Sponge-like nanostructured silicon for integrated emitters
A new approach to nanoporous silicon formation is proposed. Anomalies both in low current densities and low fluorine ion concentrations, which is lead to low uniformity of formed porous silicon, are under consideration. It is shown that at very low current densities and fluorine ion concentration...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2010
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| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Цитувати: | Sponge-like nanostructured silicon for integrated emitters / A. Hubarevich, P. Jaguiro, Y. Mukha, A. Smirnov, Ya. Solovjov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С. 294-297. — Бібліогр.: 14 назв. — англ. |
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irk-123456789-1184082017-05-31T03:07:23Z Sponge-like nanostructured silicon for integrated emitters Hubarevich, A. Jaguiro, P. Mukha, Y. Smirnov, A. Solovjov, Ya. A new approach to nanoporous silicon formation is proposed. Anomalies both in low current densities and low fluorine ion concentrations, which is lead to low uniformity of formed porous silicon, are under consideration. It is shown that at very low current densities and fluorine ion concentration high uniformity, high porosity nanoporous silicon layers can be created. Structural, electrical and optical properties of porous silicon formed in a wide range of current densities, doping levels of silicon substrates and fluorine concentrations are presented. 2010 Article Sponge-like nanostructured silicon for integrated emitters / A. Hubarevich, P. Jaguiro, Y. Mukha, A. Smirnov, Ya. Solovjov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С. 294-297. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS 78.60.Fi, 81.05.Rm, 81.07.-b http://dspace.nbuv.gov.ua/handle/123456789/118408 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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A new approach to nanoporous silicon formation is proposed. Anomalies both
in low current densities and low fluorine ion concentrations, which is lead to low
uniformity of formed porous silicon, are under consideration. It is shown that at very low
current densities and fluorine ion concentration high uniformity, high porosity
nanoporous silicon layers can be created. Structural, electrical and optical properties of
porous silicon formed in a wide range of current densities, doping levels of silicon
substrates and fluorine concentrations are presented. |
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Article |
| author |
Hubarevich, A. Jaguiro, P. Mukha, Y. Smirnov, A. Solovjov, Ya. |
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Hubarevich, A. Jaguiro, P. Mukha, Y. Smirnov, A. Solovjov, Ya. Sponge-like nanostructured silicon for integrated emitters Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Hubarevich, A. Jaguiro, P. Mukha, Y. Smirnov, A. Solovjov, Ya. |
| author_sort |
Hubarevich, A. |
| title |
Sponge-like nanostructured silicon for integrated emitters |
| title_short |
Sponge-like nanostructured silicon for integrated emitters |
| title_full |
Sponge-like nanostructured silicon for integrated emitters |
| title_fullStr |
Sponge-like nanostructured silicon for integrated emitters |
| title_full_unstemmed |
Sponge-like nanostructured silicon for integrated emitters |
| title_sort |
sponge-like nanostructured silicon for integrated emitters |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2010 |
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http://dspace.nbuv.gov.ua/handle/123456789/118408 |
| citation_txt |
Sponge-like nanostructured silicon for integrated emitters / A. Hubarevich, P. Jaguiro, Y. Mukha, A. Smirnov, Ya. Solovjov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2010. — Т. 13, № 3. — С. 294-297. — Бібліогр.: 14 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T13:55:15Z |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 294-297.
PACS 78.60.Fi, 81.05.Rm, 81.07.-b
Sponge-like nanostructured silicon for integrated emitters
A. Hubarevich1, P. Jaguiro1, Y. Mukha1, A. Smirnov1, Ya. Solovjov2
1Belarusian State University of Informatics and Radioelectronics, Laboratory of Information Displays
6, P. Brovki str., 220013 Minsk, Republic of Belarus
2SOE “Transistor Factory”, 16, Korzhenevskogo str., 220108 Minsk, Republic of Belarus
Abstract. A new approach to nanoporous silicon formation is proposed. Anomalies both
in low current densities and low fluorine ion concentrations, which is lead to low
uniformity of formed porous silicon, are under consideration. It is shown that at very low
current densities and fluorine ion concentration high uniformity, high porosity
nanoporous silicon layers can be created. Structural, electrical and optical properties of
porous silicon formed in a wide range of current densities, doping levels of silicon
substrates and fluorine concentrations are presented.
Keywords: porous silicon, nanostructure, electroluminescence.
Manuscript received 18.12.09; accepted for publication 08.07.10; published online 30.09.10.
1. Introduction
Silicon is an essential foundation in today’s
microelectronics because of its extraordinary
physicochemical, electronic and technological
properties. However, because of its indirect bandgap
structure monocrystalline silicon cannot be used as
material for light emission. At first porous self-organized
structure on silicon was created in 1956 at Bell
Laboratory. Porous silicon was widely used in
microelectronics: IPOS and FIPOS processes, SOI
wafers production. In 1990 the quantum effects and
room temperature visible luminescence was
demonstrated in porous silicon [1, 2]. This feature awoke
researchers’ interest, and the first light emission silicon
diode appeared some time later. Our group works over
avalanche type reverse biased Schottky diodes and its
microdisplays as well as optoelectronics applications [3-
5]. Standard technological parameters for formation a
high porosity nanostructured Si are high current
densities and high concentrations of hydrofluoric acid.
These regimes are not convenient, because of very short
process times (some seconds for thin layers) and toxic
(high HF vapor pressure), aggressive reagents (etching
Al layers and interconnections) are used. However,
changing to lower current densities and concentrations
leads to instability and low uniformity of the process.
In this paper, we analyze reasons of the instability
and propose a new stable and convenient technological
regime for high porosity nanostructured Si formation at
ultra small current density and fluorine ions
concentration.
2. Porous silicon formation
There are three well known regimes corresponding to the
areas in the current density – hydrofluoric acid
concentration plot, which are illustrated in Fig. 1 [6]. At
high densities-concentrations electro-polishing takes
place, at low densities-concentrations we have porous
silicon formation, and in the middle we deal with a
transient regime. Rectangular in the plot shows standard
good reproducible, well known regimes [7], while
ellipse corresponds to low uniformity processes. The
area at the bottom left corner isn’t methodically
investigated. One of the reasons of this is low buffer
capacity of very diluted hydrofluoric acid and chemical
changes during the anodizing process. To avoid from
“diluted” problem using of salts of hydrofluoric acid in
combination with an acid with high buffer capacity is
proposed.
The special case at zero current at acidified
NH4HF2 is investigated [8, 9], but it doesn’t provide
enough control on porous silicon morphology. To avoid
aggressive etching of Al by HF solutions (up to 4000 nm
per hour), it was proposed to use 14 wt.% ammonium
fluoride, 33 wt.% acetic acid in water (30 nm per hour)
as electrolyte for anodizing [10]. However, at current
densities 5-80 mA/cm2 the uniformity is far from perfect.
Note that HF vapor pressure over weak acidified
fluoride salts is significantly lower than over
hydrofluoric acid solutions. It is strong anomaly in
fluorine ions and its derivatives concentration, extrema
appear on its dependence of the fluoride salt
concentration [11].
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
294
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 294-297.
Fig. 1. Different types of porous silicon formation.
© 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Fig. 2. Porous structure versus current density [12].
Heavy negative doped monocrystalline silicon is
used as precursor for nanostructured Schottky junction
fabrication, so this material is under our investigation. In
Fig. 2 change in the porous structure versus anodizing
current density for heavy antimony doped silicon
(0.01 Ohm⋅cm, 〈100〉 orientation) in 1:2:1
HF:C2H5OH:H2O is presented [12]. Porosity anomaly
versus current density is absolutely evident. At about
10 mA/cm2 the plot turns, and morphology of porous
silicon changes from regular vertical holes (at higher
current densities) to sponge structure (at lower current
densities).
Numeric analysis that was performed by our group
earlier [13, 14] shows that these changes of porosity can
be related to increase of the electrochemical diffusion
layer (from 30 to about 500 μm) while the current
density slows down. This increase is determined by
break off solution agitate by emitted gas bubbles. At low
current densities, issue of emitted gas is small, and all
hydrogen gas can be dissolved in solution and doesn’t
form a bubble. The critical current is 4.3 mA/cm2 for
water at ambient conditions. Anodizing process can be
unstable near this value (1-10 mA/cm2), because of local
gas bubble agitating and corresponding irregular current
distribution. Note that very high porosities can be
achieved at low current densities.
3. Experimental details
Addition of ethanol to solution allows moistening
hydrophobic silicon surface and getting more
reproducible results. In our system, it is not necessary to
add a big amount of water, because we work at low
fluorine ion concentrations and weak dissociated acids.
So, the simplest solution is about 4 % of water that is
present in rectified ethanol. It is practically impossible to
predict ion concentrations in the solution due to the
“concentration anomaly” and usage of organic solvent.
In this case, we should to carry out more experiments.
N-type 〈100〉 oriented phosphorous doped silicon
substrates (0.1 Ohm⋅cm and 0.01 Ohm⋅cm) were used.
The samples were anodized in ambient conditions with
halogen lamp illumination. Current densities and
electrolyte concentrations in rectified ethanol are
summarized in Table.
Table. The range of anodization parameters.
NH4F:H3PO4:C2H5OH Current density Doping level
5 – 25 % H3PO4
0.01 – 1
mA/cm2 1021 – 1020
Pores sizes and structure of PS were observed using
the scanning electron microscope (LEO 1550 Gemini).
The thickness and porosity of the layers were measured
by Spectroscopic Ellipsometer VB-250 and calculated
then as describing. Photoluminescence and
electroluminescence were measured using spectrometer,
photoluminescence was excited by the discrete like of a
mercury lamp 330 nm. For electroluminescent
measurements 0.7 μm Al was PVD and anodized
through photoresist mask. 200×200 μm pads leaves on
the porous silicon layer. Electrical measurements of the
Schottky diodes were carried out using a special
equipment.
4. Results and discussion
In Fig. 3, voltage versus time curves are presented for
different samples after anodization.
In Fig. 4, photoluminescence spectra for two
samples of PS and monocrystalline silicon are presented.
Figs 5 and 6 shows the structure of PS. Pores sizes
are 10 to 20 nm and porosity reaches 55 % at the current
density 0.25 mA/cm2 and 75 % at the current density
0.025 mA/cm2. Thus, in the regime of small
concentration of F– ions the drop in the current density
increases porosity.
Fig. 6 shows the thickness of PS. It is 50 nm at the
current density 0.1 mA/cm2, time 500 s and solution
5 % NH4F:15 % H3PO4:C2H5OH.
The structures in Figs 5 and 6 are sponge-like.
Sponge forms with porosity 70 % and more can be used
in optical applications.
295
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 3. P. 294-297.
Fig. 3. Voltage versus time dependences.
Fig. 4. Photoluminescence spectra.
Fig. 5. The structure of PS anodized at 0.25 mA/cm2 and 5 %
NH4F:5 % H3PO4:C2H5OH.
Fig. 6. The structure of PS anodized at 0.025 mA/cm2 and
5 % NH4F:5 % H3PO4:C2H5OH.
Fig. 7. Cross-section of PS structure at 0.1 mA/cm2, 500 s and
5 % NH4F:15 % H3PO4:C2H5OH.
5. Conclusion
In this work, we report the stable and reproducible
regime to produce porous silicon layers at ultra-small
current densities and fluorine ion concentrations. The
porous silicon structure is of high porosity and sponge-
like, with a small thickness and allows using it as light
emitters, specifically in emission displays.
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