understanding the structural and physical basis of selenium based semiconductor professor zainal...

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:

solar cell

optical filter

photodetector

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 [21-24], 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

Memory switching devices

Holographic recording systems

Lithium intercalation batteries

Thermoelectric cooling

Infrared optoelectroni

c devices

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

Electronics and optoelectronics devices

Non-linear optical material

Heterojunction laser

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 , 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)

NICKEL SELENIDE (NiSe)

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 TechniquePellet 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

Mixture stirred for 24 hours

Black precipitate obtained

Dried in oven ( 70oC) for 24 hr

Structural studies by XRD Pressed into pellet

CuCl22H2O solution (solution B)

Centrifuge and wash in distill water

20 25 30 35 40 45 50 55 60

0.02 mol CuCl2.H

2O

0.03 mol CuCl2.H

2O

0.04 mol CuCl2.H

2O

0.05 mol CuCl2.H

2O

0.06 mol CuCl2.H

2O

CuSe

0.09 mol CuCl2.H

2O

Cu3Se

2Cu2Se

Inte

nsi

ty (

Arb

. Un

it)

Position ()

Se

We found that by using the

concentration of 0.03 mol

CuCl22H2O, the CuSe powder

with high purity has been

successfully produced.

XRD pattern of CuSe Sample prepared at different Molarity of CuCl2.H2O

20 25 30 35 40 45 50 55 60

0

1000

2000

3000

4000

5000

6000

7000

8000

Inte

nsi

ty (

Arb

. Un

it)

Position (2)

106

116

202

108

110

006

102

101

100

All the peaks obtained are well matched with the JCPDS data (File No. 34-0171) as Klockmannite, syn which belongs to the hexagonal system.

Orientation along (102) plane was found to be most prominent.

XRD Spectra of synthesized CuSe powder

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 PowderChemical 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

Dried in oven ( 70oC)

Structural studies by XRD Moulding into pellet

centrifuge

20 25 30 35 40 45 50 55 60

mol SnCl2

mol SnCl2

mol SnCl2

mol SnCl2

mol SnCl2

mol SnCl2

mol SnCl2

SeIn

ten

sity

(A

rb.U

nit)

Position (2)

XRD pattern of SnSe Sample prepared at different molarity of SnCl2

XRD Spectra of synthesized SnSe powder

20 25 30 35 40 45 50 55 60

0

2000

4000

6000

8000

10000

Inte

nsi

ty (

Arb

. Uni

t)

Position (242

0

402

511

30241

1

102

311

400

111

011

201

All the peaks obtained are well matched with the JCPDS data (File No. 32-1382) which belongs to the orthorhombic system.


The sharp peaks obtained indicate that the material produced is of high crystallinity.

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 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.

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.

To study the effects of concentration NiCl2·6H2O in synthesizing NiSe

Mass of the Se powder

was weighted

Mass of NiCl2·6H2O was weighted

Both mass were put together in a

beaker

Ethylenediamine were added

into the beaker

The solution were poured

into the Teflon lined autoclave

The autoclave were put into the oven for 180 C for 6 ⁰

hours

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. 98-010-1405), 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

• All the peaks obtained are well matched with the JCPDS data (File No. 98-009-1262), stilleite which belongs to the cubic system.

• The sharp peaks obtained indicate that the material produced is of high crystallinity.

XRD Spectra of synthesized ZnSe powder

Synthesis of FeSe2 sample

40 ml of distilled water was prepared .

3 ml of N2H4•H2O was prepared.

Na2SeO3 and FeCl3•6H2O was prepared.

All the starting materials were added into distilled water and stir for 3 minutes at 6 rpm.

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 grind with pestle and mortar into powder form.

The sample was weight and transferred to a sample bottle.

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, 98-004-8006).

Other oxides formed are Fe3O4 (ICSD, 98-001-7319) and Fe2O3 (ICSD, 98-009-6377).

XRD patterns of FeSe2 compound synthesized using different concentration of NiCl2·6H2O

Schematic flow chart for the Cu2SnSe3 nanoparticles preparation

Chemical Precipitation Method

selenium alkaline aqueous solution

Se + NaOHto produce Se2- and ions

Stirred for 2 hours

Mixture stir for 24 hoursprecipitate obtained

Dried in oven ( 70oC) for 24 hr

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

Centrifuge and wash in distill water

23SeO

Tin (II) complex aqueous solution

0.078 mol SnCl2∙2H2O + tartaric acid

Stirred for 2 hours

pH control

Grinding powder using mortar and pestle

20 25 30 35 40 45 50 55 60

2000

4000

6000

8000

10000

12000

14000

SnSe CuSe

0.068 mol CuCl2.2H

2O

0.060 mol CuCl2.2H

2O

0.045 mol CuCl2.2H

2O

0.030 mol CuCl2.2H

2O

Inte

nsity

(A

rb. U

nit)

Position (2 Theta)

0.015 mol CuCl2.2H

2O

Cu2SnSe

3

20 25 30 35 40 45 50 55 600

2000

4000

6000

8000

10000

12000

14000

16000

o

o

o

o

CuSe

Cu

2SnSe

3* Cu

3Se

2

0.150 mol CuCl2.2H

2O

0.090 mol CuCl2.2H

2O

0.120 mol CuCl2.2H

2O

0.083 mol CuCl2.2H

2O

0.075 mol CuCl2.2H

2O

0.068 mol CuCl2.2H

2O

Inte

nsi

ty (

Arb

. Un

it)

Position (2Theta

o Se

XRD pattern of the copper tin selenide powder synthesized by controlling the concentration of copper chloride (CuCl22H2O) 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

• The XRD results show that when excessive CuCl22H2O was added, the final product is a mixture of Cu3Se2, CuSe and Cu2SnSe3.

• Less CuCl22H2O 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

20 25 30 35 40 45 50 55 60

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Cu3Se

2

SnSe

Cu2SnSe3

pH 0.84

pH 1.09

pH 1.30

pH 1.58

pH 1.65

pH 1.77

pH 1.90

pH 3.63

Inte

nsi

ty (

Arb

. Un

it)

Position (2)

pH 6.51

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 CuCl22H2O, 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.

20 30 40 50 60 70 80

0

1000

2000

3000

4000

33

1

40

0

31

1

22

0

Inte

nsi

ty (

Arb

. Un

it)

Position 2

11

1All 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


XRD Spectra of synthesized Cu2SnSe3 powder

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

Combination of evacuated quartz ampoule & modified rocking furnace

Source material

+Evacuated ampoule

Evacuated ampoule

‘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

Synthesized XRD data well matched with JCPDS data (98-002-4334) Powder can be used as source material for vacuum evaporation

XRD pattern of synthesized SnSe powder (before deposition)

20 30 40 50 600

2000

(50

2)

(41

2)

(42

0)

(61

0)(3

12

)(4

02

)(5

11

)(1

12

)(02

0)(4

11

)(1

02

)(0

02

)(3

11

)

43172 cps

(400)(111)

(01

1)

(21

0)

(20

1)

Inte

nsi

ty (

Arb

itary

un

its)

degrees

(10

1)

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

Results (Source Material)Synthesized Cu2SnSe3

Synthesized XRD data well matched with JCPDS data (98-007-7744 ) Powder can be used as source material for vacuum evaporation

XRD pattern of synthesized Cu2SnSe3 powder (before deposition)

20 40 60 800

7000

14000

(331)/(060)

-(462)/(191)/(135)/(264)

---

-

-

-

Inte

nsi

ty (

Arb

itary

un

its)

2degrees)

(002)/(131)

(260)/(402)

(262)/(404)

-

Results (Source Material)Synthesized Cu2ZnSnSe4

Synthesized XRD data well matched with JCPDS data (98-006-7242) Powder can be used as source material for vacuum evaporation

XRD pattern of synthesized Cu2ZnSnSe4 powder (before deposition)

20 40 60 800

7000

14000

(332)/(136)

Inte

nsi

ty (

Arb

itary

un

its)

2(degrees)

(112)

(220)/(024)

(132)/(116)

(040)/(008)

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).

Mechanochemical solid state synthesis ofCd0.5Zn0.5Se

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.

38mm

30mm

38mm

4.5mm

5mm

6mm

8mm 30mm

8mm

8mm

Pellet mould with 8 mm diameter

Thin Film Deposition

Vacuum Chamber

Pressure monitor

AC Power Supply

shutter

substrate holder

glass

Sample to be deposited

High vacuum created by diffusion

pump backed by rotary pump

Vacuum Chamber

Pressure monitor

AC Power Supply

shutter

substrate holder

glass

Sample to be depositedMolybdenum/

tungstenfilament

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

needlevalve

valve

Argon gas cylinder

moisture trap

Heater (setting with thermocouple to note the temperature)

Substrate (1.5cm X 2.5cm, ITO/glass)

Copper rod

Boat (Molybdenum/ tungsten)

Electrodes (Copper):connected to high current, low voltage

Sonic nozzle ( jet dia. 0.5mm)

14 cm

To diffusion pump system

Chamber pressure gauge

Hypothesis 1

Higher argon gas volume(1) Compound (atoms/ions) heats at same temp;atoms have same mean kinetic energy (Ek = 3/2 kT)

Cu (Atomic weight: 63.546)

Zn (Atomic weight : 65.409)

Sn (Atomic weight : 118.71)

Se (Atomic weight : 78.96)

(2) Lighter atoms (Cu, Zn) have higher speed due to Ek = 1/2 mV2; Higher speed more collisions with Ar atoms lose kinetic energy

(3) Higher retained kinetic energy Sn and Se are expected to react

Ar ; inert gas

Before collision

After collision

After collision

Hypothesis 2

Compound: SnSe (50:50) Compound Cu2ZnSnSe4: (25:12.5:12.5:50)

VB

CBe-

VB

CBe-

Impurity level

e-

Pure SnSe thin film (Cu,Zn): SnSe More carriers

Propose: Argon gas injection system

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 )

Liquid nitrogen

Argongas

vacuum

Temperature controller

Argon gasRotary pump

Two probe system

Voltmeter

Current source

Variable temperature optical cryostat

Schematic Diagram for Low Temperature Two Probe Measurement System

Liquid nitrogen

Argon gasvacuum

Temperature controller

argon gas

rotary pump

Variable temperature optical cryostat

Preamplifier

Ref SignalOscilloscope

photodiode

Camera flash

Thermocouple

sample

Schematic Diagram for Low Temperature Photoflash Technique

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

20 25 30 35 40 45 50 55 60

300K

275K

250K

225K

200K

175K

150K

125K

Inte

nsi

ty (

Arb

. Un

it)

Position (2 Theta)

100K

106 11

620

210811

0

00610

210

110

0

In-situ XRD pattern of synthesized CuSe powder at 100 – 300 K

The structure was stable at the temperature range 100K – 398 K where no additional or unassigned peaks are observed

20 25 30 35 40 45 50 55 60

Pt / CuSe

323K

298K

Inte

nsity

(A

rb. U

nit)

Posistion (2 Theta)

473K

448K

423K

398K

373K

348K

Cu2Se

106

116

20210

8

110

006

102

101

100

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).

In-situ XRD pattern of synthesized CuSe powder at 298 – 473 K.

300 400 500 600 700 800 900 1000 1100 1200

65

70

75

80

85

90

95

100

105

TG DTG

Temperature, T (K)

wei

ght l

oss,

(%

)

700 K

548 K

-0.045

-0.040

-0.035

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0.000

0.005

Der

ivat

ive

wei

ght l

oss,

dm

/dt (

%/m

in)

657 K

465 K324 K

TGA and DTG curve for synthesized CuSe powder at heating rate 10 K/min

the decomposition behaviour is attributed to the formation of

Cu2Se products due to the release of elemental Se.

20 25 30 35 40 45 50 55 60

0

5000

10000

15000

20000

25000

311

220

200

111

Cu2Se (JCPDS File No. 03-065-2982)

Inte

nsi

ty (

Arb

. Un

it)

Posistion (2 )

106 11

620

2108

110

006

102

101

100

CuSe (JCPDS File No. 34-0171)

Phase transformation from CuSe to Cu2Se structure as the synthesized

CuSe powder annealed at 653 K in N2 for 12 hours

In-Situ XRD pattern of synthesized SnSe Powder at 100 K – 300 K

20 30 40 50 60

Inte

nsi

ty (

Arb

. Uni

t)

Position (2 Theta)

300 K

275 K

250 K

225 K

200 K

175 K

150 K

125 K

100 K

420

40251

1

302

411

102

311

400

111

011

201

In-Situ XRD pattern of synthesized SnSe Powder at 298 K – 473 K

20 30 40 50 60

Pt

Pt

Inte

nsi

ty (

Arb

. Un

it)

Position (2Theta)

323K

298K

473K

448K

423K

398K

373K

348K

420

402511

302

411

10231

1

400

111

011

201

The structure was stable from low temperature 100K until high temperature 473 K where no additional or unassigned peaks are observed.

This indicates that the sample powder is stable and contains no impurities.

20 30 40 50 60

0

10000

20000

30000

40000

50000

60000

70000(c)

(b)

SnSe powder (JCPDS: 48-1224)

SnSe powder annealed at 873 K (JCPDS: 48-1224)

002

22021

1

11120010

1

110

SnSnSn

502

610

501

400

Inte

nsity

(A

rb. U

nits

)

Position (2 Theta)

210

601

420

511

302

411

10231

1

111

011

201

210

221

420

402

511

302

411

10231

1

400

111

011

201

SnO2

Sn

SnSe powder annealed at 1173 K (JCPDS: 01-077-03448)

(a)

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]:

2SnSe + 3O2 = SnO2 + Sn + 2SeO2

In-Situ XRD pattern of synthesized Cu2SnSe3 Powder at 100 K – 300 K.

20 30 40 50 60 70 80

300 K

275 K

250 K

225 K

200 K

175 K

150 K

125 K

Inte

nsi

ty (

Arb

. Uni

ts)

Position 2

100 K

331

400

311

220

111

In-Situ XRD pattern of synthesized Cu2SnSe3 Powder at 298 K – 523 K.

The Cu2SnSe3

structure was very stable at the temperature range 100K – 523 K where no additional or unassigned peaks are observed

20 30 40 50 60 70 80

* Pt

*

Inte

nsi

ty (

Arb

. Un

its)

Position 2

523 K

498 K

473 K

448 K

423 K

398 K

373 K

348 K

323 K

298 K

* 331

400

311

220

111

20 30 40 50 60 70 80

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

(b)

331

40031

1

220

111

Cu2SnSe

3 powder

Sn 2O

3

Sn 2O

3

200

Cu 3S

e 2

Cu 3S

e 2

Cu 2O

Cu 2O

Cu 2O

Cu2SnSe

3 powder annealed at 753 K

Inte

nsi

ty (

Arb

. Un

its)

Position (2 Theta)

Cu 2O

331

40031

1

220

111

(a)

Comparison between the as-synthesized Cu2SnSe3 powder with the annealed

Cu2SnSe3 powder

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

(a)

(b)

(c)

(d)

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.

The big islands are formed by the agglomeration of smaller grains with length in the range of 40 - 240 nm.

10-20 20-30 30-40 40-50 50-60 60-100 100-200 200-300

0

10

20

30

40

50

60

No.

of c

ount

s

Diameter size range (nm)

FESEM image and particle size distribution histogram of synthesized CuSe powder.

10-20 20-30 30-40 40-50 50-60 60-700

5

10

15

20

No

. of c

ou

nts


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 range

• average diameter size distribution of 54.1 nm

• rod-like shape particles• highest count of

diameter size range in 30-40 nm

• average size distribution of 35.2 nm.

50 100 150 200 250 300 350 400 450 50020

30

40

50

60

70

80

90

Lg

D

Temperature, T (K)

Mea

n C

ryst

allit

e S

ize,

Lg (

nm)

-2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

Dislocation D

ensityD x 10

14 (lines/m

2)

mean crystallite size obtained from XRD at temperature range of

100 – 473 K

(a)

(b)

(c)

(d)

SnSe powder showed particles with granules, sheet-like and agglomerate slightly.

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.

SEM result for Synthesized SnSe powder

20-30 30-40 40-50 50-60 60-70 70-80 80-900

5

10

15

20

25

30

35

No

. of c

ou

nts


FESEM image and particle size distribution histogram of synthesized SnSe powder

10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100

0

2

4

6

8

10

12

14

No.

of c

ount

s


TEM image and particle size distribution histogram of synthesized SnSe powder

• 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.

• 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

100 200 300 400 500 60034

36

38

40

42

44

46

48

Mea

n cr

ysta

llit

e si

ze, L

g (nm

)

Temperature, T (K)

SEM results for synthesized Cu2SnSe3 powder

(a)

(b)

(c)

(d)

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.

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.

100 200 300 400 500 60010

15

20

25

30

35

40

Lg

D

Temperature, T (K)

Mea

n C

ryst

allit

e S

ize,

Lg (

nm)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Dislocation D

ensity, D x 10

15 (lines/m2)

20-30 30-40 40-50 50-60 60-700

20

40

60

80

100

No

. of c

ou

nts


FESEM image and particle size distribution histogram of synthesized Cu2SnSe3 powder

0-10 10-20 20-30 30-40 40-50 50-600

5

10

15

20

25

30

35

40

No

. of c

ou

nts


TEM image and (b) particle size distribution histogram of synthesized Cu2SnSe3 powder

• 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.

• 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

50 100 150 200 250 300 350 400 450 500800

850

900

950

1000

1050

region II

Ele

ctri

cal c

ondu

ctiv

ity,

(

S/cm

)

Temperature, T (K)

region I

Electrical conductivity as a function of temperature for CuSe in bulk form

variable range

hopping thermionic emission

reduction in Hall mobility

due to phonon

scattering

• the decrease of electrical conductivity can be explained by the reduction in Hall mobility, due to the influence of 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 enough energy to jump across the depletion layers at the crystallite boundaries which act as potential barriers for conduction electrons [62, 63].

Hall mobility and carrier sheet densities as a function of temperature for CuSe in bulk form

• 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].

• 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].

100 150 200 250 300

10

100 N

c

Temperature, T (K)

Hal

l mob

ilit

y,

H (

cm2 /

Vs)

T-2.52

1E19

1E20

1E21

Car

rier

she

et d

ensi

ty, N

c (cm

-2)

• 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:

• 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

Thermionic Emission

2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.99.60

9.65

9.70

9.75

9.80

9.85

9.90

9.95

10.00

ln (T

1/2 )

1000/T

Ea = (46 4) meV

kT

EexpT a

o

ln (T1/2) versus (1000/T) at 349- 449 K for CuSe in bulk form

Variable Range Hopping

0.26 0.27 0.28 0.29 0.30 0.31 0.329.20

9.25

9.30

9.35

9.40

9.45

ln (T

1/2 )

T-1/4 (K-1/4)

ln (T1/2) versus (T-1/4) at 99 - 214 K for CuSe in bulk form

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]:

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.

4/1

oho T

TexpT

100 200 300 400 500 600

0.0

0.5

1.0

1.5

2.0

2.5

Ele

ctri

cal c

ondu

ctiv

ity,

(

S/c

m)

Temperature, T (K)

Electrical conductivity as a function of temperature for SnSe in bulk form

thermionic emission

variable range

hopping

• 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.

100 150 200 250 3000.1

1

10

100

1000

10000

100000

H

Nc

Temperature, T (K)

Ha

ll m

ob

ility

, H (

cm2 /

Vs)

1E9

1E10

1E11

1E12

1E13

1E14

1E15

Ca

rrie

r S

he

et D

en

sity

, Nc (

cm-2)

T-7.15

Hall mobility and carrier sheet densities as a function of temperature for SnSe in bulk form

• 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].

1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.60.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

ln (T

)1/2

1000/T

Ea = (0.44 0.03) eV

ln (T1/2) versus (1000/T) at 396- 526 K for SnSe in bulk form.

• 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.

Thermionic Emission


0.25 0.26 0.27 0.28 0.29 0.30 0.31-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

ln (T

)1/2

T-1/4 (K-1/4)

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].

100 200 300 400 500 600

500

550

600

650

700

750

region II

region I

Ele

ctri

cal c

ondu

ctiv

ity,

(

S/cm

)

Temperature, T(K)

Electrical conductivity as a function of temperature for Cu2SnSe3 in bulk form

• 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].

reduction in Hall mobility due to

phonon scattering

variable range

hopping thermionic emission

100 150 200 250 300

1

2

3

N

c

Temperature, T (K)

Hal

l mob

ilit

y, H

(cm

2 /Vs)

T-0.72

T-2.05

5E19

1E20

1.5E20

2E20

2.5E20

Car

rier

she

et d

ensi

ty, N

c (cm

-2)

Hall mobility and carrier sheet densities as a function of temperature for Cu2SnSe3 in bulk

form

• 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].

Region I

Region II

• 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.

Thermionic Emission

1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.79.1

9.2

9.3

9.4

9.5

9.6

9.7

ln (T

1/2 )

1000/T

Ea = (54 3) meV

ln (T1/2) versus (1000/T) at 375- 523 K for Cu2SnSe3 in bulk form

• 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.


0.23 0.24 0.25 0.26 0.27 0.28 0.29

8.95

9.00

9.05

9.10

9.15

9.20

ln (T

1/2 )

T-1/4 (K-1/4)

• 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].

ln (T1/2) versus (T-1/4) at 148 – 328 K for Cu2SnSe3 in bulk form

Thermal Properties

50 100 150 200 250 300 350 400 450 5000.005

0.006

0.007

0.008

0.009

0.010

0.011

0.012

0.013

1/

Temperature, T (K)

The

rmal

Diff

usiv

ity,

(cm

2/s

)

80

100

120

140

160

180

1/ (s/cm

2)

Thermal diffusivity and reciprocal thermal diffusivity measurement as a function of

temperature on CuSe pellet

• 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

lattice heat transfer (intrinsic scattering) is dominant in

100 – 350 K

50 100 150 200 250 300 350 400 450 500 550

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

region IIIregion II

1/

Temperature, T (K)

Th

erm

al D

iffu

sivi

ty,

(cm

2/s

)

region I

250

300

350

400

450

500

550

600

650

1/

(s/cm2)

• 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


• 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

lattice heat transfer may be dominant in this three temperature

range

Thermal diffusivity and reciprocal thermal diffusivity measurement as a

function of temperature on SnSe pellet

50 100 150 200 250 300 350 400 450 500 550 6000.0028

0.0030

0.0032

0.0034

0.0036

0.0038

0.0040

0.0042

0.0044

region II

1/

Temperature, T (K)

Th

erm

al D

iffu

sivi

ty,

(cm

2/s

)

region I

220

240

260

280

300

320

340

1/

(s/cm2)

Thermal diffusivity and reciprocal thermal diffusivity measurement as a function of

temperature on Cu2SnSe3 pellet

• 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.


• 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)

lattice heat transfer may be dominant in this three temperature range

Effect of annealing process

CuSe film

250 300 350 400 450 500 550 600 650 700

2500

3000

3500

4000

4500

5000

5500

6000

6500

Ele

ctri

cal C

on

du

ctiv

ity, (S

/cm

)

Annealing Temperature (K)250 300 350 400 450 500 550 600 650 700

2.00

2.10

2.20

2.30

2.40

2.50

2.60

2.70

Eopt

nr

Annealing Temperature, T (K)

Opt

ical

Ban

d G

ap, E

op

t (eV

)

3.200

3.220

3.240

3.260

3.280

3.300

3.320

3.340

Refractive Indices, n

r

Grain size increase (reduction of grain boundary scattering)

Formation of new phase (Cu2Se)

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

20 25 30 35 40 45 50 55 60

0

5000

10000

15000

20000

25000

Cu2Se

Cu2Se

Cu2Se

Cu2Se

Cu2Se

Inte

nsi

ty (

Arb

. Uni

t)

2(Degree)

673 K

573 K

473 K

373 K

300 K

Cu2Se

373 K

473 K

XRD pattern of CuSe film annealed at various temperature

Electrical Conductivity of CuSe film as a function of annealing temperature

Optical band gap and refractive indices of CuSe film as a function of annealing

temperature


SnSe Thin Film

decrease in grain size

• formation of new phase

• (SnO2)• grain growth

drastically

373 K 473 KAs-deposited

573 K 673 K

250 300 350 400 450 500 550 600 650 700

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Ele

ctri

cal C

on

du

ctiv

ity,

(S/c

m)


20 25 30 35 40 45 50 55 600

2000

4000

6000

8000

10000

12000

14000

SnO2

SnO2

SnO2SnO

2

SnO2

373 K

473 K

573 K

673 K

Inte

nsi

ty (

Arb

. Un

it)Position (2 Theta)

300 K

SnO2

SnO

AFM images

Electrical Conductivity of SnSe film as a function of annealing temperature

XRD pattern of SnSe films annealed at various temperature

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

250 300 350 400 450 500 550 600 650 7000.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

Eopt, indirect

Eopt, direct

n


Op

tica

l Ba

nd

Ga

p, E

op

t (e

V)

1.000

1.050

1.100

1.150

1.200

1.250

1.300

1.350

Re

fractive

Ind

ices, n

r

Optical band gap and refractive indices of SnSe film as a function of annealing

temperature

This behaviour may be attributed to the removal of water vapour or defect level

from the SnSe film after annealing process .

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

20 25 30 35 40 45 50 55 600

2000

4000

6000

8000

10000

12000

14000

SnO2

SnO2

SnO2SnO

2

SnO2

373 K

473 K

573 K

673 K

Inte

nsi

ty (

Arb

. Uni

t)

Position (2 Theta)

300 K

SnO2

SnO


Cu2SnSe3 Thin Film

increase in grain size

improvement of crystallinity

373 K 473 KAs-deposited

573 K 673 K

AFM images20 25 30 35 40 45 50 55 60

0

500

1000

1500

2000

2500

673 K

573 K

473 K

373 K

311

220

Inte

nsi

ty (

Arb

. Un

it)Position (2 Theta)

300 K

111

XRD pattern of Cu2SnSe3 film annealed at various temperature

250 300 350 400 450 500 550 600 650 7002000

2500

3000

3500

4000

4500

Ele

ctri

cal C

on

du

ctiv

ity,

(S

/cm

)


Electrical Conductivity of Cu2SnSe3 film as a function of annealing

temperature

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 n r

250 300 350 400 450 500 550 600 650 7002.22

2.24

2.26

2.28

2.30

2.32

2.34

2.36

2.38

2.40

Eopt, direct

n


Op

tica

l Ba

nd

ga

p, E

op

t (e

V)

1.400

1.500

1.600

1.700

1.800

1.900

2.000

2.100

2.200

Re

fractive

Ind

ices, n

r

Optical band gap and refractive indices of Cu2SnSe3 film as a function of annealing

temperature

the change of the average grains into

effectively larger grains

REFERENCES

1. Loferski, J.J. J. Appl. Phys., 1956. 27(7): 777-784.

2. Kainthla, R.C., Pandya, D.K., Chopra, K.L. J. Electrochem. Soc., 1982. 129(1): 99-102.

3. Lakshmikumar, S.T., Rastogi, A.C. Sol. Energy Mater. Sol. Cells, 1994. 32(1): 7-19.

4. Grozdanov, I. Synth. Met., 1994. 63(3): 213-216.

5. Li, B., Xie, Y., Huang, J., Qian, Y. Ultrason. Sonochem., 1999. 6(4): 217-220.

6. Bhuse, V.M., Hankare, P.P., Garadkar, K.M., Khomane, A.S. Mater. Chem. Phys., 2003. 80(1): 82-88.

7. Dhanam, M., Manoj, P.K., Prabhu, R.R. J. Cryst. Growth, 2005. 280(3-4): 425-435.

8. Zhang, S.Y., Fang, C.X., Tian, Y.P., Zhu, K.R., Jin, B.K., Shen, Y.H., Yang, J.X. Cryst. Growth Des., 2006. 6(12): 2809-2813.

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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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