Nanocrystals of CdSe have been produced in SiOx matrix layer and in ZnSe heterostructure layer by
thermal evaporation method. Structural studies were done by X-ray diffractometer. Quantum confinement
effect of CdSe nanocrystals was analyzed from optical studies. Bulk CdSe has band-gap energy of 1.756 eV
that can be shifted to larger values by reducing the crystal size to dimensions smaller than the Bohr radius
of the exciton. Experimentally measured band-gap shifts with respect to the bulk value for quantum dot
thin films are compared with the predictions of the effective mass approximation model (i.e., Brus model)
and Quantum mechanical model. Sizes of the crystallites calculated from both models were coincident with
each other.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2779

Kumar, M. Melvin David

Rajesh, S.

Suganthi, Devadason

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 4 No 2, 02021(3pp) (2012) Том 4 № 2, 02021(3cc) (2012) 
 
 
2077-6772/2012/4(2)02021(3) 02021-1  2012 Sumy State University 
Quantum Confinement in Cadmium Selenide Multilayer Thin Films  
Using Physical Vapour Deposition Method 
 
M. Melvin David Kumar*, Suganthi Devadason, S. Rajesh 
 
Thin film laboratory, Department of Physics Karunya University, Coimbatore – 641 114, India 
 
(Received 11 September 2012; revised manuscript received 07 March 2012; published online 04 June 2012) 
 
Nanocrystals of CdSe have been produced in SiOx matrix layer and in ZnSe heterostructure layer by 
thermal evaporation method. Structural studies were done by X-ray diffractometer. Quantum confinement 
effect of CdSe nanocrystals was analyzed from optical studies. Bulk CdSe has band-gap energy of 1.756 eV 
that can be shifted to larger values by reducing the crystal size to dimensions smaller than the Bohr radius 
of the exciton. Experimentally measured band-gap shifts with respect to the bulk value for quantum dot 
thin films are compared with the predictions of the effective mass approximation model (i.e., Brus model) 
and Quantum mechanical model. Sizes of the crystallites calculated from both models were coincident with 
each other. 
 
Keywords: Multilayer thin films, Quantum Confinement, CdSe, ZnSe, SiOx. 
 
 PACS numbers: 61.05. _ a, 03.65.Xp, 74.78.Fk 
 
 
______________ 
* melvin@karunya.edu  
1. INTRODUCTION 
 
II-VI semiconductor particles with sizes of a few 
nanometers in matrix layer and in heterointerfaces 
show very attractive properties completely different 
from those of bulk materials [1]. They have potentials 
both for basic study of the three-dimensional quantum 
confinement effect in semiconductors and for applica-
tions in the field of optoelectronic devices. Number of 
devices make use of size controlled spectral tunability 
confinement induced concentration of the oscillator 
strength and ultra fast relaxation dynamics (optical 
data processing) [2-4] offered by nanocrystals. Since the 
first observations of quantum confinement in the opti-
cal absorption of semiconductor doped glasses [5], the 
nanocrystalline research has expanded immensely. The 
theory of quantization of hole states in a semiconductor 
nanocrystals has been developed taking into account 
band mixing effects [6, 7]. If the exciton Bohr radius is 
comparable to the dimensions of nanocrystallites, the 
confinement effects strongly modify hole energies and 
relax the selection rules for optical transitions which 
makes observation of a great number of electron-hole 
pair transitions possible. The presence of trap levels 
within the gap or on the surface of confined structures, 
together with the quantum confinement effect itself, 
strongly affect many properties of nanocrystalline ma-
terials and in particular, II – VI nanocrystals [8]. 
In the present work, CdSe/SiOx and CdSe/ZnSe 
nanocrystalline multilayer structures are studied. We 
report a successful production of CdSe quantum con-
finement effect in thin film matrices from SiOx and 
ZnSe by means of multilayer approach. The structural 
properties of the CdSe/SiOx and CdSe/ZnSe were stud-
ied by X-ray diffraction method. The Optical properties 
of the same layers were studied by UV-VIS NIR spec-
trophotometer. 
2. EXPERIMENTAL DETAILS 
 
CdSe/SiOx and CdSe/ZnSe nanocrystalline multilayer 
structures were prepared by consecutive thermal evapo-
ration of CdSe(99.99 % Aldrich Chem. Co.,) and SiOx (or) 
ZnSe from two independent molybdenum crucibles at a 
vacuum of 5 × 10 – 5 Pa. Corning 7059 glass substrates 
were used and sere not intentionally heated. The nomi-
nal film thickness and deposition rate were controlled by 
two calibrated quartz monitor detectors. The substrates 
were fixed at the greatest possible distance which was 
used to calculate the tooling factor of the instrument. A 
step-by-step procedure was applied in the deposition of a 
given layer in the multilayer stutures. In CdSe/SiOx 
sample, five layers of CdSe and four layers of SiOx were 
coated with the layer thickness of 50 Å and 1000 Å, re-
spectively. In CdSe/ZnSe sample, five layers of CdSe and 
Six layers of ZnSe were coated with layer thickness of 
80 Å and 500 Å, respectively. Structural studies of these 
samples (CdSe/SiOx, CdSe/ZnSe) were recorded with X-
ray (Shimadzu XRD-6000) diffractometer and transmis-
sion spectra were obtained using UV-VIS NIR spectro-
photometer. The well coincidence between experimental 
data and calculated data has been proved. 
 
3. RESULTS AND DISCUSSION  
 
3.1 Structural Properties 
 
Structural properties of CdSe/SiOx and CdSe/ZnSe 
multilayer thin films coated under specific conditions 
were analyzed from X-ray diffraction spectra. The XRD 
profiles for the samples are shown in figure (i). A peak 
approximately at 23.4  and 22.7  in spectra referring to 
(100) plane (JCPDS-8-459) of CdSe material. This shows 
that CdSe/SiOx and CdSe/ZnSe films are polycrystalline 
in nature with wurtzite structure. The broadness of the 
(100) diffraction line in the spectra indicated that the 
size of the CdSe crystallites in the films is small [9]. We 
obtained the value for size of crystallites in the range of 
1-2 nm as in Table 1. 
 QUANTUM CONFINEMENT IN CADMIUM SELENIDE… J. NANO- ELECTRON. PHYS. 4, 02021 (2012) 
 
 
 02021-2  
Table 1 – Size of the Crystallites from XRD data 
 
№ Sample 2θ(deg) d(Å) FWHM(deg) Strain(e) 
Stress(S) 
(dyn/cm2) 
D (nm) 
1 CdSe/SiOx 23.40 3.79856 6.680 0.0212 21.2 1.19 
2 CdSe/ZnSe 22.70 3.91409 6.0666 0.0522 52.2 1.31 
 
 
 
Fig. 1 – XRD profile for the samples CdSe/SiOx and 
CdSe/ZnSe 
 
The X-ray diffraction data were also used to calcu-
late the average size of the CdSe crystallites. It was 
done by using Debye-Scherer broadening formula. 
 
 
(2 )cos
D Å (1) 
 
where D is the crystallite size,  is the wavelength 
of X-ray,  is the full width at half maximum (FWHM) 
after correcting the instrument peak broadening (  
expressed in radians), and θ is the Bragg’s angle. This 
method provides an estimation of the CdSe crystallite 
size with a maximum error of about 20 % [9]. 
 
3.2 Optical Properties 
 
CdSe/SiOx and CdSe/ZnSe films coated on glass 
substrates were subjected to optical absorption using 
Hitachi 3010 UV-VIS-NIR spectrophotometer in the 
range of 190 nm - 2500 nm. In bulk CdSe material, the 
conduction band is non degenerate and almost isotropic 
whereas the valance band (mostly constituted of the 
selenide anion P orbital) [10] is threefold orbitally de-
generate. 
An important question at this point is what would 
be the effects of quantum confinement on the degener-
ate valance band of CdSe material. Based on the works 
done by Baldereschi & Lipari [11], the transitions close 
to the band gap value confirm the quantum confine-
ment. In Fig. 2(a) &2(b), it is observed that the two 
transitions close to the band gap value. Two direct 
band to band transitions are indeed observed in 
CdSe/SiOx UV spectra at 2.05 eV and 2.4 eV whereas in 
CdSe/ZnSe UV spectra, they were observed at 2.125 eV 
and 2.5 eV. This splitting of band gap confirms the 
quantum confinement of CdSe nano crystallites.  
In Fig. 3, transmission spectra of CdSe-SiOx and 
CdSe-ZnSe films were shown. A shift, which is marked  
 
 
 
Fig. 2 – Band gap graph for CdSe/SiOx (a) and CdSe/ZnSe (b) 
 
 
Fig. 3 – Transmission spectra of the samples CdSe/SiOx and 
CdSe/ZnSe 
 
 
 
 
[CdSe / ZnSe]
[CdSe / SiOx]
(100)
(100)
In
te
n
s
it
y
(a
.u
.)
2 Theta
1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8
0.00E+000
2.00E+013
4.00E+013
6.00E+013
8.00E+013
1.00E+014
1.20E+014
 
 
(
h
)2
h
1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8
0.00E+000
1.00E+013
2.00E+013
3.00E+013
4.00E+013
5.00E+013
6.00E+013
7.00E+013
8.00E+013
9.00E+013
1.00E+014
 
 
(
h
)2
h
0 250 500 750 1000 1250 1500 1750 2000 2250 2500
0
20
40
60
80
100
 
 
%
 T
Wavelength (nm)
 CdSe/ZnSe
 CdSe/SiOx
 M. MELVIN DAVID KUMAR, SUGANTHI DEVADASON, S. RAJESH J. NANO- ELECTRON. PHYS. 4, 02021 (2012) 
 
 
02021-3 
by arrow mark, towards lower wavelength region is 
observed in both spectra. Shift in the transmission 
spectra indicates the degeneracy of valance band of 
CdSe material. 
 
3.2.1 The effective mass approximation – Brus Model 
 
If the size of a CdSe crystals becomes smaller than 
the exciton radius, i.e, 5.6 nm for CdSe bulk material, 
the band gap energy increases due to quantum con-
finement [12]. Hence it has been generally proven that 
the quantum confinement effect should be observable if 
the radius of nano crystallites becomes less than the 
Bohr excitonic radius for corresponding material. Using 
the relation, 
 
 
2 2
2
2
shE
d
 (2) 
 
where d is the average size of nanocrystals, 
 = 0.38 me[13] is reduced electron – hole mass, the 
value of d = 5.2 nm and 4.6 nm have been obtained for 
the samples CdSe/SiOx and CdSe/ZnSe respectively 
and tabulated in Table 2. 
 
Table 2 – Size of the crystallites from UV-Vis data by Brus 
model 
 
S.No Sample 
Band 
gap(Eg) 
Shift in Band 
gap (Eshift) 
D (nm) 
1 CdSe/SiOx 2.05 0.294 5.19 
2 CdSe/ZnSe 2.125 0.369 4.64 
 
3.2.2 Quantum Mechanical Model 
 
Based on the work of Yu, W., Qu L., Guo W., [14], 
the condition for strong quantum confinement is 
Qdot << Qb where Qdot is radius of quantum dot and Qb 
is exciton Bohr radius (CdSe  5.6 nm).By using the 
given relation [14], 
 
 Eob = Eg + 2(Qb/Qdot)2 Ry* –   
 – 1.786 (Qb/Qdot) Ry* – 0.248 Ry (3) 
 
where Eob = Energy calculated from UV/VIS spectrum, 
Eg = bang gap (CdSe = 1.756 eV) for bulk material 
Qb = exciton Bohr radius (CdSe = 5.6 nm), Qdot = radius 
of crystallite, Ry* = Rydberg constant (CdSe = 0.016 eV), 
the size of the crystallites were calculated and well 
coincidence between the crystallite size calculated from 
Brus model and Quantum mechanical model has been 
shown in Table 3. 
 
Table 3 Size of the crystallites from UV-Vis data by Quantum 
mechanical model 
 
S.No Sample 
Band 
gap(Eg) 
Shift  
in Band 
gap(Eshift) 
R 
(nm) 
1 CdSe/SiOx 2.05 0.294 3.25 
2 CdSe/ZnSe 2.125 0.369 2.9 
 
4. CONCLUSION 
 
A new method of producing CdSe quantum dots in 
SiOx thinfilm matrix and in lattice matched hetero-
structure layer ZnSe has been proposed in this study. 
Well expressed quantum confined effects in the optical 
properties of CdSe have been observed. This method 
gives the possibility of preparing nanocrystals of vari-
ous semiconductors with a relatively narrow size dis-
tribution in relatively short times than conventional 
method. It is very useful especially in case of semicon-
ductors such as Se which form nanocrystals of very 
different sizes in a standard crystallization procedure. 
Further studies carried out in order to produce II-VI 
semiconductor nanocrystals with suitable sublayers. 
 
ACKNOWLEDGEMENT 
 
The Authors sincerely thank the management of 
Karunya University for providing all research facilities 
and encouragement. 
 
REFERENCES 
 
1. T. Toyoda, D. Arae, Q. Shen, Physica B 316-317, 476 
(2002). 
2. A.P. Alivisatos, MRS Bulletin 23, 18 (1998). 
3. M. Gratzel, H.S. Nalwa (Ed.), Handbook of Nanostruc-
tured Materials and Nanotechnology, vol. 3, (San Diego: 
Academic Press: 2000). 
4. A. Sombra, Solid State Commun. 88, 305 (1993). 
5. A. Ekimov, A. Onushenko, T. Tzehomskii, Sov. Phys. 
Chem. Glass 6, 511 (1980). 
6. A.I. Ekimov, F. Hache, M.C. Schanne-Klein, D. Ricard, 
C. Flytzanis, I.A. Kudryavtsev, T.V. Yazeva, A.V. Rodina, 
A.L. Efros, J. Opt. Soc. Am. B 10, 100 (1993). 
7. U.E. Laheld, G.T. Einevoll, Phys. Rev. B 55, 5184 (1997). 
8. G. Manolis, D. Papadimitriou, D. Nesheva, Thin Solid 
Films 495, 338 (2006). 
9. H. Arizpe-Chavez, J. Phys. Chem. Solids 61, 511 (2000). 
10. B. Pejova, I. Grozdanov, Materials Chemistry and Physics 
90, 35 (2005). 
11. A. Baldereschi, N.G. Lipari, Phys. Rev. B 3, 439 (1971). 
12. W. Hipp, H. Karl, I. Grobhans, B. Stritzker, Mat. Sci. 
Engg. B 101, 318 (2003). 
13. D. Nesheva,Z. Levi, Semicond. Sci. Tech. 12, 1319 (1997). 
14. W.W. Yu, L. Qu, W. Guo, X. Peng, Chem. Mater. 15(14), 
2854 (2003). 
15. P. Reimann, Phys. Rep. 361, 57 (2002). 
 


English

Quantum Confinement in Cadmium Selenide Multilayer Thin Films Using Physical Vapour Deposition Method

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 4 No 2, 02021(3pp) (2012) Том 4 № 2, 02021(3cc) (2012)   2077-6772/2012/4(2)02021(3) 02021-1  2012 Sumy State University Quantum Confinement in Cadmium Selenide Multilayer Thin Films  Using Physical Vapour Deposition Method  M. Melvin David Kumar*, Suganthi Devadason, S. Rajesh  Thin film laboratory, Department of Physics Karunya University, Coimbatore – 641 114, India  (Received 11 September 2012; revised manuscript received 07 March 2012; published online 04 June 2012)  Nanocrystals of CdSe have been produced in SiOx matrix layer and in ZnSe heterostructure layer by thermal evaporation method. Structural studies were done by X-ray diffractometer. Quantum confinement effect of CdSe nanocrystals was analyzed from optical studies. Bulk CdSe has band-gap energy of 1.756 eV that can be shifted to larger values by reducing the crystal size to dimensions smaller than the Bohr radius of the exciton. Experimentally measured band-gap shifts with respect to the bulk value for quantum dot thin films are compared with the predictions of the effective mass approximation model (i.e., Brus model) and Quantum mechanical model. Sizes of the crystallites calculated from both models were coincident with each other.  Keywords: Multilayer thin films, Quantum Confinement, CdSe, ZnSe, SiOx.   PACS numbers: 61.05. _ a, 03.65.Xp, 74.78.Fk   ______________ * melvin@karunya.edu  1. INTRODUCTION  II-VI semiconductor particles with sizes of a few nanometers in matrix layer and in heterointerfaces show very attractive properties completely different from those of bulk materials [1]. They have potentials both for basic study of the three-dimensional quantum confinement effect in semiconductors and for applica-tions in the field of optoelectronic devices. Number of devices make use of size controlled spectral tunability confinement induced concentration of the oscillator strength and ultra fast relaxation dynamics (optical data processing) [2-4] offered by nanocrystals. Since the first observations of quantum confinement in the opti-cal absorption of semiconductor doped glasses [5], the nanocrystalline research has expanded immensely. The theory of quantization of hole states in a semiconductor nanocrystals has been developed taking into account band mixing effects [6, 7]. If the exciton Bohr radius is comparable to the dimensions of nanocrystallites, the confinement effects strongly modify hole energies and relax the selection rules for optical transitions which makes observation of a great number of electron-hole pair transitions possible. The presence of trap levels within the gap or on the surface of confined structures, together with the quantum confinement effect itself, strongly affect many properties of nanocrystalline ma-terials and in particular, II – VI nanocrystals [8]. In the present work, CdSe/SiOx and CdSe/ZnSe nanocrystalline multilayer structures are studied. We report a successful production of CdSe quantum con-finement effect in thin film matrices from SiOx and ZnSe by means of multilayer approach. The structural properties of the CdSe/SiOx and CdSe/ZnSe were stud-ied by X-ray diffraction method. The Optical properties of the same layers were studied by UV-VIS NIR spec-trophotometer. 2. EXPERIMENTAL DETAILS  CdSe/SiOx and CdSe/ZnSe nanocrystalline multilayer structures were prepared by consecutive thermal evapo-ration of CdSe(99.99 % Aldrich Chem. Co.,) and SiOx (or) ZnSe from two independent molybdenum crucibles at a vacuum of 5 × 10 – 5 Pa. Corning 7059 glass substrates were used and sere not intentionally heated. The nomi-nal film thickness and deposition rate were controlled by two calibrated quartz monitor detectors. The substrates were fixed at the greatest possible distance which was used to calculate the tooling factor of the instrument. A step-by-step procedure was applied in the deposition of a given layer in the multilayer stutures. In CdSe/SiOx sample, five layers of CdSe and four layers of SiOx were coated with the layer thickness of 50 Å and 1000 Å, re-spectively. In CdSe/ZnSe sample, five layers of CdSe and Six layers of ZnSe were coated with layer thickness of 80 Å and 500 Å, respectively. Structural studies of these samples (CdSe/SiOx, CdSe/ZnSe) were recorded with X-ray (Shimadzu XRD-6000) diffractometer and transmis-sion spectra were obtained using UV-VIS NIR spectro-photometer. The well coincidence between experimental data and calculated data has been proved.  3. RESULTS AND DISCUSSION   3.1 Structural Properties  Structural properties of CdSe/SiOx and CdSe/ZnSe multilayer thin films coated under specific conditions were analyzed from X-ray diffraction spectra. The XRD profiles for the samples are shown in figure (i). A peak approximately at 23.4  and 22.7  in spectra referring to (100) plane (JCPDS-8-459) of CdSe material. This shows that CdSe/SiOx and CdSe/ZnSe films are polycrystalline in nature with wurtzite structure. The broadness of the (100) diffraction line in the spectra indicated that the size of the CdSe crystallites in the films is small [9]. We obtained the value for size of crystallites in the range of 1-2 nm as in Table 1.  QUANTUM CONFINEMENT IN CADMIUM SELENIDE… J. NANO- ELECTRON. PHYS. 4, 02021 (2012)    02021-2  Table 1 – Size of the Crystallites from XRD data  № Sample 2θ(deg) d(Å) FWHM(deg) Strain(e) Stress(S) (dyn/cm2) D (nm) 1 CdSe/SiOx 23.40 3.79856 6.680 0.0212 21.2 1.19 2 CdSe/ZnSe 22.70 3.91409 6.0666 0.0522 52.2 1.31    Fig. 1 – XRD profile for the samples CdSe/SiOx and CdSe/ZnSe  The X-ray diffraction data were also used to calcu-late the average size of the CdSe crystallites. It was done by using Debye-Scherer broadening formula.   (2 )cosD Å (1)  where D is the crystallite size,  is the wavelength of X-ray,  is the full width at half maximum (FWHM) after correcting the instrument peak broadening (  expressed in radians), and θ is the Bragg’s angle. This method provides an estimation of the CdSe crystallite size with a maximum error of about 20 % [9].  3.2 Optical Properties  CdSe/SiOx and CdSe/ZnSe films coated on glass substrates were subjected to optical absorption using Hitachi 3010 UV-VIS-NIR spectrophotometer in the range of 190 nm - 2500 nm. In bulk CdSe material, the conduction band is non degenerate and almost isotropic whereas the valance band (mostly constituted of the selenide anion P orbital) [10] is threefold orbitally de-generate. An important question at this point is what would be the effects of quantum confinement on the degener-ate valance band of CdSe material. Based on the works done by Baldereschi & Lipari [11], the transitions close to the band gap value confirm the quantum confine-ment. In Fig. 2(a) &2(b), it is observed that the two transitions close to the band gap value. Two direct band to band transitions are indeed observed in CdSe/SiOx UV spectra at 2.05 eV and 2.4 eV whereas in CdSe/ZnSe UV spectra, they were observed at 2.125 eV and 2.5 eV. This splitting of band gap confirms the quantum confinement of CdSe nano crystallites.  In Fig. 3, transmission spectra of CdSe-SiOx and CdSe-ZnSe films were shown. A shift, which is marked     Fig. 2 – Band gap graph for CdSe/SiOx (a) and CdSe/ZnSe (b)   Fig. 3 – Transmission spectra of the samples CdSe/SiOx and CdSe/ZnSe     [CdSe / ZnSe][CdSe / SiOx](100)(100)Intensity(a.u.)2 Theta1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.80.00E+0002.00E+0134.00E+0136.00E+0138.00E+0131.00E+0141.20E+014  (h)2h1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.80.00E+0001.00E+0132.00E+0133.00E+0134.00E+0135.00E+0136.00E+0137.00E+0138.00E+0139.00E+0131.00E+014  (h)2h0 250 500 750 1000 1250 1500 1750 2000 2250 2500020406080100  % TWavelength (nm) CdSe/ZnSe CdSe/SiOx M. MELVIN DAVID KUMAR, SUGANTHI DEVADASON, S. RAJESH J. NANO- ELECTRON. PHYS. 4, 02021 (2012)   02021-3 by arrow mark, towards lower wavelength region is observed in both spectra. Shift in the transmission spectra indicates the degeneracy of valance band of CdSe material.  3.2.1 The effective mass approximation – Brus Model  If the size of a CdSe crystals becomes smaller than the exciton radius, i.e, 5.6 nm for CdSe bulk material, the band gap energy increases due to quantum con-finement [12]. Hence it has been generally proven that the quantum confinement effect should be observable if the radius of nano crystallites becomes less than the Bohr excitonic radius for corresponding material. Using the relation,   2 222shEd (2)  where d is the average size of nanocrystals,  = 0.38 me[13] is reduced electron – hole mass, the value of d = 5.2 nm and 4.6 nm have been obtained for the samples CdSe/SiOx and CdSe/ZnSe respectively and tabulated in Table 2.  Table 2 – Size of the crystallites from UV-Vis data by Brus model  S.No Sample Band gap(Eg) Shift in Band gap (Eshift) D (nm) 1 CdSe/SiOx 2.05 0.294 5.19 2 CdSe/ZnSe 2.125 0.369 4.64  3.2.2 Quantum Mechanical Model  Based on the work of Yu, W., Qu L., Guo W., [14], the condition for strong quantum confinement is Qdot << Qb where Qdot is radius of quantum dot and Qb is exciton Bohr radius (CdSe  5.6 nm).By using the given relation [14],   Eob = Eg + 2(Qb/Qdot)2 Ry* –    – 1.786 (Qb/Qdot) Ry* – 0.248 Ry (3)  where Eob = Energy calculated from UV/VIS spectrum, Eg = bang gap (CdSe = 1.756 eV) for bulk material Qb = exciton Bohr radius (CdSe = 5.6 nm), Qdot = radius of crystallite, Ry* = Rydberg constant (CdSe = 0.016 eV), the size of the crystallites were calculated and well coincidence between the crystallite size calculated from Brus model and Quantum mechanical model has been shown in Table 3.  Table 3 Size of the crystallites from UV-Vis data by Quantum mechanical model  S.No Sample Band gap(Eg) Shift  in Band gap(Eshift) R (nm) 1 CdSe/SiOx 2.05 0.294 3.25 2 CdSe/ZnSe 2.125 0.369 2.9  4. CONCLUSION  A new method of producing CdSe quantum dots in SiOx thinfilm matrix and in lattice matched hetero-structure layer ZnSe has been proposed in this study. Well expressed quantum confined effects in the optical properties of CdSe have been observed. This method gives the possibility of preparing nanocrystals of vari-ous semiconductors with a relatively narrow size dis-tribution in relatively short times than conventional method. It is very useful especially in case of semicon-ductors such as Se which form nanocrystals of very different sizes in a standard crystallization procedure. Further studies carried out in order to produce II-VI semiconductor nanocrystals with suitable sublayers.  ACKNOWLEDGEMENT  The Authors sincerely thank the management of Karunya University for providing all research facilities and encouragement.  REFERENCES  1. T. Toyoda, D. Arae, Q. Shen, Physica B 316-317, 476 (2002). 2. A.P. Alivisatos, MRS Bulletin 23, 18 (1998). 3. M. Gratzel, H.S. Nalwa (Ed.), Handbook of Nanostruc-tured Materials and Nanotechnology, vol. 3, (San Diego: Academic Press: 2000). 4. A. Sombra, Solid State Commun. 88, 305 (1993). 5. A. Ekimov, A. Onushenko, T. Tzehomskii, Sov. Phys. Chem. Glass 6, 511 (1980). 6. A.I. Ekimov, F. Hache, M.C. Schanne-Klein, D. Ricard, C. Flytzanis, I.A. Kudryavtsev, T.V. Yazeva, A.V. Rodina, A.L. Efros, J. Opt. Soc. Am. B 10, 100 (1993). 7. U.E. Laheld, G.T. Einevoll, Phys. Rev. B 55, 5184 (1997). 8. G. Manolis, D. Papadimitriou, D. Nesheva, Thin Solid Films 495, 338 (2006). 9. H. Arizpe-Chavez, J. Phys. Chem. Solids 61, 511 (2000). 10. B. Pejova, I. Grozdanov, Materials Chemistry and Physics 90, 35 (2005). 11. A. Baldereschi, N.G. Lipari, Phys. Rev. B 3, 439 (1971). 12. W. Hipp, H. Karl, I. Grobhans, B. Stritzker, Mat. Sci. Engg. B 101, 318 (2003). 13. D. Nesheva,Z. Levi, Semicond. Sci. Tech. 12, 1319 (1997). 14. W.W. Yu, L. Qu, W. Guo, X. Peng, Chem. Mater. 15(14), 2854 (2003). 15. P. Reimann, Phys. Rep. 361, 57 (2002).  

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Quantum Confinement in Cadmium Selenide Multilayer Thin Films Using Physical Vapour Deposition Method

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