ABSTRACT
Ternary thin films of Iron Copper Sulphide (FeCuS), Iron Zinc Sulphide (FeZnS), Lead Silver Sulphide (PbAgS), Copper Silver Sulphide (CuAgS) and Copper Zinc Sulphide (CuZnS) were
grown using cheap and simple solution growth technique with EDTA, TEA and NH3 as
complexing agents. The deposited films were characterized using PYE-UNICO-UV-2102 PC
spectrophotometer, and optical microscopy. The results suggest that some of the films have
crystal structures. From the spectral analysis of absorbance/transmittance, the optical and solid
state properties were deduced. The other optical properties so obtained include the reflectance,
absorption coefficient, refractive index, extinction coefficient, optical conductivity and thickness, while the solid state properties are dielectric constant and band gap energy.
For all the five categories of thin films grown (i.e. FeCuS, FeZnS, PbAgS, CuAgS and
CuZnS), absorbance was high in UV and low in VIS-NIR-regions, while the
transmittance were low in UV-region and high in VIS-NIR-regions. The reflectances
were high in UV-region and low in the VIS-NIR-regions.
For FeCuS, FeZnS, PbAgS, CuAgS and CuZnS, the absorption coefficient ranged from
0.1x106 m-1 to 1.65x106 m-1, 0.2x106 m-1 to 2.3x106 m-1, 0.5x106 m-1 to 0.9x106 m-1, 0.5x106 m-1 to 1.28x106 m-1 and 0.24x106 m-1 to 1.6x106 m-1, respectively. The real part of
the refractive index ranged from 1.2 to 2.3, 0.72 to 2.3, 0.1 to 2.3, 1.94 to 2.28 and 1.6 to
2.3, respectively. The corresponding values of optical conductivity ranged from
0.03x1014 s-1 to 0.6x1014 s-1, 0.07x1014 s-1, 0.06x1014 s-1 to 0.6x1014 s-1, 0.24x1014 s-1 to 0.6x1014 s-1 and 0.12x1014 s-1 to 0.6x1014 s-1, respectively. The extinction coefficient,
ranged from 0.005 to 0.038, 0.004 to 0.056, 0.010 to 0.140, 0.025 to 0.064 and 0.008 to
0.082, respectively. The direct band gap ranged from 2.4eV to2.8eV for FeCuS, 2.9eV
for FeZnS, 1.5eV to 2.1eV for PbAgS, 2.3eV for CuAgS and 2.2eV to 2.4eV for CuZnS.
The values of the indirect band gap were in the range 0.6eV to 1.0eV for FeCuS, 1.9eV
for FeZnS, 0.3eV to 0.8eV for PbAgS, 1.1eV for CuAgS and 0.4eV to 0.9eV for CuZnS.
The real part of the dielectric constant ranged from 1.4 to 5.2, 0.7 to 5.2, 0.4 to 5.2, 3.8 to
5.2 and 2.2 to 5.2, respectively, while the corresponding imaginary part of the dielectric
constant ranged from 0.008 to 0.136, 0.008 to 0.164, 0.010 to 0.390, 0.100 to 0.290 and
0.030 to 0.360, respectively.
The range of band gaps, 1.5eV to 2.9eV makes the films suitable for solar cells
fabrication; this is in agreement with the finding for the film FeCdS.
TABLE OF CONTENTS
Title------------------------ii
Certification--------------------------.iii
Dedication------------------------iv
Acknowledgement----------------------.v
Table of Contents----------------------.vi-xiii
List of Figures ------------.------------xiv-xvi
List of Plates------------------------xvii
List of Slides------------------------.xviii
List of Set Ups ----------------------xvii
Abstract------------------------xviii-xix
CHAPTER ONE
1.1.0 Introduction------------------------1
1.2.0 Benefits of Thin Films--------------------.2
1.3.0 Aim and Objectives of the Study--.--------------.3-4
CHAPTER TWO
2.1.0 Optical and Solid State Properties of Thin Film--.----------5
2.1.1 Transmittance----------------------5-6
2.1.2 Absorbance----------------------.6
2.1.3 Reflectance--------------------.7
2.1.4 Absorption Coefficient--------------------7-8
2.1.5 Optical Density------------------------.--8-9
2.2.0 Band gap and Absorption Edge--------.----------9-12
2.2.1 Absorption Edge --------------------.----12-13
2.2.2 Optical Constants--------------------13-14
2.2.3 Dielectric Constant----------------.------14-15
2.2.4 Optical Conductivity--------------------15
2.2.5 Extinction Coefficient Factor----------------.15
2.3.0 Dispersion----.----------------.15-16
2.4.0 Photoconductivity----.--------------------16-17
2.5.0 Luminescence--.----------------17-18
2.6.0 Electrical Conductivity--.------------------18
2.7.0 Thermal Conductivity------------------.18-19
2.8.0 Spectral Selective Surfaces Aspect of Solar Energy Application----------19
2.8.1 Spectral Selectivity--------------.------.19-20
2.8.2 Solar Spectral Selective Absorber Surfaces--------------.20-21
2.8.3 Semiconductor-Metal tandems----------------------21
2.8.4 Heat Mirrors--------------------21-22
2.8.5 Dark Mirrors--------------------------22
2.8.6 Antireflection Coatings--------------------22-23
2.8.7 Spectral Splitting and Cold Mirror Coatings--------------23
2.8.8 Radiative Cooling Materials----------------23
2.8.9 Window Coatings--------------------23-24
2.9.0 Solar Control Coatings----------------24
2.9.1 Low Thermal Transmittance----------------24
2.9.2 Materials for Solar Control and Low Thermal Transmittance------------24-25
2.9.3 Window Coatings with Dynamic Properties--------------------25-26
CHAPTER THREE
3.0 Methods for Thin Film Growth --.--------------.27
3.1.1 Thermal Evaporation--.----------------27-29
3.1.2 Epitaxial Growth--.--------------------29-30
3.1.2.1 Molecular Beam Epitaxial (MBE)----------------.30-32
3.1.2.2 Liquid Phase Epitaxy ------------------32
3.1.3 Sputtering--------------------------32-34
3.1.4 Chemical Vapour Deposition (CVD)--------------34-36
3.1.5 Spray Pyrolysis ------------------.37
3.1.6 Plasma Technique----------------37-38
3.1.7 Sol-gel Thin Film Formation------------------.38
3.1.8 Precursor Sol----------------------38-39
3.1.8.1 Sol-gel Dip Coating------------------.39
3.1.8.2 Spin Coating--------------------39-40
3.1.8.3 Spin Deposition of Halide and Chalcogenide Films--------.40-41
3.1.9 The Solution Growth Technique------------.----41-44
3.1.9.1 Thin Film Condensation Formation Mechanism------.----.44-45
3.1.9.2 Doping by Chemical Bath Deposition--------------.45
CHAPTER FOUR
The Measurement Techniques of Thin Film Characteristics and Materials--------46
4.1.0 Measurement Techniques of Thin Film Characteristics--------.46
4.1.1 Film Thickness--------------------.46
4.1.1.1 Micro balance (gravimetric ) Technique-------------- --47
4.1.1.2 Optical Technique--------------------.47-48
4.1.2 Absorbance/Transmittance Measurement----------48
4.1.3 Method of Determining the Composition of Thin Films--------.--48-49
4.1.3.1 Atomic Absorption Spectroscopic (AAS) Method------------.49
4.1.3.2 X-ray Fluorescence------------------.49-50
4.1.3.3 Infrared Spectroscopy----------------50-51
4.1.3.4 Qualitative and Quantitative Chemical Analysis (QCA)------52
4.2.0 Structural Characterization--------------52-53
4.2.1 Crystallographic Structure and Topography--------------.53-54
4.2.1 Transmission Electron Microscopy (TEM)----------53-54
4.2.2 Surface Structure------------------54
4.2.2.1 LEED Technique----------------------.54
4.2.2.2 RHEED Technique------------------.54-55
4.2.2.3 Photo Electron Spectroscopy (PES) --------------.55
4.2.2.4 Optical Microscopy------------------.55-56
4.3.0 Methodology----------.----------------.57-58
4.3.1 Iron Copper Sulphide--.------------------58-60
4.3.2 Optical and Solid State Characterization------------60
4.3.3 Film Thickness Measurement----------------60-61
4.4. Morphological Analysis----------------.------.--61
CHAPTER FIVE
5.0 Results and Observations--------------.----62
5.1 Optical Properties of Iron Copper Sulphide (FeCuS)--------.--.----62
5.1.1 Absorbance (A) ----------------------62
5.1.2 Transmittance (T) --------------------.62
5.1.3 Reflectance (R ) ------------------------62-63
5.1.4 Absorption Coefficient ( α ) ----------------63
5.1.5 Refractive Index (n) ------------------63
5.1.6 Optical Conductivity (σo ) ------------------64
5.1.7 Extinction Coefficient ( k) ----------------64
5.2 Solid State Properties----------------.64
5.2.1 Band gap Energy (Eg) ----------------------64-65
5.2.2 Dielectric Constant (real part) (ε r ) --------------65
5.2.3 Dielectric Constant ( imaginary part ) (ε i ) ------------65
5.3 Optical Properties of Iron Zinc Sulphide (FeZnS)----------65
5.3.1 Absorbance (A) --------------------.65
5.3.2 Transmittance (T) ------------------.66
5.3.3 Reflectance (R) ------------------.66
5.3.4 Absorption Coefficient (α ) ------------------.66
5.3.5 Refractive Index (n) ----------------66-67
5.3.6 Optical Conductivity (σo) ----------------67
5.3.7 Extinction Coefficient ( k) ----------------.67
5.4 Solid State Properties----------------67
5.4.1 Band gap Energy ( Eg)----------------67
5.4.2 Dielectric Constant (real ) (ε r) ------------------.68
5.4.3 Dielectric Constant (imaginary part ) (ε i )------------.68
5.5 Optical Properties of Lead Silver Sulphide ( PbAgS)------------68
5.5.1 Absorbance (A) .--------------------68
5.5.2 Transmittance ( T )------------------69
5.5.3 Reflectance ( R ) --------------------69
5.5.4 Absorption Coefficient (α ) ------------------.69
5.5.5 Refractive Index ( n) ------------------.69-70
5.5.6 Optical Conductivity (σo ) ------------------.--70
5.5.7 Extinction Coefficient ( k ) ------------------.70
5.6 Solid State Properties--------------------71
5.6.1 Band gap Energy ( Eg ) ------------------71
5.6.2 Dielectric Constant (real part ) (ε r ) ------------------.71
5.6.3 Dielectric Constant ( imaginary part ) (ε i )------------------71-72
5.7 Optical Properties of Copper Silver Sulphide (CuAgS)----------72
5.7.1 Absorbance (A) ------------------.72
5.7.2 Transmittance ( T ) --------------------72
5.7.3 Reflectance ( R ) --------------------.72
5.7.4 Absorption Coefficient (α ) ----------------73
5.7.5 Refractive Index (n ) ------------------73
5.7.6 Optical Conductivity (σo ) ------------------.73
5.7.7 Extinction Coefficient ( k) ------------------73
5.8 Solid State Properties ------------------73
5.8.1 Band gap Enegry ( Eg ) ----------------73-74
5.8.2 Dielectric Constant (real part ) (ε r) --------------.74
5.8.3 Dielectric Constant (imaginary part ) (ε i )--------------.74
5.9 Optical Properties of Copper Zinc Sulphide (CuZnS)----------74
5.9.1 Absorbance ( A ) ----------------.74
5.9.2 Transmittance ( T ) --------------------75
5.9.3 Reflectance ( R ) ------------------.--.75
5.9.4 Absorption Coefficient (α ) ------------------75-76
5.9.5 Refractive Index ( n) ------------------.76
5.9.6 Optical Conductivity (σo) --------------76
5.9.7 Extinction Coefficient ( k ) ----.------------77
5.10 Solid State Properties------------------.77
5.10.1 Band gap Energy ( Eg) ------------------77-78
5.10.2 Dielectric Constant (real part ) (ε r ) --------------.78
5.10.3 Dielectric Constant ( imaginary part ) (ε i ) ----------78
CHAPTER SIX
6.0 Analysis and Discussion----------------------.80
6.1 The Spectral Analysis--.------------------80
6.2 Other Optical Properties------------------80
6.3 Solid State Properties--------------------.80-81
CHAPTER SEVEN
Conclusion and Recommendations ----------------82
7.0 Conclusion----------------------82-84
7.1 Recommendation--------------------.85
REFERENCES------------------------.86-99
Appendix A. Figures------------------.100-154
Appendix B Plates----.----------------155-157
Appendix C Slides--------------------158-159
Appendix D Set Ups ------------------160-161
LIST OF FIGURES
Figure 5.1 Graph of absorbance (A) versus wavelength for FeCuS thin film------100
Figure 5.2 Graph of transmittance (T) versus wavelength for FeCuS thin film--------.101
Figure 5.3 Graph of reflectance (R) versus wavelength for FeCuS thin film------.102
Figure 5.4 Graph of absorption coefficient versus photon energy for FeCuS thin film------.103
Figure 5.5 Graph of refractive index versus photon energy for FeCuS thin film------.104
Figure 5.6 Graph of optical conductivity versus photon energy for FeCuS thin film--.105
Figure 5.7 Graph of extinction coefficient versus photon energy for FeCuS thin film--106
Figure 5.8 Graph of α2
versus photon energy for FeCuS thin film--.------.107
Figure 5.9 Graph of α1/2
versus photon energy for FeCuS thin film------------------108
Figure 5.10 Graph of dielectric constant (real part) versus photon energy for FeCuS thin film.109
Figure 5.11 Graph of dielectric constant (imaginary part) versus photon energy for FeCuS thin
film----------------------------.110
Figure 5.12 Graph of absorbance (A) versus wavelength for FeZnS thin film------.111
Figure 5.13 Graph of transmittance (T) versus wavelength for FeZnS thin film----112
Figure 5.14 Graph of reflectance (R ) versus wavelength for FeZnS thin film------113
Figure 5.15 Graph of absorption coefficient versus photon energy for FeZnS thin film--114
Figure 5.16 Graph of refractive index versus photon energy for FeZnS thin film--------115
Figure 5.17 Graph of optical conductivity versus photon energy for FeZnS thin film----.116
Figure 5.18 Graph of extinction coefficient versus photon energy for FeZnS thin film--.117
Figure 5.19 Graph of α2
versus photon energy for FeZnS thin film----.--------------.118
Figure 5.20 Graph of α1/2
versus photon energy for FeZnS thin film--.--------.119
Figure 5.21 Graph of dielectric constant (real part) versus photon energy for FeZnS thin film.120
Figure 5.22 Graph of dielectric constant (imaginary part) versus photon energy for FeZnS thin
film----------------------------.121
Figure 5.23 Graph of absorbance (A) versus wavelength for PbAgS thin film------.122
Figure 5.24 Graph of transmittance (T) versus wavelength for PbAgS thin film------------123
Figure 5.25 Graph of reflectance (R ) versus wavelength for PbAgS thin film------------124
Figure 5.26 Graph of absorption coefficient versus photon energy for PbAgS thin film--125
Figure 5.27 Graph of refractive index versus photon energy for PbAgS thin film------126
Figure 5.28 Graph of optical conductivity versus photon energy for PbAgS thin film--127
Figure 5.29 Graph of extinction coefficient versus photon energy for PbAgS thin film------128
Figure 5.30 Graph of α2
versus photon energy for PbAgS thin film--------.129
Figure 5.31 Graph of α1/2
versus photon energy for PbAgS thin film--------130
Figure 5.32 Graph of dielectric constant (real part) versus photon energy for PbAgS thin film.131
Figure 5.33 Graph of dielectric constant (imaginary part) versus photon energy for PbAgS thin
film----------------------------.132
Figure 5.34 Graph of absorbance (A) versus wavelength for CuAgS thin film------------133
Figure 5.35 Graph of transmittance (T) versus wavelength for CuAgS thin film--------.134
Figure 5.36 Graph of reflectance (R ) versus wavelength for CuAgS thin film------------135
Figure 5.37 Graph of absorption coefficient versus photon energy for CuAgS thin film------.136
Figure 5.38 Graph of refractive index versus photon energy for CuAgS thin film------.137
Figure 5.39 Graph of optical conductivity versus photon energy for CuAgS thin film----------138
Figure 5.40 Graph of extinction coefficient versus photon energy for CuAgS thin film--139
Figure 5.41 Graph of α2
versus photon energy for CuAgS thin film----------.140
Figure 5.42 Graph of α1/2
versus photon energy for CuAgS thin film--------------------.141
Figure 5.43 Graph of dielectric constant (real part) versus photon energy for CuAgS thin
film----------------------------142
Figure 5.44 Graph of dielectric constant (imaginary part) versus photon energy for CuAgS thin
film----------------------------143
Figure 5.45 Graph of absorbance (A) versus wavelength for CuZnS thin film------144
Figure 5.46 Graph of transmittance versus wavelength for CuZnS thin film--------.145
Figure 5.47 Graph of reflectance (R ) versus wavelength for CuZnS thin film------------146
Figure 5.48 Graph of absorption coefficient versus photon energy for CuZnS thin film--147
Figure 5.49 Graph of refractive index versus photon energy for CuZnS thin film------.148
Figure 5.50 Graph of optical conductivity versus photon energy for CuZnS thin film----149
Figure 5.51 Graph of extinction coefficient versus photon energy for CuZnS thin film--150
Figure 5.52 Graph of α2
versus photon energy for CuZnS thin film----------.151
Figure 5.53 Graph of α1/2
versus photon energy for CuZnS thin film------------------.152
Figure 5.54 Graph of dielectric constant (real part) versus photon energy for CuZnS thin film.153
Figure 5.55 Graph of dielectric constant (imaginary part) versus photon energy for CuZnS thin
film----------------------------.154
LIST OF PLATES
Plate 5.1 Photomicrograph of FeCuS------------------155
Plate 5.2 Photomicrograph of FeZnS------------------156
Plate 5.3 Photomicrograph of PbAgS------------------156
Plate 5.4 Photomicrograph of CuAgS------------------157
Plate 5.5 Photomicrograph of CuZnS------------------157
LIST OF SLIDES
Slide 5.1 Picture of FeCuS thin film------------------158
Slide 5.2 Picture of FeZnS thin film------------------158
Slide 5.3 Picture of PbAgS thin film------------------159
Slide 5.4 Picture of CuAgS thin film------------------159
Slide 5.5 Picture of CuZnS thin film------------------159
LIST OF SET UPS
Set Up 3.1 Experimental Set Up ----------------------160
Set up 4.1 Flow Chart for the Growth Process --.--------.--------161
