Synthesized Cu 2 SnSe 3

Report
UNDERSTANDING THE STRUCTURAL AND
PHYSICAL BASIS OF SELENIUM BASED
SEMICONDUCTOR
Professor Zainal Abidin Talib
Dr. Josephine Liew Ying Chyi
Professor W. Mahmood Mat Yunus
INTRODUCTION
Copper Selenide

belongs to a family of chalcogenide materials
 has received great attention due to its particular
photoelectrical properties and wide applications in
electronic and optoelectronic devices [1-12] such as:
photodetector
optical filter
solar cell
schottky-diodes
thermoelectric
converter

The attraction of this binary material also depends on its
feasibility to use as a precursor material to incorporate indium
or other elements made available and lead to formation of
ternary compound such as copper indium diselenide (CuInSe2)
or other multinary material for thin film solar cell application
[13-17].

It has a wide range of stoichiometric compositions (CuSe, Cu2Se,
Cu3Se2, Cu7Se4, Cu5Se4, CuSe2) and non-stoichiometric
composition (Cu2-xSe) [8, 18]

Copper selenide can be constructed into several well
documented crystallographic (phases and structural) forms
such as orthorhombic [17, 19-21], monoclinic [22], cubic [2124], tetragonal [17, 21], hexagonal [24-26] etc depending on
their compositions form by various preparation technique [22,
27].
Tin Selenide (SnSe)

Tin Selenide is a p-type (IV-VI) semiconductor with attractive electronic and
optical properties [1, 28-38] which bring numerous applications such as:
Photovoltaic system
Radiation detector
Holographic
recording systems
Infrared
optoelectroni
c devices
Memory
switching
devices
Lithium intercalation
batteries
Thermoelectric
cooling





Tin Selenide are classified as narrow-gap semiconductors
(bandgap 1 – 2 eV) and are capable of absorbing major part
of solar energy for photovoltaic applications[1, 28, 39, 40].
Tin monoselenide is a p-type semiconductor with an
orthorhombic structure.
The tin(II) selenide crystals are construct by tightly bound
layers which formed by double planes with zigzag chains of
tin and selenium atoms[41].
The highly layered structure, typical of all orthorhombic
chlacogenide crystals, causes a strong anisotropy of physical
properties of tin(II) selenide.
Because of their anisotropic character, the tin (II) selenide
chalcogenides becomes an attractive layered compounds,
and can be used as cathode materials in lithium intercalation
batteries[42].
Copper Tin Selenide (Cu2SnSe3)

Ternary chalcogenide materials having a semiconductor nature are
currently attracting the attention of investigators due to their outstanding
optical-thermal-electrical-mechanical properties and wide variety of
potential applications in the fields like [43 – 52]:
Photovoltaic cell
thermoelectric
Heterojunction laser
Non-linear
optical material
Electronics and optoelectronics
devices

The study of these materials is important since their band gap and lattice
parameters can be varied by changing the cation composition, low melting
temperature at around 690oC, high mean atomic weight and high refractive
indices [51, 53 – 55].

Copper indium diselenide (CuInSe2) currently is one of the main compound
used in photovoltaic application.

However, indium are not cheap, therefore replacing indium with tin will
potentially be cost-competitive as tin supply are more abundant and cheaper.

Preparation of copper tin selenide system will lead to lower production cost
and making supply situation more stable.
NICKEL SELENIDE (NiSe)
Nickel Selenide , a p-type semiconductor with a band-gap of 620nm
(2.0eV) reveals significant electronic and magnetic properties.
NiSe is formed from Nickel and Selenium due to the valence electronic
configuration of Ni (3d84s2) and the small difference in electronegativity
between Ni (χ = 1.9) and Se (χ = 2.4)
IRON SELENIDE (FeSe2)
• Semiconductors
• Potential material for future applications in
magnetoelectronics
• Potential material for future applications in
optoelectronic devices
ZINC SELENIDE (ZnSe)
• ZnSe is good candidates for applications in various
optoelectronic devices such as light emitting diodes (LED),
semiconductor laser and photodetector.
• This is because of the nanometer size structure makes the
electronic energy state discrete.
• When the diameter of nanocrystals is decreased, the
energy separation and quantum effect will be enhanced.
OBJECTIVE

Fabrication of selenium based semiconductor
(CuSe, SnSe, NiSe2, Cu2SnSe3) in powder form
(compositional analysis) and thin film (deposition
condition analysis).

Optical, electrical and thermal properties
characterization of the Se based semiconductor.

Evaluate the temperature dependence of the
selenium based semiconductor from the observation
of structural, electrical, optical and thermal
properties changes at various temperature.
IMPORTANT OF STUDIES

It is evident that for the future well-being of nations, a supply of energy
based on a renewable source which is economically and environmentally
acceptable has to be developed.

Successful production of an efficient metal chalcogenide solar cell and
modules requires the coupling of fabrication techniques with a basic
understanding of the devices.

There is a need to develop a greater fundamental sciences and engineering
basis for the selenium based semiconductor material devices and
processing requirement.

In this work, we have fill the information gap on literature about the
fundamental study of the structural, electrical, thermal and optical studies in
polycrystalline CuSe, SnSe, NiSe2, ZnSe, FeSe2 and Cu2SnSe3 material.

This fundamental knowledge will guide us to find out the fabrication and
design parameters, which are imposed by current technology, material
specifications and irradiation conditions to maximize the solar cell efficiency.
Sample Preparation
Powder preparation – Chemical Precipitation Technique
Pellet preparation – Moulding
Thin film preparation – Thermal Evaporation Technique
CuSe Powder Preparation
Chemical Precipitation Method
Selenium alkaline aqueous solution
(12 M NaOH + 3.948 g Se)
(Solution A) Stirred for 2 hours
CuCl22H2O
solution (solution B)
Mixture stirred for 24 hours
Black precipitate obtained
Centrifuge and wash in distill water
Dried in oven ( 70oC) for 24 hr
Structural studies by XRD
Pressed into pellet
XRD pattern of CuSe Sample prepared at different
Molarity of CuCl2.H2O
 Se




Cu3Se2
Cu2Se



CuSe
0.09 mol CuCl2.H2O
  


Intensity (Arb. Unit)

0.06 mol CuCl2.H2O
  
 













0.05 mol CuCl2.H2O




0.04 mol CuCl2.H2O


 
  

0.03 mol CuCl2.H2O


20

25
 
30

35
 
40
Position ()
45
 0.02 mol CuCl .H O
2
2
  

50
55
60
We found that
by using the
concentration of
0.03 mol
CuCl22H2O,
the CuSe
powder with
high purity has
been
successfully
produced.
XRD Spectra of synthesized CuSe powder
102
8000
All the peaks
obtained are well
matched with the
JCPDS data (File
No. 34-0171) as
Klockmannite, syn
which belongs to
the hexagonal
system.
7000
110
5000
2000
202
108
106
1000
Orientation along
(102) plane was
found to be most
prominent.
116
101
3000
006
4000
100
Intensity (Arb. Unit)
6000
0
20
25
30
35
40
Position (2)
45
50
55
60
EDX spectrum for synthesized CuSe powder
• There are three
prominent peaks
corresponding to
the Cu, Se and Au
element.
• The Au signal
detected in the EDX
spectrum is the
results of gold
coating on sample
to prevent charging.
• small signal of C and O observed is expected from the
background environment and carbon tape holding the powder
sample.
• There are no other impurities elements were found by EDX
spectrum.
Synthesis SnSe Powder
Chemical Precipitation Method
Selenium alkaline aqueous solution
(0.56 mol NaOH + 1.974 g Se)
(Solution A) (50 ml water)
Stirred for 2 hours
Tin (II) complex aqueous Solution
(SnCl2 + 9 g tartaric acid)
(solution B)
Stirred for 2 hours
Mixture stirred for 24 hours
Black precipitate obtained
wash in sequence using membrane filter
centrifuge
Dried in oven ( 70oC)
Structural studies by XRD
Moulding into pellet
Intensity (Arb.Unit)
Se

 
 

 
 




mol SnCl2




mol SnCl2
mol SnCl2


mol SnCl2

mol SnCl2
mol SnCl2

20
25
30

35
40
45
mol SnCl2
50
55
60
Position (2)
XRD pattern of SnSe Sample prepared at different molarity of SnCl2
111
XRD Spectra of synthesized SnSe powder
All the peaks
obtained are well
matched with the
JCPDS data (File
No. 32-1382)
which belongs to
the orthorhombic
system.
8000
6000
Orientation along
(111) plane was
found to be most
prominent.
400
The sharp peaks
obtained indicate
that the material
produced is of
high crystallinity.
402
420
511
302
411
102
2000
011
311
4000
201
Intensity (Arb. Unit)
10000
0
20
25
30
35
40
Position (2
45
50
55
60
EDX spectrum for synthesized SnSe powder
Strong peaks
corresponding to Sn, Se
and Au element are found
in the spectrum, and no
impurity peaks are
detected in the EDX
spectrum.
The elemental analysis was carried out only for Sn and Se
element and the average atomic percentage of Sn:Se is 52.36 :
47.64 in the ratio range 1.1 : 1 which is nearly stoichiometry and
close to the expected value of 1:1 (SnSe) in agreement with the
XRD data.
The Au peak observed in
the EDX spectrum is due
to the gold sputtering
coating on the sample to
prevent charging while
the carbon and oxygen
peaks are due to the
dissolved atmospheric
CO2 or carbon tape
holding the powder
sample.
To study the effects of concentration
NiCl2·6H2O in synthesizing NiSe
Both mass were
put together in a
beaker
Mass of the Se
powder was
weighted
The autoclave
were put into the
oven for 180⁰C
for 6 hours
Mass of
NiCl2·6H2O
was weighted
The solution
were poured into
the Teflon lined
autoclave
Ethylenediamine
were added into
the beaker
XRD patterns of NiSe2 compound synthesized
using different concentration of NiCl2·6H2O
XRD Spectra of synthesized NiSe2 powder
•
All the peaks
obtained are well
matched with the
JCPDS data (File
No. 98-0101405), Nickel (IV)
Selenide which
belongs to the
cubic system.
•
The sharp peaks
obtained indicate
that the material
produced is of
high crystallinity.
Synthesis of ZnSe Compound
XRD pattern of ZnSe synthesized with
different ratio ZnCl2/Se
XRD Spectra of synthesized ZnSe powder
•
All the peaks
obtained are well
matched with the
JCPDS data (File
No. 98-0091262), stilleite
which belongs to
the cubic system.
•
The sharp peaks
obtained indicate
that the material
produced is of
high crystallinity.
Synthesis of FeSe2 sample
40 ml of distilled
water was prepared .
3 ml of N2H4•H2O
was prepared.
All the starting
materials were added
into distilled water
and stir for 3 minutes
at 6 rpm.
Na2SeO3 and FeCl3•6H2O
was prepared.
The sample was transferred into 50 ml
Stainless Teflon-lined autoclave and heated
up at 140°C for 12 hours.
The sample was
filtered with distilled
water in a centrifuge
for 15 times.
The sample was dry
in an oven at 60°C
for 48 hours.
The sample was
weight and
transferred to a
sample bottle.
The sample was grind
with pestle and mortar
into powder form.
XRD patterns of FeSe2 compound synthesized
using different concentration of NiCl2·6H2O
The FeSe2 peaks in
the entire pattern
obtained can be
identified as
orthorhombic FeSe2
with lattice constant
a=4.80 Å, b=5.78 Å,
c=3.58 Å, which
matched the value in
the standard data
(ICSD, 98-0048006).
Other oxides formed
are Fe3O4 (ICSD,
98-001-7319) and
Fe2O3 (ICSD, 98009-6377).
Schematic flow chart for the Cu2SnSe3
nanoparticles preparation
Chemical Precipitation Method
selenium alkaline aqueous
solution
Se + NaOH
to produce Se2- and SeO 32 ions
Stirred for 2 hours
Tin (II) complex aqueous
solution
0.078 mol SnCl2∙2H2O +
tartaric acid
Stirred for 2 hours
Cu (II) tartrate complex solution
(0.015, 0.030, 0.045, 0.060, 0.068,
0.075, 0.083, 0.090, 0.120 and 0.150
mol) CuCl2∙2H2O + tartaric acid
Stirred for 2 hours
pH control
Mixture stir for 24 hours
precipitate obtained
Centrifuge and wash in distill water
Dried in oven ( 70oC) for 24 hr
Grinding powder using mortar and pestle
XRD pattern of the copper tin selenide powder synthesized by controlling the
concentration of copper chloride (CuCl22H2O) from 0.015 to 0.150 mol with the
concentration of tin chloride (SnCl2∙2H2O) and Se fixed at 0.078 and 0.025 mol respectively
 Cu2SnSe3

Intensity (Arb. Unit)
12000


10000


6000


 
2000

0.060 mol CuCl2.2H2O
0.045 mol CuCl2.2H2O

 
14000
 


12000

10000
8000



0.120 mol CuCl2.2H2O

 




o

  
  
0.083 mol CuCl2.2H2O

o


0.090 mol CuCl2.2H2O



2000



6000
0.150 mol CuCl2.2H2O



o Se
CuSe

4000
 



  o
o
0.015 mol CuCl2.2H2O

* Cu3Se2

 0.030 mol CuCl .2H O
2
2

 Cu2SnSe3
16000
0.068 mol CuCl2.2H2O


 CuSe



4000



8000
SnSe
Intensity (Arb. Unit)
14000

0.075 mol CuCl2.2H2O

0.068 mol CuCl2.2H2O

0
20
25
30
35
40
45
Position (2 Theta)
50
55
60
20
25
30
35
40
45
50
55
60
Position (2Theta
• The XRD results show that when excessive CuCl22H2O was added, the final
product is a mixture of Cu3Se2, CuSe and Cu2SnSe3.
• Less CuCl22H2O concentration will lead to formation of SnSe and Cu2SnSe3
mixture.
• All these results indicate that the binary compounds such as CuSe and SnSe will
become intermediates during the formation of product Cu2SnSe3.
• 0.068 mol CuCl2.2H2O concentration has been chosen as the optimum amount to
further test on the pH condition
Cu2SnSe3
20000
18000








16000
Intensity (Arb. Unit)
Cu3Se2
SnSe
14000


 
pH 0.84

 
pH 1.09
pH 1.30
12000
pH 1.58
10000
pH 1.65
8000
pH 1.77
6000
pH 1.90

4000
pH 3.63
2000

0
20
25


30
35
 

40
 
45
50
pH 6.51
55
60
Position (2)
XRD pattern of copper tin selenide powder synthesized at different
pH condition (pH 0.84, 1.09, 1.30. 1.58, 1.65, 1.77, 1.90, 3.63,
6.51) with 0.068 mol CuCl22H2O, 5.2 M SnCl2∙2H2O and 0.5 M Se
concentration
the growth solution
of pH at 1.30 is the
optimum acidity
condition which
favors the formation
of Cu2SnSe3 phase
without any other
impurities.
220
XRD Spectra of synthesized Cu2SnSe3 powder
All the peaks
obtained are well
matched with the
JCPDS data (File
No. 01-089-2879)
as Copper Tin
Selenide which
belongs to the
cubic system
111
3000
2000
311
1000
Orientation along
(220) plane was
found to be most
prominent.
331
400
Intensity (Arb. Unit)
4000
0
20
30
40
50
Position 2
60
70
80
EDX spectrum of synthesized Cu2SnSe3 powder
• The results show the prominent peaks in the EDX spectrum are attributed to Cu (34.54%),
Sn (18.48%) and Se (46.97%).
• The Au signal detected in the EDX spectrum is the results of gold sputtering on powder
sample to prevent charging while the carbon and oxygen signal are expected due to the
dissolved atmospheric CO2 or carbon tape holding the powder samples.
• No other impurity elements are found in the EDX spectrum.
• The calculated average atomic ratio of Cu:Sn:Se appears to be nearly stoichiometric (2.1 :
1.1 : 2.9) which is close to the expected value of (2 : 1 : 3) the nominal composition of
Cu2SnSe3 as suggested by the XRD study.
Methodology
Evacuated ampoule
+
Evacuated ampoule
Combination of
evacuated quartz
ampoule
& modified rocking
furnace
Source material
‘A furnace for producing chalcogenide based alloy
and a method for producing thereof’ by Talib, Z. A.,
Sabli, N., Yunus, W. M. M., Shaari, A. H. (MyIPO
Paten Pending: PI2012700841)
Results (Source Material)
Synthesized SnSe
XRD pattern of synthesized SnSe powder (before deposition)
 43172 cps
2000
(111)
(402)
(312)
(610)
(420)
(412)
(502)
(002)
(102)
(112)
(411)
(020)
(011)
(210)
(101)
(201)
Intensity (Arbitary units)
(311)
(511)
(400)
0
20
30
40
50
60
Sabli, N., Talib, Z. A., Yunus, W. M. M., Zainal, Z.,
Hilal, H. S., and Fujii, M. (2014). SnSe thin film
electrodes prepared by vacuum evaporation:
Enhancement of photoelectrochemical efficiency by
argon gas condensation method. Electrochemistry,
82(1), 1-6
degrees
 Synthesized XRD data well matched with JCPDS data (98-002-4334)
 Powder can be used as source material for vacuum evaporation
Results (Source Material)
Synthesized Cu2SnSe3
XRD pattern of synthesized Cu2SnSe3 powder (before deposition)
(002)/(131)
Intensity (Arbitary units)
14000
(331)/(060)
7000
(260)/(402)
(262)/
(404)
(462)/(191)
/(135)/(264)
0
20
40
60
80
2degrees)
 Synthesized XRD data well matched with JCPDS data (98-007-7744 )
 Powder can be used as source material for vacuum evaporation
Results (Source Material)
Synthesized Cu2ZnSnSe4
XRD pattern of synthesized Cu2ZnSnSe4 powder (before deposition)
(112)
Intensity (Arbitary units)
14000
(220)/(024)
7000
(132)/(116)
(332)/(136)
(040)/(008)
0
20
40
60
Sabli, N., Talib, Z. A., Yunus, M., Mahmood,
W., Zainal, Z., Hilal, H. S., and Fujii, M. (2013).
CuZnSnSe Thin Film Electrodes Prepared by
Vacuum Evaporation: Enhancement of Surface
Morphology and Photoelectrochemical
Characteristics by Argon Gas. In Materials
Science Forum (Vol. 756, pp. 273-280).
80
2(degrees)
 Synthesized XRD data well matched with JCPDS data (98-006-7242)
 Powder can be used as source material for vacuum evaporation
Mechanochemical solid state synthesis of
Cd0.5Zn0.5Se
The starting materials were high-purity cadmium (99.99%),
zinc (99.99%) and selenium (99.99%) elemental powders
purchased from Alfa Aesar. Mixtures at the desired atomic
ratios were placed in a stainless steel grinding jar with
stainless balls under an inert atmosphere. The intensive
grinding the mixtures was performed in a high-energy
planetary ball mill PM 100 (Retsch) with a ball-to-powder
ratio of 10:1. Grinding balls of 3 mm in diameter were
used. The milling time was varied from 5 to 20 hours at a
speed of 500 rpm. Small quantities of the as-milled
powders were removed from the grinding jar at various
time
intervals
for
microstructural
and
optical
characterization.
Pellet Sample Preparation


The synthesized CuSe and Cu2SnSe3 powders were weighed in the desired
amount and then placed into the 8mm diameter mould to form a pellet shape
sample by using a hydraulic press (SPECAC USA, model 15011) of 3 ton
pressure.
The pelletization process is to force the particles into close proximity.
8mm
4.5mm
8mm
38mm
38mm
5mm
6mm
30mm
8mm
Pellet mould with 8 mm diameter
30mm
Thin Film Deposition
Vacuum
Chamber
substrate holder
Pressure
monitor
Molybdenum/
tungsten
filament
shutter
glass
Sample to be
deposited
AC Power Supply
High vacuum
created by diffusion
pump backed by
rotary pump
Thermal Evaporation System (Edwards Auto 306 Vacuum Coating)
Methodology
Install argon
gas supply &
nozzle to
flow argon
Heater (setting with
thermocouple to note the
temperature)
Substrate (1.5cm X 2.5cm,
ITO/glass)
Boat (Molybdenum/
tungsten)
Copper rod
14 cm
Electrodes (Copper)
:connected to high
current, low voltage
needle
valve
valve
Chamber pressure gauge
moisture
trap
Sonic nozzle ( jet
dia. 0.5mm)
To diffusion pump system
Argon gas cylinder
Hypothesis 1
After collision
(3) Higher retained kinetic
energy Sn and Se are
expected to react
Cu (Atomic weight: 63.546)
Zn (Atomic weight : 65.409)
Sn (Atomic weight : 118.71)
Se (Atomic weight : 78.96)
Ar ; inert gas
Propose: Argon gas
injection system
Before collision
(1) Compound (atoms/ions)
Higher argon gas volume
heats at same temp;
atoms have same mean kinetic
energy (Ek = 3/2 kT)
After collision
(2) Lighter atoms (Cu, Zn)
have higher speed due to Ek =
1/2 mV2; Higher speed more
collisions with Ar atoms
lose kinetic energy
Hypothesis 2
(Cu,Zn): SnSe
Pure SnSe thin film
e-
CB
VB
Compound: SnSe (50:50)
More carriers
e - e-
CB
Impurity level
VB
Compound Cu2ZnSnSe4: (25:12.5:12.5:50)
Annealing process




For the heat treatment process, the CuSe and Cu2SnSe3 film
were placed on the quartz boat and heated with gas N2 (1cc/min)
by using furnace.
The annealing process was carried out at a temperature raised
from room temperature 26 oC to 100 oC, 200 oC, 300 oC, 400 oC
at an increasing rate (2 oC/min).
Upon reaching the required temperature, it was maintained for 3
hours.
The temperature was then natural cooling to room temperature
for 24 hours.
Methodology
XRD (PanAnalytical X’pert PRO PW3040)
FESEM, EDX and TEM
Field Emission Scanning
Electron Microscope
(JOEL JSM-6700F)
Transmission
Electron
Microscope
(Hitachi H7100
TEM)
Energy Dispersive X-Ray (EDX)
(LEO 1455 VP SEM )
Schematic Diagram for Low Temperature Two Probe
Measurement System
Voltmeter
Current
source
Temperature
controller
Argon gas
Rotary
pump
Liquid
nitrogen
Argon
gas
vacuum
Variable temperature
optical cryostat
Two probe system
Schematic Diagram for Low Temperature Photoflash
Technique
Temperature
controller
argon gas
Preamplifier
Liquid
nitrogen
rotary pump
Argon gas
vacuum
sample
Signal Ref
Oscilloscop
e
photodiode
Thermocoupl
e
Camera
flash
Variable temperature
optical cryostat
Laser flash NETZSCH (LFA 457) Microflash for high
temperature thermal diffusivity measurement
Microstructure Analysis using AFM (Quesant Q-Scope
250)
The characterization of surface morphology of the CuSe thin films was studied by atomic force
microscopy (AFM) technique (Quesant Q-Scope 250) in tapping mode at ambient temperature.
Ellipsometer Technique (ELX-02C)





Ellipsometer measures the change of polarization upon reflection or transmission.
The ellipsometer mechanics consists of a transmitter unit (He-Ne laser – 632.8 nm) and a
receiver unit (polarising prism) fixed at the end of adjustable arms.
Ellipsometry is an indirect method, i.e. in general the measured Ψ and Δ cannot be converted
directly into the optical constants of the sample, a model analysis must be performed.
Using an iterative procedure (least-squares minimization) unknown optical constants and/or
thickness parameters are varied, and Ψ and Δ values are calculated using the Fresnel equations.
The calculated Ψ and Δ values, which match the experimental data best, provide the optical
constants and thickness parameters of the sample
Fiber Optic Spectrophotometer
The optical studies of CuSe film analyzed using Ocean Fiber Optics
Spectrophotometer.
The transmittance spectra in the region 300nnm – 800nm has been collected and
optical parameters such as optical absorption coefficient and optical band gap has been
evaluated.
Structural Analysis
X-Ray Powder Diffraction
108
202
116
110
006
106
300K
100
101
102
In-situ XRD pattern of synthesized CuSe powder at
100 – 300 K
50
55
The structure was
stable at the
temperature range
100K – 398 K
where no
additional or
unassigned peaks
are observed
Intensity (Arb. Unit)
275K
250K
225K
200K
175K
150K
125K
100K
20
25
30
35
40
45
Position (2 Theta)
60
In-situ XRD pattern of synthesized CuSe powder at
298 – 473 K.
 Cu Se
At temperature
started from 423
K, an additional
peak is observed at
2 = 45.38 which
corresponding to
d-spacing value of
1.99 Å. This peak
was identified to
the standard
pattern of
stoichiometric
Cu2Se called
bellidoite (JCPDS
29-0575).

116

202
110
106
006
2
108
473K
100
101
102
Pt / CuSe
Intensity (Arb. Unit)
448K

423K
398K
373K
348K
323K
298K
20
25
30
35
40
45
Posistion (2 Theta)
50
55
60
TGA and DTG curve for synthesized CuSe
powder at heating rate 10 K/min
105
700 K
70
-0.035
-0.040
65
-0.045
657 K
300
400
500
600
700
800
900
1000
Temperature, T (K)
1100
1200
20000
15000
10000
5000
the decomposition behaviour
is attributed to the formation of
Cu2Se products due to the
release of elemental Se.
CuSe (JCPDS File No. 34-0171)
202
116
-0.030
311
75
108
-0.025
Cu2Se (JCPDS File No. 03-065-2982)
220
80
25000
110
-0.020
106
TG
DTG
200
-0.015
85
006
-0.010
90
111
-0.005
102
324 K 465 K
100
101
weight loss, (%)
95
Phase transformation from CuSe to
Cu2Se structure as the synthesized
CuSe powder annealed at 653 K in N2
for 12 hours
Intensity (Arb. Unit)
0.000
Derivative weight loss, dm/dt (%/min)
0.005
548 K
100
50
55
0
20
25
30
35
40
45
Posistion (2 )
60
Intensity (Arb. Unit)
420
402
511
302
411
311
011
400
102
300 K
201
111
In-Situ XRD pattern of synthesized SnSe Powder at 100 K – 300 K
275 K
250 K
225 K
200 K
175 K
150 K
125 K
100 K
20
30
40
Position (2 Theta)
50
60
Intensity (Arb. Unit)
Pt
The structure was
stable from low
temperature 100K
until high
temperature 473 K
where no
additional or
unassigned peaks
are observed.
420
402
511
302
102
411
Pt
311
011
111
400
473K
201
In-Situ XRD pattern of synthesized SnSe Powder at 298 K – 473 K
448K
423K
398K
373K
This indicates that
the sample powder
is stable and
contains no
impurities.
348K
323K
298K
20
30
40
Position (2Theta)
50
60
Annealing at 1173 K destroys
the SnSe lattice (peaks of
SnSe disappear in the sample)
and leads to formation of SnO2
and Sn phases in the
presence of oxygen and
release of free selenium
followed the reaction in eq.
(5.9) [56, 57]:
70000
(c)
400
(b)
002
Sn Sn
220
211
200
111
101
110
Sn Sn
50000
SnSe powder annealed at 873 K
(JCPDS: 48-1224)
40000
30
502
601
610
420
511
302
411
501
102
311
Position (2 Theta)
50
420
511
221
402
411
40
302
0
20
2SnSe + 3O2 = SnO2 + Sn +
2SeO2 
SnSe powder (JCPDS: 48-1224)
102
10000
(a)
SnO2
311
20000
011
011
111 111
400
201
210
30000
201
210
Intensity (Arb. Units)
60000
SnSe powder annealed at 1173 K
(JCPDS: 01-077-03448)
60
Intensity (Arb. Units)
331
400
311
111
220
In-Situ XRD pattern of synthesized Cu2SnSe3 Powder
at 100 K – 300 K.
300 K
275 K
250 K
225 K
200 K
175 K
150 K
125 K
100 K
20
30
40
50
Position 2
60
70
80
400
*
*
331
* Pt
311
111
220
In-Situ XRD pattern of synthesized Cu2SnSe3 Powder
at 298 K – 523 K.
523 K
Intensity (Arb. Units)
498 K
473 K
448 K
423 K
398 K
373 K
348 K
323 K
298 K
20
30
40
50
Position 2
60
70
80
The Cu2SnSe3
structure was very
stable at the
temperature range
100K – 523 K
where no
additional or
unassigned peaks
are observed
(b)
111
10000
220
11000
Cu2SnSe3 powder annealed at 753 K
(a)
3000
331
Cu2O
400
Cu2O
311
Cu2SnSe3 powder
1000
400
311
2000
331
4000
Sn2O3
220
5000
Cu2O
200
6000
Cu3Se2
Cu3Se2
7000
Sn2O3
Cu2O
8000
111
Intensity (Arb. Units)
9000
0
20
30
40
50
60
70
Position (2 Theta)
Comparison between the as-synthesized
Cu2SnSe3 powder with the annealed
Cu2SnSe3 powder
80
some additional characteristic
peaks attributed to the Cu3Se2
(JCPDS: 03-065-1656), Cu2O
(JCPDS: 01-077-0199) and
Sn2O3 (JCPDS: 25-1259)
phase are observed after the
Cu2SnSe3 powder annealed at
773 K.
Additional peaks present in
Figure 5.35 are caused by the
recrystallization and oxidation
of the material at higher
annealing temperature [58].
Morphology
SEM result for Synthesized CuSe powder
Fig (a-d) shows the SEM
micrograph of the CuSe
powder at 50000 ×, 20000 ×,
10000 × and 2500
magnification which showed
particles rod-like shape.
It is observed that the smallest
grain size is of the order of 37
nm.
(a)
(c)
(b)
(d)
The big islands are formed by
the agglomeration of smaller
grains with length in the range
of 40 - 240 nm.
• Rod like shape particles
• highest count of diameter
size range in 30-40 nm
range
• average diameter size
distribution of 54.1 nm
60
No. of counts
50
40
30
20
10-20
20-30
30-40
40-50
50-60
60-100
100-200 200-300
Diameter size range (nm)
80
10.0
70
8.0
60
6.0
Lg
D
50
4.0
40
2.0
30
0.0
14
FESEM image and particle size distribution histogram of
synthesized CuSe powder.
Mean Crystallite Size, Lg (nm)
0
12.0
Dislocation DensityD x 10 (lines/m )
10
90
2
20
-2.0
50
20
150
200
250
300
350
400
450
500
Temperature, T (K)
mean crystallite size obtained
from XRD at temperature range of
100 – 473 K
15
No. of counts
100
10
5
0
10-20
20-30
30-40
40-50
50-60
60-70
Diameter size range (nm)
TEM image and particle size distribution histogram of
synthesized CuSe powder
• rod-like shape particles
• highest count of
diameter size range in
30-40 nm
• average size distribution
of 35.2 nm.
SEM result for Synthesized SnSe powder
SnSe powder
showed particles with
granules, sheet-like
and agglomerate
slightly.
(a)
(c)
The SEM micrograph
confirm the layered
structure growth of
the SnSe synthesis
using chemical
precipitation method.
It is observed that the
average grain size of
the small spherical
grains is  29.14 nm.
(b)
(d)
35
30
No. of counts
25
20
15
10
5
0
20-30
30-40
40-50
50-60
60-70
70-80
80-90
Diameter size range (nm)
• flake-like or plate-like structure is
built up by the interconnected
network or overlapping of nanorod
of the SnSe particles which
agglomerates together and link to
layered semiconductor.
• the highest count of diameter size
is in 40-50 nm range
• average diameter size distribution
of (50.6  1.2) nm.
48
FESEM image and particle size distribution
histogram of synthesized SnSe powder
Mean crystallite size, Lg (nm)
46
14
12
No. of counts
10
44
42
40
38
36
8
34
100
6
200
300
400
500
600
Temperature, T (K)
4
2
0
10-20
20-30
30-40
40-50
50-60
60-70
70-80
Diameter size range (nm)
TEM image and particle size distribution
histogram of synthesized SnSe powder
80-90
90-100
• dispersion leads to the breakup
of the flake-like or layered-like
structure network into individual
nanorod particles.
• highest count of particle size
range in 40-50 nm
• average size distribution of (48.5
 2.8) nm
SEM results for synthesized Cu2SnSe3 powder
Fig. (a-d) shows the SEM
micrograph of the Cu2SnSe3
powder at 50000 ×, 20000 ×,
10000 × and 2500
magnification which show
particles with granules like
shape.
(a)
(c)
It is observed that the average
grain size of the small
spherical grains is  36 nm.
The grains are well defined,
spherical, of almost similar
size, which indicates that the
powder produced from the
precipitation technique was
homogenous and uniform.
(b)
(d)
• powder is homogeneous,
spherical in shape and
slightly agglomerate.
• the highest count of
diameter size range as (30
-40) nm
• average diameter size
distributions as 36.3 nm.
100
No. of counts
80
60
40
20
40
3.0
35
2.5
30
2.0
25
1.5
20
1.0
0
30-40
40-50
50-60
60-70
FESEM image and particle size distribution
histogram of synthesized Cu2SnSe3 powder
15
Mean Crystallite Size, Lg (nm)
Diameter size range (nm)
Lg
15
0.5
2
D
40
10
100
35
Dislocation Density, D x 10 (lines/m )
20-30
200
300
400
500
0.0
600
Temperature, T (K)
No. of counts
30
25
20
15
10
5
0
0-10
10-20
20-30
30-40
40-50
Diameter size range (nm)
TEM image and (b) particle size distribution
histogram of synthesized Cu2SnSe3 powder
50-60
• homogeneous distribution
of the small spherical
nanoparticles
• The highest count of
diameter size range is
obtained to be in between
20-30 nm
• the average size
distribution being of 23.0
nm.
Electrical Properties
Electrical conductivity as a function of
temperature for CuSe in bulk form
Electrical conductivity,  (S/cm)
1050
reduction in
Hall mobility
due to
phonon
scattering
1000
950
region I
900
variable
range
hopping
850
800
50
100
150
200
250
300
• the decrease of electrical
conductivity can be
explained by the
reduction in Hall mobility,
due to the influence of
region II
impurity, defect
scattering, lattice
scattering or surface
scattering [10, 59 – 61].
• the increase of the
electrical conductivity
with the temperature can
be explained as a
consequent of thermal
activation of the
electrons which gained
thermionic
enough energy to jump
emission
across the depletion
layers at the crystallite
boundaries which act as
potential barriers for
350
400
450
500 conduction electrons [62,
63].
Temperature, T (K)
Hall mobility and carrier sheet densities as a function of
temperature for CuSe in bulk form
1E21
100
•
-2
2
Hall mobility, H (cm / Vs)
Nc
1E20
10
Carrier sheet density, Nc (cm )

-2.52
T
•
The Hall mobility of the CuSe
pellet decreases from (92.9 
0.9) to (5.61  0.06) cm2/Vs as
the temperature increased from
100 to 300 K
The impurities or defects inside
the polycrystalline compound
will develop space charge
polarization with the large
concentration of the charge
carrier and subsequently
induced trapping or localization
process which decrease the
electrical conductivity [64].
1E19
100
150
200
250
300
Temperature, T (K)
•
•
the carrier sheet density of the CuSe pellet increase from (2.54  0.03)  1019 to (3.08
 0.03)  1019 cm-2 with increasing temperature which corresponds to the behaviour
normally observed in a non-degenerate semiconductor trend.
This behaviour can be explained by the usual impurity concentration in which the
excitation of conduction electrons occurs from impurity centres [65].
Thermionic Emission
•
10.00
9.95
9.90
Ea = (46
1/2
ln (T )
9.85
4) meV
9.80
•
9.75
9.70
9.65
9.60
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
1000/T
ln (T1/2) versus (1000/T) at 349- 449 K for
CuSe in bulk form
•
The temperature dependence of
the conductivity in the higher
temperature range (349- 449 K)
follows the thermionic emissions
over the grain boundary potential
model and obeys Seto’s [66, 67]
extended version of the Petritz
model using equation:
  Ea 
 T   o exp

 kT 
The linearity of the plots reveals
that thermally-assisted thermionic
emission over the grain boundary
potential contributes to the
conduction mechanism and the
grain boundary scattering of
charge carriers is more
predominant in the samples
investigated.
It is believed that the small value
of activation energy in the this
temperature region is the energy
required to overcome the grain
boundary potential in this
polycrystalline materials
The hopping conduction mechanism
should dominate at low temperatures
since the electrons do not have
sufficient energy to cross the
potential barrier through thermionic
emission.
According to Mott, variable range
hopping is expected to be
predominant at the lowest
temperature as electron can hops to
the nearest neighbouring empty site
or move to a more energetically
similar remote site and leads to
conductivity–temperature
dependence follows equation [68,
69]:
  To 1 / 4 
 T   ho exp   
  T  
Variable Range Hopping
9.45
9.40
1/2
ln (T )
9.35
9.30
9.25
9.20
0.26
0.27
0.28
0.29
-1/4
T
0.30
0.31
0.32
-1/4
(K )
ln (T1/2) versus (T-1/4) at 99 - 214 K for CuSe in
bulk form
the linear variation observed
between 99 – 214 K with a good fit to
the conductivity–temperature data
indicates that the possible
conduction mechanism at these
temperatures can be described by
Mott’s [67, 70] variable range
hopping law.
Electrical conductivity as a function of
temperature for SnSe in bulk form
•
2.5
Electrical conductivity,  (S/cm)
2.0
•
1.5
•
variable
range
hopping
1.0
thermionic
emission
0.5
0.0
100
200
300
400
Temperature, T (K)
500
600
The electrical conductivity is found to
increase slowly in the temperature
range 100 K-396 K followed by a
drastically increase above 420 K.
The nature of response exhibits the
ordinary semiconducting behaviour of
the material throughout the
temperature range.
The substantial increase in electrical
conductivity of the SnSe pellet is
mainly determined by the carrier
sheet density of the sample which
depict the carrier sheet density of the
SnSe pellet follows an exponential
temperature dependence of a typical
semiconductors.
Hall mobility and carrier sheet densities as a
function of temperature for SnSe in bulk form
10000
1E14
•
•
T
1000
1E13
-7.15
2
Hall mobility, H (cm / Vs)
-2
1E15
Carrier Sheet Density, Nc (cm )
100000
1E12
H
100
Nc
1E11
10
1E10
1
1E9
0.1
100
150
200
Temperature, T (K)
250
300
•
the mobility decreases as
the temperature increased
from 100 to 300 K.
In polycrystalline
semiconductors the
transport of carrier is driven
by scattering mechanism at
intercrystallite boundaries,
rather than by intracrystallite
characteristics.
Based on the grain
boundary trapping theory,
the decrease of mobility and
steep rise of the carrier is
due to the total carrier
depletion of the grains which
able to capture and
therefore immobilize free
carriers [71, 72].
Thermionic Emission
•
4.0
3.5
ln (T)
1/2
3.0
Ea = (0.44
2.5
0.03) eV
2.0
•
1.5
1.0
0.5
1.9
2.0
2.1
2.2
2.3
2.4
2.5
1000/T
ln (T1/2) versus (1000/T) at 396- 526 K
for SnSe in bulk form.
2.6
The variation of ln (T1/2) with
inverse temperature is found to be
fit linearly in the temperature range
from 396 to 526 K for the SnSe
pellet indicating that the conduction
in this system is through the
thermally assisted thermionic
emissions over the grain boundary
potential model [66, 67].
Conductivity in SnSe pellet
increases exponentially with
temperature indicating the heat
induced energy which overcome the
barrier at the grain boundaries
within the sample.
Variable Range Hopping
0.5
•
0.0
-0.5
•
ln (T)
1/2
-1.0
-1.5
-2.0
•
-2.5
-3.0
-3.5
-4.0
0.25
0.26
0.27
0.28
-1/4
T
0.29
0.30
0.31
-1/4
(K )
ln (T1/2) versus (T-1/4) at 113 – 243 K for
SnSe in bulk form
The linear dependence of the ln
(T1/2) vs. T-1/4 can be interpreted
as hopping transport phenomena.
The possible conduction
mechanism at these temperatures
ranges may be due to a wide
range of localization and variable
range hopping conduction in the
localized states [67, 70].
At lower temperature, the localized
states conduction gradually
becoming predominant due to the
fact that the probably of thermal
release of the carriers from the
localized states near the mobility
edge becomes rapidly smaller and
charge carrier is more likely to hop
to a neighbor site in the distribution
[73].
Electrical conductivity as a function of
temperature for Cu2SnSe3 in bulk form
•
Electrical conductivity,  (S/cm)
750
reduction in Hall
mobility due to
phonon scattering
700
•
650
region I
600
region II
550
variable
range
hopping
thermionic
emission
•
500
100
200
300
400
Temperature, T(K)
500
600
A decrease in conductivity
observed for the Cu2SnSe3
pellet in region I (99 – 375
K) follow the Hall mobility
results closely
The increase of the
electrical conductivity in
region II indicates the
carriers within these
polycrystalline material
obtain sufficient energy to
cross the potential barriers
at the grain boundaries.
The increase of carrier
sheet density resulted from
the reduction of the
intergrain barriers above
375 K also increase the
conductivity [72].
Hall mobility and carrier sheet densities as a
function of temperature for Cu2SnSe3 in bulk
form
3
2.5E20
•
1.5E20

Region I
1E20
Nc
1
-0.72
T
150
200
250
•
5E19
Region II
100
-2
-2.05
T
2
Hall mobility,H (cm /Vs)
2
Carrier sheet density, Nc (cm )
2E20
300
Temperature, T (K)
•
•
•
The carrier sheet density increases as the temperature
•
increased from 100 to 300 K.
At higher temperature (200 – 300 K), the increase of carrier
sheet density can be explained by a usual impurity concentration
in which the excitation of conduction electrons occurs from
impurity centres [65].
Further temperature decrease down to 100 K leads to an
exponential decrease of the carrier sheet density due to freezing
of electrons to the shallow level impurities.
The Hall mobility of the Cu2SnSe3
compound decreases as the
temperature increases from 100 to
300 K attributed to the increased
scattering due to the influence of
impurity, defect scattering, lattice
scattering, neutral or ionized impurity
scattering and grain boundary
scattering or surface scattering [10,
59 – 61, 74, 75].
The temperature dependence of Hall
mobility fit the classical scattering
mechanism at region I indicating that
acoustic lattice scattering is a
dominant effect in the carrier
transport from 125 to 200 K.
At region II, it is believed that the
presence of grain boundaries in
polycrystalline material explained
according to Seto’s grain boundary
trapping theory will affect the results
of the temperature dependence
mobility for Cu2SnSe3 pellet [66].
Thermionic Emission
9.7
•
the variation of conductivity as
a function of temperature in
higher temperature range
(375 – 523 K) is explained by
the polycrystalline nature of
the Cu2SnSe3 pellet with
existence of potential barriers
at grain boundaries followed
the model of thermionic
emissions across grain
boundary barrier conduction
[66, 71, 76, 77].
•
The conductivity of these
polycrystalline Cu2SnSe3
pellet depends sensitively on
the grain boundaries such as
the potential barriers and
space charge region that are
built up around them.
9.6
1/2
ln (T )
9.5
Ea = (54
3) meV
9.4
9.3
9.2
9.1
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
1000/T
ln (T1/2) versus (1000/T) at 375- 523
K for Cu2SnSe3 in bulk form
2.7
Variable Range Hopping
9.20
•
The ln (T1/2) vs. T-1/4 plots in Figure
fit linear for the temperature range of
(148 - 328 K) which obeys the Mott’s
T-1/4 law propose the occurrence of
variable range hopping conduction
as the most suitable conduction
mechanism for explaining the
conduction process in this
temperature range.
•
In the hopping conduction, electron
can hops to the nearest
neighbouring empty site or move to
a more energetically similar remote
site according to Mott [78].
9.15
1/2
ln (T )
9.10
9.05
9.00
8.95
0.23
0.24
0.25
0.26
-1/4
0.27
0.28
0.29
-1/4
T (K )
(T-1/4) at 148
ln (T1/2) versus
– 328 K for
Cu2SnSe3 in bulk form
Thermal Properties
Thermal diffusivity and reciprocal thermal
diffusivity measurement as a function of
temperature on CuSe pellet
0.013
180
•
0.012
0.011
•
2
Thermal Diffusivity,  (cm /s)
160
140
0.010

120
1/
2
0.008
1/ (s/cm )
0.009
100
0.007
•
0.006
80
•
0.005
50
100
150
200
250
300
350
Temperature, T (K)
lattice heat transfer
(intrinsic scattering) is dominant in
100 – 350 K
400
450
500
Thermal diffusivity decreased
from 1.20  10-2 to 6.01  10-3
cm2/s as temperature increased
from 100 to 473 K.
increase of phonon scattering
(as phonons pass through the
sample, they are scattered by
the heavier atom which
contributed by the carriers in
the compound, grain
boundaries as well as other
phonons)
decrease in the mobility of free
charge carrier as shown in Hall
mobility results
Phonon scattering can be
separate into temperature
dependent intrinsic scattering
factor and temperature
independent extrinsic scattering
factor
Thermal diffusivity and reciprocal
thermal diffusivity measurement as a
function of temperature on SnSe pellet
•
0.0040
650
600
•
2
region III
550
region II
0.0030
500
450

0.0025
1/
350
0.0020
2
400
1/ (s/cm )
Thermal Diffusivity,  (cm /s)
0.0035
•
region I
300
0.0015
250
50
100
150
200
250
300
350
400
450
Temperature, T (K)
lattice heat transfer may be
dominant in this three temperature
range
500
550
•
thermal diffusivity results decrease
from 3.80  10 -3 to 1.60  10 -3
cm2/s as the temperature
increased from 100 to 523 K
increase of phonon scattering (as
phonons pass through the sample,
they are scattered by the heavier
atom which contributed by the
carriers in the compound, grain
boundaries as well as other
phonons)
decrease in the mobility of free
charge carrier as shown in Hall
mobility results (scattering process
and phonon collisions decrease
the mobility of charge carriers and
subsequently decrease the
thermal diffusivity)
Phonon scattering can be
separate into temperature
dependent intrinsic scattering
factor and temperature
independent extrinsic scattering
factor
Thermal diffusivity and reciprocal thermal
diffusivity measurement as a function of
temperature on Cu2SnSe3 pellet
0.0044
340
2
320
region II
0.0040
300
0.0038

0.0036
280
1/
2
1/ (s/cm )
Thermal Diffusivity,  (cm /s)
0.0042
0.0034
260
region I
0.0032
240
0.0030
0.0028
50
100
150
200
250
300
350
400
450
500
550
220
600
Temperature, T (K)
lattice heat transfer may be dominant in
this three temperature range
• the thermal diffusivity value
decreases from 4.18  10-3 to 2.97
 10-3 cm2/s when the temperature
increased from 100 to 523 K.
• increase of phonon scattering (as
phonons pass through the sample,
they are scattered by the heavier
atom which contributed by the
carriers in the compound, grain
boundaries as well as other
phonons)
• decrease in the mobility of free
charge carrier as shown in Hall
mobility results (scattering process
and phonon collisions decrease the
mobility of charge carriers and
subsequently decrease the thermal
diffusivity)
Effect of annealing process
CuSe film
Optical band gap and refractive indices of
CuSe film as a function of annealing
temperature
Electrical Conductivity of CuSe film as a
function of annealing temperature
6500
2.70
5000
Grain size
increase
(reduction of
grain boundary
scattering)
4500
4000
3500
2.60
3.320
Optical Band Gap, Eopt (eV)
5500
3.340
Formation of
new phase
(Cu2Se)
3000
350
400
450
500
2.40
3.280
2.30
550
600
650
3.260
2.20
3.240
2.10
3.220
2.00
3.200
700
250
Annealing Temperature (K)
Cu2Se
673 K
Cu2Se
20000
Cu2Se
15000
573 K
10000
473 K
Cu2Se
Cu2Se
473 K
5000
350
400
373 K
300 K
0
20
25
450
500
550
600
650
700
Unsaturated defects in the
localized state are gradually
removed.
The reduction number of
unsaturated defects decreases
the density of localized states in
the band structure
Cu2Se
373 K
300
Annealing Temperature, T (K)
25000
Intensity (Arb. Unit)
300
3.300
nr
2500
250
Eopt
2.50
Refractive Indices, nr
Electrical Conductivity, (S/cm)
6000
30
35
40
45
50
55
60
2(Degree)
XRD pattern of CuSe film annealed at various temperature
Effect of annealing process
SnSe Thin Film
Electrical Conductivity of SnSe film as a XRD pattern of SnSe films annealed at
function of annealing temperature
various temperature
0.12
14000
• formation of
new phase
• (SnO2)
• grain growth
drastically
0.08
0.06
12000
Intensity (Arb. Unit)
Electrical Conductivity, (S/cm)
0.10
0.04
decrease in
grain size
0.02
SnO2
SnO2
673 K
10000
SnO2
SnO2
8000
573 K
6000
473 K
4000
SnO2
SnO2
SnO
373 K
2000
300 K
0.00
0
20
250
300
350
400
450
500
550
600
Annealing Temperature, T (K)
As-
373 K
650
700
25
30
35
40
45
50
55
Position (2 Theta)
AFM images
473 K
573 K
673 K
60
Optical band gap and refractive indices of
SnSe film as a function of annealing
temperature
2.8
Eopt for the annealed SnSe film is obtained
based on the direct allowed transition
mechanism.
sharp change of Eopt may be connected to
partial convertion of tin selenide film to tin
oxide film
1.350
2.6
2.4
Eopt, indirect
2.2
Eopt, direct
1.250
1.200
1.8
1.150
1.6
1.4
1.100
1.2
1.050
1.0
0.8
250
14000
SnO2
12000
Intensity (Arb. Unit)
n
2.0
Refractive Indices, nr
Optical Band Gap, Eopt (eV)
1.300
SnO2
673 K
10000
8000
573 K
6000
473 K
4000
300
350
400
450
500
550
600
Annealing Temperature, T (K)
650
1.000
700
SnO2
SnO2
SnO2
SnO
373 K
2000
300 K
0
20
25
30
35
40
45
50
55
Position (2 Theta)
This behaviour may be
attributed to the removal of
water vapour or defect level
from the SnSe film after
annealing process .
SnO2
During annealing, unsaturated defects in the localized
state are gradually removed.
The reduction number of unsaturated defects decreases
the density of localized states in the band structure and
consequently decreased the the nr
60
Effect of annealing process
Cu2SnSe3 Thin Film
Electrical Conductivity of Cu2SnSe3
film as a function of annealing
temperature
XRD pattern of Cu2SnSe3 film
annealed at various temperature
4500
3500
673 K
increase in grain
size
improvement of
crystallinity
311
4000
2000
Intensity (Arb. Unit)
Electrical Conductivity,  (S/cm)
111
220
2500
3000
2500
573 K
1500
473 K
1000
373 K
500
300 K
2000
250
0
300
350
400
450
500
550
600
Annealing Temperature, T (K)
Asdeposited
373 K
650
700
20
AFM images
473 K
25
30
35
40
45
50
55
Position (2 Theta)
573 K
673 K
60
Optical band gap and refractive indices of
Cu2SnSe3 film as a function of annealing
temperature
2.40
2.200
2.38
2.100
2.000
2.34
1.900
2.32
1.800
2.30
1.700
Eopt, direct
2.28
n
2.26
1.600
2.24
1.500
2.22
250
Refractive Indices, nr
Optical Band gap, Eopt (eV)
2.36
the change of the
average grains into
effectively larger
grains
1.400
300
350
400
450
500
550
600
650
700
Annealing Temperature, T (K)
During annealing, unsaturated defects in the localized state are gradually removed.
The reduction number of unsaturated defects decreases the density of localized states in the band
structure and consequently decreased the the nr
The increase of surface roughness at the Cu2SnSe3 films interface contributed to the increased
surface optical scattering and optical loss which might lead to decrease of the nr
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ACKNOWLEDGEMENTS
The authors would like to thank the Ministry of
Education and Universiti Putra Malaysia for
their financial support through (FRGS
5524428), (RUGS 9341400) and (Geran
Putra 9433966)
Thank you

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