Uddhao N. Ingle1,
Milind S. Kale2
1Depatment of Electronics,
Smt. G.G. Khadse College , Muktainagar Dist. Jalgaon
2Department of Electronics,
D.N.C.V.P.S. Shirish MadhukarraoChaudhari College, Jalgaon
Corresponding Author: uddhaoingle@gmail.com
ABSTRACT:
Cu
doped ZnTe thin films were deposited onto glass substrates by using thermal
evaporation technique. The structure analysis of the film was performed by XRD
technique. The surface morphological analysis was carried out by using optical
microscope. The optical band gap were calculated by UV-VIS spectrometry
analysis. The XRD revels that, the thin films are polycrystalline in nature.
The crystal structure is found to be hexagonal shape. The microscopic images
revels that films are homogenous and particles are uniformly deposited on the substrate.
Optical band gap, was calculated from the absorption spectra is situated in the
range of 2 eV.
Keywords: Cu
doped ZnTe Thin films, XRD, UV-VIS.
1. INTRODUCTION
The II-VI compound group semiconductor
materials is an important semiconductor material because of its extensive
potentials applications for the development of various modern technologies of
solid-state devices like blue light emitting diodes, laser diodes, solar cells,
microwave devices, etc. ZnTe is one of the interesting materials for potential
photovoltaic applications in different opto-electronics devices such as photodiodes,
solar cells, and LED [1-4]. The ZnTe can be used as a window material in solar
cells. In addition, it reduces the toxic nature of CdS thin films in currently developed
thin film solar cells [5].
A variety of methods have been developed
for the preparation of Cu doped ZnTe thin films such as physical vapor
deposition under vacuum, molecular beam epitaxy, CBD, Sillar, Chemical vapor
deposition, Solution growth, spray pyrolysis, molecular beam epitaxy etc [2, 6,
7].
In this paper, structural, morphological
and optical properties of Cu doped ZnTe thin film grown by thermal evaporation
technique, are investigate.
2. EXPERIMENTAL
First of all, the Cu doped ZnTe powder
were prepared by using Cu (NO3)2 , ZnCl2 and
Telluride (Te) metal powder by reflux method in chemical synthesis technique. After chemical
synthesis process, filter the precipitate and washed the solid with distilled
water and ethanol to remove byproducts and un-reacted materials. Finally, dry
the powder under IR lamp for 2-3 hours .Then black or gray precipitate was
formed which indicate the formation of ZnTe:Cu powder. Then the prepared powder
compound of ZnTe:Cu was used for the deposition and were placed in a Mo boat by
using Thermal Evaporation Technique .
The prepared powder compound of Cu doped ZnTe was
used for the deposition.
During the deposition, the pressure was keep
about 10−5 torr. The substrate to source distance was keeping about 13
cm. The samples of different thicknesses were deposit under similar conditions.
The thickness of the films was monitored by quartz crystal digital thickness
monitor (Model No. DTM-101), provided by Hind-Hi Vac. The deposition rate was
maintained 5 - 10 Ã…/sec throughout sample preparation.
Before thermal evaporation, the glass
substrates were clean thoroughly using detergent, chromic acid, isopropyl
alcohol, pure distilled water and finally acetone.
3. RESULTS AND DISCUSSION
3.1. X-ray diffraction (XRD) Analysis:
To study the structural properties, the
grown sample was characterized by XRD technique. The XRD patterns of grown Cu doped ZnTe thin
film having thickness of 1000 Ã… is shown
in figure 1.
Figure
1: The XRD patterns of Cu doped ZnTe thin film.
The XRD patterns shows the samples is polycrystalline
with orthorhombic crystal structure. The 2θ peak observed at 24.8°, 33.5°,
47.35°, 49.5° and 65° exhibit the formation of the hexagonal structure phase of
Cu doped ZnTe which correspond to the (0 1 10), (1 4 11), (022), (202) and (041)
planes of reflections. The presence of number of peaks indicates that the films
are polycrystalline in nature. The values of lattice parameters are found a =
5.379, b = 5.9471 and c = 5.01. The crystal
size was calculated by Scherrer equitation.
Crystallite
size = (0.94 x λ) / (β x Cos Θ)
Where, λ = wavelength of incident X-Ray, β = Full width at
half maxima in radian and Θ =
Bragg angle/diffracted angle. The crystal size was found to be 346.60.
3.2. Morphological Analysis:
The surface morphological properties, the
grown sample was observed under optical microscope. The figure 2 shows the optical microscopic
image of grown Cu doped ZnTe thin film having thickness of 1000 Ã….
Figure
2: Optical microscopic images of Cu doped ZnTe thin film.
From the micrograph images, it is
observed that the film is uniform. The nano size grains were uniformly
distributed over smooth homogeneous background and well cover on substrate. The
sample is free from any microscopy defect like cracks or peeling. Similarly it
is observed that the particles forms the cluster with random shape.
3.3. UV-VIS Analysis:
To study the optical properties were
studied with UV-VIS spectrometry. The figure 3 shows the optical properties of
grown Cu doped ZnTe thin film having thickness of 1000 Ã….
The optical absorption spectra were
obtain in 350 nm to 900 nm wavelength range by employing a Shimadzu 2450
UV-Visible model of the spectrophotometer. According to absorbance and
transmittance it is found that the film has high absorbance. The optical band
gap of these films has been calculated using the relation (Tauc 1974).
αhν =
A (hν – Eg)n
where, hν is the photon energy, α is the absorption coefficient, Eg the band gap, A is
constant and, n = 0.5 for direct band gap material and n = 2 for indirect band
gap material.
Figure
3: Optical properties of grown Cu doped ZnTe thin film
Figure
4: Band gap of grown Cu doped ZnTe Thin Film.
The plot of (αhν)2 versus hν for
Cu doped ZnTe films is presented in Fig. 4. The straight line portion is
extrapolated to cut the x-axis, which gives the energy gap. This figure clearly
shows the the optical band gap is 2 eV [8], which is in good agreement for
solar cell and other optical devices. Hence, the Cu doped ZnTe, can be used in development
of efficient photovoltaic application.
Conclusions
The study of Cu doped ZnTe thin films
deposited by vacuum thermal evaporation technique revealed the sample is a
polycrystalline structure. The grown sample is homogenous and free from any
defects. The optical band gap is 2 eV allowing it to efficiently capture
high-energy. Materials with this band gap has enhanced stability and
high-performance, due to which is in good agreement for solar cell
manufacturing.
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