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Studying The Optical Properties of CdO and CdO: Bi Thin Films

Authors:
  • Mustansiriyah University

Abstract

Cadmium Oxide and Bi doped Cadmium Oxide thin films are prepared by using the chemical spray pyrolysis technique a glass substrate at a temperature of (400⁰C) with volumetric concentration (2,4)%. The thickness of all prepared films is about (400±20) nm. Transmittance and Absorbance spectra are recorded in the wave length ranged (400-800) nm. The nature of electronic transitions is determined, it is found out that these films have directly allowed transition with an optical energy gap of (2.37(eV for CdO and) 2.59, 2.62) eV for (2% ,4%) Bi doped CdO respectively. The optical constants have been evaluated before and after doping.
Baghdad Science Journal Vol.13(3)2016
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DOI: http://dx.doi.org/10.21123/bsj.2016.13.3.0593
Studying The Optical Properties of CdO and CdO: Bi Thin
Films
Zain A. Muhammad * Ahmed T. Hassan **
Yasmeen Z. Dawood*
* Al-Mustansiriyah University, College of Education, Physics Department
** Ministry of Education, Directorate General for Education/ Baghdad AL-Karkh / 1
Received 10/3 /2016
Accepted 13/6 /2016
This work is licensed under a Creative Commons Attribution-NonCommercial-
NoDerivatives 4.0 International Licens
Abstract:
Cadmium Oxideand Bi doped Cadmium Oxidethin films are prepared by
using the chemical spray pyrolysis technique a glass substrate at a temperature of
(400C) with volumetric concentration (2,4)%. The thickness of all prepared films is
about (400±20) nm. Transmittance and Absorbance spectra are recorded in the wave
length ranged (400-800) nm. The nature of electronic transitions is determined, it is
found out that these films have directly allowed transition with an optical energy gap
of (2.37 eV for CdO and 2.59, 2.62) eV for (2% ,4%) Bi doped CdO respectively.
The optical constants have been evaluated before and after doping.
Key words: CdO-Bi) Thin Films, Optical Properties.
Introduction:
Cadmium Oxide (CdO) is one of these
important semiconductors oxides which
use for a variety of application,
including ,smart window ,sensor, solar
cell, optical communication, anti-
reflection coatings and phototransistor
and flat panel display photodiodes [1-
7].Various techniques have been used to
deposited CdO thin films such as sol-
gel [8], chemical bath deposition [9]
chemical vapor deposition [11] The
spray pyrolysis [14] . In this paper CdO
and (CdO:Bi) thin film is prepared by
spray pyrolysis technique in addition to
investigating their optical properties by
using (PU- 8800- UV/VIS
Spectrophotometer).
Experimental Details:
The CdO solution is prepared with
(0.1M) using cadmium acetate (Cd (CH3
COO)2 . 2H2 O) as a precursor salt and
distilled water as a solvent (100 ml). Bi
doped CdO thin films are prepared with
(0.1M) using Bismuth nitrate
pentahydrate (Bi(NO3 )3 ∙5H 2 O) which
is dissolved in a distilled water (25
ml). Preparing films are sprayed on
borcilecat glass substrate after cleaning
them and putting them on an electrical
heater for about (30mins). Each
spraying period lasts for about (8 sec)
followed by about (5mins) waiting
period to avoid a too strong cooling of
the substrate. By using weighting
method and electronic balance Metter
AE-160), the thickness of all prepared
Open Access
Baghdad Science Journal Vol.13(3)2016

films is (400±20) nm. It has been found
out that the following deposition
parameters give good stoichiometric
form surface: substrate temperature
(400C), spray rate (10 ml /min), air
pressure (105 N/m2), distance between
sprayer nozzle and substrate of (29±1)
cm.
The transmittance and absorbance
spectra have been recorded in the wave
lengths ranged (400-800) nm by using
(PU-8800-UV/VIS Spectrophotometer)
with two bands provided by Philips
Company. Put the glass substrate like
the glass used for spraying in the back
window, and then put the deposited film
in to be a source window .All the
processes happen in the room
temperature.
Calculations:
Reflectance can be evaluated from the
following relation.
R + T + A = 1 …………. (1)
The absorption coefficient ( cm-1) is
calculated in the fundamental absorption
region using Lambert law (fig (4)) [15].
)exp( tII o
……. (2)
t is film thickness , I is the intensity of
transmitted light.
If ( I / I ) = T then α=Ln (1/ T )/t…(3)
to measure the optical band gap for the
thin films, we use the Tauc's relation as
follows[16]:
    ………….(4)
where A is constant, photon energy,
Eg the optical energy gap and an index
(n) could take different values according
to the type of electronic transition.
The extinction coefficient ( Ko ) can be
calculated by the following relation
[17]:
Ko = α λ / 4π ……..(5)
λ: is wave length and α: The
absorption coefficient.
Refractive index, one of the
fundamental properties of an optical can
be evaluated from the relation [8].
 
 
 
 
 
R
R
k
R
R
no
1
1
1
1
12/1
2
2
2
….(6)
The real 1) dielectric constant and
imaginary 2) dielectric constant are
determined using the relation:
ε1 = ( n2 - Ko2 ) ........(7)
ε2 = ( 2 n Ko ) ......... (8)
Results and Discussion:
The spectral distribution of
transmittance (T) and absorbance (A) is
measured using UV-Visible
spectrophotometer in the range 400-800
nm for Cadmium Oxideand Bi doped
Cadmium Oxidethin films as in
Figure(1) and Figure (2) respectively.
From these figures, the decrease of
transmittance at 4 % Bi doped cadmium
oxide and increase at 2 % Bi doped
cadmium oxide can be noticed both in
the range about (500-800)nm. Also, we
notice the absorbance in the lower wave
length increase with increasing Bi-
doping in the CdO thin films and
decrease directly with wave length.
Reflectance can be calculated from the
relation (1). We observe from figure (3)
that reflectance has a maximum value
(80 %) at about 450 nm for all films and
decrease with increasing the
wavelength. The absorption coefficient
( cm-1) is calculated in the fundamental
absorption region using Lambert law
(figure (4)).
From the relation (4) we have been
estimated The band gap of the films.
The Cadmium Oxide has a direct band
gap ranging (2.2 - 2.7) eV [17]. To
obtain the optical band gap Eg, the
graph (αhυ)2 of (hυ) versus was plotted.
by extrapolating the straight line to the
hυ axis at (αhυ) = 0 as shown in Figure
(5), we can measure the optical band
gap energies Eg. We notice from figure
(5) that Bi doping increases the optical
energy gap, this is explained on the
basis of quantum size effect. The
obtained values of Eg (2.37, 2.59 and
Baghdad Science Journal Vol.13(3)2016
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2.62 eV) are in good agreement with
those reported for CdO thin films
prepared by other techniques [13-14].
Figure (6) shows the extinction
coefficient (Ko) as a function of wave
length with different doping
concentration of Bi. The extinction
coefficient decreases as the wave length
increases, and it increases as the doping
concentration increases.
The value of refractive index (n) are
calculated by using equation (6). from
Figure(7) It is seen that the refractive
index n changes with the wave length
and shows peak, In the region between
400 and 500 nm.
Figures 8 and 9 show the variation of
the real and imaginary dielectric
constant with the wave length for CdO
and (CdO:Bi) thin films . The complex
dielectric constant characterize the
optical properties of any solid material
[19]. We notice that the shape of the (ε1)
curve with the wave length is the same
as the refractive index curve. Also,
Imaginary part of dielectric constant 2)
has the same behavior as the extinction
coefficient (Ko) because they are joined
by previous relation (8).
Conclusions:
Undoped and Bi doped CdO thin film on
the glass substrates have been prepared
by Chemical Spray Pyrolysis technique.
Optical energy gap is increased with an
increase of Bi doping .The obtained
values of Eg (2.37, 2.59 and 2.62 eV) Bi
doping affect all optical constants.
Fig. ( 2 ): Absorbance versus Wave Length
for CdO and (CdO:Bi) Thin Films .
Fig. (3): Reflectance versus Wave Length for
CdO and (CdO:Bi) Thin Films .
Fig. (4): Absorption Coefficient versus
Photon Energy for CdO and (CdO:Bi) Thin
Films .
0
5
10
15
20
25
30
35
40
45
50
300 500 700 900
Transmittance %
Wavelength (nm)
0
0.5
1
1.5
2
2.5
3
3.5
300 400 500 600 700 800 900
Absorbance
Wavelength (nm)
45
50
55
60
65
70
75
80
85
300 400 500 600 700 800 900
Reflectance
Wavelength (nm)
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
1 2 3 4
Absorption Coefficient cm -1
Photon Energy (eV)
Fig. ( 1 ): Transmittance versus Wave
Length For CdO and (CdO:Bi) Thin Films.
Baghdad Science Journal Vol.13(3)2016
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Fig. (5): Allowed Direct Energy Gap for CdO
and (CdO:Bi) Thin Films .
Fig( 6): Extinction Coefficient versus Wave
Length for CdO and (CdO:Bi) Thin Films .
Fig. (7): Refractive Index versus Wave
Length for CdO and (CdO:Bi) Thin Film.
Fig( 8): Real part of Dielectric Constant
versus Wave Length for CdO and (CdO:Bi)
Thin Films.
0
2E+10
4E+10
6E+10
8E+10
1E+11
1.2E+11
1.4E+11
1 1.5 2 2.5 3 3.5
(αhν)2 (eV/cm)2
Photon Energy (eV)
pure
Eg=
0
2E+10
4E+10
6E+10
8E+10
1E+11
1.2E+11
1.4E+11
1.6E+11
1.8E+11
2E+11
1 2 3 4
(αhν)2 (eV/cm)2
Photon Energy (eV)
Eg=
0
5E+10
1E+11
1.5E+11
2E+11
2.5E+11
3E+11
1 1.5 2 2.5 3 3.5
(αhν)2 (eV/cm)2
photon Energy (eV)
Eg=
0
0.1
0.2
0.3
0.4
0.5
0.6
300 500 700 900
Extinction Coefficient
wavelength (nm)
0
5
10
15
20
25
300 500 700 900
Refractive index
Wavelength (nm)
0
50
100
150
200
250
300
350
400
450
300 500 700 900
Real part of Dielectric Constant(ε1)
Wavelength (nm)
Baghdad Science Journal Vol.13(3)2016
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Fig( 9): Imaginry part of Dielectric Constant
versus Wave Length for CdO and (CdO:Bi)
Thin Films.
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Transparent tin-doped cadmium oxide (Sn–CdO) thin films with different Sn concentration were deposited on quartz glass substrates by pulse laser deposition (PLD) at 400 °C. The film’s crystallographic structure, optical and electrical properties were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), UV–VIS spectrophotometer and Hall system. Results show that doping of Sn enhances the film’s [111] preferred orientation and causes slight shift in the (200) Bragg angle towards higher value. The optical band gaps (Eg) of the Sn-doped films were found to increase with the increase of Sn doping concentration. In addition, proper doping of Sn evidently improves the electrical properties of CdO, such as the resistivity of the CdO film with 2.9 at% Sn doping is about one-twelfth of that of the CdO film, while the carrier concentration is about 13 times of that of the undoped. The improvements both in optical and electrical properties endow that the Sn–CdO thin films have potential application as TCO material for different optoelectronic device applications.
Article
In the present investigation thin films of cadmium oxide (CdO) have been deposited onto the glass substrates by spray pyrolysis technique using 0.2M non-aqueous solution of the cadmium acetate. Cadmium acetate has been used as a precursor due to its relatively lower decomposition temperature. The films were deposited by using air as a carrier gas with the spray rate of 6mlmin−1. The films were deposited onto the ultrasonically cleaned glass substrates at different substrate temperatures ranging from 573 to 773K at the step of 25K. The X-ray diffraction (XRD) studies show that the films are polycrystalline with preferred orientation along (111) plane. It is further revealed that the films deposited at 623K show better crystallinity as compared to the films deposited at lower and higher substrate temperatures. The dc electrical resistivity measurement was carried out in the temperature range 300–500K and it is found that films prepared at 623K substrate temperature exhibit lower resistivity which is complementary to XRD results. Optical absorption studies of the films have been carried out in the wavelength range 350–850nm and the data were analyzed to determine the band gap energy of the deposited material. The band gap energy is estimated to be 2.31eV. These results are in good agreement with those reported earlier by others.
Article
Cadmium Oxide films have been prepared by vacuum evaporation method on a glass substrate at room temperature. Detailed structural, optical, and electrical properties of the films are presented at different annealing temperatures. The crystal structure of the samples was studied by X- ray diffraction. The spectral absorption coefficient of the CdO film at the fundamental absorption region (450-650nm) was determined using the spectral data of transmittance. The direct and indirect band gap energies were determined and found to be 2.33 eV and 1.95 eV respectively. The third order optical nonlinearities χ(3) of CdO films has been measured used the z-can technique. The real and imaginary parts of χ(3) have been measured at 514 nm and found to be 1.7x10-3 esu and 3.0x10-3 esu, respectively. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Article
This paper deals with the dc magnetron reactive sputtering of cadmium in an oxygen and argon atmosphere. The dependence of cathode potential on the oxygen partial pressure has been explained in terms of cathode poisoning effects. The cadmium oxide films formed during this process have been studied for their structural, electrical and optical properties. At an optimum oxygen partial pressure of 1×10−3 mbar, the films were single phase with polycrystalline in nature. The films showed resistivity of 4.6×10−3 Ω cm, Hall mobility of 53 cm2/V s, carrier concentration of 3.5×1019 cm−3, with an optical transmission of 85% in the wavelength range 600–1600 nm and with a band gap of 2.46 eV.
Gassensitivityand characterization of cadmium oxide CdO semiconducting thin film deposited by spray pyrolysis technique
  • R L A K Mishra
  • S G Sharma
  • Prakash
Mishra, R. L. A. K. Sharma, and S. G. Prakash. 2009. Gassensitivityand characterization of cadmium oxide CdO semiconducting thin film deposited by spray pyrolysis technique. Digest J. Nanomater. Biostru., 4,511.