1. THE OPTICAL PROPERTIES OF CdSe/ZnSe SUPERLATTICE
BY ELECTRODEPOSITION TECHNIQUE
I. L. Ikhioya and A. J. Ekpunobi
Department of physics Industrial Physics, Nnamdi AzikiweUniversity,
Awka, Anambra State, Nigeria.
Email: ikhioyalucky@gmail.com, Mobile no: +23408038684908
Department of Physics and Industrial Physics, Nnamdi Azikiwe University,
Awka, Anambra State, Nigeria.
Email: ajekpunobi@yahoo.com, Mobile no: +23408038763056
Keywords: Thin Film, Indium tin oxide (ITO), Electrodeposition, Cd, ZnSe, Seo2, characterization,
application.
Abstract
Cadmium selenide/Zinc selenide (CdSe/ZnSe) superlattice have been successfully deposited on a
glass substrate (Indium Tin oxide) by electrodeposition technique (ED) or electrochemical deposition
technique (ECD). The absorbance was measured using M501 UV-visible spectrophotometer in the
wavelength range of 300nm-900nm. Observation show that the absorbance of CdSe/ZnSe
superlattice films is in the range of 0.07-0.18. Cadmium selenide/Zinc selenide (CdSe/ZnSe) thin films
semiconductor were investigated at room temperature.
INTRODUCTION
The growth of II–VI wide-band-gap semiconductor superlattice has attracted considerable attention
due to their novel physical properties and a wide range of applications in optoelectronic devices. The
applications include the use of II–VI compound based materials as light sources, in full color displays
and for increasing the information density in optical recording. Thin films of CdSe/ZnSe II–VI
compounds grown on III–V compound substrates are of particular interest in the device applications
of light emitting diodes (LEDs) and laser diodes (LDs) of visible and UV spectral region due to their
good operation stability in terms of temperature variation and lifetime. (F. Fisher, et al., 1997, T. B.
Ng, et al., 1997, F. Vigue, et al., 2000) According to theoretical prediction and subsequent
experimental verification, the CdSe/ZnSe containing II–VI compounds had been found to possess an
enhanced ability to significantly reduce the defects propagation due to a more prevalence of strong
covalent bonding and lattice hardening in the materials. (A. Waag, et al., 1997, J. Y. Zhang, et al.,
2000). The strong covalent bonding in CdSe/ZnSe-based II–VI compounds achieves a considerable
lattice hardening which avoids multiplication of defects during the operation of II–VI semiconductor
laser devices. (A. Mun˜oz, et al., 1996, A. Waag, et al., 1996) Up-to date, in spite of the
anticipated advantages of the Be-based II–VI compounds. The temperature dependence of the
energy and broadening of interband electronic transitions can yield important information
concerning the physical properties of the materials such as electron (exciton)–phonon interactions,
excitonic effects, etc. The practical aspect of this investigation is related to the control of the
operating of the laser structure itself.
Integration of II-VI and III-V CdSe/ZnSe into a heterovalent multijunction solar cell can make it
possible to increase energy conversion efficiency in comparison with the solar cells based on III-V
semiconductors alone due to optimization of the captured spectrum of solar radiation (Y. H. Zhang,
et al., 2008).

2. MATERIALS AND METHODS
Cadmium selenide/Zinc selenide (CdSe/ZnSe) superlattice thin films were deposited by
electrodeposition technique using 20cm3
of 0.063m of selenium IV oxide (Seo2) mixed 20cm3
of
0.069m of cadmium (Cd) and 5cm3
of potassium tetraoxosulphate VI (K2SO4) solution. Then, 5cm3
of
0.4m of tetraoxosulphate VI acid (H2SO4). Which used to acidify the solution, it was added into the
mixture and stirred well. The indium doped tin oxide (ITO) glass was used as substrate. The
ultrasonically cleaned glass substrate was immersed vertically into the solution for electrodeposition
process. The films growth was carried out at 300k. The films were deposited in various deposition
periods of (60-180s). During deposition process, the deposited films were tested for adhesion by
subjecting it to a steady stream of distilled water. Optical absorbance study was carried out using
M501 UV-Visible spectrophotometer. The films coated indium thin oxide glass was placed across the
sample radiation pathway while the uncoated the reference path. The absorption data were
manipulated for the determination of band gap energy
RESULTS AND DISCUSSIONS
Figure 1-10 shows the optical properties of CdSe/ZnSe superlattice films deposited in a glass
substrate were studied at room temperature. The plot of optical absorbance with photon energy
shows a very low absorption of energy in the lower photon energy VIS-IR regions with value of 0.07
and high absorption in ultra violet region with a value of 0.18. This makes the film a good window
layer for solar cell application. The low absorption of energy makes CdSe/ZnSe superlattice useful for
optical components in high laser window and multispectral applications, providing good imaging
characteristics (D. Soundararajan et al., 2009
Fig. 1. Plot of absorbance against photon
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 1 2 3 4 5
Absorbance(arbitraryunit)
Photon Energy, eV
SLIDE BB
SLIDE CC
SLIDE DD

3. The optical transmittance of the films shows transmission of 0.65% in the UV region for all the films
and 0.83% in the near IR region. The high transmission range of CdSe/ZnSe superlattice make the
material useful in manufacturing optical components, windows, mirrors, lenses for high power IR
laser, (Murali et al., 2008 and D. Soundararajan et al., 2009 ).
Fig. 2. Plot of transmittance against wavelength
The optical reflectance of the films shows that the films reflect much at UV region and decay in the
IR region with a reflectance of 0.161-0.080 (slide DD).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 200 400 600 800 1000
Transmittance(%)
Wavelength (nm)
SLIDE BB
SLIDE CC
SLIDE DD

4. Fig. 3. Plot of reflectance against wavelength
The refractive index decays with decreases in the photon energy. CdSe/ZnSe superlattice show a
high refractive index with range of 2.3-1.7 (slide DD). The high refractive index possessed by
CdSe/ZnSe films made it suitable as anti reflection coatings.
Fig.4. Plot of refractive index against photon energy
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 200 400 600 800 1000
Reflectance(%)
Wavelength (nm)
SLIDE BB
SLIDE CC
SLIDE DD
0
0.5
1
1.5
2
2.5
0 1 2 3 4 5
Refractiveindex,n
Photon Energy (eV)
SLIDE BB
SLIDE CC
SLIDE DD

5. The extinction coefficient with photon energy of CdSe/ZnSe superlattice films show that the
extinction coefficient decays with decrease with photon energy. The optical conductive increases
and decays with the photon energy. The real and imaginary dielectric constant decreases as
wavelength increases and photon energy decreases.
Fig.5. Plot of extinction coefficient against photon energy.
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0 1 2 3 4 5
ExtinctionCoefficient
Photon Energy (eV)
SLIDE BB
SLIDE CC
SLIDE DD

6. Fig.6. Plot of optical conductive against photon energy.
Fig.7. Plot of real dielectric constant against photon energy.
0
5E+12
1E+13
1.5E+13
2E+13
2.5E+13
3E+13
3.5E+13
4E+13
0 1 2 3 4 5
OpticalConductivity
Photon Energy (eV)
SLIDE BB
SLIDE CC
SLIDEDD
0
1
2
3
4
5
6
0 1 2 3 4 5
RealDielectricConstant
Photon Energy (eV)
SLIDEBB
SLIDECC
SLIDEDD

7. Fig. 8. Plot of real dielectric constant against wavelength
Fig.9. Plot of imaginary dielectric constant against photon energy.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 1 2 3 4 5
ImaginaryDielectricConstant
Photon Energy (eV)
SLIDEBB
SLIDECC
SLIDEDD
0
1
2
3
4
5
6
0 200 400 600 800 1000
RealDielectricConstant
Wavelength (nm)
SLIDEBB
SLIDECC
SLIDEDD

8. Fig.10. Plot of imaginary dielectric constant against wavelength
Conclusion
CdSe/ZnSe thin films have been successfully prepared by electrodeposition technique. Since the
transmittance of the CdSe/ZnSe approximately remains constant at the visible and near infrared
range, this make CdSe/ZnSe a good candidate to be used as an antireflection coatings, within this
spectral range. Furthermore, the value of refractive index remain nearly constant in the wavelength
rang 400-900nm; this behavior represents an optical stability within this spectral range.
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