Journal of Analysis and Computation (JAC) · 11/7/2018 · Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), , ISSN 0973-2861 Volume XI, Issue I,

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.

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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)





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





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)





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





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





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.,





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.

Reference

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[2] M. K. Bhal, J. Phys. C: Solid State phys.

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[3] F. Hanus, M. Wautelet, J. Appl. Phys.

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[4] F. Hanus, M. Wautelet, Appl. Surf.

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[5] F. Pertlik, Mineralogy and Petrology, 71,

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[6] Y. Lefebvre, J. L. Bocquet, J. Phys: B.

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[7] J. Goldstein, D. Newbury, D. Joy, C.

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Documents

Journal of Analysis and Computation (JAC) · 11/7/2018 · Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), , ISSN 0973-2861 Volume XI, Issue I,