Influence of material, surface reconstruction and strain on submonolayer growth at Si(111) and Ge(111) surfaces [Elektronische Ressource] / vorgelegt von Vasily Cherepanov

Vasily Cherepanov

Sujets

• Physik

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2004
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

"Influence of material, surface reconstruction and strain on submonolayer
growth at Si(111) and Ge(111) surfaces"


Von der Fakultät für Mathematik, Informatik und Naturwissenschaften der Rheinisch-
Westfälischen Technischen Hochschule Aachen zur Erlangung des akademischen
Grades eines Doktors der Naturwissenschaften genehmigte Dissertation

vorgelegt von


M.Sc. (Rus) Vasily Cherepanov
aus Omsk, Russische Föderation


Berichter: Priv. Doz. Dr. B. Voigtländer
Universitätsprofessor Dr. H. Ibach


Tag der mündlichen Prüfung: 23. Juli 2004



Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar



ABSTRACT
The present work is dedicated to the experimental investigation of the factors that
may influence the initial stage of the epitaxial growth on the Ge(111) and Si(111)
surfaces. In particular the influence of strain, surface reconstruction, and material on the
surface diffusion, nucleation, and growth of two-dimensional islands was explored. A
set of the template surfaces, which are different only in one particular feature
(reconstruction, strain, material) was prepared to study the dependence of the growth on
these properties. The scanning tunnelling microscopy measurements of the density of
2D islands and the density of small clusters after submonolayer deposition as the
functions of temperature were used to study the nucleation and growth on Ge(111) and
Si(111) template surfaces. It is found that the densities of 2D islands and small clusters
on the template surfaces change drastically with the deposition temperature and strongly
depend on the choice of material, applied strain, particular reconstruction of the surface.
In order to analyze the experimental data on the template surfaces a theoretical model
with a unified treatment of the coupled system of small clusters and 2D islands was
developed. It follows from the model that the densities of 2D islands and small clusters
are determined by competition for the free adatoms between 2D islands and clusters. A
comparison of predictions of the proposed model with the experimental data for the
growth of Si on the Si(111)-(7x7) reveals that the critical size of the stable small cluster
is equal to one and the effective barrier for adatom incorporation into the islands is
small. Using the effective energies extracted from the temperature dependence of the
density of 2D islands and small clusters it is possible to determine the value of the
diffusion barrier on the template surface. The energy barrier to remove the stacking fault
and the binding energy of adatoms to the small clusters, which are different for different
materials, reconstruction, and applied strain, are the important parameters controlling
the density of 2D islands and small clusters during epitaxial growth.
The barrier for a diffusion jump from one HUC to another is found to be smaller on
the (5x5) reconstructed surface than on the (7x7) reconstructed surface, while the
effective diffusion length is the same on both surfaces (the same 2D island density). The
difference in the energy barriers for conversion of the faulted HUC to the normal
stacking on the (5x5) and (7x7) reconstructed surfaces results in the large difference of
the density of the small clusters on these surfaces.
The diffusion barrier is found to be the same (within the measurement accuracy) on
the compressively strained and relaxed Ge(111)-(7x7) surface both for the Si and Ge.
The main effect of the strain is a change of the binding energy of adatoms with the
small clusters. The change of the binding energy with strain has opposite sign for Si and
Ge cases.
The major contribution to the effect of the material on the nucleation and growth
comes from the bond strength of Si and Ge. The different bond strength changes the
bonding of adatoms to the small clusters when the deposited material changes from Si to
Ge and when the substrate changes from Si to Ge as well.
In order to study the effect of strain on the attachment of adatoms to the edges of the
growing 2D islands a series of measurements of the island size distribution for
deposition of Si and Ge on the Si(111)-(7x7) surface was performed. The scaling
function for island size distribution was found to be the same for Si and Ge 2D islands
on the Si(111)-(7x7) surface which shows that the 4.2% compressive strain does not
make a considerable influence on the process of attachment of adatoms to 2D islands in
the regime of submonolayer growth of Ge on Si(111) substrate.
The measurements of the island size distributions for Si and Ge in surfactant
mediated growth reveal different scaling functions for Si and Ge deposition on Bi-
terminated Si(111) surface. Moreover, it is found that the scaling function changes with
temperature. The main mechanism, which results in the difference of the scaling
functions was revealed with the help of Kinetic Monte-Carlo simulations. The edges of
the Ge islands are passivated by the surfactant much stronger than the edges of the Si
islands. The consequence of the strong step edge passivation is the transition from the
growth limited by the surface diffusion to the growth limited by the attachment kinetics.
As the deposition temperature increases the role of the passivation vanishes and the
kinetic regime of the island growth changes to the diffusion limited one.






















Table of contents i
TABLE OF CONTENTS
1 Introduction ................................................................................................................. 1
2 Growth fundamentals ................................................................................................. 3
2.1 Structure of Si(111) and Ge(111) surfaces....................................................................3
2.2 Atomistic processes at surfaces ......................................................................................6
2.3 Growth modes ..................................................................................................................8
2.4 Rate equation theory of nucleation..............................................................................10
2.5 Scaling of island sizes.....................................................................................................13
2.6 Epitaxy of Si and Ge on Si(111) ...................................................................................15
2.6.1 Surface diffusion on Si(111)-(7x7) surface .............................................................16
2.6.2 Small clusters on Si(111)-(7x7) ................................................................................18
2.6.3 Nucleation and growth of 2D islands on (7x7) reconstructed surface ................20
2.7 Surfactant-mediated epitaxy ........................................................................................23
2.7.1 Termination of surface by surfactant .....................................................................23
2.7.2 Growth on surfactant terminated surface..............................................................24
2.7.3 Growth of Ge on Bi-terminated Si(111) surface....................................................27
2.8 Influence of strain ..........................................................................................................28
2.8.1 Modification of the surface structure by strain.....................................................28
2.8.2 Influence of strain on diffusion................................................................................29
3 Experimental techniques .......................................................................................... 31
3.1 MBE system....................................................................................................................32
3.2 Sample preparation .......................................................................................................33
3.3 Tip preparation ..............................................................................................................33
3.4 Sample heating and temperature measurement ........................................................34
3.5 STM design .....................................................................................................................35
4 Growth kinetics and island density ......................................................................... 39 ii
4.1 Creation of the template surfaces ................................................................................41
4.1.1 Strained and relaxed Ge(111) surfaces...................................................................41
4.1.2 Ge(111) surfaces with different reconstruction .....................................................42
4.1.3 Surfaces of different material ..................................................................................43
4.1.4 Experimental details of the creation of templates .................................................44
4.2 Intermixing of Ge and Si........................................