Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix
Investigated in this paper have been polarization properties of photoluminescence in solid and porous nc-Si−SiOx light emitting structures passivated in HF vapor. These structures were produced by thermal vacuum evaporation of silicon monoxide SiO powder onto polished c-Si substrates. After annealin...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2015
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| Цитувати: | Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix / K.V. Michailovska, I.Z. Indutnyi, O.O. Kudryavtsev, M.V. Sopinskyy, P.E. Shepeliavyi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 3. — С. 324-329. — Бібліогр.: 17 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1212252025-02-10T01:15:04Z Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix Michailovska, K.V. Indutnyi, I.Z. Kudryavtsev, O.O. Sopinskyy, M.V. Shepeliavyi, P.E. Investigated in this paper have been polarization properties of photoluminescence in solid and porous nc-Si−SiOx light emitting structures passivated in HF vapor. These structures were produced by thermal vacuum evaporation of silicon monoxide SiO powder onto polished c-Si substrates. After annealing in vacuum for 15 min at the temperature 975 °C, SiOx films were decomposed to SiO₂ with Si nanoclusters embedded in the oxide matrix. Comparison of polarizations, inherent to exciting light and that of film photoluminescence, enabled to find the polarization memory effect in the passivated structures. In anisotropic porous nc-Si−SiOx samples, obtained by oblique deposition in vacuum, there is also well-defined orientation dependence of the PL polarization degree in the sample plane. This dependence is related to the orientation of oxide nanocolumns that form the structure of the porous layer. The above effects are associated with transformation during etching in HF the symmetric Si nanoparticles to asymmetric elongated ones. 2015 Article Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix / K.V. Michailovska, I.Z. Indutnyi, O.O. Kudryavtsev, M.V. Sopinskyy, P.E. Shepeliavyi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 3. — С. 324-329. — Бібліогр.: 17 назв. — англ. 1560-8034 DOI: 10.15407/spqeo18.03.324 PACS 78.67.Bf, 78.55.-m, 42.25.Ja https://nasplib.isofts.kiev.ua/handle/123456789/121225 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Investigated in this paper have been polarization properties of photoluminescence in solid and porous nc-Si−SiOx light emitting structures passivated in HF vapor. These structures were produced by thermal vacuum evaporation of silicon monoxide SiO powder onto polished c-Si substrates. After annealing in vacuum for 15 min at the temperature 975 °C, SiOx films were decomposed to SiO₂ with Si nanoclusters embedded in the oxide matrix. Comparison of polarizations, inherent to exciting light and that of film photoluminescence, enabled to find the polarization memory effect in the passivated structures. In anisotropic porous nc-Si−SiOx samples, obtained by oblique deposition in vacuum, there is also well-defined orientation dependence of the PL polarization degree in the sample plane. This dependence is related to the orientation of oxide nanocolumns that form the structure of the porous layer. The above effects are associated with transformation during etching in HF the symmetric Si nanoparticles to asymmetric elongated ones. |
| format |
Article |
| author |
Michailovska, K.V. Indutnyi, I.Z. Kudryavtsev, O.O. Sopinskyy, M.V. Shepeliavyi, P.E. |
| spellingShingle |
Michailovska, K.V. Indutnyi, I.Z. Kudryavtsev, O.O. Sopinskyy, M.V. Shepeliavyi, P.E. Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Michailovska, K.V. Indutnyi, I.Z. Kudryavtsev, O.O. Sopinskyy, M.V. Shepeliavyi, P.E. |
| author_sort |
Michailovska, K.V. |
| title |
Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix |
| title_short |
Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix |
| title_full |
Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix |
| title_fullStr |
Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix |
| title_full_unstemmed |
Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix |
| title_sort |
polarization memory of photoluminescence related with si nanoparticles embedded into oxide matrix |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2015 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/121225 |
| citation_txt |
Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix / K.V. Michailovska, I.Z. Indutnyi, O.O. Kudryavtsev, M.V. Sopinskyy, P.E. Shepeliavyi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 3. — С. 324-329. — Бібліогр.: 17 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT michailovskakv polarizationmemoryofphotoluminescencerelatedwithsinanoparticlesembeddedintooxidematrix AT indutnyiiz polarizationmemoryofphotoluminescencerelatedwithsinanoparticlesembeddedintooxidematrix AT kudryavtsevoo polarizationmemoryofphotoluminescencerelatedwithsinanoparticlesembeddedintooxidematrix AT sopinskyymv polarizationmemoryofphotoluminescencerelatedwithsinanoparticlesembeddedintooxidematrix AT shepeliavyipe polarizationmemoryofphotoluminescencerelatedwithsinanoparticlesembeddedintooxidematrix |
| first_indexed |
2025-12-02T10:26:31Z |
| last_indexed |
2025-12-02T10:26:31Z |
| _version_ |
1850391859416793088 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 3. P. 324-329.
doi: 10.15407/spqeo18.03.324
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
324
PACS 78.67.Bf, 78.55.-m, 42.25.Ja
Polarization memory of photoluminescence related
with Si nanoparticles embedded into oxide matrix
K.V. Michailovska, I.Z. Indutnyi, O.O. Kudryavtsev, M.V. Sopinskyy, P.E. Shepeliavyi
V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
41, prospect Nauky, 03028 Kyiv, Ukraine
Abstract. Investigated in this paper have been polarization properties of photo-
luminescence in solid and porous nc-Si−SiOx light emitting structures passivated in HF
vapor. These structures were produced by thermal vacuum evaporation of silicon
monoxide SiO powder onto polished c-Si substrates. After annealing in vacuum for
15 min at the temperature 975 °C, SiOx films were decomposed to SiO2 with Si
nanoclusters embedded in the oxide matrix. Comparison of polarizations, inherent to
exciting light and that of film photoluminescence, enabled to find the polarization
memory effect in the passivated structures. In anisotropic porous nc-Si−SiOx samples,
obtained by oblique deposition in vacuum, there is also well-defined orientation
dependence of the PL polarization degree in the sample plane. This dependence is related
to the orientation of oxide nanocolumns that form the structure of the porous layer. The
above effects are associated with transformation during etching in HF the symmetric Si
nanoparticles to asymmetric elongated ones.
Keywords: Si nanoparticle, oxide matrix, photoluminescence, polarized luminescence,
polarization memory.
Manuscript received 26.03.15; revised version received 29.07.15; accepted for
publication 03.09.15; published online 30.09.15.
1. Introduction
Porous silicon and thin-film nc-Si−SiOx structures
containing Si nanoclusters (nc-Si) embedded into the
SiOx matrix attract attention of many researchers,
because of their promising applications in advanced
electronic and optoelectronic devices. Both materials
show an intense and wide photoluminescence (PL)
emission peaking in the near-infrared or visible
spectrum. However, they essentially differ in
polarization of their PL. In porous silicon, the
polarization memory effect (PM), that is the correlation
between polarization of excited light and polarization
property of photoluminescence (PL), was found, and its
features and mechanism were studied [1-5]. However, in
thin-film nc-Si−SiOx structures, in which silicon
nanoparticles (nc-Si) are embedded into SiOx matrix, the
PM effect was not observed. This result was obtained for
nc-Si−SiOx structures formed by high-temperature
annealing of non-stoichiometric silicon oxide SiOx in
inert atmosphere or vacuum. Because of the isotropy of
amorphous oxide, silicon nanoparticles formed during
annealing are also isotropic, so the effect of PM in these
structures does not manifest itself.
In the previous works, it was shown [6, 7] that the
treatment of these structures in solution or vapors of
hydrofluoric acid can significantly increase the PL
intensity and shift the PL peak position to short-wave
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 3. P. 324-329.
doi: 10.15407/spqeo18.03.324
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
325
region due to partial etching of nc-Si and passivation of
their surface. It can be assumed that this etching can
change the shape of symmetric nanoparticles, similarly
to that in porous silicon, and leads to the PM effect.
Especially effective etching and passivation takes place
in developed by us porous nc-Si−SiOx structures that are
formed by oblique deposition of Si monoxide (SiO) in
vacuum and the following high-temperature annealing of
obtained SiOx layer [8, 9]. These layers have a porous
columnar structure with oxide nanocolumns inclined at a
certain angle to the sample surface. During high-
temperature annealing of these films, the thermally
stimulated formation of Si nanoinclusions occurs in a
restricted volume of the SiOx columns. Because of free
space (cavities) between the oxide columns, the
structures is more susceptible to chemical treatments,
e.g., to etching in HF solution or vapor [10, 11]. These
light-emitting structures demonstrate asymmetry in
optical properties even before etching [12], so it seems
desirable to investigate the polarization properties of
their PL.
In this paper, the polarization properties of solid
and porous passivated in HF vapour nc-Si−SiOx light
emitting structures were investigated.
2. Experiment
The investigated nc-Si−SiOx light-emitting structures
were produced by thermal evaporation of 99.9% pure
silicon monoxide SiO (Cerac Inc.) powder in vacuum
((1…2)×10–3 Pa) onto polished c-Si substrates. The
substrates were arranged at the angles (α) of 0° and 60°
relatively to the normal to the substrate surface with the
direction to the evaporator (normal and oblique
deposition). The evaporation rate was monitored in situ
by the quartz-crystal-oscillator monitor system (КИТ-1).
The deposited film thickness was measured using
МИИ-4 micro-interferometer and amounted 400 to
950 nm. Because of additional oxidation by residual
gases in the vacuum chamber during evaporation of SiO,
the obtained SiOx films were compositionally
nonstoichiometric (x > 1). The films were annealed in
vacuum for 15 min at the temperature close to 975 °C.
This high-temperature annealing induces decomposition
of SiOx into Si and SiO2 and formation of Si nanoclusters
embedded in the oxide matrix. Passivation of the nc-
Si−SiOx structures obtained in this manner was carried
in the closed cell with HF vapor flow at the temperature
30 °С in the presence of etching-assisting ultraviolet
light.
The PL spectra were excited using linearly
polarized emission of a semiconductor laser (with the
wavelength 415 nm) at nearly normal incidence to the
surface of the samples, and emitted light was collected in
the direction normal to the surface. Polarization of the
exciting light was rotated by a λ/2 phase plate and
cleaned by a linear polarizer. Another sheet polarizer
(analyzer) was placed in the detection path. PL spectra
were measured at room temperature within the
wavelength range 500 to 850 nm. These spectra were
normalized to the spectral sensitivity of the experimental
system and were corrected with respect to the
polarization dependent response of the measurement
system.
3. Results and discussion
The structure of obliquely deposited SiOx films was
studied by SEM apparatus (ZEISS EVO 50XVP,
Oberkochen, Germany) in the previous papers [6, 11].
These films have a porous inclined pillar-like structure
with the pillar (column) diameters of 10 to 100 nm.
Porosity of the films depends on the angle of deposition
and equals to 34% for α = 60° [8], while the inclination
of the formed oxide nanocolumns relatively to the
normal to the sample surface was 26…29° [12]. High-
temperature annealing of these films does not change
porosity and pillar-like structure of the samples. Porosity
of the normally deposited SiOx films was less than 10%,
these films were isotropic, and after annealing they were
practically nonporous [13].
Fig. 1 shows the PL spectra of nc-Si−SiOx sample
deposited in vacuum at the angle 0°, annealed at 975 °C
in vacuum, and then etched in HF vapor (curves 1 and
2). The curve 1 corresponds to the orientation of the
analyzer, which selects polarization of PL parallel to
polarization of exciting radiation, and the curve 2 −
orientation of the analyzer that is perpendicular to
polarization of excitation. As seen from the figure, the
intensity of PL polarized in parallel to polarization of
excitation (curve 1) is much higher than the PL
component polarized in the perpendicular direction
(curve 2), i.e., in the investigated sample the PM effect is
really observed.
600 640 680 720 760
0
2
4
6
8
10
0.0
0.2
0.4
0.6
0.8
1.0
PL
in
te
ns
ity
, a
rb
. u
ni
ts
λ, nm
eex II edet
eex ⊥ edet 1
2
3
λex = 415 nm
P
ol
ar
iz
at
io
n
de
gr
ee
, ρ
Fig. 1. PL spectra of solid nc-Si−SiOx sample annealed in
vacuum, then treated with HF vapors (1, 2). The curve 1
corresponds to parallel orientation of the analyzer to
polarization of the exciting radiation, and the curve 2 −
orientation of the analyzer in the perpendicular direction. The
curve 3 − value of degree of the linear polarization of PL for
this sample.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 3. P. 324-329.
doi: 10.15407/spqeo18.03.324
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
326
The effect of PM can be illustrated by the degree of
linear polarization of the PL, which is known to be
defined with the expression:
⊥
⊥
+
−
=ρ
II
II
|
| .
Here, I|| is the intensity of the photoluminescence
polarized in parallel to that of the excited light and I⊥ −
intensity of photoluminescence polarized in the
perpendicular direction. The curve 3 in Fig. 1 corresponds
to the ρ value inherent to the investigated sample. Near to
the PL maximum, ρ has the value close to 0.2 and
increases in the short-wave region of the spectrum, which
is similar to the results for porous silicon [2, 3].
Fig. 2 shows the PL intensity dependence on the
angle between polarization of the exciting radiation and
orientation of the analyzer for the same sample as in
Fig. 1, recorded near the PL peak (700 nm). The curves
1 and 2 correspond to two mutually perpendicular
orientations of the excitation polarization. For these
orientations, the ρ values are equal to 0.23 and 0.22, i.e.,
they coincide within the measurement errors, which
indicates that the PM effect is isotropic in the plane of
the sample.
As shown by previous investigations in similar solid
nc-Si−SiOx samples annealed in vacuum or inert gas, but
not processed in HF, there is much weaker PL and no PM
effect. Thus, within the measurement errors ρ = 0
throughout the investigated range of PL spectra. Similar
results were obtained for the sample of porous nc-
Si−SiOx, produced using vacuum deposition of SiO at the
angle 60° and annealed for 15 min. The spectral depen-
dence of PL obtained at orientation of the analyzer
parallel and perpendicular to the polarization of the
exciting radiation coincide, and the ρ value is zero over all
the studied spectral range. These results were obtained for
any orientation of the excitation polarization relatively to
the projection of the inclined SiOx nanocolumns. Thus, in
oblique deposited porous nc-Si−SiOx structures that
exhibit optical anisotropy due to tilting the SiOx columns
[12], the PM effect is not manifested, too.
0.6
0.7
0.8
0.9
1.0
0
30
60
90
120
150
180
210
240
270
300
330
0.6
0.7
0.8
0.9
1.0
P
L
in
te
ns
ity
, a
rb
. u
n.
(1)
(2)
λex = 415 nm
λdet = 700 nm
Fig. 2. Polar plot of the PL intensity for nc-Si−SiOx sample,
which spectra are shown in Fig. 1 for two mutually
perpendicular orientations of excitation polarization (1, 2). The
PL wavelength is 700 nm.
600 640 680 720 760
0.0
0.2
0.4
0.6
0.8
1.0
0.10
0.15
0.20
0.25
0.30
0.35
0.40
PL
in
te
ns
ity
, a
rb
. u
ni
ts
λ, nm
eex II edet
eex
1
2
3
edet
λex = 415 nm
Po
la
riz
at
io
n
de
gr
ee
, ρhν
eex
Fig. 3. PL spectra of porous nc-Si−SiOx sample annealed in
vacuum, then treated with HF vapors for parallel (1) and
perpendicular (2) orientations of the analyzer relatively to
polarization of exciting radiation, which is oriented in parallel
to the projection of SiOx nanocolumns on the sample plane. 3 −
value of the degree of PL linear polarization.
But after treatment in HF vapor, the luminescent
properties of nc-Si−SiOx structures are changed, in
particular, there is a significant shift of the PL maximum
to the visible part of spectrum and increase in the PL
intensity. These changes are explained by decrease in the
nc-Si size during etching and passivation of the surface
[9]. Besides that, the dependence of PL polarization on
excitation polarization direction appears in the porous
nc-Si−SiOx structures, just as in solid samples. Fig. 3
shows PL spectra of the porous nc-Si−SiOx sample
obtained by deposition at the angle 60° and annealed at
975 °C in vacuum for 15 min, then treated with HF
vapor. The curves 1 and 2 correspond to orientation of
the analyzer parallel and perpendicular to polarization of
the exciting radiation, which is oriented in parallel to the
projection of the inclined SiOx nanocolumns on the
sample plane. It can be seen that the intensity of PL
component polarized in parallel to polarization of the
exciting radiation is substantially higher than the
intensity of PL polarized in the perpendicular direction.
The curve 3 in this figure represents the degree of PL
linear polarization.
But unlike results shown in Fig. 1, the PM effect on
the porous nc-Si−SiOx structures has its peculiarities.
Fig. 4 shows the PL spectra of the same sample as in
Fig. 3, but for the case of excitation polarization
perpendicular to the projection of inclined SiOx
nanocolumns on the sample plane. It can be seen that the
difference between I|| and I⊥ is significantly smaller as
compared with the case where this sample during
measurement was fixed at the position when polarization
of the exciting light coincides with the direction of
nanocolumns projection.
More clearly, PM anisotropy in the sample plane
is manifested in dependences of the PL intensity on
the angle between polarization of the exciting radiation
and orientation of the analyzer. Fig. 5 shows such
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 3. P. 324-329.
doi: 10.15407/spqeo18.03.324
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
327
dependences for two orientations of the excitation
polarization relatively to the projection of SiOx
nanocolumns. For parallel orientation of the excitation
polarization and nanocolumns projection, the PM effect
is pronounced much efficiently than for perpendicular
orientation, and ρ values at the PL maximum are equal
to 0.19 and 0.09, respectively.
This result is similar to that observed in porous
silicon formed by electrochemical etching of Si with
orientation [100] in the presence of linearly polarized
light illumination [2], which indicated the existence of
PM anisotropy in the plane of the sample.
It was proposed several mechanisms that determine
the PM effect. In [14], PL polarization anisotropy of
elongated particles associated with the structure of the
valence band due to quantum confinement in two
directions − parallel and perpendicular to the longer axis
of the particle. More common explanation − within the
dielectric model in which porous silicon is considered as a
composite that includes elongated and flattened silicon
nanocrystals preferentially oriented as elongated nc-Si
along the [100] direction [1-3]. The probability of optical
absorptions and emission is proportional to the square of
the electric field inside the nc-Si and, therefore,
nanocrystals with their longest dimensions aligned along
the polarization direction of exciting light will
preferentially absorb and emit photons. Then PM is the
result of selective excitation that part of the nonspherical
silicon nanoparticles whose longer axis is parallel to
polarization of exciting radiation [1, 4, 15]. Both
interpretations as on the basis of quantum size effects and
within the dielectric model associate the PM effect with
asymmetric, elongated nanoparticles that emit PL.
Another necessary condition to observe this effect
is a significant dielectric contrast between the
nanoparticles and their environment. As shown
experimentally in the work [16] by reducing the
dielectric contrast between InP and ZnO nanofiber using
Ta2O5 deposition, the authors managed to reduce the
value of ρ by 84…86%. In the same paper, the model
was developed for calculation of the PL intensity
dependence on the angle between the directions of
exciting light polarization and that of detected one for
the structure that contains nanowires (or elongated
nanoparticles) randomly oriented in the plane of the
sample (similar to our continuous nc-Si−SiOx structures
processed in HF). The main parameters of this model is
the dielectric constants of the emitting nanoparticles (or
nanofibers) and dielectric environment in which these
emitters are embedded. Fig. 6 shows the angular
dependence of the normalized PL intensity (points −
experimental values, solid line − approximation of the
experiment using polynomial) for continuous nc-Si−SiOx
sample annealed in vacuum, then processed in HF vapor,
the same as presented in Figs 1 and 2. The dotted curve
shows the results of simulation that obtained using the
expression [16]:
600 640 680 720 760
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.1
0.2
0.3
0.4
PL
in
te
ns
ity
, a
rb
. u
ni
ts
λ, nm
λex= 415 nm
Po
la
riz
at
io
n
de
gr
ee
, ρ
eex II edet
eex
1
eex
hν
edet
2
3
O
Fig. 4. PL spectra of the same sample as in Fig. 3, but for
orientation of excitation polarization perpendicular to the
projection of SiOx nanocolumns on the sample plane.
0.5
0.6
0.7
0.8
0.9
1.0
0
30
60
90
120
150
180
210
240
270
300
330
0.5
0.6
0.7
0.8
0.9
1.0
(1)
(2)
P
L
in
te
ns
ity
(a
rb
. u
ni
ts
)
λex = 415nm
λdet = 680nm
Fig. 5. Polar plot of the PL intensity for nc-Si−SiOx sample,
which spectra are shown in Figs 3 and 4 for two mutually
perpendicular orientations of excitation polarization −
parallel orientation of the excitation polarization and
nanocolumns projection (1) and perpendicular orientation
(2). The PL wavelength is 680 nm.
-90 -60 -30 0 30 60 90 120 150 180 210 240 270 300
0.5
0.6
0.7
0.8
0.9
1.0
N
or
m
al
iz
ed
P
L
in
te
ns
ity
θ, degree
1
2
λ
ex
= 415 nm
λdet = 680 nm
Fig. 6. Dependence of the normalized PL intensity on the
angle (θ) between excitation and detection polarizations for
continuous nc-Si−SiOx sample annealed in vacuum, then
treated with HF vapor. 1 − simulation results, 2 −
experimental values. The PL wavelength − 680 nm.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 3. P. 324-329.
doi: 10.15407/spqeo18.03.324
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
328
where εe and ε are dielectric functions of environment
and emitting nanoparticles, accordingly, θ is the angle
between excitation and detection.
The value of the dielectric function ε for silicon
nanoparticles was calculated taking into account their
size [17] and was equal to 8.8. For SiOx matrix, if taking
into account its porosity and composition, εe = 1.96 [13].
One can see minor differences between the experimental
and calculated curves, which indicates adequacy of the
model and close values of selected parameters to the real
values of the dielectric functions for the nanoparticles
and matrix.
4. Conclusion
In the samples deposited at the angle 0°,
thermostimulated decomposition of SiOx and formation
of nc-Si occur in the isotropic continuous film, therefore
nanoparticles also have isotropic (nearly spherical)
shape, and the PM effect is not observed. In porous
samples deposited at the angle 60°, which are optically
anisotropic due to inclination of SiOx nanocolumns, the
PM effect is not observed, too. It means that silicon
nanoparticles formed in the SiOx columns during
annealing are also spherically symmetrical, and
polarization of PL is mainly determined by the shape of
particles that emit light. Anisotropy of the dielectric
matrix is not manifested through the dependence of PL
polarization on the excitation polarization.
After treatment with HF, the luminescent properties
of nc-Si−SiOx structures are changed. The results
obtained in this paper show that this etching leads not
only to the reduced sizes of silicon nanoparticles, but
also to changes in their shape to the elongated
anisotropic one. In the continuous nc-Si−SiOx structures,
in the plane of the sample there are no preferrential
orientations of anisotropic silicon nanoparticles. But in
the porous matrix, anisotropy of PM is observed in the
plane of substrate. It means that anisotropic elongated
silicon nanoparticles have preferred orientation in the
film, and the projection of this orientation on the plane
of the sample coincides with the direction of projection
of the SiOx nanocolumns. It has been assumed that
orientation of the longer axes in nc-Si coincides with
orientation of SiOx nanocolumns. This assumption is
consistent with the conditions of etching in porous
matrix: dissolution occurs starting from the surface of
the nanocolumns, so first the side surface of nc-Si is
dissolved, since it is closer to the column surfaces,
which leads to elongation of nanoparticles along the axis
of the column.
References
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