Study of three dimensional germanium islands and ultrathin Si_1tnxGe_1tn1_1tn-_1tnx films grown by chemical vapour deposition on Si(111)-(7x7) [Elektronische Ressource] / Selvi Gopalakrishnan

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• Physik

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• Publié par: universitat_ulm
• Publié le: 01 janvier 2005
• Nombre de lectures: 3
• Langue: English
• Poids de l'ouvrage: 6 Mo

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STUDY OF THREE DIMENSIONAL
GERMANIUM ISLANDS AND ULTRATHIN
Si Ge FILMS GROWN BY CHEMICAL x 1-x
×VAPOUR DEPOSITION ON Si(111)-(7 7)



Selvi Gopalakrishnan
M.Sci. Stud. (U. of Newcastle, Aust.), B.Sc. (NUS, Singapore)



A thesis submitted to fulfil the requirements for the award of the degree


Dr. rer. nat.



Department of Surface Chemistry and Catalysis
University of Ulm, Germany



July 2005







































































Fac quod aequum est
non quod facile est
















































































































Dean of the Faculty of Science : Prof. Dr. Klaus-Dieter Spindler

st1 Examiner : Prof. Dr. R.J. Behm
nd2 Examiner : Prof. Dr. N. Hüsing

Date of Submission : July 2005




Declaration










I hereby certify that the work embodied in this thesis is the result of original research and has
not been submitted for a higher degree to any other University or Instituition.





















Selvi Gopalakrishnan



Acknowledgement



This thesis could not have been completed without the assistance and encouragement of a
number of people and I would be forever indebted to them.

Firstly, I would like to thank Prof. Dr. R.J. Behm for giving me the opportunity to carry the
research towards my PhD in his department and for his support during my stay in Germany
and PD. Dr. H. Rauscher for supervising my research and for all his timely comments with
regards to the thesis. I would also like to thank Prof. Dr. N. Hüsing from the Department of
Solidstate Chemistry who has kindly consented to be the second examiner of this thesis and
Prof. Dr. G. Groß from the Department of Molecular Botanics and Prof. Dr. M. Pietralla from
the Department of Experimental Physics for graciously consenting to be members of the
panel of examiners for my final examination to fulfil the requirements for the award of the
degree Dr. rer. nat.

A special thanks to Dr. Harry Hoster for his help in the setting up and installation of the PCI
6024 E interface card and for writing the labview program for the computer controlled
reconstruction program which ensured that I had a nearly perfect Si(111)-(7 ×7) surface for
every experiment .

I would like to say a big thank you to both Thomas Häring from the mechanical workshop and
Gerd Braith from the electrical workshop, without whose assistance nothing in the basement
laboratory would have worked the way it was supposed to, Verena Botzenhart who is not only
an all around good person but also one of the best secretaries whom I had the pleasure of
knowing and also to all my co-workers past and present, who have lent a helping hand (or
two) whenever I needed it .

I would also like to thank Klaus Seemann, who carried out his Studienarbeit in this
department, during which we carried out most of the experiments described in Chapter 5 of
this thesis.

I would like to acknowledge the Graduate College GRK 328 at the University of Ulm for
providing me with the funds to carry out my research for the first three years of my stay here.

Finally, I would like to acknowledge the friendship and support of friends and former
colleagues past and present from Siltronic (formerly Wacker Siltronic), Burghausen, Portland
(Oregon) and Singapore. ABSTRACT



This work probed at the atomic level, processes that occur during the Ge three dimensional
island formation and on ultrathin Si Ge epitaxial growth by chemical vapour deposition on x 1-x
the Si(111)-(7 ×7) substrate with the aid of surface probe techniques such as STM and AFM,
XPS, as well as TEM imaging of any 3D island formation.

This work could essentially be divided into two parts. The first part studied the growth of the
strained Ge on Si system with emphasis on the characterisation of the CVD grown three
dimensional germanium islands on a standard Si(111)-(7 ×7) substrate as well as on a
surface modified Si(111)-(7 ×7) substrate. The characterisation was carried out using a
combination of techniques. XPS was used to calculate the effective coverages of deposited
germanium, the STM was used to image the top most layers whenever possible and AFM,
cross-sectional TEM and HRTEM to image the three dimensional islands. The possible causes
of the surface modification were also examined.

In the second part of this work the growth morphologies ultrathin Si Ge layers grown on the x 1-x
Si(111)-(7 ×7) substrate at 750 K where the hydrogen desorption rate from the Si(111) surface
is low and at 850 K which was the temperature at which the rate of hydrogen desorption from
the Si(111) surface was a maximum were investigated. In addition modelling of ultrathin
layer growth was carried out using two existing growth models.


Table of Contents



Chapter 1 : Introduction 1


Chapter 2 : Literature Review 6
2.1 Introduction 6

2.2 Surface Reconstruction 6
2.2.1 Introduction
2.2.2 Definitions
2.2.3 Principles of Semiconductor Surface Reconstructions 7
2.2.4 Si(111) – (7 ×7) DAS Structure 7

2.3 Epitaxy 9
2.3.1 Introduction 9
2.3.2 Epitaxial Growth modes 10
2.3.3 Chemical Vapour Deposition 11
2.3.3.1 Introduction 11
2.3.3.2 Mechanism of CVD
2.3.3.3 Kinetics thin layer CVD 12
2.3.4 SiGe Epitaxy 13
2.3.4.1 Ge on Si[100] 13
2.3.4.2 Si(111) 14
2.3.4.3 Si Ge epitaxial growth on silicon 15 x 1-x


Chapter 3 : Experimental Procedure 17
3.1 Introduction 17

3.2 X-Ray Photoelectron Spectroscopy 19
3.2.1 Introduction 19
3.2.2 Theory 19
3.2.2.1 Process of photoelectron and Auger 19
electron emission
3.2.2.2 Koopman’s Approximation 21
3.2.2.3 Spin Orbit Splitting 21
3.2.2.4 Chemical Shift
3.2.3 Instrumentation 22
3.2.3.1 Introduction 22
3.2.3.2 Vacuum Requirements 22
3.2.3.3 X-ray Source 3.2.3.4 Electron Energy Analyser 24
3.2.3.5 Detector 25
3.2.4 Data Processing 26

3.3 Scanning Tunnelling Microscopy 27
3.3.1 Introduction 27
3.3.2 Theory of tunnelling 27
3.3.2.1 Time independent elastic tunnelling 27
through a one dimensional rectangular potential barrier
3.3.2.2 Perturbation Theory of STM 30
- Tersoff Haman Model
3.3.3 Instrumentation 32
3.4 Sample Preparation 33 3.4.1 Storage and Handling 33
3.4.2 Standard Si(111) – (7 ×7) sample 34
3.4.2.1 Clean Si(111) sample 34 3.4.2.2 Reconstruction from Si(111) – (2 × 1) to (7 ×7) 34
3.4.3 Standard Ge(111) – (1 ×1) sample 35
3.4.3.1 Clean Ge(111) sample 36 3.4.4 Chemical Vapour Deposition 36
3.4.4.1 Preparation of the precursor gas supply lines 36
3.4.4.2 CVD Procedure

Chapter 4 : Characterisation of Ge structures grown 37
by CVD on standard and XPS exposed
× Si(111) – (7 7) surfaces
4.1 Introduction 37

4.2 Characterisation of 3D Ge growth by CVD on standard 37
and irradiated Si(111) – (7 × 7) by STM and AFM
4.2.1 Experimental Procedure 37
4.2.2 Results 38
4.2.3 Discussion 44

4.3 TEM Characterisation of 3D Ge growth by 45
CVD Si(111)-(7 ×7)
4.3.1 Introduction 45
4.3.2 Sample Preparation 46
4.3.3 Results 46
4.3.4 Discussion 50

4.4 Summa