Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface
The influence of porous alumina template morphology on silicon film growth during deposition by PE CVD has been investigated. As it was shown, the structural properties of silicon phases depend on the pore geometry and surface morphology of the anodized porous alumina substrate. In the case of porou...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2017
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| Цитувати: | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface / P.V. Parfenyuk, A.A. Evtukh, I.M. Korobchuk, V.I. Glotov, V.V. Strelchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 3. — С. 330-334. — Бібліогр.: 19 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860295865342623744 |
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| author | Parfenyuk, P.V. Evtukh, A.A. Korobchuk, I.M. Glotov, V.I. Strelchuk, V.V. |
| author_facet | Parfenyuk, P.V. Evtukh, A.A. Korobchuk, I.M. Glotov, V.I. Strelchuk, V.V. |
| citation_txt | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface / P.V. Parfenyuk, A.A. Evtukh, I.M. Korobchuk, V.I. Glotov, V.V. Strelchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 3. — С. 330-334. — Бібліогр.: 19 назв. — англ. |
| collection | DSpace DC |
| container_title | Semiconductor Physics Quantum Electronics & Optoelectronics |
| description | The influence of porous alumina template morphology on silicon film growth during deposition by PE CVD has been investigated. As it was shown, the structural properties of silicon phases depend on the pore geometry and surface morphology of the anodized porous alumina substrate. In the case of porous alumina formation in one stage, ripple-like morphology takes place. The growth of a-Si:H film is observed during deposition. After two-stage anodization, the porous alumina has a tipped/ribbed morphology. In this case, usually a-Si:H film grows on the bottom of the pores, and nc-Si:H/a-Si:H one grows on the tips. In the case of deep pores, the nanocrystalline nc-Si:H film grows only above the top of the pores. The obtained results could be used when developing new types of photocells, sensors, nanophotonics, and ionics devices.
|
| first_indexed | 2026-03-21T06:43:58Z |
| format | Article |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 330-334.
doi: https://doi.org/10.15407/spqeo20.03.330
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
330
PACS 78.30.Ly, 78.55.Mb, 81.05.Gh, 81.70.Fy
Peculiarities of nanocrystalline silicon films
growth on porous anodic alumina surface
P.V. Parfenyuk1, A.A. Evtukh1,2, I.M. Korobchuk2, V.I. Glotov3, V.V. Strelchuk1
1 V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, Kyiv, Ukraine,
E-mail: anatoliy.evtukh@gmail.com
2Institute of High Technologies, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
3Institute of Microdevices, Kyiv, Ukraine
Abstract. The influence of porous alumina template morphology on silicon films growth
at deposition by PE CVD has been investigated. As it was shown, the structural
properties of silicon phases depend on the pore geometry and surface morphology of the
anodized porous alumina substrate. In case of porous alumina formation in one stage,
ripple-like morphology takes place. The growth of a-Si:H film is observed at deposition.
After two-stage anodization, the porous alumina has tipped/ribbed morphology. In this
case, usually a-Si:H film grows on the bottom of the pores, and nc-Si:H/a-Si:H one
grows on the tips. In the case of deep pores, the nanocrystalline nc-Si:H film grows only
above the top of the pores. The obtained results could be used when developing new
types of photocells, sensors, nanophotonics and ionics devices.
Keywords: amorphous phase, nanocrystalline silicon films, porous anodic alumina,
chemical vapor deposition, textured surface, Raman spectra.
Manuscript received 25.03.17; revised version received 07.08.17; accepted for
publication 06.09.17; published online 09.10.17.
1. Introduction
The nanocrystalline silicon films are very attractive for
optoelectronics, especially photovoltaics applications.
As it was shown [1], the films of amorphous
hydrogenized silicon that include the silicon
nanocrystalls with the size of several nanometers and
bulk concentration of several percents have higher
sensitivity and stability in comparison with homogenous
a-Si:H films. Significant advantages have been made in
recent years to improve the efficiency of single and
multi-junction solar cells incorporating nanocrystalline
silicon (nc-Si:H). Nanocrystalline silicon is an adsorbing
material, which is crucial for obtaining thin film tandem
solar cells with a high efficiency [2, 3].
As a rule, nc-Si:H is obtained using the chemical
vapor deposition (CVD) method. The variety of direct
CVD techniques has been used to yields materials with
good optoelectronic properties [4-9]. But among them
only plasma enhanced chemical vapor deposition (PE
CVD) has been established for industrial applications
[10]. The high RF-power and high hydrogen dilution are
two critical parameters in conventional PE CVD method
that facilitate nanocrystalization [11]. The high RF-
power causes surface damage by high-energy ion
bombardment, and high hydrogen dilution of silane
retards the deposition rate of nc-Si:H films [12] and have
constrained the film deposition to a narrow substrate
temperature range [13]. The lower deposition rate
increases the process operation time, and hence the cost
whereas narrow substrate temperature range involves
difficulty in controlling the hydrogen distribution in the
film, which is responsible for light-induced degradation
of electronic properties [14]. The new approach to form
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 330-334.
doi: https://doi.org/10.15407/spqeo20.03.330
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
331
nc-Si:H films by PE CVD is based on the growth on
textured substrates, namely porous anodic aluminum
(PAA) substrates [15, 16].
The aim of this article is to study the surface
morphology influence of the porous anodic alumina
(PAA) substrate on the structural characteristics of the
nanocrystalline silicon.
2. Experimental
2.1. Preparation of porous anodic alumina templates
To prepare the template of porous alumina substrate, the
electrochemical oxidation of 0.05 mm thick aluminum
foil was used. Before anodizing, the foil was degreased
in acetone in ultrasonic bath, and then washed in
deionized (DI) water.
The two-step anodizing processing was performed
using 4% H3PO4 electrolyte. In a first step of anodizing,
Al foil samples (area 2×2 cm2) were prepared in 4%
H3PO4 under the following conditions: solution
temperature 15 °C, anodizing voltage 130 V, anodizing
current 8 mA, duration 10 min. In the anodizing process,
thin porous oxide layer was formed on the surface of Al
foil. Then, the oxide layer was etched for 75 min in
phosphoric-chromic acid solution (35 ml 85% H3PO4 +
20 g CrO3 /1000 ml) at 70 °C to produce the
nanostructured Al surface with regular pattern concaves
and nanotips [16]. The array served as template for
further processing.
The second anodizing process was performed in the
same solution for the anodizing voltage 120 V to form
desired porous alumina layer. This layer was etched
further partially in the abovementioned acid solution to
get the tips/ribs-like alumina morphology. In some
cases, the anodizing/etching processing was repeated to
get cone-like pores. The resulting samples were washed
several times in deionized water and dried at 80 °C.
2.2. Deposition of hydrogenated silicon thin films
Hydrogenated silicon (a/nc-Si:H) thin films were
prepared using the plasma enhanced chemical vapor
deposition (PE CVD) technique with the mixture of
argon (Ar), hydrogen (H2) and silane (SiH4) gases. The
deposition parameters are shown in Table.
Parameters of Si:H thin film deposition.
Parameter Value
Microwave power 700 W
Base pressure (1…2)·10–5 Torr
Working pressure 1.5·10–2 Torr
Substrate temperature 200 °C
Gas flow rates
(a) Silane (SiH4) 100 sccm
(b) Hydrogen 1000 sccm
(c) Argon (Ar) 1000 sccm
Deposition time 18 min
The hydrogen dilution ratio [H2]/[SiH4] was kept
constant at 10, and the average deposition rate was about
10 nm/min.
2.3. Characterization
Raman spectra were measured with a Triplemate SPEX
spectrometer equipped with a liquid nitrogen-cooled LN
1340PB (Princeton Instruments) multichannel CCD
camera. The spectra were excited by a 488-nm argon
laser line with a power at the sample surface of no
higher than 5 mW. The excitation wavelength was
chosen so as to reduce the light penetration depth and
prevent formation of the substrate spectrum, and the
excitation power was low in order to preclude light-
induced sample crystallization. The sample was placed
in the focal plane of a microscope which objective with
an operation distance of 2 mm and an aperture of 0.6,
served to focus the laser beam and collect the scattered
radiation. The laser beam spot on the sample surface was
2 µm in diameter. In the experiments, 180° scattering
geometry was used. Raman spectra of films were
measured with the resolution 5 cm–1. The
photoluminescence spectra of the deposited films were
measured using the Raman spectrometer. Nanocrys-
talline phase volume was determined from Raman
spectra by using the method described in [17].
Morphologies of initial substrate and deposited
layers were characterized using the scanning electron
microscope (MIRA3 TESCAN).
3. Results and discussion
The properties of nanocrystalline silicon films are
determined by surface morphology of the porous anodic
alumina substrate. After the one-step anodization, PAA
template has ripple-like surface morphology with a
nanopore array. Typically, PAA layer has a duplex
nature, which is composed of inner and outer sublayers
[18]. In this case, PAA is very thin due to the short
etching process. As a result, the pore walls are almost
removed and only the inner oxide layer of about a few
nanometers is observable. It is expected that the porous
alumina layer is too weak and can be easily broken by
mechanical stress such as bending.
In a two-step anodization, the self-organized
nanopores array is created on the aluminum surface. The
layer become thinner after partial etching, the inner and
outer sublayers are retained in the pore structure of the
porous anodic alumina substrate and aluminium surface
acquires tipped/ribbed morphology. Thus, at anodization
of aluminum foil by one-step and a two-step
anodization, the surface and morphology of the porous
anodic alumina, the structure of formed oxide is very
different. A strong difference is also observed in the
structure of silicon deposited on such a surface.
So, the films contain only amorphous phase, when
they are deposited on ripple-like surface obtained with
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 330-334.
doi: https://doi.org/10.15407/spqeo20.03.330
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
332
one-step anodization. Morphology of Si:H films
deposited on tipped/ribbed surface displays two separate
phases. Si:H films grown from the bottom of the oxide
layer has smooth morphology, which is analogus to the
Si:H layer deposited at the one-step anodization.
However, Si:H films deposited on the tipped region
show columnar/wall structure, and this part consists of
the nanocrystalline phase [18]. Therefore, it can be
considered that there are two different growth types in
the case of the films grown on tipped/ribbed surface, and
the growth rate of nc-Si:H films is higher than that of a-
Si:H.
An important result of the studies of
nanocrystalline silicon is the dependence of its structural
properties on the pore size. Figs 1a and 1b show the
images of initial PAA templates after two-step
anodization. As can be seen, the nanopores array of
average diameter 452±35 nm, interpore distance
500±24 nm and thickness of 1960±83 nm formed on the
surface of aluminum. The phosphoric acid anodizing
processing was chosen because of the following reasons.
The alumina pores has their maximum size compared to
other porous-forming electrolytes, and electrochemical
processing in phosphoric acid could provide formation
of duplex-layered oxide with anion species concentrated
in the outer layer of the oxide. The species could form
inclusions of wavellite Al3(OH)3(PO4)2·5H2O, augelite
Al2(PO4)(OH)3, or another aluminum phosphate
hydroxides in alumina to facilitate its subsequent etching
in phosphoric-chromic acid solution.
SEM image of silicon films with the thickness
200 nm deposited on an anodized porous aluminum
substrate are shown in Fig. 2. In our case of deep pores,
the a-S:H film is not deposited on the bottom of the
pores. There is no amorphous phase at large depth of the
pores, because the growth of amorphous phase starts at
the bottom of shallow pores, and the nanocrystalline
phase grows on the top of pores. In our case, the
nanocrystalline nc-Si:H film grows above the top of the
pores.
Raman spectroscopy demonstrates growing contri-
bution of the crystalline phase with deposition duration,
confirming the crystalline nature of the films (Fig. 3).
The following Gaussian components were used for de-
convolution of experimental Raman spectra. The first
two ones, at 330 and 400 cm–1, represented the longi-
tudinal acoustic (LA) phonon mode and longitudinal
optical (LO) phonon of a-Si:H, correspondingly. The
transversal optical (TO) phonon mode was deconvoluted
into two bands: TO1 at 475 cm–1 for α-Si:H, and TO2 at
490 cm–1 for intermediate nanocrystalline silicon phase.
Crystalline silicon was represented by the rather sharp
main peak (CB1) at 521 cm–1. The crystallinity of the
film Xc = Ic /Ia, where Ic, Ia are the integrated intensities
of the crystalline and amorphous peaks, was equal to
32%.
The photoluminescence spectrum of the
nanocrystalline silicon films demonstrated strong rather
broad and pronounced peak at ~2.21 eV varying in
height depending on the Si layer thickness (Fig. 4).
Fig. 1. SEM images of surface morphology inherent to initial PAA templates after two-step anodization: (a) plane view, (b) cross
section view.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 3. P. 330-334.
doi: https://doi.org/10.15407/spqeo20.03.330
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
333
Fig. 2. SEM image of Si:H thin film deposited on PAA
templates after two-step anodization.
Fig. 3. Raman spectra of the nanocrystalline silicon films
deposited on PAA templates (λex is the wavelength of laser
excitation).
Fig. 4. PL spectra of the nanocrystalline silicon films deposited
on PAA templates (λex is the wavelength of laser excitation).
As it is known, correlation between Si nanocrystals
diameter d and photoluminescence peak energy Emax
could be ascribed to quantum confinement and has the
look [19]:
[ ] [ ]( ) 39.1
0max 73.3 nmdeVEE g += , (1)
where Eg0 is the band gap of bulk crystalline Si. The size
of nanocrystallites was estimated with account of the
maximum position for the radiation peak and for 2.21 eV
was equal to 2.6 nm.
4. Conclusions
The effect of the textured surface of PAA templates and
pore size on the morphological and structural properties
of hydrogenated silicon thin films grown using the PE-
CVD method has been studied with SEM, Raman and
photoluminescence spectroscopy. The Si:H films
deposited on ripple-like surface grows uniformly and
consist mainly of amorphous phase. However, the film
grown on the tipped/ribbed template shows novel
morphology of heterogeneous a-Si:H/nc-Si:H mixed
phase. The crystallinity of the layer and nanocrystallite
sizes were weakly dependent on the pore size. A pure
amorphous phase does not exist at a large depth of the
pore.
Acknowledgments
This work was partially funded by State Fund for
Fundamental Researches of Ukraine, grant F64/6-2016.
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|
| id | nasplib_isofts_kiev_ua-123456789-214950 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2026-03-21T06:43:58Z |
| publishDate | 2017 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Parfenyuk, P.V. Evtukh, A.A. Korobchuk, I.M. Glotov, V.I. Strelchuk, V.V. 2026-03-05T12:04:14Z 2017 Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface / P.V. Parfenyuk, A.A. Evtukh, I.M. Korobchuk, V.I. Glotov, V.V. Strelchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 3. — С. 330-334. — Бібліогр.: 19 назв. — англ. 1560-8034 PACS: 78.30.Ly, 78.55.Mb, 81.05.Gh, 81.70.Fy https://nasplib.isofts.kiev.ua/handle/123456789/214950 https://doi.org/10.15407/spqeo20.03.330 The influence of porous alumina template morphology on silicon film growth during deposition by PE CVD has been investigated. As it was shown, the structural properties of silicon phases depend on the pore geometry and surface morphology of the anodized porous alumina substrate. In the case of porous alumina formation in one stage, ripple-like morphology takes place. The growth of a-Si:H film is observed during deposition. After two-stage anodization, the porous alumina has a tipped/ribbed morphology. In this case, usually a-Si:H film grows on the bottom of the pores, and nc-Si:H/a-Si:H one grows on the tips. In the case of deep pores, the nanocrystalline nc-Si:H film grows only above the top of the pores. The obtained results could be used when developing new types of photocells, sensors, nanophotonics, and ionics devices. This work was partially funded by the State Fund for Fundamental Research of Ukraine, grant F64/6-2016. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface Article published earlier |
| spellingShingle | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface Parfenyuk, P.V. Evtukh, A.A. Korobchuk, I.M. Glotov, V.I. Strelchuk, V.V. |
| title | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface |
| title_full | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface |
| title_fullStr | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface |
| title_full_unstemmed | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface |
| title_short | Peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface |
| title_sort | peculiarities of nanocrystalline silicon films growth on porous anodic alumina surface |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/214950 |
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