vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF ABBREVIATIONS
xiv
LIST OF APPENDIXES
xvi
INTRODUCTION
1
1.1
Background of Research
1
1.2
Problem Statement
3
1.3
Objectives of the study
4
1.4
Scope of the study
4
1.5
Significance of the study
5
LITERATURE REVIEW
7
2.1
Introduction to silicon (Si)
7
2.2
Nanocrystalline silicon (nc-Si)
8
2.2.1
Structure and Morphology
9
2.2.2
Electronic Quantum Confinement Effect
10
viii
2.2.3
Photoluminescence Properties of Nanocrystalline
13
Silicon
2.3
3
Plasma Enhanced Chemical Vapor Deposition (PECVD)
14
METHODOLOGY
18
3.1
Substrate Cleaning
18
3.2
Analytical Tools
19
3.2.1
Spectroscopic Ellipsometer
19
3.2.2
Field Emission Scanning Electron Microscopy
20
(FESEM)
4
3.2.3
Atomic Force Microscopy
21
3.2.4
Energy Dispersive X-Ray Spectroscopy (EDX)
22
3.2.5
Fourier Transform Infrared spectroscopy (FTIR)
23
3.2.6
Raman spectroscopy
23
3.2.7
UV/Vis spectrometer
24
3.2.8
Photoluminescence spectroscopy
25
RESULTS AND DISCUSSION: STRUCTURAL
26
PROPERTIES OF NANOCRYSTALLINE SILICON
4.1
Thickness of films
26
4.2
Surface Morphology
30
4.2.1
Surface Morphology by Field Emission Scanning
30
Electron Microscope (FESEM)
4.2.2
Surface Morphology by Atomic Force Microscope
33
(AFM)
4.2.1
Effect of Deposition Time
34
4.2.2
Effect of Substrate Temperature
37
4.2.3
Effect of RF Power
39
4.3
Chemical Composition study
42
4.3.1
Energy Dispersive X-ray Spectrometry Analysis
42
4.3.2
Fourier Transform Infra-Red Spectra Analysis
44
4.4
Film Crystallinity and Size of Nanocrystals
46
4.4.1
Raman spectroscopy
46
4.4.1.1 Effect of Deposition Time
46
ix
5
4.4.1.2 Effect of Substrate Temperature
51
4.4.1.3 Effect of RF Power
52
RESULTS AND DISCUSSION: OPTICAL PROPERTIES
55
OF NANOCRYSTALLINE SILICON
6
5.1
Transmission
55
5.2
Absorption Coefficient
56
5.2.1
Effect of deposition time
57
5.2.2
Effect of substrate temperature
60
5.2.3
Effect of RF power
62
5.3
Optical Bandgap by Absorption Analysis
64
5.3.1
Effect of deposition time
64
5.3.2
Effect of substrate temperature
66
5.3.3
Effect of RF power
67
5.4
Photoluminescence Analysis
69
5.4.1
Effect of deposition time
69
5.4.2
Effect of substrate temperature
73
5.4.3
Effect of RF power
75
SUMMARY AND CONCLUSIONS
77
6.1
Summary and conclusion
77
6.2
Suggestion
80
REFERENCES
82
APPENDIXES
91
x
LIST OF TABLES
TABLE NO.
4.1
TITLE
PAGE
Summary of Raman analysis for samples deposited at
50
various deposition time
4.2
Summary of Raman analysis for samples deposited at
52
different substrate temperature
4.3
Summary of Raman analysis for samples deposited at
54
different RF power
5.1
Optical band gap, Egopt as a function of deposition time
65
5.2
Optical band gap, Egopt as a function of substrate temperature
67
5.3
Optical band gap, Egopt as a function of RF power
68
5.4
Bandgap energy of nc-Si films as a function of deposition time as 72
calculated from the absorption plot and PL spectra
5.5
Bandgap energy of nc-Si films as a function of substrate
74
temperature as calculated from the absorption plot and PL spectra
5.6
Bandgap energy of nc-Si films as a function of RF power as
calculated from the absorption plot and PL spectra
76
xi
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
Three thin film growth modes
10
2.2
Quantum confinement effect in varied systems from atoms
12
to bulk materials
2.3
Illustration of process that occur in a PECVD chamber
17
3.1
Typical ellipsometry configuration
20
3.2
Schematic illustration of FESEM principle
21
3.3
Block diagram of AFM principle
22
3.4
Raman spectroscopy system at USM
24
4.1
Dependence of film thickness on deposition time
27
4.2
Dependence of film thickness on substrate temperature
28
4.3
Dependence of film thickness on RF power
29
4.4
FESEM micrographs of (a) bare sapphire, and those of films
32
grown at (b) 12 watt , (c) 16 watt, (d) 20 watt
4.5
AFM images of blank corning glass 7059 substrate with a
33
RMS of 0.215 nm
4.6
AFM topography image of nc-Si deposited on corning glass
35
substrate after a) 5 minutes, b) 10 minutes, c) 15 minutes,
and d) 20 minutes of deposition time
4.7
Island-shaped silicon grain grown on substrate
36
4.8
Graph of RMS (nm) and average grain diameter (nm) as a
36
function of deposition time at 24W and 300°C
xii
4.9
AFM topography image of nc-Si deposited on corning glass
38
substrate at deposition temperature of a) 100 °C , b) 200 °C,
c) 300 °C, and d) 400 °C
4.10
Graph of RMS (nm) and average grain diameter (nm) as a
39
function of deposition temperature at 24W and 15 minutes
4.11
AFM topography image of nc-Si deposited on corning glass
40
substrate at varied plasma power a) 12W , b) 14W, c) 20W,
and d) 24W
4.12
Graph of RMS (nm) and average grain diameter (nm) as a
41
function of RF power at 15 minutes and 300°C
4.13
EDX spectrum of nc-Si grown on sapphire at (a) 15 minutes,
42
300°C, 12 watt, (b) 15 minutes, 300°C, 16 watt, (c) 15 minutes,
300°C, 20 watt
4.14
FTIR transmission spectra for samples deposited at
45
(a) 15 minutes, 300°C, 16 watt, (b) 15 minutes, 300°C, 24 watt,
(c) 15 minutes, 100°C, 24 watt and (d) 15 minutes, 400°C, 24 watt
4.15
Raman spectra of nc-Si films grown at various deposition time
47
of 5, 10, 15 and 20 minutes
4.16
Peak frequency and average grain size of nc-Si grown at
48
5, 10, 15 and 20 minutes
4.17
Crystalline volume fraction, Xc as a function of deposition time
50
4.18
Raman spectra for films deposited at 100°C, 200°C, 300°C
51
and 400°C respectively.
4.19
Raman spectra of nc-Si deposited at 12 W, 16 W, 20 W and 24 W 53
of RF power
4.20
Crystalline volume fraction, Xc as a function of RF power
54
5.1
Transmittance spectra of nc-Si at various substrate temperature
56
5.2
Absorption coefficient spectra of nc-Si at different deposition
58
time
5.3
Absorption coefficient spectra of nc-Si as a function of substrate
61
temperature
5.4
Absorption coefficient spectra of nc-Si as a function of
RF power
63
xiii
5.5
Plots of optical bandgap, Egopt as calculated from Tauc’s
65
equation for different deposition time
5.6
Plots of optical bandgap, Egopt as calculated from Tauc’s
66
equation for different substrate temperature
5.7
Plots of optical bandgap, Egopt as calculated from Tauc’s
68
equation for different RF power
5.8
PL spectra of nc-Si as a function of deposition time at low
70
wavelength
5.9
PL spectra of nc-Si films grown at 5 and 10 minutes at higher
70
wavelength
5.10
PL spectra of nc-Si films grown at 300°C and 400°C
73
5.11
PL spectra of nc-Si films grown at 100°C and 200°C
74
5.12
PL spectra of nc-Si films grown at 20 watt and 24 watt
75
5.13
PL spectra of nc-Si films grown at 12 watt
76
xiv
LIST OF ABBREVIATIONS / SYMBOLS
nc-Si
-
Nanocrystalline silicon
Si
-
Silicon
Ge
-
Germanium
SE
-
Spectroscopic ellipsometer
PL
-
Photoluminescence
EDX
-
Energy Dispersive X-ray Spectroscopy
AFM
-
Atomic Force Microscope
XRD
-
X-ray Diffraction
PECVD
-
Plasma Enhanced Chemical Vapour Deposition
FESEM
-
Field Emission Scanning Electron Microscopy
FTIR
-
Fourier Transform Infrared Spectroscopy
Eg
-
Energy gap
Xc
-
Crystalline volume fraction
Ia
-
Integrated intensity for amorphous phase
Ic
-
Integrated intensity for crystalline phase
Im
-
Integrated intensity for grain boundary phase
δ
-
Average grain size
Δω
-
Peak shift for nanocrystalline silicon compared to the
crystalline silicon
RF
-
Radio frequency
π
-
Pi = 3.1415926
SiH4
-
Silane
Ar
-
Argon
RMS
-
Root mean square
at. %
-
Atomic percentage
xv
Al2O3
-
Sapphire
O
-
Oxygen
H
-
Hydrogen
sym
-
symmetric
λ
-
Wavelength
eV
-
Electron volt
Egopt
-
Optical energy bandgap
α
-
Absorption coefficient
T
-
Transmittance
hν
-
Photon energy
uv
-
Ultraviolet
d
-
Spacing between atomic planes in crystalline phase
e-h
-
electron-hole
VB
-
valence band
CB
-
conduction band
Eg (∞)
-
bulk bandgap
me, mh
-
effective masses of electron and hole

-
bulk optical dielectric constant or relative permittivity
B
-
Bohr exciton radius
0, 
-
permittivity of vacuum and relative permittivity of the
semiconductor
μ
-
reduced mass of the electron and hole
e
-
electron charge
Eu
-
Urbach energy
k
-
wavenumber
d
-
thickness of film
n
-
index of refraction
ke
-
extinction coefficient
c, v
-
velocity of light in vacuum and medium
xvi
LIST OF APPENDIXES
APPENDIX
TITLE
PAGE
A
Properties of Bulk Crystalline Silicon
91
B
Energy Band Structures of Direct and Indirect
92
Bandgap Semiconductor
C
Absorption Coefficient of Bulk Crystalline
93
Silicon
D
Homemade 150MHz Plasma Enhanced
Chemical vapor Deposition (PECVD) at Ibnu
Sina Institute, UTM
94