xi
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
vi
DEDICATION
vii
ACKNOWLEDGEMENTS
viii
ABSTRACT
ix
ABSTRAK
x
TABLE OF CONTENTS
xi
LIST OF TABLES
xiv
LIST OF FIGURES
xvi
LIST OF SYMBOLS
xix
LIST OF APPENDICES
xx
INTRODUCTION
1.0
General Introduction
1
1.1
Research Background
2
1.2
Problem Statement
4
1.3
Objectives
4
1.4
Research Scope
5
1.5
Significant of Study
5
1.6
Thesis Overview
6
LITERATURE REVIEW
2.0
Introduction
7
2.1
Semiconductor Thin Film
8
2.1.1
8
2.2
Thermoelectric Thin Film
Bismuth Telluride
11
xii
2.2.1
3
4
11
2.3
Structural Properties and morphology of
Semiconductor Thin Films
13
2.4
Thin Film Deposition Using Radio-Frequency
Magnetron Sputtering
14
METHODOLOGY
3.0
Introduction
20
3.1
Sample Preparation
20
3.1.1
Sputtering Target
20
3.1.2
Substrate
21
3.2
Deposition of Bi2Te3 Thin Films
22
3.3
Atomic Force Microscopy
27
3.4
In-situ Annealing Utilizing Atomic Force
Microscopy
31
3.5
X-Ray Diffraction
32
3.6
Scanning Electron microscopy
34
RESULTS AND DISCUSSION
4.0
Introduction
37
4.1
Optimization of Parameters
38
4.2
Structural Properties and Surface Morphology
43
4.2.1
Effect of Substrate Temperature
44
4.2.2
Effect of Argon Flow Rate
52
4.2.3
Effect of Deposition Time
59
4.2.4
Effect of RF Power
65
4.3
In-situ Annealing of Bi2Te3 Thin Films using
AFM
4.3.1
4.3.2
5
Crystal Structure
70
Heat Treatment Effect to Surface
Roughness, Grain Size and Grain
Density
70
Rapid Cooling Effect of Surface
Roughness, Grain Size and Grain
Density
73
CONCLUSIONS
5.0
Conclusions
76
5.1
Suggestions for Future Work
78
xiii
REFERENCES
79
APPENDIX
85
xiv
LIST OF TABLES
TABLE NO.
TITLE
2.1
General properties of Bi2Te3 at room
temperature
13
2.2
Evaporation and sputtering comparison
19
3.1
Optimization of deposition parameters of Bi2Te3
thin films with different deposition temperature
25
3.2
Deposition parameters of Bi2Te3 thin films with
different deposition temperature
26
3.3
Deposition parameters of Bi2Te3 thin films with
different argon flow rate
26
3.4
Deposition parameters of Bi2Te3 thin films with
different deposition time
26
3.5
Deposition parameters of Bi2Te3 thin films with
different radio-frequency power
27
4.1
PAGE
Substrate temperature dependent of surface
morphology
44
Substrate temperature dependent of structural
properties
52
4.3
Argon flow rate dependent of surface
morphology
53
4.4
Argon flow rate dependent of structural
properties
58
4.5
Deposition time dependent of surface
morphology
59
4.2
xv
4.6
Deposition time dependent of structural
properties
64
4.7
RF power dependent of surface morphology
65
4.8
Properties of Bi2Te3 thin film undergone heat
treatment
73
4.9
Properties of Bi2Te3 thin film undergone rapid
cooling
75
xvi
LIST OF FIGURES
FIGURE NO.
TITLE
2.1
Trade-off between electrical conductivity (σ),
Seebeck coefficient (α), and thermal conductivity
(κ) that involves increasing the number for free
carriers from insulator to metals
PAGE
9
2.2
Bi2Te3 crystal structure
12
2.3
Side view of a circular planar magnetron magnetic
field
16
2.4
Top view of a typical circular planar magnetron
magnetic field
16
2.5
Sputtering process illustration in molecular level
17
2.6
Three modes of thin-film growth
18
3.1
Substrate cleaning process
21
3.2
RF magnetron sputtering system
23
3.3
Schematic description of AFM operation
28
3.4
The cantilever and the tip system
29
3.5
The principles of a feedback loop
30
3.6
The Bragg condition for diffraction
32
3.7
X-ray Diffraction (XRD)
33
3.8
Scanning Electron Microscopy Diagram
36
xvii
4.1
FESEM images of Bi2Te3 thin films deposited at (a)
150 ºC, (b) 200 ºC and (c) 250 ºC
4.2
FESEM images of Bi2Te3 thin films deposited at
250 ºC for (a) 5k and (b) 25k magnification in SEI
and LEI mode respectively
4.3
Bi and Te content in Bi2Te3 films as a function of
deposition temperature
4.4
EDX spectra for Bi2Te3 films deposited at 200 ºC
4.5
AFM images of Bi2Te3 thin films topology deposited
at (a) 50 ºC,
(b) 75 ºC, (c) 100 ºC (d) 125 ºC and (e) 150 ºC
4.6
4.7
Histogram for substrate temperature dependent of
surface morphology
40
41
42
42
45
47
SEM images of Bi2Te3 thin films cross-section
deposited at (a) 50 ºC, (b) 75 ºC, (c) 100 ºC
(d) 125 ºC and (e) 150 ºC
49
4.8
XRD pattern for Bi2Te3 thin films deposited at 50ºC,
75ºC, 100ºC, 125ºC and 150ºC
50
4.9
AFM images of Bi2Te3 thin films topology
deposited at (a) 5 cm3 min-1, (b) 10 cm3 min-1,
(c) 15 cm3 min-1 (d) 20 cm3 min-1 and (e) 25 cm3
min-1
53
4.10
Histogram for argon flow rate dependent of surface
morphology
55
4.11
SEM images of Bi2Te3 thin films cross section
deposited at (a) 5 cm3 min-1, (b) 10 cm3 min-1,
(c) 15 cm3 min-1
56
XRD pattern for Bi2Te3 thin films deposited at
5 cm3 min-1, 10 cm3 min-1, 15 cm3 min-1, 20 cm3
min-1 and 25 cm3 min-1
57
4.12
xviii
4.13
4.14
4.15
4.16
AFM images of Bi2Te3 thin films topology deposited
at (a) 300 s, (b) 450 s, (c) 600 s (d) 750 s and
(e) 900 s
60
Histogram for deposition time dependent of surface
morphology
62
XRD pattern for Bi2Te3 thin films deposited at 300
s, 450 s, 600 s, 750 s and 900 s
63
AFM images of Bi2Te3 thin films topology deposited
at (a) 50 W, (b) 100 W, (c) 150 W (d) 200 W and (e)
250 W
66
4.17
Histogram for RF power dependent of surface
morphology
68
4.18
XRD pattern of Bi2Te3 thin films topology deposited
at (a) 50 W, (b) 100 W, (c) 150 W, (d) 200 W and
(e) 250 W
69
4.19
4.20
AFM images of Bi2Te3 thin film on Si (111)
substrate undergone heat treatment utilizing Atomic
Force Microscopy with various temperatures
(a) 20 ºC, (b) 150 ºC, (c) 200 ºC, (d) 250 ºC,
(e) 300 ºC, (f) 350 ºC, and (g) 400 ºC
AFM images of Bi2Te3 thin film on Si (111)
substrate undergone rapid cooling utilizing Atomic
Force Microscopy under various temperatures
(a) 450 ºC, (b) 500 ºC and (c) 550 ºC
71
74
xix
LIST OF SYMBOLS
α
-
Seebeck coefficient
AFM
-
Atomic force microscopy
B
-
Magnetic field
Cu
-
Copper
d
-
Interplanar spacing
E
-
Electrical field
EDX
-
Energy dispersion x-ray
F
-
Force
FESEM
-
Field emission scanning electron microscopy
FWHM
-
Full width high maximum
HVC
-
High vacuum coater
κ
-
Thermal conductivity
κE
-
Electrical thermal conductivity
κL
-
Lattice thermal conductivity
λ
-
Wavelength
MOCVD
-
Metal-organic chemical vapor deposition
σ
-
Electrical conductivity
RF
-
Radio frequency
SEM
-
Scanning electron microscopy
SPM
-
Scanning probe microscopy
T
-
Temperature
TEM
-
Transmission electron microscopy
XRD
-
X-ray diffraction
ZT
-
Thermoelectric figure of merit
xx
LIST OF APPENDICES
APPENDIX
TITLE
A
Publication
PAGE
85