Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.11, pp.1051-1060, 2011
jmmce.org Printed in the USA. All rights reserved
1051
Spectro-Structural Characterization of Chalcogenide Films
Containing Cd, Te and Se
T.M. Rajakumar
1*
, C. Sanjeeviraja
2
and R. Chandramani
3
1
Department of Physics, Bharathiar University, Coimbatore, India
1
Department of Physics, Dayananda Sagar College of Engineering, Bangalore-560 078, India
2
Department of Physics, Alagappa University, Karaikudi-630 003, India
3
Department of Physics, Dayananda Sagar College of Engineering, Bangalore-560 078, India
*Corresponding Author: [e-mail]
ABSTRACT
Chalcogenide films find many applications in electronics as memory device, laser writer &
xerography. To tailor the property to the requirement, various compositions of Cd, Te and Se
have been deposited and characterized optically. Films have been deposited by thermal
evaporation as well as by electron beam evaporation. Thermal analysis such as TGA, DTA and
DSC has been carried out before deposition to ensure the composition. Dependence of Eg on the
composition has been justified from (T% data) Transmittance measurements. Drastic changes in
optical property due to annealing in the range 200°C to 400°C have been investigated.
Key words: Chalcogenide, E
g
, TGA, DTA, DSC, XRD, Transmittance, Annealing
1. INTRODUCTION
The semiconductor compounds belonging to the Cadmium Chalcogenide family such as Cd Se
Te can be advantageously used as thin poly crystalline/ amorphous films for various technical
applications such as memory device, xerography, and excellent laser writer sensitivity because of
their direct Eg ranging from 1.6 to 2.2 eV [1, 2]. Among the various methods in use, the
deposition or growth of films by thermal evaporation is simple. The method can be successfully
applied to get films of many semi conducting materials.

1052 T.M. Rajakumar, C. Sanjeeviraja and R. Chandramani Vol.10, No.11
In the present study, to tailor the properties of the films to the requirement, various compositions
of Cd, Te, Se having the formula Cd
y
Te
x-y
Se
1-x
have been deposited and characterized optically.
Many of the films with the composition 0 ≤ x ≤ 1, and 0 ≤ y ≤ 1 have been deposited by
vacuum thermal evaporation [3]. Other films have been deposited by electron beam evaporation
[4]. In this case, before depositing the films, to make sure of the desired composition of the
compounds, thermal analysis such as TGA, DTA & DSC have been carried out. Compositional
dependence of Eg in Cadmium Chalcogenide has been investigated through optical
characterization. Some of the samples have been annealed at 200°C to 400°C. Effects of
annealing on optical property have been analyzed [5, 6].
2. MATERIALS & METHODS
Commercially available glass and quartz slides were used as substrates. Substrates were first
washed with chromic acid, next cleaned with detergent, rinsed with acetone and finally, cleaned
with double distilled water before using. Elements Cd, Te, Se were procured in pure form from
Aldrich and are used for depositing film.
Cd
y
Te
x-y
Se
1-x
thin films were deposited on glass and quartz substrates by thermal vapor
deposition technique with vacuum of ≈ 10
-5
torr, using ‘HIND HIVAC 12A4’ equipment.
Tantalum boat sources were used for the evaporation of stochiometric powder of the CdTeSe
ternary compound. Also thin films of Cd
y
Te
x-y
Se
1-x
were deposited on glass and quartz
substrates by electron beam evaporation technique at vacuum of ≈ 10
-5
torr, using ‘HINDIVAC
12A4D’ & ‘EBG-PS-3K’ gun powder supply equipment. UV-VIS-IR studies were carried out
using Micro pack DH-2000 equipment. The transmission spectra in the region 180 nm to 1100
nm has been collected and optical parametersα, K, n and E
g
have been evaluated. Structural
analysis has been carried out by XRD and EDAX. Stylus method has been used to determine the
thickness of the film.
3. RESULTS AND DISCUSSION
3.1 XRD
X-ray diffraction (XRD) is a versatile, non-destructive technique that reveals detailed
information about the chemical composition and crystallographic structure of natural and
manufactured materials. For all the combinations of Cd Te Se samples XRD has been taken.
XRD confirms (ascertains) the amorphous nature of the sample. Amorphous nature has
increased with increasing Chalcogenide content. Typical X-ray diffraction pattern of the films
deposited on different substrates is given in Fig. 1(a) and Fig. 1(b). The X-ray diffraction
pattern of the films, possessing various compositions, reveals that irrespective of the

Vol.10, No.11 Spectro-Structural Characterization of Chalcogenide Films 1053
deposition method and nature of substrate, the films were found to be amorphous in nature
with slight shift in 2θ values shown in Table-1 [7].
Position [°2Theta]
20 30 40 5060 70
Counts
0
20
40
60
80
Sample - 1
Position [°2Theta]
20 30 4050 60 70
Counts
0
20
40
60
80
Sample - 6
Fig. 1(a) Fig. 1(b)
X-ray diffraction pattern of Cd
0.8
Te
0.1
Se
0.1
X-ray diffraction pattern of Cd
0.5
Te
0.4
Se
0.1
Table – 1.
Sl.No Method Composition 2θ
θθ
θ
1
2
3
4
5
6
7
8
9
10
Thermal evaporation
Thermal evaporation
Thermal evaporation
Thermal evaporation
Thermal evaporation
Electron beam evaporation
Electron beam evaporation
Annealed at 200°
Electron beam evaporation
Annealed at 400°
Electron beam evaporation
Electron beam evaporation
Cd
0.8
Te
0.1
Se
0.1
Cd
0.7
Te
0.2
Se
0.1
Cd
0.6
Te
0.2
Se
0.2
Cd
0.6
Te
0.3
Se
0.1
Cd
0.5
Te
0.4
Se
0.1
Cd
0.6
Te
0.2
Se
0.2
Cd
0.6
Te
0.2
Se
0.2
Cd
0.6
Te
0.2
Se
0.2
Cd
0.7
Te
0.2
Se
0.1
Cd
0.8
Te
0.1
Se
0.1
22.5°
24°
29°
23°
29°
23.5°
21.5°
21°
22°
23°
3.2 Stylus – Thickness Measurement:
Thickness of the thin film is the most significant parameter, which plays important role in the
properties of the thin film. Film thickness measurement (t) techniques are based on different
principles such as the mass difference, light absorption, interference effects, conductivities,
capacitance etc., of the films. Stylus method is a promising method to determine the thickness.
The effect of applying a rounded stylus to thin metallic films on glass substrates has been
investigated using diamond and steel styli with tip radii of approximately 25 µm and loadings of
up to 230 g. In many applications, particularly in the case of the interference filters, an

1054 T.M. Rajakumar, C. Sanjeeviraja and R. Chandramani Vol.10, No.11
antireflection coating etc., the success of the fabrication depends only on the deposition of
specific thickness of the film.
The thickness of the films was estimated to be approximately 290 nm to 790 nm using the stylus
surface profilometer. Measurements have been done at two or three places. The values obtained
confirm the uniformity of the film.
3.3 TGA, DTA and DSC Analysis
3.3.1 TGA and DTA graphs for sample Cd
0
.
6
Te
0.2
Se
0.2
While depositing the films, to ensure the desired composition x of the compound, TGA, DTA,
and DSC studies have been carried out. TGA analysis provides a quantitative measurement of
any weight changes associated with thermally induced transitions. The TGA peak for the sample
is shown in Fig. 2(a).
In DTA, the difference in temperature between the sample and a thermally inert reference
material is measured as a function of temperature. Any transition that the sample undergoes
results in liberation or absorption of energy by the sample with a corresponding deviation of its
temperature from that of the reference. The DTA peak for the sample is shown in Fig 2(a).
In DSC, the sample and reference materials are subjected to a precisely programmed temperature
change. When a thermal transition occurs in the sample, thermal energy is added to either the
sample or the reference in order to maintain both the sample and reference at the same
temperature. Since the energy transferred is exactly equivalent in magnitude to the energy
absorbed or evolved in the transition, the balancing energy yields a direct calorimetric
measurement of the transition energy. The DSC peak value for the sample is 494.43°C [Fig
2(b)].
Fig 2(a) Fig 2(b)
DTA & TGA graph for sample Cd
0
.
6
Te
0.2
Se
0.2
DSC graph for sample Cd
0
.
6
Te
0.2
Se
0.2

Vol.10, No.11 Spectro-Structural Characterization of Chalcogenide Films 1055
3.4 Optical Measurements
Transmission spectra in the region 180 – 1100 nm has been collected using Micro pack DH-2000
equipment. The T% were used to evaluate the optical parameters such asα, k, n, and E
g
. From
Transmittance spectra, the absorption coefficient ‘α’ has been evaluated using the formula






=Tt
1
log
303.2
α
------------ (1)
where ‘t’ is the thickness of the film and ‘T’ is the transmittance percentage [2].
The value of absorption coefficient (α) provides valuable information about the inter band
transition and hence the energy band structure of the materials.
Extinction coefficient ‘K’ has been evaluated using the formula
π
λα
4
=K --------- (2)
where ‘λ’ is the wavelength and ‘α’ is the absorption coefficient.
Refractive index ‘n’ has been evaluated using the formula
Rk
n
π
α
λ
4
= ---------- (3)
where ‘R’ is the reflectance percentage.
The observed values of λ, T% and calculated values of α, k, n, and E
g
are shown in Table- 2.
Plots of (a) T% Vs λ (b) (αhγ)
2
Vs E
g
(Tauc plot) are shown in Figure 3(a) & (b). Optical band
gap energy has been evaluated from the Tauc plot (αhγ)
2
Vs E
g
. [8].
Table -3 shows the band gap energy (E
g
) for different compositions. Variation of E
g
with
composition is shown in Fig 3.4(c). E
g
has increased with increase in Cd from 50% to 70% and
has answered for decrease in E
g
for 80%. Similar change or turning point is observed even in
electrical properties [9].
Fig 3(a ) Fig 3(b)
Sample-2 Wavelength Vs T% graph Sample-2 E
g
Vs (αhγ)
2
graph
0
10
20
30
40
50
0.000.50 1.001.502.00 2.50 3.00 3.50
(
8 88 8
h
8 88 8
)
2x
1
0
1
3
Eg in eV
S-2 Eg vs (8 88 8h8 88 8)2

1056 T.M. Rajakumar, C. Sanjeeviraja and R. Chandramani Vol.10, No.11
Cd Composition vs Eg
1.5
2
2.5
4050 6070 8090
Cd% in Composition ---->
Eg in eV --->
Fig 3(c)
Optical band gap vs the composition of Cd in CdTeSe graph.
Table-2
Sample-2: Cd
0.7
Te
0.1
Se
0.2
Thickness of the film:640 nm
λ λλ λ in
nm
T
α αα α
x 10
5
α αα α
2
X10
13
E in
eV K
( (( (α αα α h γ γγ γ )
2
x 10
13
n
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1.82
0.88
1.50
2.74
4.66
7.31
10.54
14.24
18.50
22.92
27.42
30.66
32.85
34.07
62.58
73.80
65.54
56.21
47.90
40.86
35.15
30.46
26.36
23.01
20.22
18.47
17.39
16.82
3.91
5.44
4.29
3.16
2.29
1.67
1.23
0.92
0.69
0.52
0.40
0.34
0.30
0.28
3.36
2.94
2.61
2.35
2.14
1.96
1.81
1.68
1.57
1.47
1.38
1.31
1.24
1.18
0.174
0.235
0.235
0.223
0.209
0.195
0.182
0.169
0.157
0.146
0.136
0.132
0.131
0.134
44.30
47.11
29.36
17.52
10.50
6.42
4.05
2.62
1.71
1.14
0.78
0.58
0.46
0.39
1.01
1.00
1.01
1.02
1.04
1.07
1.11
1.16
1.22
1.29
1.37
1.44
1.48
1.51
Table-3 Optical band gap energies
Sample No Composition Eg in eV
sample-1(S-1)
sample-2(S-2)
sample-3(S-3)
sample-4(S-4)
sample-5(S-5)
sample-6(S-6)
Cd
0.8
Te
0.1
Se
0.1
Cd
0.7
Te
0.1
Se
0.2
Cd
0.7
Te
0.1
Se
0.2
Cd
0.6
Te
0.2
Se
0.2
Cd
0.6
Te
0
.
3
Se
0.1
Cd
0.5
Te
0.4
Se
0.1
1.6
2.05
2.2
1.95
1.95
1.75

Vol.10, No.11 Spectro-Structural Characterization of Chalcogenide Films 1057
3.5 Annealing Studies
A sample answering for complete reflection changes to comparable(R & T) for annealing at
200°C. Finally it changes to complete T% for 400°C annealing. Values are shown in Table – 4
and Fig 4(a).
When ‘T’ and ‘R’ are comparable, Absorption coefficient has been evaluated using the formula
[9]
(
)





−
=T
R
t
2
1
log
303.2
α
Effects of annealing on the optical property of the films are really surprising. Annealing of the
films has resulted in drastic change in R & T%. A good reflecting film has changed to
comparable R & T and finally to a film with good T%.
Another effect of annealing is drastic change in Eg has also been noticed.
Annealing the sample-7 (S-7), E
g
has decreased from 1.95 (S-8:1.8) to 1.75 (1.3) for 200°C,
where as for 400°C annealing, E
g
has increased to 2.65 (2.6). Band gap variation with annealing
is shown in Table-(5). The plots of band gap Vs temperature is shown in Fig 4(b) and (c) for
Sample-7(S-7) and sample-8(S-8) respectively.
Table – 4 Sample-7
T % R%
wavelength
As
deposited
Annealed
at 200°C
Annealed
at 400° C
As
deposited
Annealed
at 200° C
Annealed
at 400° C
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
3.21
3.08
4.18
5.65
7.23
8.70
9.82
10.54
10.97
11.27
11.55
11.69
11.70
11.64
42.29
42.79
44.82
47.06
49.11
50.50
51.00
50.74
50.20
50.10
50.52
50.99
51.36
51.75
90.45
93.38
94.77
95.61
95.60
94.95
94.06
92.81
91.15
89.68
89.03
88.87
88.39
87.79
96.78
96.91
95.81
94.35
92.76
91.29
90.17
89.45
89.02
88.72
88.44
88.30
88.29
88.35
57.70
57.20
55.17
52.94
50.88
49.49
48.99
49.25
49.79
49.90
49.47
49.01
48.63
48.24
9.54
6.61
5.22
4.38
4.39
5.04
5.93
7.19
8.85
10.31
10.96
11.12
11.60
12.20

1058 T.M. Rajakumar, C. Sanjeeviraja and R. Chandramani Vol.10, No.11
S-7 Wavelength vs R & T %
40
60
80
100
02004006008001000 1200
Wavelength
R% & T%
R%- As depositedR%-Anneald at 200°C
T%-Anneald at 200°CT%-Anneald at 400°C
Fig 4(a)
S-7 Wavelength Vs R & T%.
S-8 Variation of band gap energy with annealing
As deposited
Annld at 200
0
C
Annld at 400
0
C
0
0.5
1
1.5
2
2.5
3
Temperat ure
Band gap energy
Fig 4(b) Fig 4(c)
S-7 Variation of band gap with annealing. S-8
Variation of band gap with annealing.
Table-5. Band gap variations.
Optical Band gap in eV
Sample Composition As
Deposited
Annealed
at 200
0
C
Annealed
at 400
0
C
S-7
S-8
Cd
0.6
Te
0.2
Se
0.2
Cd
0.7
Te
0.2
Se
0.1
1.95
1.8
1.75
1.3
2.65
2.6
As
deposited Annld at
200
0
C
Annld at
40 0
0
C
0
0.5
1
1.5
2
2.5
3
B
a
n
d
g
a
p
e
n
e
r
g
y
T emperature
S-7 Variation of band gap with
annealing

Vol.10, No.11 Spectro-Structural Characterization of Chalcogenide Films 1059
4. CONCLUSIONS
Cd chalcogenides for various compositions, 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1 were prepared by thermal
evaporation as well as by electron beam evaporation.
• XRD has confirmed the amorphous nature of the films.
• Uniformity of the films has been confirmed by Stylus measurement.
• Dependence of band gap with the composition has been justified by optical studies.
• Transmittance percentage has varied from 0.889 to 34.09 for Cd varying in the
range 0 ≤ x ≤ 1.
• Increase in Cd has resulted in increase of E
g
which is a cumulative effect of the increase
of Cd along with decrease in Se.
• Annealing at 200°C has resulted in decrease of E
g
.
• Effects of annealing on the optical property of the films are really surprising. Annealing
of the films has resulted in drastic changes in the optical properties.
• Drastic change in E
g
also been noticed after annealing at 200°C and 400°C.
• Study reveals that slow rate changes occurring at low temperature ranges 200°C to 400°C
can be used to control the optical/electrical property and finally optical band gap in a
precise manner.
• Further work to confirm the exact turning point in E
g
is in progress.
ACKNOWLEGMENT
The authors thank Dr.Premachandra Sagar, Vice Chairman, Dayananda Sagar Institutions,
Bangalore, India for his continuous encouragement.
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1060 T.M. Rajakumar, C. Sanjeeviraja and R. Chandramani Vol.10, No.11
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