with outstanding properties such
as a wide band gap, high thermal conductivity, large breakdown field, and high saturation
electron drift velocity. Hence, SiC finds its application niche in the area of high power,
high frequency electronic devices. Furthermore, due to high thermal and chemical
stability and radiation hardness SiC devices can operate in harsh environments where
more conventional semiconductors such as silicon cannot be used. Owing to these
potential applications SiC was intensively investigated over many years. In this context,
electronic and structural properties of SiC surfaces were studied as well. This is
especially true for two hexagonal (0001) and (0001) surfaces on account of their
importance in a field of SiC crystal growth as well as substrates for SiC device
fabrication. The atomic structures of many of the different stable reconstructions of
SiC{0001} surfaces are now well established.
Recently, SiC has attracted noticeable interest from quite a different perspective. It
was proposed to use SiC as a host substrate for the fabrication of atomically thin graphitic
layers [1, 2]. Thin graphite film forms on the surface of SiC as a result of a
decomposition reaction taking place at high temperatures. SiC decomposes into Si that
sublimates from the surface and C atoms that remain and rearrange into a graphitic film.
On the two hexagonal SiC surfaces such graphite layers are aligned parallel to the {0001}
plane but also retain a well-defined azimuthal orientations with respect to the substrate.
Hence, such films are now often called “epitaxial” although the films do not originate
from the deposition of carbon onto the surface which is the conventional meaning of
epitaxial growth. Generally speaking, the processing conditions can be adjusted so that a
controlled number of atomic layers will grow down to a single layer which is cal