Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell
A photovoltaic cell, based on copper and indium selenide (CuInSe₂) thin layers, with a good efficiency can be achieved by simple, easy to implement and low cost techniques. The high refractive index materials used as absorbers in photovoltaic cells cause high reflection losses (about 30%). Thin C...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2013
|
| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Цитувати: | Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell / Abdelhakim Mahdjoub, Lazhar Hadjeris // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 4. — С. 379-381. — Бібліогр.: 8 назв. — англ. |
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irk-123456789-1178132017-05-27T03:04:44Z Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell Abdelhakim Mahdjoub Lazhar Hadjeris A photovoltaic cell, based on copper and indium selenide (CuInSe₂) thin layers, with a good efficiency can be achieved by simple, easy to implement and low cost techniques. The high refractive index materials used as absorbers in photovoltaic cells cause high reflection losses (about 30%). Thin CdS and ZnO films that are, respectively, the buffer layer and the window of the cell have lower indices and are naturally suited to antireflective applications. Also, a suitable choice of the film thickness leads to minimization of reflection losses, resulting in a significant improvement of the photovoltaic efficiency. The aim of this work is to provide easy solutions that reduce reflection losses to less than 4% while respecting technological constraints. 2013 Article Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell / Abdelhakim Mahdjoub, Lazhar Hadjeris // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 4. — С. 379-381. — Бібліогр.: 8 назв. — англ. 1560-8034 PACS 84.60.Jt, 86.40.jn http://dspace.nbuv.gov.ua/handle/123456789/117813 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
| description |
A photovoltaic cell, based on copper and indium selenide (CuInSe₂) thin
layers, with a good efficiency can be achieved by simple, easy to implement and low cost
techniques. The high refractive index materials used as absorbers in photovoltaic cells
cause high reflection losses (about 30%). Thin CdS and ZnO films that are, respectively,
the buffer layer and the window of the cell have lower indices and are naturally suited to
antireflective applications. Also, a suitable choice of the film thickness leads to
minimization of reflection losses, resulting in a significant improvement of the
photovoltaic efficiency. The aim of this work is to provide easy solutions that reduce
reflection losses to less than 4% while respecting technological constraints. |
| format |
Article |
| author |
Abdelhakim Mahdjoub Lazhar Hadjeris |
| spellingShingle |
Abdelhakim Mahdjoub Lazhar Hadjeris Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Abdelhakim Mahdjoub Lazhar Hadjeris |
| author_sort |
Abdelhakim Mahdjoub |
| title |
Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell |
| title_short |
Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell |
| title_full |
Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell |
| title_fullStr |
Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell |
| title_full_unstemmed |
Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell |
| title_sort |
reflection loss minimization for a zno/cds/cuinse₂ photovoltaic cell |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2013 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/117813 |
| citation_txt |
Reflection loss minimization for a ZnO/CdS/CuInSe₂ photovoltaic cell / Abdelhakim Mahdjoub, Lazhar Hadjeris // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 4. — С. 379-381. — Бібліогр.: 8 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT abdelhakimmahdjoub reflectionlossminimizationforaznocdscuinse2photovoltaiccell AT lazharhadjeris reflectionlossminimizationforaznocdscuinse2photovoltaiccell |
| first_indexed |
2025-07-08T12:50:39Z |
| last_indexed |
2025-07-08T12:50:39Z |
| _version_ |
1837083175988232192 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 4. P. 379-381.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
379
PACS 84.60.Jt, 86.40.jn
Reflection loss minimization for a ZnO/CdS/CuInSe2
photovoltaic cell
Abdelhakim Mahdjoub and Lazhar Hadjeris
Laboratoire des Matériaux et Structure des Systèmes Electromécaniques et leur Fiabilité (LMSSEF) Université Larbi
Ben M’hidi d’Oum El Bouaghi, Algérie
E-mail: abdelmah@yahoo.com
Abstract. A photovoltaic cell, based on copper and indium selenide (CuInSe2) thin
layers, with a good efficiency can be achieved by simple, easy to implement and low cost
techniques. The high refractive index materials used as absorbers in photovoltaic cells
cause high reflection losses (about 30%). Thin CdS and ZnO films that are, respectively,
the buffer layer and the window of the cell have lower indices and are naturally suited to
antireflective applications. Also, a suitable choice of the film thickness leads to
minimization of reflection losses, resulting in a significant improvement of the
photovoltaic efficiency. The aim of this work is to provide easy solutions that reduce
reflection losses to less than 4% while respecting technological constraints.
Keywords: reflectivity, optical index, thickness, photovoltaic efficiency.
Manuscript received 03.07.13; revised version received 05.09.13; accepted for
publication 23.10.13; published online 16.12.13.
1. Introduction
The photovoltaic efficiency of thin film solar cells,
based on CuInSe2 vacuum deposited in laboratories,
reached 17.5%, while Cu(In,Ga)As hold 19.9% record
performance on Mo sheet [1-3] and 14.1% on plastic
sheet. The industry offers flexible cells on Mo with
efficiencies of 6 to 11% [2]. Deposition techniques with
low cost, used in our laboratory (chemical bath,
electrodeposition and ultrasonic spray pyrolysis), are
expected to return conversion efficiencies around 10%.
These can be significantly improved, if the reflection
losses are reduced. Indeed, thin films (CdS and ZnO)
that constitute, respectively, the buffer layer and the
window of the cell have indices lower than those of
CuInSe2. They are thus naturally adapted to
antireflection applications. It is there important to
determine the optimal thickness that minimizes
reflection losses, while remaining objective regarding
technological limitations. Conventional material for
antireflection coatings for this kind of solar cells is MgF2
chosen for its low refractive index [4]. In this work, we
propose to apply an antireflection coating made of
porous silica chemically stable, mechanically resistant,
good dielectric and with low refractive index above the
metal grid to avoid heaviness of the technological
process.
2. Quality criterion
To evaluate the performance of the proposed
antireflection solutions, we chose like quality criterion
the effective reflectivity Reff weighted by Φ(λ) in the
standard AM1.5 solar spectrum [5]. The lower the
effective reflectivity is, the less one has losses by
reflection in the solar cell.
.
2
1
2
1
d
dR
Reff (1)
Calculation covers the spectral range located
between 300 and 1100 nm, representing practically the
whole solar spectrum.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 4. P. 379-381.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
380
For the studied solar cell represented in Fig. 1 and
which is a thin-film structure, the spectral reflectance
R(λ) is calculated by applying the theory of stratified
media in its simple matrix form [6]. In our case we
consider normal incidence and calculation will be held
using Eq. (2):
.
cossin~
sin~cos
1
1
1
1
2
1
1
1
0
0
ss
s
N
j jjj
jjj
r
i
En
E
n
n
n
n
E
E
(2)
Ei, Er and Es are, respectively, the incident, reflected and
transmitted electric fields associated to the solar
radiation. ñj(λ) and dj represent, respectively, the
complex indices and the thicknesses of each layer. δj is
the phase shift of the electromagnetic wave due to the jth
strate and it is given by relation (3):
jjj dn~
2
. (3)
Then, the reflectance R for each wavelength λ is
calculated using Eq. (4):
i
r
i
r
E
E
E
E
R . (4)
Introducing experimental values of optical indices
determined by ellipsometric measurements on the used
materials [7], it will be a question, thereafter, of finding
suitable optical parameters for our stratified structure
leading to the lowest possible effective reflectivity.
3. CuInSe2 reflectance
The CuInSe2 (or CIS) absorber of the thin films cell
requires a thickness about a few microns [1]. From the
optical viewpoint, this thickness completely covers glass
and its molybdenum metallization. The spectral
reflectivity obtained on a CIS/Mo/glass structure is the
same one as that obtained on a simple substrate of
CuInSe2 (Fig. 2). The losses by reflections are estimated
in the considered wavelength range at 26.5%.
4. Reflectance of ZnO/CdS/CuInSe2 structure
By depositing the buffer layer (50 nm of CdS) on
CuInSe2 absorber, on the one hand, the heterojunction of
the solar cell is carried out and, on the other hand, the
reflection losses are reduced to 13% (Fig. 3). This
antireflection effect is observed because the refractive
index of CdS is lower than that of CuInSe2. In addition,
a thin CdS film allows to collect photo-generated
carriers and provide a good conversion efficiency.
By adding a layer of 300-nm ZnO transparent and
conductive (TCO), which plays the dual role of window
and conductive grid, reflection losses become 11.5%
(Fig. 4). This is because the refractive index of ZnO is
lower than that of CdS. It remains that these losses are
significant, and they can still be reduced.
Fig. 1. Thin-film structure solar cell.
Fig. 2. Reflectance of CuInSe2/Mo/glass.
Fig. 3. Reflectance of CdS/CuInSe2/Mo/glass.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 4. P. 379-381.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
381
5. Proposed solution
In order to reduce the reflection losses, without weighing
down the technological process, we propose to add a thin
layer of porous silica with low refraction index on the
surface of the photovoltaic cell, after deposition of the
metal grids. Searching for optimal thicknesses (objective
technologically) suggests us the following solution:
100nmSiO2/260nmZnO/50nmCdS/CuInSe2.
This structure would make it possible to reduce the
losses by reflection to less than 4%.
Fig. 4. Reflectance of ZnO/CdS/CuInSe2/Mo/glass.
Fig. 5. Optimized reflectance of SiO2/ZnO/CdS/CuInSe2/
Mo/glass.
By introducing these results into a simulator of
solar cell, minimization of the losses by reflection
improves the photocurrent (or Isc, the short circuit
current) by more than 30%. The energetic conversion
efficiency η is then increased by more than 15% (see
calculated values of Isc and η indicated in Figs 4 and 5.
With a similar solar cell but using MgF2 as antireflection
coating, J. Abushama et al. found a yield of 15% [8].
6. Conclusion
Control of thin film deposition and optimization of the
choice of materials and thicknesses make it possible to
reduce reflection losses of photovoltaic cells. In the case
of CuInSe2 thin films based cells, these losses can be
reduced to less than 4% resulting in more than 15%
improved photovoltaic efficiency. Thus, the addition of a
porous silica layer, dielectric with low refractive index,
allows besides a clear reduction in the losses by
reflection, to ensure protection with respect to the
ambient conditions without for that weighing down the
technological process.
References
1. T.M. Razykov, C.S. Ferekides, D. Morel, E.
Stefanakos, H.S. Ullal, H.M. Upadhyaya, Solar
energy, Solar photovoltaic electricity: Current
status and future prospects // Solar Energy, 85(8),
p. 1580-1608 (2011).
2. I. Repins, M.A. Contreras, B. Egaas, C. DeHart, J.
Scharf, C.L. Perkins, B. To, R. Noufi, 19.9%-
efficient ZnO/CdS/CuInGaSe2 solar cell with
81.2% fill factor // Progr. Photovolt.: Res. Appl.
16(3), p. 235-239 (2008).
3. J.A.M. AbuShama, S. Johnston, T. Moriarty, G.
Teeter, K. Ramanathan, and R. Noufi, Properties of
ZnO/CdS/CuInSe2 solar cells with improved
performance // Progr. Photovolt.: Res. Appl.
12(39), p. 39-45 (2004).
4. N. Dahan, Z. Jehl, T. Hildebrandt, J.-J. Greffet, F.
Guillemoles, Optical approaches to improve the
photocurrent generation in Cu(In,Ga)Se2 solar cells
with absorber thicknesses down to 0.5μm // J. Appl.
Phys. 112 (2012).
5. L. Remache, L. Fourmond, E. Mahdjoub, A.
Dupuis, J. Lemiti, Design of porous
silicon/PECVD SiOx antireflection coatings for
silicon solar cells // Materials Science &
Engineering B, 176(1), January 15, p. 45-48
(2011).
6. M. Born, and E. Wolf, Principles of Optics:
Electromagnetic Theory of Propagation,
Interference and Diffraction of Light. Oxford,
Pergamon Press, 1964.
7. A. Mahdjoub, L. Hadjeris, L. Herissi, M.
Benbouzid, N. Attaf, M.S. Aida, T.
Easwarakhanthan, B. Assouar and J. Bougdira,
Ellipsometric investigation on optical properties of
ZnO thin films prepared by spray pyrolysis //
Intern. Conf. on Optics (ICO’08), Setif, Algeria,
November 8-10 (2008).
8. J. AbuShama, R. Noufi, S. Johnston, S. Ward, and
X. Wu // 31th IEEE Photovoltaics Specialists
Conference and Exhibition, Lake Buena Vista,
Florida, January 3-7 (2005).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 4. P. 379-381.
PACS 84.60.Jt, 86.40.jn
Reflection loss minimization for a ZnO/CdS/CuInSe2
photovoltaic cell
Abdelhakim Mahdjoub and Lazhar Hadjeris
Laboratoire des Matériaux et Structure des Systèmes Electromécaniques et leur Fiabilité (LMSSEF) Université Larbi Ben M’hidi d’Oum El Bouaghi, Algérie
E-mail: abdelmah@yahoo.com
Abstract. A photovoltaic cell, based on copper and indium selenide (CuInSe2) thin layers, with a good efficiency can be achieved by simple, easy to implement and low cost techniques. The high refractive index materials used as absorbers in photovoltaic cells cause high reflection losses (about 30%). Thin CdS and ZnO films that are, respectively, the buffer layer and the window of the cell have lower indices and are naturally suited to antireflective applications. Also, a suitable choice of the film thickness leads to minimization of reflection losses, resulting in a significant improvement of the photovoltaic efficiency. The aim of this work is to provide easy solutions that reduce reflection losses to less than 4% while respecting technological constraints.
Keywords: reflectivity, optical index, thickness, photovoltaic efficiency.
Manuscript received 03.07.13; revised version received 05.09.13; accepted for publication 23.10.13; published online 16.12.13.
1. Introduction
The photovoltaic efficiency of thin film solar cells, based on CuInSe2 vacuum deposited in laboratories, reached 17.5%, while Cu(In,Ga)As hold 19.9% record performance on Mo sheet [1-3] and 14.1% on plastic sheet. The industry offers flexible cells on Mo with efficiencies of 6 to 11% [2]. Deposition techniques with low cost, used in our laboratory (chemical bath, electrodeposition and ultrasonic spray pyrolysis), are expected to return conversion efficiencies around 10%. These can be significantly improved, if the reflection losses are reduced. Indeed, thin films (CdS and ZnO) that constitute, respectively, the buffer layer and the window of the cell have indices lower than those of CuInSe2. They are thus naturally adapted to antireflection applications. It is there important to determine the optimal thickness that minimizes reflection losses, while remaining objective regarding technological limitations. Conventional material for antireflection coatings for this kind of solar cells is MgF2 chosen for its low refractive index [4]. In this work, we propose to apply an antireflection coating made of porous silica chemically stable, mechanically resistant, good dielectric and with low refractive index above the metal grid to avoid heaviness of the technological process.
2. Quality criterion
To evaluate the performance of the proposed antireflection solutions, we chose like quality criterion the effective reflectivity Reff weighted by Φ(λ) in the standard AM1.5 solar spectrum [5]. The lower the effective reflectivity is, the less one has losses by reflection in the solar cell.
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l
l
l
l
l
F
l
l
F
l
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d
d
R
R
eff
(1)
Calculation covers the spectral range located between 300 and 1100 nm, representing practically the whole solar spectrum.
For the studied solar cell represented in Fig. 1 and which is a thin-film structure, the spectral reflectance R(λ) is calculated by applying the theory of stratified media in its simple matrix form [6]. In our case we consider normal incidence and calculation will be held using Eq. (2):
.
cos
sin
~
sin
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cos
1
1
1
1
2
1
1
1
0
0
ú
û
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j
j
j
j
j
j
j
r
i
E
n
E
n
n
n
n
E
E
(2)
Ei, Er and Es are, respectively, the incident, reflected and transmitted electric fields associated to the solar radiation. ñj(λ) and dj represent, respectively, the complex indices and the thicknesses of each layer. δj is the phase shift of the electromagnetic wave due to the jth strate and it is given by relation (3):
j
j
j
d
n
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2
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p
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(3)
Then, the reflectance R for each wavelength λ is calculated using Eq. (4):
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E
E
E
R
.
(4)
Introducing experimental values of optical indices determined by ellipsometric measurements on the used materials [7], it will be a question, thereafter, of finding suitable optical parameters for our stratified structure leading to the lowest possible effective reflectivity.
3. CuInSe2 reflectance
The CuInSe2 (or CIS) absorber of the thin films cell requires a thickness about a few microns [1]. From the optical viewpoint, this thickness completely covers glass and its molybdenum metallization. The spectral reflectivity obtained on a CIS/Mo/glass structure is the same one as that obtained on a simple substrate of CuInSe2 (Fig. 2). The losses by reflections are estimated in the considered wavelength range at 26.5%.
4. Reflectance of ZnO/CdS/CuInSe2 structure
By depositing the buffer layer (50 nm of CdS) on CuInSe2 absorber, on the one hand, the heterojunction of the solar cell is carried out and, on the other hand, the reflection losses are reduced to 13% (Fig. 3). This antireflection effect is observed because the refractive index of CdS is lower than that of CuInSe2. In addition, a thin CdS film allows to collect photo-generated carriers and provide a good conversion efficiency.
By adding a layer of 300-nm ZnO transparent and conductive (TCO), which plays the dual role of window and conductive grid, reflection losses become 11.5% (Fig. 4). This is because the refractive index of ZnO is lower than that of CdS. It remains that these losses are significant, and they can still be reduced.
Fig. 1. Thin-film structure solar cell.
Fig. 2. Reflectance of CuInSe2/Mo/glass.
Fig. 3. Reflectance of CdS/CuInSe2/Mo/glass.
5. Proposed solution
In order to reduce the reflection losses, without weighing down the technological process, we propose to add a thin layer of porous silica with low refraction index on the surface of the photovoltaic cell, after deposition of the metal grids. Searching for optimal thicknesses (objective technologically) suggests us the following solution:
100nmSiO2/260nmZnO/50nmCdS/CuInSe2.
This structure would make it possible to reduce the losses by reflection to less than 4%.
Fig. 4. Reflectance of ZnO/CdS/CuInSe2/Mo/glass.
Fig. 5. Optimized reflectance of SiO2/ZnO/CdS/CuInSe2/
Mo/glass.
By introducing these results into a simulator of solar cell, minimization of the losses by reflection improves the photocurrent (or Isc, the short circuit current) by more than 30%. The energetic conversion efficiency η is then increased by more than 15% (see calculated values of Isc and η indicated in Figs 4 and 5. With a similar solar cell but using MgF2 as antireflection coating, J. Abushama et al. found a yield of 15% [8].
6. Conclusion
Control of thin film deposition and optimization of the choice of materials and thicknesses make it possible to reduce reflection losses of photovoltaic cells. In the case of CuInSe2 thin films based cells, these losses can be reduced to less than 4% resulting in more than 15% improved photovoltaic efficiency. Thus, the addition of a porous silica layer, dielectric with low refractive index, allows besides a clear reduction in the losses by reflection, to ensure protection with respect to the ambient conditions without for that weighing down the technological process.
References
1.
T.M. Razykov, C.S. Ferekides, D. Morel, E. Stefanakos, H.S. Ullal, H.M. Upadhyaya, Solar energy, Solar photovoltaic electricity: Current status and future prospects // Solar Energy, 85(8), p. 1580-1608 (2011).
2.
I. Repins, M.A. Contreras, B. Egaas, C. DeHart, J. Scharf, C.L. Perkins, B. To, R. Noufi, 19.9%-efficient ZnO/CdS/CuInGaSe2 solar cell with 81.2% fill factor // Progr. Photovolt.: Res. Appl. 16(3), p. 235-239 (2008).
3.
J.A.M. AbuShama, S. Johnston, T. Moriarty, G. Teeter, K. Ramanathan, and R. Noufi, Properties of ZnO/CdS/CuInSe2 solar cells with improved performance // Progr. Photovolt.: Res. Appl. 12(39), p. 39-45 (2004).
4.
N. Dahan, Z. Jehl, T. Hildebrandt, J.-J. Greffet, F. Guillemoles, Optical approaches to improve the photocurrent generation in Cu(In,Ga)Se2 solar cells with absorber thicknesses down to 0.5μm // J. Appl. Phys. 112 (2012).
5.
L. Remache, L. Fourmond, E. Mahdjoub, A. Dupuis, J. Lemiti, Design of porous silicon/PECVD SiOx antireflection coatings for silicon solar cells // Materials Science & Engineering B, 176(1), January 15, p. 45-48 (2011).
6.
M. Born, and E. Wolf, Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light. Oxford, Pergamon Press, 1964.
7.
A. Mahdjoub, L. Hadjeris, L. Herissi, M. Benbouzid, N. Attaf, M.S. Aida, T. Easwarakhanthan, B. Assouar and J. Bougdira, Ellipsometric investigation on optical properties of ZnO thin films prepared by spray pyrolysis // Intern. Conf. on Optics (ICO’08), Setif, Algeria, November 8-10 (2008).
8.
J. AbuShama, R. Noufi, S. Johnston, S. Ward, and X. Wu // 31th IEEE Photovoltaics Specialists Conference and Exhibition, Lake Buena Vista, Florida, January 3-7 (2005).
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
379
_1453035339.unknown
_1456039184.unknown
_1452957629.unknown
_1452957765.unknown
|