chapter – 5 optical properties of znx...
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114
CHAPTER – 5
OPTICAL PROPERTIES OF ZnX CRYSTALS AND THINFILMS
5.1 INTRODUCTION
Optical properties of wide band gap II-VI semiconductors are of great importance
because of their relevance for short wave length optical devices. Thus study of the optical
properties of these compounds gives important understanding of their electronic properties
and band structures. The optical band gap is one of the most important optical parameters
especially in case of the wide band gap compounds. It can have the remarkable effect at the
application point of view in electro-optic instrumentation.
Generally, optical characterization may include Microscopy, Ellipsometry, Photo
luminescence, Transmission spectroscopy, Absorption spectroscopy, Raman Spectroscopy,
Reflectance, Modulation, Cathode luminescence to determine optical properties of any
semiconductors crystal or thin films which are of great importance for many applications
including interference devices (such as antireflection coatings, laser mirrors, monochromatic
filters etc.)as well as optoelectronics, integrated optics, solar engineering, microelectronics
and optical sensor technology.
Spectrophotomatric methods determine the spectral dependence of reflectance and
transmittance or absorption for semiconducting compounds within the spectral range of
interest [1-3]. Reflectance and transmittance are measured at near normal incidence and
normal incidence respectively using various types of spectrophotometers.
Ellipsomatric methods analyze changes in the state of polarized light, that has been
transmitted through and reflected from films and their systems [4, 5]. Ellipsometers are
oblique incident light within the spectral ranges of interest.
Interferometry uses interferometers to characterize films [6-8]. Interferograms which
may be resulted from reflected or transmitted lights are analyzed to determine the geometric
quantities of thin films including thickness and boundary roughness.
115
Photo thermal methods determine the absorption of materials that form thin films [9-
13]. Measured changes in temperature, optical or thermo physical properties of thin films,
can be used to calculate the absorbance.
Complete optical characterization of the compound (crystals or thin films) requires
determining all the optical properties of materials and therefore proper selection of the
optical characterization technique is very important.
A survey of literature related to the optical band gap of wide band gap II-VI
compounds clearly indicates that following methods may be adopted for this study.
Analysis of following optical spectra
1. Absorption Spectra
2. Reflectance Spectra
3. Electro reflectance Spectra
4. Thermo reflectance Spectra
Photo electrochemical Methods
1. Quantum yield ( vs h plot) analysis
2. Action Spectra
3. Capacitance measurements
Intrinsic conduction measurements at high temperature
Photoemission studies
Band structure calculations
Out of above listed methods, we have adopted optical absorption technique for the
present study.
5.2 OPTICAL ABSORPTION
Optical absorption spectroscopy is the spectroscopic technique that measures the
absorption of radiation as a function of frequency or wave length due to its interaction with a
sample. The sample absorb the energy i.e. photons from the radiating field. The intensity of
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the absorption varies as a function of frequency and this variation is called the absorption
spectrum.
This is the most promising technique to measure the semiconductor band gap. Here in
this technique the photons of particular wave length are directed towards the sample under
test, and the resultant transmission is measured. The photons having higher energy then band
gap will get absorbed while those having lower energy than band gap, will be transmitted.
The fundamental absorption refers to band or to exciton transition i.e. to the exciation
of an electron from the valance band to the conduction band. The fundamental absorption
which manifests itself by rapid rise in absorption can be used to determine the energy gap of
semiconductors.
If a beam of photons with Eg < h falls on a semiconductor sample, there will be
some predictable amount of absorption determined by properties of material. The ratio of
transmitted to incident radiation intensity is expected to depend on photon wavelength and
the thickness of the sample.
When a photon beam of intensity I0 (photons/cm2.sec) transmits through a slab of
medium of thickness x, the beam of photons attenuates in accordance with the exponential
law
I = I0 e-x
where “” is called the absorption coefficient. It can be obtained by measuring I0 / I of
intensities, where I is the intensity of transmitted beam of photons.
5.2.1 DIRECT AND INDIRECT TRANSITIONS
The absorption process in semiconductors can be described as an example of
electronic transition process. These electronic transition processes give rise to inter band
absorption in solids, which are of two types, direct and indirect transitions.
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In a direct transition, an electron in a Bloch energy band state below the Fermi level
absorbs a photon and makes a vertical transition to an upper empty state in a conduction
band. The characteristics of such transition are defined by the following conditions:
if KK (5.1)
ivfc KEKE (5.2)
Where,
if KandK are final and initial wave vectors respectively in the valence and
conduction bands respectively and is the photon energy. Equation (5.2) expresses energy
conservation.
Generally at high temperatures phonons are present and can participate in
absorption process. Such phonon assisted transitions can not be vertical because the phonon
momentum ħ must be added to the right hand side of above equation (5.1) and similarly the
condition in the equation (5.2) has to include the energy of the absorbed (or emitted) phonon.
This type of the transitions are said to be non-vertical or “indirect.” A schematic of both the
transitions are shown in figure 5.1.
(a) Direct Transition (b) Indirect Transition
Figure 5.1 Schematic diagram showing (a) Direct transition and (b) Indirect
transition.
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5.2.2 ENERGY GAP DETERMINATION
The absorption coefficient “” is directly proportional to
(ħ - Eg)r
hTherefore for direct transition,
h = A(h - Eg)r (5.3)
Where, h = photon energy
Eg = energy for direct transition
A = parameter depending on temperature, photon and phonon energies.
r = dimensionality dependent component (given in table-5.1)
And for indirect transition,
rpjgj
j EEhBh (5.4)
Where, h = photon energy'gE = energy for indirect transition
Epj= energy of phonons assisting at indirect transition
B = parameter depending on temperature, photon and phonon energies.
r = dimensionality dependent component (given in table-5.1)
Type of
Transition
Direct In-direct
2-Dimentional 3-Dimentional 2-Dimentional 3-Dimentional
Allowed 0
(step function)
1/2 1 2
Forbidden 1 3/2 2 3
Table 5.1 Values of “r” for various types of band gap transitions.
119
However, for the analysis of the experimental results obtained at constant
temperature, relations (5.3) and (5.4) are sufficient and they are most often used while
interpreting results on absorption spectra obtained from semiconducting materials. The
exponent “r” in above equations depends upon whether the transition is symmetry allowed or
not and the constants A and B will assume different values for the allowed and forbidden
transitions. For indirect transitions, the detailed form equation (5.4) is given as Vlachos et al.
[54]; Elkorashy [55, 56] .
2
1
''
1
1
1
1
i
rig
T
eirig
T
aii kEE
eE
BkEE
eE
Bii
(5.5)
Where Bai and Bei are coefficients associated with absorption and emission of the ith phonon,
E the photon energy, E’g the indirect energy gap and i is a phonon equivalent temperature
defined by the equation
ipi kE (5.6)
The use of equations (5.4)-(5.6) for analyzing the absorption spectrum is valid for
semiconductors having a three dimensional (3D) structure, but for anisotropic layered
materials, one has to assume a two dimensional (2D) form of the density of states as
discussed by Fivaz [57] and Brebner [58]. In these cases the density of states is a constant
independent of the energy and the expressions showing the dependence of in terms of
direct and indirect transitions get modified as
rgEhA (5.7)
(Goldberg et al. [42]) for direct transitions and
120
2
1
''
1
1
1
1
i
rig
T
iei
rig
T
aii kEE
e
BkEE
e
Bi
(5.8)
Elkorashy [59, 60] for indirect transitions.
The symbols in equations (5.7) and (5.8) have the same meaning as explained
earlier in equations [(5.3)-(5.6)]. Again the exponent r depends on the dimensionality of the
bands and whether the transitions are symmetry allowed or forbidden. Once again the
coefficients A’, B’ai and B’ei will be different for symmetry allowed and forbidden transitions.
Possible values of r are given in Table 5.1( Lee et al. [61], Goldberg et al. 63] and Kam et al.
[62]).
By plotting graphs of (h)1/r against h for various values of “r” given in
Table 5.1, it is possible to determine which of the conditions given in this table dominate.
Extrapolations of the straight line portions of these plots to zero absorption will give the
appropriate value of the energy gaps of the layered semiconductors.
5.3 EXPERIMENTAL
5.3.1 OPTICAL ABSORPTION BY CRYSTALS OF ZnX (X = S, Se, Te)
Optical properties of grown crystals of ZnS, ZnSe and ZnTe were studied using UV-
VIS-NIR spectrophotometer (Perkin Elmer, USA, Model : Lambda 19) in the range of 200
to 2000 nm wave length at Sophisticated Instrumentation Centre for Applied Research and
Testing (SICART), at Vallbh Vidyanagar. To collect the absorption spectra of the crystals,
small fine crystals of ZnS, ZnSe and ZnTe were pasted on three different thick black papers
with a very fine opening in the centre of the paper. A finely holed blank black paper was
used as a reference. The absorption spectra obtained at room temperature were used for
further analysis.
121
5.3.2 OPTICAL ABSORPTION BY THIN FILMS OF ZnX (X = Se, Te)
Optical absorption spectra of thin films of ZnSe of various thicknesses (1000Å,
2000Å, 3000Å, and 5000Å) deposited at various substrate temperatures (303K, 373K and
448K) were collected using UV-VIS spectrophotometer in the visible range (370 to 720 nm)
at Applied Physics Department, M. S. University of Baroda, at Vadodara.
Optical absorption spectra of thin films of ZnTe of various thicknesses
(1000Å, 2000Å, 3000Å, and 5000Å) deposited at various substrate temperatures (303K,
373K and 448K) were collected using UV-VIS-NIR spectrophotometer (Perkin Elmer, USA,
Model : Lambda 19) in the range of 200 to 2000nm, at Sophisticated Instrumentation Centre
for Applied Research and Testing (SICART), at Vallbh Vidyanagar. In case of both ZnSe
and ZnTe thin films coated on glass substrates, uncoated glass slides were used as a reference
and observed data were used for further calculations.
5.4 RESULTS AND DISCUSSION
The typical absorption spectra obtained for the grown crystals of ZnS, ZnSe and ZnTe
are shown in figure-5.2 in the range of 200 to 2000 nm wave length. It is clear from the
spectra that all three crystals show a considerable absorption in the visible region of the
electromagnetic spectrum. A careful study of these spectra revel the presence of absorption
edge in the range between 400 to 600 nm wavelengths which is an indication of their wide
band gap. It is reported widely in literature that, ZnX (X = S, Se, Te) in both bulk crystalline
and thin film form possess direct band gap and therefore, equation 5.3 has been used to
analyze further the obtained spectral response with the value of r = ½. Thus a plot of (h)2
vs h has been used to obtain optical band gap of all three crystals as shown in figure 5.3.
The optical band gap has been calculated for all three crystals using the intercept on the
energy axis by extrapolating the straight line region of these curves as shown in the figure-
5.3. Variations of reflectance (R), transmittance (T) and absorption (A), extinction coefficient
(k) and refractive index ( n) and real and imaginary part of dielectric constant (Ei) and (Er) of
the grown crystals of ZnS, ZnSe and ZnTe, with wavelength are shown in figure 5.4, 5.5 and
122
00.20.40.60.81
1.21.41.6
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnS Crystal
Wave length (nm)
Absorpt
ion (%)
0
1
2
3
4
5
6
7
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnSe Crystal
Wavelength (nm)
Absorpt
ion (%)
0
1
2
3
4
5
6
7
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnTe Crystal
Wavelength (nm)
Absorpt
ion (%)
00.20.40.60.81
1.21.41.6
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnS Crystal
Wave length (nm)
Absorpt
ion (%)
00.20.40.60.81
1.21.41.6
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnS Crystal
Wave length (nm)
Absorpt
ion (%)
0
1
2
3
4
5
6
7
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnSe Crystal
Wavelength (nm)
Absorpt
ion (%)
0
1
2
3
4
5
6
7
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnSe Crystal
Wavelength (nm)
Absorpt
ion (%)
0
1
2
3
4
5
6
7
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnTe Crystal
Wavelength (nm)
Absorpt
ion (%)
0
1
2
3
4
5
6
7
200 400 600 800 1000 1200 1400 1600 1800 2000
ZnTe Crystal
Wavelength (nm)
Absorpt
ion (%)
0
50100
150
200
250300
350
400
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6
ZnS Crystal
Photon energy (eV)(
h)2
0
20
40
60
80
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
ZnSe crystal
Photon energy (eV)
(h
)2
0
10
20
30
40
0 0.4 0.8 1.2 1.6 2 2.4 2.8
ZnTe crystal
Photon energy (eV)
(h
)2
0
50100
150
200
250300
350
400
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6
ZnS Crystal
Photon energy (eV)(
h)2
0
50100
150
200
250300
350
400
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6
ZnS Crystal
Photon energy (eV)(
h)2
0
20
40
60
80
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
ZnSe crystal
Photon energy (eV)
(h
)2
0
20
40
60
80
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
ZnSe crystal
Photon energy (eV)
(h
)2
0
10
20
30
40
0 0.4 0.8 1.2 1.6 2 2.4 2.8
ZnTe crystal
Photon energy (eV)
(h
)2
0
10
20
30
40
0 0.4 0.8 1.2 1.6 2 2.4 2.8
ZnTe crystal
Photon energy (eV)
(h
)2(c
m-2
mv2
)(c
m-2
mv2
)(c
m-2
mv2
)
0
50100
150
200
250300
350
400
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6
ZnS Crystal
Photon energy (eV)(
h)2
0
20
40
60
80
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
ZnSe crystal
Photon energy (eV)
(h
)2
0
10
20
30
40
0 0.4 0.8 1.2 1.6 2 2.4 2.8
ZnTe crystal
Photon energy (eV)
(h
)2
0
50100
150
200
250300
350
400
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6
ZnS Crystal
Photon energy (eV)(
h)2
0
50100
150
200
250300
350
400
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2 5.6 6
ZnS Crystal
Photon energy (eV)(
h)2
0
20
40
60
80
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
ZnSe crystal
Photon energy (eV)
(h
)2
0
20
40
60
80
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2
ZnSe crystal
Photon energy (eV)
(h
)2
0
10
20
30
40
0 0.4 0.8 1.2 1.6 2 2.4 2.8
ZnTe crystal
Photon energy (eV)
(h
)2
0
10
20
30
40
0 0.4 0.8 1.2 1.6 2 2.4 2.8
ZnTe crystal
Photon energy (eV)
(h
)2(c
m-2
mv2
)(c
m-2
mv2
)(c
m-2
mv2
)
5.6 respectively. Optical band gap obtained for crystals has been tabulated in the table.5.2. It
is clear from the table 5.2 that optical band gaps for all three crystals are in good agreement
with their respective reported values of table 5.3.
Figure 5.2 UV-VIS-NIR absorption Figure 5.3 Spectral variation of (h)2vsspectra of ZnX (X = S, Se, Te) photon energy (h) ofcrystals. ZnX (X=S, Se, Te) crystals.
123
0
1
2
3
4
5
6
7
8
200 400 600 800 1000 1200 1400 1600 1800 2000
w ave len g th (n m )
A(%
)
0.558
0.564
0.57
0.576
0.582
0.588
0.594
0.6
0.606
0.612
R, T
(%)
TAR
ZnTecrystal
0
1
2
3
4
5
6
7
8
9
1 0
2 0 0 5 0 0 8 0 0 1 1 0 0 1 4 0 0 1 7 0 0 2 0 0 0
w a v e le n g th (n m )
A(%
)
0 .5
0 .5 2
0 .5 4
0 .5 6
0 .5 8
0 .6
0 .6 2
R, T
(%)
TARZnSeCrystal
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 .4
1 .6
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
A(%
)
0 .5 9 7
0 .5 9 8
0 .5 9 9
0 .6
0 .6 0 1
0 .6 0 2
0 .6 0 3
0 .6 0 4
0 .6 0 5
0 .6 0 6
0 .6 0 7
0 .6 0 8
R,
T(%
)
TARZnScrystal
0
1
2
3
4
5
6
7
8
200 400 600 800 1000 1200 1400 1600 1800 2000
w ave len g th (n m )
A(%
)
0.558
0.564
0.57
0.576
0.582
0.588
0.594
0.6
0.606
0.612
R, T
(%)
TAR
ZnTecrystal
0
1
2
3
4
5
6
7
8
9
1 0
2 0 0 5 0 0 8 0 0 1 1 0 0 1 4 0 0 1 7 0 0 2 0 0 0
w a v e le n g th (n m )
A(%
)
0 .5
0 .5 2
0 .5 4
0 .5 6
0 .5 8
0 .6
0 .6 2
R, T
(%)
TARZnSeCrystal
0
1
2
3
4
5
6
7
8
200 400 600 800 1000 1200 1400 1600 1800 2000
w ave len g th (n m )
A(%
)
0.558
0.564
0.57
0.576
0.582
0.588
0.594
0.6
0.606
0.612
R, T
(%)
TAR
ZnTecrystal
0
1
2
3
4
5
6
7
8
9
1 0
2 0 0 5 0 0 8 0 0 1 1 0 0 1 4 0 0 1 7 0 0 2 0 0 0
w a v e le n g th (n m )
A(%
)
0 .5
0 .5 2
0 .5 4
0 .5 6
0 .5 8
0 .6
0 .6 2
R, T
(%)
TARZnSeCrystal
0
1
2
3
4
5
6
7
8
9
1 0
2 0 0 5 0 0 8 0 0 1 1 0 0 1 4 0 0 1 7 0 0 2 0 0 0
w a v e le n g th (n m )
A(%
)
0 .5
0 .5 2
0 .5 4
0 .5 6
0 .5 8
0 .6
0 .6 2
R, T
(%)
TARZnSeCrystal
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 .4
1 .6
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
A(%
)
0 .5 9 7
0 .5 9 8
0 .5 9 9
0 .6
0 .6 0 1
0 .6 0 2
0 .6 0 3
0 .6 0 4
0 .6 0 5
0 .6 0 6
0 .6 0 7
0 .6 0 8
R,
T(%
)
TARZnScrystal
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 .4
1 .6
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
A(%
)
0 .5 9 7
0 .5 9 8
0 .5 9 9
0 .6
0 .6 0 1
0 .6 0 2
0 .6 0 3
0 .6 0 4
0 .6 0 5
0 .6 0 6
0 .6 0 7
0 .6 0 8
R,
T(%
)
TAR
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 .4
1 .6
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
A(%
)
0 .5 9 7
0 .5 9 8
0 .5 9 9
0 .6
0 .6 0 1
0 .6 0 2
0 .6 0 3
0 .6 0 4
0 .6 0 5
0 .6 0 6
0 .6 0 7
0 .6 0 8
R,
T(%
)
TARZnScrystal
Figure 5.4 Spectral variation of absorption (A), reflectance (R) and transmittance(T) vs wavelength of ZnX (X = S, Se, Te) crystals.
124
0 .0 E +0 0
2 .0 E -0 6
4 .0 E -0 6
6 .0 E -0 6
8 .0 E -0 6
1 .0 E -0 5
1 .2 E -0 5
1 .4 E -0 5
1 .6 E -0 5
1 .8 E -0 5
2 .0 E -0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .9 6
3 .9 8
4
4 .0 2
4 .0 4
4 .0 6
4 .0 8
4 .1
n
knZnSCrystal
0 .0 E + 0 0
2 .0 E -0 5
4 .0 E -0 5
6 .0 E -0 5
8 .0 E -0 5
1 .0 E -0 4
1 .2 E -0 4
1 .4 E -0 4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .5
3 .6
3 .7
3 .8
3 .9
4
4 .1
n
kn
ZnSecrystal
0 .0 E +0 0
2 .0 E -0 5
4 .0 E -0 5
6 .0 E -0 5
8 .0 E -0 5
1 .0 E -0 4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .4 5
3 .5 5
3 .6 5
3 .7 5
3 .8 5
3 .9 5
4 .0 5
4 .1 5
n
knZnTecrystal
0 .0 E +0 0
2 .0 E -0 6
4 .0 E -0 6
6 .0 E -0 6
8 .0 E -0 6
1 .0 E -0 5
1 .2 E -0 5
1 .4 E -0 5
1 .6 E -0 5
1 .8 E -0 5
2 .0 E -0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .9 6
3 .9 8
4
4 .0 2
4 .0 4
4 .0 6
4 .0 8
4 .1
n
knZnSCrystal
0 .0 E +0 0
2 .0 E -0 6
4 .0 E -0 6
6 .0 E -0 6
8 .0 E -0 6
1 .0 E -0 5
1 .2 E -0 5
1 .4 E -0 5
1 .6 E -0 5
1 .8 E -0 5
2 .0 E -0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .9 6
3 .9 8
4
4 .0 2
4 .0 4
4 .0 6
4 .0 8
4 .1
n
knZnSCrystal
0 .0 E + 0 0
2 .0 E -0 5
4 .0 E -0 5
6 .0 E -0 5
8 .0 E -0 5
1 .0 E -0 4
1 .2 E -0 4
1 .4 E -0 4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .5
3 .6
3 .7
3 .8
3 .9
4
4 .1
n
kn
ZnSecrystal
0 .0 E + 0 0
2 .0 E -0 5
4 .0 E -0 5
6 .0 E -0 5
8 .0 E -0 5
1 .0 E -0 4
1 .2 E -0 4
1 .4 E -0 4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .5
3 .6
3 .7
3 .8
3 .9
4
4 .1
n
kn
ZnSecrystal
0 .0 E +0 0
2 .0 E -0 5
4 .0 E -0 5
6 .0 E -0 5
8 .0 E -0 5
1 .0 E -0 4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .4 5
3 .5 5
3 .6 5
3 .7 5
3 .8 5
3 .9 5
4 .0 5
4 .1 5
n
knZnTecrystal
0 .0 E +0 0
2 .0 E -0 5
4 .0 E -0 5
6 .0 E -0 5
8 .0 E -0 5
1 .0 E -0 4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0w a v e le n g th (n m )
k
3 .4 5
3 .5 5
3 .6 5
3 .7 5
3 .8 5
3 .9 5
4 .0 5
4 .1 5
n
knZnTecrystal
Figure 5.5 Spectral variation of extinction coefficient (k), and refractive index (n) vswavelength of ZnX (X = S, Se, Te) crystals.
125
15.4
15.5
15.6
15.7
15.8
15.9
16
16.1
16.2
16.3
16.4
200 400 600 800 1000 1200 1400 1600 1800 2000
wavelength (nm )
Er
4 .75
4.8
4.85
4.9
4.95
5
Ei
ErE iZnS-crystal
10
11
12
13
14
15
16
17
200 400 600 800 1000 1200 1400 1600 1800 2000
w avelength (nm )
Er
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
Ei
ErE iZnSe-crystal
1 3 .7
1 4 .2
1 4 .7
1 5 .2
1 5 .7
1 6 .2
1 6 .7
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
w a v e le n g th (n m )
Er
4
4 .1
4 .2
4 .3
4 .4
4 .5
4 .6
4 .7
4 .8
4 .9
5
Ei
E rE iZnTe-crystal
15.4
15.5
15.6
15.7
15.8
15.9
16
16.1
16.2
16.3
16.4
200 400 600 800 1000 1200 1400 1600 1800 2000
wavelength (nm )
Er
4 .75
4.8
4.85
4.9
4.95
5
Ei
ErE iZnS-crystal
15.4
15.5
15.6
15.7
15.8
15.9
16
16.1
16.2
16.3
16.4
200 400 600 800 1000 1200 1400 1600 1800 2000
wavelength (nm )
Er
4 .75
4.8
4.85
4.9
4.95
5
Ei
ErE iZnS-crystal
10
11
12
13
14
15
16
17
200 400 600 800 1000 1200 1400 1600 1800 2000
w avelength (nm )
Er
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
Ei
ErE iZnSe-crystal
10
11
12
13
14
15
16
17
200 400 600 800 1000 1200 1400 1600 1800 2000
w avelength (nm )
Er
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
Ei
ErE iZnSe-crystal
1 3 .7
1 4 .2
1 4 .7
1 5 .2
1 5 .7
1 6 .2
1 6 .7
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
w a v e le n g th (n m )
Er
4
4 .1
4 .2
4 .3
4 .4
4 .5
4 .6
4 .7
4 .8
4 .9
5
Ei
E rE iZnTe-crystal
1 3 .7
1 4 .2
1 4 .7
1 5 .2
1 5 .7
1 6 .2
1 6 .7
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
w a v e le n g th (n m )
Er
4
4 .1
4 .2
4 .3
4 .4
4 .5
4 .6
4 .7
4 .8
4 .9
5
Ei
E rE iZnTe-crystal
Figure 5.6 Spectral variation of real part (Er) and imaginary part (Ei) of dielectricconstant vs wavelength for ZnX (X = S, Se, Te) crystals.
126
The typical absorption spectra obtained for the thin films of ZnSe of various
thicknesses (1000Å, 2000Å, 3000Å, and 5000Å,) deposited at various substrate temperatures
(303K, 373K and 448K) are shown in figure 5.7 (a) and figure 5.7 (b), (c), (d). From the
absorption spectra, it is clear that the absorption edge is present in the visible range. It can be
seen that the percentage of absorption is the highest for the thin films deposited at the lowest
(303K) substrate temperature. Optical band gaps again based on equation 5.3 with r = ½,
have been found by extrapolation on the energy axis for (h)1/r against h straight line
region as shown in figure 5.8. From the table 5.4, it is clear, that the maximum value of the
optical band gap is for the thin film of thickness 1000Å, deposited at substrate temperature
303K and the same is minimum for the thin films of thickness 5000Å, deposited at the
substrate temperature of 448 K. In between these two values, the gradual variation in optical
band gap is observed, depending upon their thickness and substrate temperatures. The values
of observed band gaps of ZnSe thin films table 5.4 are in good agreement with the reported
values in table 5.5 and other literatures [37, 41].
Absorption spectra obtained for ZnTe thin films of various thicknesses (1000Å,
2000Å, 3000Å and 5000Å,) deposited at various substrate temperatures (303K, 373K and
448K) are shown in figure 5.9. As mentioned earlier, the (h)1/2 vs h curves (figures 5.10)
have been used to evaluate the optical band gap for all these films of ZnTe. A high
absorption with sharp absorption edges is observed in case of ZnTe thin films in comparison
to ZnSe thin films. This may be because of the different detector systems that have been
employed in two separate spectrophotometers used for optical absorption study of both sets
of thin films. The optical band gap, as determined by the method mentioned above, is
tabulated in table 5.6 for all deposited thin films of ZnTe and they are found to be in good
agreement with the reported values by previous workers as given in table 5.7 and other
literatures [27, 31, 35, 37, 38, 64, 68, 69]. From table 5.6 it is clear that the maximum value
of optical band gap is obtained for the thin film with minimum thickness and minimum
substrate temperature.
It is clear from all observations that optical band gap is inversely proportional to the
thickness of the film as well as the substrate temperature of the deposited films [22-50]. The
127
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
370 395 420 445 470 495 520 545 570 595 620 645 670 695 720
Ts = 448KTs = 373KTs = 303K
ZnSe-(a)
Wavelength (nm)
Absorpt
ion (%)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
370 395 420 445 470 495 520 545 570 595 620 645 670 695 720
Ts = 448KTs = 373KTs = 303K
ZnSe-(a)
Wavelength (nm)
Absorpt
ion (%)
variations of refractive index (), and extinction coefficient (k) with wavelength for ZnSe
and ZnTe thin films of various thickness, deposited at various substrate temperatures are
shown in figures 5.11 & 5.12 and 5.13 & 5.14 respectively for ZnSe and ZnTe thin films. It
is clear from the figures that both optical constants (k and ) are found to be sensitive to the
film thickness as well as the substrate temperatures. The refractive index decreases
monotonically with an increase in substrate temperatures. This was found to be most
noticeable near the absorption edge. A large decrease in refractive index in the short
wavelength range can also be seen. Similar results are also reported by various investigators
[33, 51-53].
Figure 5.7 (a) UV-VIS Absorption spectra of ZnSe thin films of thickness1000Å deposited at various substrate temperatures.
128
0
0 .1
0 .2
0 .3
0 .4
0 .5
0 .6
0 .7
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe-(b)
Wavelength (nm)
Abso
rption
(%)
0
0 .1
0 .20 .3
0 .4
0 .5
0 .60 .7
0 .8
0 .9
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe-(c)
Wavelength (nm)
Abso
rption
(%)
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 0 3 KT s = 3 7 3 K
ZnSe-(d)
Wavelength (nm)
Abso
rption
(%)
0
0 .1
0 .2
0 .3
0 .4
0 .5
0 .6
0 .7
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe-(b)
Wavelength (nm)
Abso
rption
(%)
0
0 .1
0 .2
0 .3
0 .4
0 .5
0 .6
0 .7
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe-(b)
Wavelength (nm)
Abso
rption
(%)
0
0 .1
0 .20 .3
0 .4
0 .5
0 .60 .7
0 .8
0 .9
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe-(c)
Wavelength (nm)
Abso
rption
(%)
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 0 3 KT s = 3 7 3 K
ZnSe-(d)
Wavelength (nm)
Abso
rption
(%)
0
0 .1
0 .20 .3
0 .4
0 .5
0 .60 .7
0 .8
0 .9
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe-(c)
Wavelength (nm)
Abso
rption
(%)
0
0 .1
0 .20 .3
0 .4
0 .5
0 .60 .7
0 .8
0 .9
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe-(c)
Wavelength (nm)
Abso
rption
(%)
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 0 3 KT s = 3 7 3 K
ZnSe-(d)
Wavelength (nm)
Abso
rption
(%)
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
3 7 0 3 9 5 4 2 0 4 4 5 4 7 0 4 9 5 5 2 0 5 4 5 5 7 0 5 9 5 6 2 0 6 4 5 6 7 0 6 9 5 7 2 0
T s = 4 4 8 KT s = 3 0 3 KT s = 3 7 3 K
ZnSe-(d)
Wavelength (nm)
Abso
rption
(%)
Figure 5.7 (b), (c), (d) UV-VIS Absorption spectra of ZnSe thin films of thickness(b) 2000Å, (c) 3000Å and (d) 5000Å deposited at varioussubstrate temperature.
129
0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe – (A)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )
0
5 E + 1 0
1 E + 1 1
1 .5 E + 1 1
2 E + 1 1
2 .5 E + 1 1
1 .5 1 .6 1 .7 1 .8 1 .9 2 2 .1 2 .2 2 .3 2 .4 2 .5 2 .6 2 .7 2 .8 2 .9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (B)
Photon energy (eV)
(h
)2
(cm
-2 ev2 )
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (C)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )
0 .0 0 E + 0 0
2 .0 0 E + 0 9
4 .0 0 E + 0 9
6 .0 0 E + 0 9
8 .0 0 E + 0 9
1 .0 0 E + 1 0
1 .2 0 E + 1 0
1 .4 0 E + 1 0
1 .6 0 E + 1 0
1 .8 0 E + 1 0
1 .5 1 .6 1 .7 1 .8 1 .9 2 2 .1 2 .2 2 .3 2 .4 2 .5 2 .6 2 .7 2 .8 2 .9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (D)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe – (A)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe – (A)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )
0
5 E + 1 0
1 E + 1 1
1 .5 E + 1 1
2 E + 1 1
2 .5 E + 1 1
1 .5 1 .6 1 .7 1 .8 1 .9 2 2 .1 2 .2 2 .3 2 .4 2 .5 2 .6 2 .7 2 .8 2 .9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (B)
Photon energy (eV)
(h
)2
(cm
-2 ev2 )
0
5 E + 1 0
1 E + 1 1
1 .5 E + 1 1
2 E + 1 1
2 .5 E + 1 1
1 .5 1 .6 1 .7 1 .8 1 .9 2 2 .1 2 .2 2 .3 2 .4 2 .5 2 .6 2 .7 2 .8 2 .9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (B)
Photon energy (eV)
(h
)2
(cm
-2 ev2 )
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (C)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (C)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )
0 .0 0 E + 0 0
2 .0 0 E + 0 9
4 .0 0 E + 0 9
6 .0 0 E + 0 9
8 .0 0 E + 0 9
1 .0 0 E + 1 0
1 .2 0 E + 1 0
1 .4 0 E + 1 0
1 .6 0 E + 1 0
1 .8 0 E + 1 0
1 .5 1 .6 1 .7 1 .8 1 .9 2 2 .1 2 .2 2 .3 2 .4 2 .5 2 .6 2 .7 2 .8 2 .9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (D)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )
0 .0 0 E + 0 0
2 .0 0 E + 0 9
4 .0 0 E + 0 9
6 .0 0 E + 0 9
8 .0 0 E + 0 9
1 .0 0 E + 1 0
1 .2 0 E + 1 0
1 .4 0 E + 1 0
1 .6 0 E + 1 0
1 .8 0 E + 1 0
1 .5 1 .6 1 .7 1 .8 1 .9 2 2 .1 2 .2 2 .3 2 .4 2 .5 2 .6 2 .7 2 .8 2 .9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe – (D)
Photon energy (eV)
(h
)2
(cm
-2ev
2 )
Figure 5.8 Spectral variation of (h)2 vs Photon energy (h) for thin films of ZnSeof thickness (A) 1000Å , (B) 2000Å, (C) 3000Å and (D) 5000Å deposited atvarious substrate temperatures.
130
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 3 0 3 K
T s = 3 7 3 K
T s = 4 4 8 K
ZnTe–(A)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(B)
Wavelength (nm)
Abso
rptio
n
0
0 .5
1
1 .5
2
2 .5
3
3 .5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(C)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T S = 3 7 3 K
T S = 3 0 3 K
ZnTe–(D)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 3 0 3 K
T s = 3 7 3 K
T s = 4 4 8 K
ZnTe–(A)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 3 0 3 K
T s = 3 7 3 K
T s = 4 4 8 K
ZnTe–(A)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(B)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(B)
Wavelength (nm)
Abso
rptio
n
0
0 .5
1
1 .5
2
2 .5
3
3 .5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(C)
Wavelength (nm)
Abso
rptio
n
0
0 .5
1
1 .5
2
2 .5
3
3 .5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(C)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T S = 3 7 3 K
T S = 3 0 3 K
ZnTe–(D)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T S = 3 7 3 K
T S = 3 0 3 K
ZnTe–(D)
Wavelength (nm)
Abso
rptio
n(%
)(%
)(%
)(%
)
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 3 0 3 K
T s = 3 7 3 K
T s = 4 4 8 K
ZnTe–(A)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(B)
Wavelength (nm)
Abso
rptio
n
0
0 .5
1
1 .5
2
2 .5
3
3 .5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(C)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T S = 3 7 3 K
T S = 3 0 3 K
ZnTe–(D)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 3 0 3 K
T s = 3 7 3 K
T s = 4 4 8 K
ZnTe–(A)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 3 0 3 K
T s = 3 7 3 K
T s = 4 4 8 K
ZnTe–(A)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(B)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(B)
Wavelength (nm)
Abso
rptio
n
0
0 .5
1
1 .5
2
2 .5
3
3 .5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(C)
Wavelength (nm)
Abso
rptio
n
0
0 .5
1
1 .5
2
2 .5
3
3 .5
4
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe–(C)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T S = 3 7 3 K
T S = 3 0 3 K
ZnTe–(D)
Wavelength (nm)
Abso
rptio
n
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
4 . 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T S = 3 7 3 K
T S = 3 0 3 K
ZnTe–(D)
Wavelength (nm)
Abso
rptio
n(%
)(%
)(%
)(%
)
Figure 5.9 UV-VIS Absorption spectra of ZnTe Thin Films of thicknesses (A) 1000Å,(B) 2000Å, (C) 3000Å and (D) 5000Å deposited at various substratetemperatures.
131
0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
Z n S e – ( A )
P h o t o n e n e r g y ( e V )
(h
)2
0
5 E + 1 0
1 E + 1 1
1 . 5 E + 1 1
2 E + 1 1
2 . 5 E + 1 1
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( B )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
Z n S e – ( A )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
Z n S e – ( A )
P h o t o n e n e r g y ( e V )
(h
)2
0
5 E + 1 0
1 E + 1 1
1 . 5 E + 1 1
2 E + 1 1
2 . 5 E + 1 1
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( B )
P h o t o n e n e r g y ( e V )
(h
)2
0
5 E + 1 0
1 E + 1 1
1 . 5 E + 1 1
2 E + 1 1
2 . 5 E + 1 1
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( B )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( C )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
2 . 0 0 E + 0 9
4 . 0 0 E + 0 9
6 . 0 0 E + 0 9
8 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 2 0 E + 1 0
1 . 4 0 E + 1 0
1 . 6 0 E + 1 0
1 . 8 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( D )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( C )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( C )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
2 . 0 0 E + 0 9
4 . 0 0 E + 0 9
6 . 0 0 E + 0 9
8 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 2 0 E + 1 0
1 . 4 0 E + 1 0
1 . 6 0 E + 1 0
1 . 8 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( D )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
2 . 0 0 E + 0 9
4 . 0 0 E + 0 9
6 . 0 0 E + 0 9
8 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 2 0 E + 1 0
1 . 4 0 E + 1 0
1 . 6 0 E + 1 0
1 . 8 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( D )
P h o t o n e n e r g y ( e V )
(h
)2
(cm
-2m
v2)
(cm
-2m
v2)
(cm
-2m
v2)
(cm
-2m
v2)
0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
Z n S e – ( A )
P h o t o n e n e r g y ( e V )
(h
)2
0
5 E + 1 0
1 E + 1 1
1 . 5 E + 1 1
2 E + 1 1
2 . 5 E + 1 1
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( B )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
Z n S e – ( A )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
1 . 0 0 E + 1 0
2 . 0 0 E + 1 0
3 . 0 0 E + 1 0
4 . 0 0 E + 1 0
5 . 0 0 E + 1 0
6 . 0 0 E + 1 0
7 . 0 0 E + 1 0
8 . 0 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
Z n S e – ( A )
P h o t o n e n e r g y ( e V )
(h
)2
0
5 E + 1 0
1 E + 1 1
1 . 5 E + 1 1
2 E + 1 1
2 . 5 E + 1 1
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( B )
P h o t o n e n e r g y ( e V )
(h
)2
0
5 E + 1 0
1 E + 1 1
1 . 5 E + 1 1
2 E + 1 1
2 . 5 E + 1 1
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( B )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( C )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
2 . 0 0 E + 0 9
4 . 0 0 E + 0 9
6 . 0 0 E + 0 9
8 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 2 0 E + 1 0
1 . 4 0 E + 1 0
1 . 6 0 E + 1 0
1 . 8 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( D )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( C )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
5 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 5 0 E + 1 0
2 . 0 0 E + 1 0
2 . 5 0 E + 1 0
3 . 0 0 E + 1 0
3 . 5 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( C )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
2 . 0 0 E + 0 9
4 . 0 0 E + 0 9
6 . 0 0 E + 0 9
8 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 2 0 E + 1 0
1 . 4 0 E + 1 0
1 . 6 0 E + 1 0
1 . 8 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( D )
P h o t o n e n e r g y ( e V )
(h
)2
0 . 0 0 E + 0 0
2 . 0 0 E + 0 9
4 . 0 0 E + 0 9
6 . 0 0 E + 0 9
8 . 0 0 E + 0 9
1 . 0 0 E + 1 0
1 . 2 0 E + 1 0
1 . 4 0 E + 1 0
1 . 6 0 E + 1 0
1 . 8 0 E + 1 0
1 . 5 1 . 6 1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2 2 . 3 2 . 4 2 . 5 2 . 6 2 . 7 2 . 8 2 . 9 3
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Z n S e – ( D )
P h o t o n e n e r g y ( e V )
(h
)2
(cm
-2m
v2)
(cm
-2m
v2)
(cm
-2m
v2)
(cm
-2m
v2)
Figure 5.10 Spectral variation of (h)2 vs Photon energy (h) for thin films of ZnTeof thickness (A) 1000Å ,(B) 2000Å, (C) 3000Å and (D) 5000Å deposited atvarious substrate temperatures.
132
4 . 0 6
4 . 0 6 5
4 . 0 7
4 . 0 7 5
4 . 0 8
4 . 0 8 5
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 1000Å
Wave length (nm)
Refra
ctive
Inde
x ()
4 . 0 3
4 . 0 4
4 . 0 5
4 . 0 6
4 . 0 7
4 . 0 8
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 3000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 .0 4 5
4 .0 5
4 .0 5 5
4 .0 6
4 .0 6 5
4 .0 7
4 .0 7 5
4 .0 8
4 .0 8 5
4 .0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 2000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 . 0 2
4 . 0 3
4 . 0 4
4 . 0 5
4 . 0 6
4 . 0 7
4 . 0 8
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 5000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 . 0 6
4 . 0 6 5
4 . 0 7
4 . 0 7 5
4 . 0 8
4 . 0 8 5
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 1000Å
Wave length (nm)
Refra
ctive
Inde
x ()
4 . 0 6
4 . 0 6 5
4 . 0 7
4 . 0 7 5
4 . 0 8
4 . 0 8 5
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 1000Å
Wave length (nm)
Refra
ctive
Inde
x ()
4 . 0 3
4 . 0 4
4 . 0 5
4 . 0 6
4 . 0 7
4 . 0 8
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 3000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 . 0 3
4 . 0 4
4 . 0 5
4 . 0 6
4 . 0 7
4 . 0 8
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 3000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 .0 4 5
4 .0 5
4 .0 5 5
4 .0 6
4 .0 6 5
4 .0 7
4 .0 7 5
4 .0 8
4 .0 8 5
4 .0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 2000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 .0 4 5
4 .0 5
4 .0 5 5
4 .0 6
4 .0 6 5
4 .0 7
4 .0 7 5
4 .0 8
4 .0 8 5
4 .0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 2000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 . 0 2
4 . 0 3
4 . 0 4
4 . 0 5
4 . 0 6
4 . 0 7
4 . 0 8
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 5000Å
Wavelength (nm)
Refra
ctive
inde
x ()
4 . 0 2
4 . 0 3
4 . 0 4
4 . 0 5
4 . 0 6
4 . 0 7
4 . 0 8
4 . 0 9
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe- 5000Å
Wavelength (nm)
Refra
ctive
inde
x ()
Figure 5.11 Spectral variation of refractive index () vs wavelength for thin films ofZnSe of various thicknesses, deposited at various substrate temperatures.
133
0 . 0 0 E + 0 0
5 . 0 0 E - 0 7
1 . 0 0 E - 0 6
1 . 5 0 E - 0 6
2 . 0 0 E - 0 6
2 . 5 0 E - 0 6
3 . 0 0 E - 0 6
3 . 5 0 E - 0 6
4 . 0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe - 1000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 6
5 .0 0 E - 0 6
6 .0 0 E - 0 6
7 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 3000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 6
5 .0 0 E - 0 6
6 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 2000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 65 .0 0 E - 0 6
6 .0 0 E - 0 6
7 .0 0 E - 0 6
8 .0 0 E - 0 6
9 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 5000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 . 0 0 E + 0 0
5 . 0 0 E - 0 7
1 . 0 0 E - 0 6
1 . 5 0 E - 0 6
2 . 0 0 E - 0 6
2 . 5 0 E - 0 6
3 . 0 0 E - 0 6
3 . 5 0 E - 0 6
4 . 0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe - 1000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 . 0 0 E + 0 0
5 . 0 0 E - 0 7
1 . 0 0 E - 0 6
1 . 5 0 E - 0 6
2 . 0 0 E - 0 6
2 . 5 0 E - 0 6
3 . 0 0 E - 0 6
3 . 5 0 E - 0 6
4 . 0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnSe - 1000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 6
5 .0 0 E - 0 6
6 .0 0 E - 0 6
7 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 3000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 6
5 .0 0 E - 0 6
6 .0 0 E - 0 6
7 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 3000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 6
5 .0 0 E - 0 6
6 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 2000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 6
5 .0 0 E - 0 6
6 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 2000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 65 .0 0 E - 0 6
6 .0 0 E - 0 6
7 .0 0 E - 0 6
8 .0 0 E - 0 6
9 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 5000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
0 .0 0 E + 0 0
1 .0 0 E - 0 6
2 .0 0 E - 0 6
3 .0 0 E - 0 6
4 .0 0 E - 0 65 .0 0 E - 0 6
6 .0 0 E - 0 6
7 .0 0 E - 0 6
8 .0 0 E - 0 6
9 .0 0 E - 0 6
3 7 0 4 2 0 4 7 0 5 2 0 5 7 0 6 2 0 6 7 0 7 2 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnSe - 5000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient
(k)
Figure 5.12 Spectral variation of extinction coefficient (k) vs wavelength for thin filmsof ZnSe of various thicknesses, deposited at various substratetemperatures.
134
3 .8 5
3 .9
3 .9 5
4
4 .0 5
4 .1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-1000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-2000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Znte-3000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-5000Å
Wavelength (nm)
Refra
ctive
index
()
3 .8 5
3 .9
3 .9 5
4
4 .0 5
4 .1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-1000Å
Wavelength (nm)
Refra
ctive
index
()
3 .8 5
3 .9
3 .9 5
4
4 .0 5
4 .1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-1000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-2000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-2000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Znte-3000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
Znte-3000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-5000Å
Wavelength (nm)
Refra
ctive
index
()
3 . 8 5
3 . 9
3 . 9 5
4
4 . 0 5
4 . 1
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe-5000Å
Wavelength (nm)
Refra
ctive
index
()
Figure 5.13 Spectral variation of refractive index () vs wavelength for thin films ofZnTe of various thicknesses, deposited at various substrate temperatures.
135
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 1000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 2000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 3000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe- 5000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 1000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 1000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 2000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 3000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe- 5000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 2000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 2000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 3000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 KT s = 3 7 3 KT s = 3 0 3 K
ZnTe- 3000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe- 5000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
0 . 0 E + 0 0
4 . 0 E - 0 6
8 . 0 E - 0 6
1 . 2 E - 0 5
1 . 6 E - 0 5
2 . 0 E - 0 5
2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0
T s = 4 4 8 K
T s = 3 7 3 K
T s = 3 0 3 K
ZnTe- 5000Å
Wavelength (nm)
Extin
ctio
nco
effic
ient (
k)
Figure 5.14 Spectral variation of extinction coefficient (k) vs wavelength for thin filmsof ZnTe of various thicknesses, deposited at various substratetemperatures.
136
2.262.20ZnTe03
2.672.60ZnSe02
3.603.68ZnS01
Reported Values [14-21](eV)
Band Gap(eV)
crystalSr.No.
2.262.20ZnTe03
2.672.60ZnSe02
3.603.68ZnS01
Reported Values [14-21](eV)
Band Gap(eV)
crystalSr.No.
77Chemical Vapor Transport method,(NH4)I carrier gas
2.21ZnTe-Crystals
71
72
73
SPR crystals by annealing at 1000-1100 C.Physical Vapor Transport techniqueon the bases of Schieber’s conditions,PA spectrometerChemical Vapor Transport method,(NH4)3Cl5 transporting agent(0.12mmol)
2.67
2.78
2.69
ZnSe-Crystals
74
75
76
ZnS Nanoparticles using polyvinylAlcohol, Bulk ZnS band gap.ZnS nanocrystals through chemicalprecipitation methodChemical Transport reactions,Bromine as transport agent
3.68
3.92
3.54
ZnS-Crystals
ReferencesGrowth conditionsOptical band gap(eV)
Material
77Chemical Vapor Transport method,(NH4)I carrier gas
2.21ZnTe-Crystals
71
72
73
SPR crystals by annealing at 1000-1100 C.Physical Vapor Transport techniqueon the bases of Schieber’s conditions,PA spectrometerChemical Vapor Transport method,(NH4)3Cl5 transporting agent(0.12mmol)
2.67
2.78
2.69
ZnSe-Crystals
74
75
76
ZnS Nanoparticles using polyvinylAlcohol, Bulk ZnS band gap.ZnS nanocrystals through chemicalprecipitation methodChemical Transport reactions,Bromine as transport agent
3.68
3.92
3.54
ZnS-Crystals
ReferencesGrowth conditionsOptical band gap(eV)
Material
Table – 5.2 Optical band gaps of grown crystals of ZnS, ZnSe and ZnTe.
Table – 5.3 Reported values of Optical band gap of crystals of ZnS, ZnSe and ZnTe.
137
2 . 5 24 4 8
2 . 5 43 7 3
2 . 5 73 0 35 0 0 0
2 . 5 44 4 8
2 . 5 53 7 3
2 . 5 73 0 33 0 0 0
2 . 5 04 4 8
2 . 5 63 7 3
2 . 6 23 0 32 0 0 0
2 . 5 74 4 8
2 . 6 03 7 3
2 . 6 23 0 31 0 0 0
O p t i c a l B a n d G a p( e V )
S u b s t r a t e T e m p e r a t u r e( K )
T h i c k n e s s( Å )
Z n S e T h i n F i l m s
2 . 5 24 4 8
2 . 5 43 7 3
2 . 5 73 0 35 0 0 0
2 . 5 44 4 8
2 . 5 53 7 3
2 . 5 73 0 33 0 0 0
2 . 5 04 4 8
2 . 5 63 7 3
2 . 6 23 0 32 0 0 0
2 . 5 74 4 8
2 . 6 03 7 3
2 . 6 23 0 31 0 0 0
O p t i c a l B a n d G a p( e V )
S u b s t r a t e T e m p e r a t u r e( K )
T h i c k n e s s( Å )
Z n S e T h i n F i l m s
48
23
78
48
79
44
The scanning e-beam (powerdensity=1.5kW/cm2) evaporated filmson to microscopic glass slide at differentsubstrate temperatures (RT, 100, 200,3000C).Thin films of ZnSe deposited
potentiostatically from an unstirred,deareated aqueous solution ontotitanium and glass coated with fluorinedoped tin oxide) and ITO substrates.Vacuum evaporated films onto Si(111)and glass substrates.Films prepared by spray pyrolysis ontoglass substrates at differenttemperatures(4000C to 4500C)e-beam evaporated films on glasssubstrates at differenttemperatures(RT-2500)Deposition of ZnSe thin films byevaporation at evaporation temperaturebetween850-10800C and substratetemperature between 150 and 2500C
2.95-2.70
2.6
2.72-2.60
2.65-2.70
2.94-2.69
2.48-3.4
ZnSethinfilms
ReferencesGrowth conditionsOptical band gap(eV)
Material
48
23
78
48
79
44
The scanning e-beam (powerdensity=1.5kW/cm2) evaporated filmson to microscopic glass slide at differentsubstrate temperatures (RT, 100, 200,3000C).Thin films of ZnSe deposited
potentiostatically from an unstirred,deareated aqueous solution ontotitanium and glass coated with fluorinedoped tin oxide) and ITO substrates.Vacuum evaporated films onto Si(111)and glass substrates.Films prepared by spray pyrolysis ontoglass substrates at differenttemperatures(4000C to 4500C)e-beam evaporated films on glasssubstrates at differenttemperatures(RT-2500)Deposition of ZnSe thin films byevaporation at evaporation temperaturebetween850-10800C and substratetemperature between 150 and 2500C
2.95-2.70
2.6
2.72-2.60
2.65-2.70
2.94-2.69
2.48-3.4
ZnSethinfilms
ReferencesGrowth conditionsOptical band gap(eV)
Material
Table-5.4 Measured optical band gaps of ZnSe Thin Films .
Table-5.5 Reported optical band gap of ZnSe Thin Films.
138
1 . 7 44 4 8
1 . 7 83 7 3
1 . 8 23 0 35 0 0 0
1 . 9 44 4 8
2 . 0 83 7 3
2 . 1 03 0 33 0 0 0
1 . 8 04 4 8
1 . 8 43 7 3
1 . 8 63 0 32 0 0 0
1 . 8 64 4 8
2 . 0 93 7 3
2 . 1 33 0 31 0 0 0
O p t i c a l B a n d G a p( e V )
S u b s t r a t e T e m p e r a t u r e( K )
T h i c k n e s s( Å )
Z n T e T h i n F i l m s
1 . 7 44 4 8
1 . 7 83 7 3
1 . 8 23 0 35 0 0 0
1 . 9 44 4 8
2 . 0 83 7 3
2 . 1 03 0 33 0 0 0
1 . 8 04 4 8
1 . 8 43 7 3
1 . 8 63 0 32 0 0 0
1 . 8 64 4 8
2 . 0 93 7 3
2 . 1 33 0 31 0 0 0
O p t i c a l B a n d G a p( e V )
S u b s t r a t e T e m p e r a t u r e( K )
T h i c k n e s s( Å )
Z n T e T h i n F i l m s
66
67
32
33
65
Direct combination of gaseous Zn and Tein H and He atmosphere at 6000CSubstrate: corning7059 glass polishedwith 1 m alumina .Electrodeposition on tin conductive oxidesubstrates in aqueous solution containingTeO2 and ZnCl2Thin films prepared by vacuumevaporation onto glass substrates at 300-450K.Thermal evaporation of ZnTe powderfrom Mo boat at 10-5Torr onto glasssubstrates at different substratetemperatures.Electrodeposited films on F:SnO2 glasssubstrates
2.25
2.25
1.95-2.40
2.00-2.30
2.15
ZnTeThinFilms
ReferencesGrowth conditionsOptical band gap(eV)
Material
66
67
32
33
65
Direct combination of gaseous Zn and Tein H and He atmosphere at 6000CSubstrate: corning7059 glass polishedwith 1 m alumina .Electrodeposition on tin conductive oxidesubstrates in aqueous solution containingTeO2 and ZnCl2Thin films prepared by vacuumevaporation onto glass substrates at 300-450K.Thermal evaporation of ZnTe powderfrom Mo boat at 10-5Torr onto glasssubstrates at different substratetemperatures.Electrodeposited films on F:SnO2 glasssubstrates
2.25
2.25
1.95-2.40
2.00-2.30
2.15
ZnTeThinFilms
ReferencesGrowth conditionsOptical band gap(eV)
Material
Table-5.6 Measured optical band gap of ZnTe Thin Films.
Table-5.7 Reported optical band gap of ZnTe thin films.
139
5.5 CONCLUSIONS
Following conclusions are drawn from the careful study of optical absorption spectra
obtained for ZnX (X= S, Se and Te) crystals grown by DVT technique and thin films
deposited by thermal evaporation method.
(i) All spectra show a considerable absorption of incident photon energy in the
visible range of EM spectrum.
(ii) Thus, a well defined fundamental absorption edge as observed in the range 400-
500 nm for all spectra has been used for the determination of optical band gap of
materials under study both in bulk crystalline as well as thin film form.
(iii) In case of pure DVT grown ZnX (x=S, Se and Te) crystals, ZnS crystals possess
maximum band gap of 3.68 eV and ZnTe crystals possess minimum band gap of -
2.20 eV. ZnSe crystals show intermediate band gap of 2.6 eV. These values are
determined using equation 5.2 with r=1/2 and they are in good agreement with the
reported values as shown in table 5.3.
(iv) In case of thermally evaporated thin films of ZnSe, the absolute value of %
absorption is found to be low and remains below 1% all throughout the range of
incident photon energy. This may be due to the poor detector response and the
low intensity of incident photons in a given optical geometry of optical
components used in the spectrophotometer. However as these factors do not affect
the position of fundamental absorption edge; these types of spectra are normally
used to evaluate the optical band gap using equation 5.2.
(v) It is observed that for all the deposited films the increase in the substrate
temperature has similar effect of decreasing optical band gap in the range 2.62-
2.52 eV as shown in the figure 5.15.
(vi) Thickness dependence of optical band gap is not so significant but there is a
general trend of decreasing band gap with increasing thickness as shown in the
figure 5.15.
140
0
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
2 . 5 2 . 5 2 2 . 5 4 2 . 5 6 2 . 5 8 2 . 6 2 . 6 2 2 . 6 4
3 0 3 K
3 7 3 K
4 4 8 K
Z n S e
O p tica l B an d G ap (eV )
Film
Th
ickn
ess
(Å)
3 0 0
3 2 0
3 4 0
3 6 0
3 8 0
4 0 0
4 2 0
4 4 0
4 6 0
2 . 5 2 . 5 5 2 . 6
1 0 0 0 Å
2 0 0 0 Å
3 0 0 0 Å
5 0 0 0 Å
O p tica l B an d G ap (eV )
Su
bst
rate
Tem
per
atu
re (
K) Z n S e
0
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
2 . 5 2 . 5 2 2 . 5 4 2 . 5 6 2 . 5 8 2 . 6 2 . 6 2 2 . 6 4
3 0 3 K
3 7 3 K
4 4 8 K
Z n S e
O p tica l B an d G ap (eV )
Film
Th
ickn
ess
(Å)
0
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
2 . 5 2 . 5 2 2 . 5 4 2 . 5 6 2 . 5 8 2 . 6 2 . 6 2 2 . 6 4
3 0 3 K
3 7 3 K
4 4 8 K
Z n S e
O p tica l B an d G ap (eV )
Film
Th
ickn
ess
(Å)
3 0 0
3 2 0
3 4 0
3 6 0
3 8 0
4 0 0
4 2 0
4 4 0
4 6 0
2 . 5 2 . 5 5 2 . 6
1 0 0 0 Å
2 0 0 0 Å
3 0 0 0 Å
5 0 0 0 Å
O p tica l B an d G ap (eV )
Su
bst
rate
Tem
per
atu
re (
K) Z n S e
3 0 0
3 2 0
3 4 0
3 6 0
3 8 0
4 0 0
4 2 0
4 4 0
4 6 0
2 . 5 2 . 5 5 2 . 6
1 0 0 0 Å
2 0 0 0 Å
3 0 0 0 Å
5 0 0 0 Å
O p tica l B an d G ap (eV )
Su
bst
rate
Tem
per
atu
re (
K) Z n S e
3 0 0
3 2 0
3 4 0
3 6 0
3 8 0
4 0 0
4 2 0
4 4 0
4 6 0
1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2
1 0 0 0 Å2 0 0 0 Å3 0 0 0 Å5 0 0 0 Å
Z n T e T h in F ilm s
O p t ic a l B a n d G a p (e V )
Su
bs
tra
teT
em
pe
ratu
re (
K)
0
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2
3 0 3 K
3 7 3 K
4 4 8 K
Z n T e T h in F ilm s
O p t ic a l B a n d G a p (e V )Fil
m T
hic
kn
es
s (
Å)
3 0 0
3 2 0
3 4 0
3 6 0
3 8 0
4 0 0
4 2 0
4 4 0
4 6 0
1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2
1 0 0 0 Å2 0 0 0 Å3 0 0 0 Å5 0 0 0 Å
Z n T e T h in F ilm s
O p t ic a l B a n d G a p (e V )
Su
bs
tra
teT
em
pe
ratu
re (
K)
3 0 0
3 2 0
3 4 0
3 6 0
3 8 0
4 0 0
4 2 0
4 4 0
4 6 0
1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2
1 0 0 0 Å2 0 0 0 Å3 0 0 0 Å5 0 0 0 Å
Z n T e T h in F ilm s
O p t ic a l B a n d G a p (e V )
Su
bs
tra
teT
em
pe
ratu
re (
K)
0
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2
3 0 3 K
3 7 3 K
4 4 8 K
Z n T e T h in F ilm s
O p t ic a l B a n d G a p (e V )Fil
m T
hic
kn
es
s (
Å)
0
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
1 . 7 1 . 8 1 . 9 2 2 . 1 2 . 2
3 0 3 K
3 7 3 K
4 4 8 K
Z n T e T h in F ilm s
O p t ic a l B a n d G a p (e V )Fil
m T
hic
kn
es
s (
Å)
Figure 5.15 Variation of Optical band gap of ZnSe thin films with their thicknessand substrate temperature.
Figure 5.16 Variation of optical band gap of ZnTe thin films with substratetemperature and films thickness.
141
(vii) In case of thermally evaporated thin films of ZnTe, the absolute value of %
absorption is found to be good and remains below 4% all throughout the range of
incident photon energy.
(viii) It is observed that for all the deposited films of ZnTe, the increase in the substrate
temperature has similar effect of decreasing optical band gap in the range 2.13-
1.74 eV as shown in the figure 5.16.
(ix) Thickness dependence of optical band gap is not so significant but there is a
general trend of decreasing band gap with increasing thickness as shown in
the figure 5.16 .
142
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