Journal of Analysis and Computation (JAC) · 11/7/2018 · Journal of Analysis and Computation...
Transcript of Journal of Analysis and Computation (JAC) · 11/7/2018 · Journal of Analysis and Computation...
Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), www.ijaconline.com, ISSN 0973-2861
Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 1
ANNEALING EFFECT OF CUTE THIN FILMS
A. Selvaraj & G. Kanchana
Assistant Professor , Department Of Physics,
NPR Arts & Science College, Natham, Dindigul.
ABSTRACT
Thin films of cupric telluride (CuTe) of thickness 900nm have been prepared by thermal evaporation
technique,deposited at the rate of 15.3 Α/sec on to well-cleaned glass substrate kept at 200 K under
vacuum of better than 10-5Torr.The bulk sample of CuTe also has been taken for investigations. The
deposited films were annealed at two different temperature (150 °C and 250 °C) for one hour under
vaccum atmosphere and then used for characterization. X ray diffraction studies confirmed that the
composition and the polycrystalline nature of CuTefilms.The SEM studies have been confirmed that
the smooth surface of the CuTe thinfilm. The elemental analyzed by EDAX. The optical properties were
observed by UV visible and PL spectrum. In the PL spectrum whereas the peak intensity has been
varied.. The grain size of CuTe thin films were estimated by around 40.6nm for 150°C and 54.1nm for
250°C sample.
Keyword: CuTe, Thin films, Thermal evaporation, XRD, SEM&EDAX, UV Visible and PL.
1. Introduction
Copper telluride belongs to the copper
chalcogenide (I-VI) compound) group of
material. Chalcogenide is a chemical
compound consisting of at least one
chalcogen anion and at least one more
electropositive element. The term
chalcogenide is more commonly reserved
for sulfide, selenides, tellurides, rather than
oxide. Many metal ores exist as
chalcogenides. Photoconductive
chalcogenide glasses are used in xerography.
Some pigments and catalysts are also based
on chalcogenides. The Copper telluride have
different crystal structure depending upon
the value of x (1<x<2) Cu2-xTe and are
usually p-type compound semiconductor. It
is suitable for application in solar cells,
photodetectors, electrodetector, electrode
and other electronic application such as for
micro wave shielding coating and non-
volatile memories [1].The binary
semiconductor CuTe has an energy gap Eg
around 1.5 eV at room temperature, very
close to the range for optimum solar energy
conversion. For this reason this material is
of considerable interest for device
application. The crystallographic structure of
mineral vulcanite CuTe (a=3.16 Å, b= 4.08
Å and c=6.94 Å is orthorhombic, Pmmn(59)
space group andit is highly birefringent and
pleiochroic.[2].Bahl [3] hasstudied the K
absorption edge on CuTe and he has
estimated that the K absorption edge shift
towards the high-energy side is due to the
transfer of electron from tellurium to copper.
Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), www.ijaconline.com, ISSN 0973-2861
Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 2
Attempts have been made to use CuTe as a
photovoltaic cell. Detailed structural studies
of CuTe and optical studies have been made
by several workers[4-6].However,
CopperTelluride has rarely been the subject
of study.
In recent years, Annealing effect of CuTe
thin films are very useful technique for the
study of application of solar cells and their
interactions with other excitations. The
efficiency solar cell CuTe thin film was 14%
for the prepared sample. In this paperwe
present the preliminary results of the study
of the optical characteristics of thin
films.The efficiency solar cell CuTe thin
film was 14% for the prepared sample. The
have attempt has been made previously to
investigate the optical characteristics of thin
films of CuTe was 22%.
2. Experimental
Cooper Telluride (CuTe) alloy purchased
from M/S Aldrich (India) company with
99.99% purity was used for preparing thin
films by thermal evaporation. A
knownamount of CuTe material was taken
and evaporated the entire charge from a
molybdenum boat under a vacuum better
than 2 × 10-5 mbar on well cleaned glass
substrates of 0.01 × 0.03 m2. The glass
substrates were cleaned with hot chromic
acid and distilled water before mounting
them in the vacuum chamber. Copper
telluride films of thickness 900 nm were
deposited at the rate of 15.5 Å/s. The
thickness of films and the deposition rate
were monitored using a digital quartz-crystal
thickness monitor. The as grown CuTe films
were annealed at 150°C and 250°C for 2
hours at a pressure of 2×10-3 mbar and
afterannealing the films were allowed to
cool down to a room temperature in
vacuum.Fig. 1 shows the X ray diffraction
pattern of CuTe thin films. This has
confirmed composition of CuTe in films and
its polycrystalline nature. The surface
morphological studies were analyzed by
SEM (Scanning Electron Microscope). The
compositional information was also obtained
from Energy Dispersive Analysis of X-rays
(EDAX)measurements. Optical studies were
analyzed by UV Visible and
Photoluminescence spectrum.
30 60
0
700
1400
In
ten
sit
y
2
150C(a)
250C(b)(0 1
0)
(0 2
0)
(1 2
1)
(1 3
1)
(0 4
1)
(0 1
0)
(0 2
0)
(0 4
1)
(1 3
1)
(1 2
1)
(a)
(b)
Figure 1 XRD pattern of copper telluride
thin films of 900nm thickness annealed at
150°C(a) and 250°C(b)
Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), www.ijaconline.com, ISSN 0973-2861
Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 3
Figure 2(a) SEM image for 900nm
thickness of copper telluride thin film
annealed at 150°C
Figure 2(b) SEM image for 900nm
thickness of copper telluride thin film
annealed at 250°C
Figure3(a): EDAX spectra for 150°C CuTe
Figure 3(b): EDAX spectra for 250°C
CuTe
Table 3 (a) Element are present in
thesample
Com
posi
tio
n Atomic
percentage (%)
Weight
percentage (%)
Cu Te Tot Cu Te Tot
150
°C
30.
7
69.
2
100 18.1 81.9 10
0
250
°C
48.
4
51.
5
100 31.8 68.1
10
0
1 2 3 4 5 6 7 8 9 10keV
0
2
4
6
8
10
12
cps/eV
Te Te Te Cu Cu
2 4 6 8 10 12keV
0
2
4
6
8
10
cps/eV
Te Te Te Cu Cu
Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), www.ijaconline.com, ISSN 0973-2861
Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 4
400 600 800 10000.18
0.19
0.20
0.21
0.22
0.23
0.24
0.25
Ab
so
rba
nc
e
wavelength(nm)
150C
(a)
Figure4(a)&(b) The absorption spectra for
CuTe thin films of thickness 900nm
annealed at 150°C and 250°C
1 2 3 4 5 6 7
0
100
200
300
400
500
600
h
photonenergy(eV)
150°C
3.94 eV
1 2 30
10
20
30
40
50
(h)2
Photonenergy (eV)
250C
2.04 eV
Figure 4(a)&(b)Tauc-extrapolation graph
for CuTe thin films for different annealing
temperature (150°C and 250°C)
4(a)&(b) Band gap are presented in
table
400 500 600 700 800 900 10001.5
1.6
1.7
1.8
1.9
2.0
Ab
sorb
an
ce
Wavelength (nm)
250C
(b)
Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), www.ijaconline.com, ISSN 0973-2861
Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 5
Annealing
temperature (°C)
Band gap (eV)
150°C 3.94
250°C 2.04
400 450 500 550 6000
500
1000
1500
2000
2500
Inte
nsi
ty
wavelength(nm)
150C(a)
250C(b)
(b)
(a)
Figure 4.1 photoluminescence spectra of
CuTe thin films for different annealing
temperature (150°C and 250°C)
3. Results and discussion
Structural analysis
Figures 1 shows that the XRD patterns of
copper telluride thin films of thickness
900nm annealed at 150°C and 250°C.From the XRD analysis of CuTe thin film the
diffraction peaks observed at 2θ=12.87,
25.76, 44.54, 52.74 and 60.61, which is
indexed the corresponding hkl plane values
(010), (020), (121), (131) and (041)
respectively. When the annealing
temperature increases from 150°C to 250°C
CuTe thin film, the peak intensity increases
and the particle size gets increased. The
XRD result confirmed that the structure is in
orthoromphic and these results are good
agreement with JCPDS NO : (07-0110) data
The crystallite size have been calculated
using Debye-Scherrer formula (D),
D = 𝐾𝜆
𝛽 cosӨ x
180
𝜋
Where,
K→ Shape factor (Taken as 0.94 for
spherical particles)
β→ Full Width Half Maximum of
the prominent peak
λ→ Wavelength of X-ray
θ→ Diffraction (Bragg) angle
The grain size are presented in table
Annealing
Temperature
( °C)
2Ө
Deg
FWHM hkl Grain
Size(D)
nm
150 12.870 0.1968 001 40.6
250 12.925 0.1476 010 54.1
The amorphouse phase is reduced with
increasing annealing temperature, since
more energy is supplied for crystallite
growth, thus resulting in an improvement in
crystallinity of CuTe films. Therefore, it is
believed that the annealing temperature
increases with increase in crystalline size
and the reduction in amorphouse phase of
CuTe films.
Morphological studies
Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), www.ijaconline.com, ISSN 0973-2861
Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 6
Figures 2(a) and 2(b) shows that SEM
pictures of typical 900nm thickness of
copper telluride thin films which are
annealed at temperatures 150°C and 250°C.
SEM was used for morphology and size
distribution investigation of the thin films.
The SEM images have a good appearance
and useful for judging the surface structure
of the coated surface. The SEM image of
150°C annealed film clearly shows the
crystallite size of CuTe thin film. The SEM
image of 250°C annealed film are uniformly
high smooth surface [7].
Elemental analysis
Figures 3(a) shows the EDAX spectrum of
CuTe thin film annealed at 150°C. The
spectrum clearly indicates that the presence
of Cu and Te without other impurities. From
the EDAX data it was found that the weight
percentage of Copper and telluride varied
between 18.1- 81.9(%).
Figures 3(b) shows the EDAX spectrum of
CuTe thin film annealed at 250°C. The
spectrum clearly indicates that the presence
of Cu and Te without other impurities.From
the EDAX data it was found that the weight
percentage of Copper and telluride varied
between 31.8- 68.1(%).
From the table 3(a), we conclude that, when
increasing the annealing temperature of
copper telluride thin films, the weight
percentage of copper increases and telluride
decreases.
Optical studies
The present study is aimed to study
the optical properties of various annealing
temperature of 900nm thin films of copper
telluride. Here we have taken two optical
measurement such as UV-Vis and
photoluminescence studies to estimate the
optical band gap of the sample.
Absorption studies
Figures 4(a)&(b) shows that the absorption
spectrum for the different annealing
temperature (150°C and 250°C) of copper
telluride thin films with the thickness
900nm. The figure indicates that the films
have high absorbance in the visible regions.
It is observed that the maximum absorption
peak shift slightly towards the smaller
wavelength with the increasing annealing
temperature.
The absorption tends to be very high in the
UV region for all the annealing temperature.
There is a very high absorption of energy in
the near visible region. The deposited films
have high absorbance in the UV visible
region[8].
Optical band gap (Eg) was determined by
analyzing the optical data with the
expression for the optical absorption
coefficient (α) and photon energy (һν) using
the Tauc relation,
𝛼 =𝐾(ℎ𝜈−𝐸𝑔)
ℎ𝜈
𝑛
2
Where K is a constant, the value of n is
equal to one for a direct-gap material, and
four for an indirect-gap material. Plots of
(αһν)2versus (һν) were drawn using the
above equation. Extrapolation of the linear
portion of the plot of energy axis yielded the
direct band gap value.
The amorphous phase is reduced with
increasing annealing temperature, since
more energy is supplied for crystallite
growth, the resulting in an improvement in
crystallinity of CuTe films. Therefore, it is
believed that both the increasing in
crystallite size and the reduction in
amorphous phase, may be the reason for
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Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 7
decreasing in band gap of annealed
CuTefilms[9].
Photoluminescence studies
Figures 4.1 shows that the
photoluminescence spectra of CuTe thin
films with thickness 900nm at different
annealing temperature (150°C and 250°C).
The photoluminescence spectra of CuTe thin
films of thickness 900nmn recorded at
different annealing temperature (150°C and
250°C). A strong emission band in visible
range is observed for the CuTe films of
different annealing temperature 150°C and
250°C. There is a strong peak observed at
about 503nm. The emission peak intensity
increased with increasing annealing
temperature. As the bandgap of CuTe is
about 3.92eV. This value is relatively very
close to the value of UV-bandgap. There is
no remarkable shift is observed from the PL
curve. Only the intensity variation is
observed.
4. Conclusion
Copper telluride thin film of 900nm were
prepared on a glass substrate by thermal
evaporation technique under the vaccum
pressure of 10-5Torr. The prepared thin film
of CuTe was annealed at two different
temperatures (150°C and 250°C) for 1hour
under vaccum atmosphere. The films were
subjected to XRD, SEM and EDAX, UV-
Visible spectroscopic and
photoluminescence study.
From the XRD patterns of the annealed
CuTe thin films of different temperature
showed polycrystalline nature and have a
orthoromphic structure with a preferred
orientation along (010) plane. The crystallite
size increases (40.6nm to 54.1nm) with
increasing annealing temperature with
decrease of microstrain and dislocation
density.
The surface morphology of the sample were
characterized by scanning electron
microscopy. The SEM image have a good
appearance and the film surface structure is
highly smooth. The crystallite quality
increased with increased annealing
temperature which understood by studying
the microstructural properties.
From the EDAX analysis, The spectrum
clearly indicates that the presence of Cu and
Te without other impurities. The weight
percentage of Cu and Te (18.1- 81.9) %
varies when increasing the annealing
temperature of 150°C and The weight
percentage of Cu and Te31.8- 68.1 % varies
when increasing the annealing temperature
of 250°C.
From the UV-Visible absorption spectra,
while increasing the annealing temperature,
the absorption peaks were obtained at
572nm for 150°C and 655nm for 250°C. The
deposited films have high absorbance in the
UV visible region. It is observed that the
maximum absorption peak shift slightly
towards the smaller wavelength with the
increasing annealing temperature. The
optical band gap CuTe decreases ( 3.94eV to
2.04eV ) with increasing annealing
temperature (150°C to 250°C).
From the PL studies, A strong emission
band in visible range is observed for the
CuTe films of different annealing
temperature 150°C and 250°C. There is a
strong peak observed at about 503nm. As
the bandgap of CuTe is about 3.92eV. There
is no remarkable shift is observed from the
PL curve. Only the intensity variation is
observed.
Acknowledgement
I express my deepest gratitude and
indebtedness to my Supervisor and guide
Dr.K.Neyvasagam, M.Sc., M.Phil.,PGDCA.,
Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), www.ijaconline.com, ISSN 0973-2861
Volume XI, Issue I, Jan- October 2018
A. Selvaraj & G. Kanchana 8
Ph.D. Associate professor, Department of
Physics, The Madura College, Madurai for
his immeasurable help and valuable
suggestion throughout this study and for the
successful completion of the report in time.
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