Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures
In this work the experimental observation of passivation of silicon surface by ultrathin dielectric film in Al/Si/nematic/Indium Tin Oxide(ITO) structure performed on the base of low resistive (~ several Ωxcm) n-type conductivity silicon sample is presented. It is shown that when the DC voltage with...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2004
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| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Цитувати: | Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures / M.I. Gritsenko, S.I. Kucheev, P.M. Lytvyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 2. — С. 154-156. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-1181652017-05-30T03:04:55Z Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures Gritsenko, M.I. Kucheev, S.I. Lytvyn, P.M. In this work the experimental observation of passivation of silicon surface by ultrathin dielectric film in Al/Si/nematic/Indium Tin Oxide(ITO) structure performed on the base of low resistive (~ several Ωxcm) n-type conductivity silicon sample is presented. It is shown that when the DC voltage with polarity +U on silicon is applied to the structure a passivation effect of silicon surface takes place. It is found that a silicon surface passivated by dielectric film changes an initial alignment of liquid crystal 5CB. In the structure with passivating silicon surface a frequency range of structure photosensitivity extends due to limitation of current leakage through Si/liquid crystal interface. Keywords: nematic, silicon, passivation, alignment, photosensitivity, light modulator. 2004 Article Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures / M.I. Gritsenko, S.I. Kucheev, P.M. Lytvyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 2. — С. 154-156. — Бібліогр.: 9 назв. — англ. 1560-8034 PACS: 81.65.Rv http://dspace.nbuv.gov.ua/handle/123456789/118165 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 |
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In this work the experimental observation of passivation of silicon surface by ultrathin dielectric film in Al/Si/nematic/Indium Tin Oxide(ITO) structure performed on the base of low resistive (~ several Ωxcm) n-type conductivity silicon sample is presented. It is shown that when the DC voltage with polarity +U on silicon is applied to the structure a passivation effect of silicon surface takes place. It is found that a silicon surface passivated by dielectric film changes an initial alignment of liquid crystal 5CB. In the structure with passivating silicon surface a frequency range of structure photosensitivity extends due to limitation of current leakage through Si/liquid crystal interface.
Keywords: nematic, silicon, passivation, alignment, photosensitivity, light modulator. |
| format |
Article |
| author |
Gritsenko, M.I. Kucheev, S.I. Lytvyn, P.M. |
| spellingShingle |
Gritsenko, M.I. Kucheev, S.I. Lytvyn, P.M. Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Gritsenko, M.I. Kucheev, S.I. Lytvyn, P.M. |
| author_sort |
Gritsenko, M.I. |
| title |
Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures |
| title_short |
Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures |
| title_full |
Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures |
| title_fullStr |
Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures |
| title_full_unstemmed |
Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures |
| title_sort |
passivation of silicon surface by ultrathin dielectric film in m/si/nematic/ito structures |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2004 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118165 |
| citation_txt |
Passivation of silicon surface by ultrathin dielectric film in M/Si/nematic/ITO structures / M.I. Gritsenko, S.I. Kucheev, P.M. Lytvyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 2. — С. 154-156. — Бібліогр.: 9 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T13:29:40Z |
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2025-07-08T13:29:40Z |
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1837085635680141312 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics. 2004. V. 7, N 2. P. 154-156.
© 2004, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine154
PACS: 81.65.Rv
Passivation of silicon surface by ultrathin dielectric film
in M/Si/nematic/ITO structures
M.I. Gritsenko, S.I. Kucheev, P.M. Lytvyn*
Chernigov Pedagogical University, 53, G.Polubotka str., 14038 Chernigov, Ukraine
*V. Lashkaryov Institute of Semiconductor Physics, prospect Nauky 45, 03028 Kyiv, Ukraine
E-mail: kucheev@cn.relc.com
Abstract. In this work, the experimental observation of passivation of silicon surface by
ultrathin dielectric film in Al/Si/nematic/Indium Tin Oxide(ITO) structure performed on the
base of low resistive (~ several Ω×cm) n-type conductivity silicon sample is presented. It is
shown that when the DC voltage with polarity +U on silicon is applied to the structure a
passivation effect of silicon surface takes place. It is found that a silicon surface passivated by
dielectric film changes an initial alignment of liquid crystal 5CB. In the structure with
passivating silicon surface, a frequency range of structure photosensitivity extends due to
limitation of current leakage through Si/liquid crystal interface.
Keywords: nematic, silicon, passivation, alignment, photosensitivity, light modulator.
Paper received 15.12.03; accepted for publication 17.06.04.
1. Introduction
Metal/Si/SiO2/nematic/transparent electrode structures
(M/Si/SiO2/nematic/ITO) are used in a broad range of
electrooptical devices including optically addressed space
light modulators (OA SLM) [1�4]. A functional opera-
tion of these structure is based on a silicon surface deple-
tion effect [5] that is caused by means of external electric
field of ITO electrode. SiO2 oxide film having thickness
up to 0.1�1 µm possesses a well insulating properties and
frequently playing a role of dielectric light mirror. Such
dielectric films fully exclude a charge transferring from
a field electrode into silicon sample. A controlled charge
embedded into oxide and repeatability of properties of
Si�SiO2 interface ensure a high stability of such devices [6].
However, the structures containing no SiO2 dielec-
tric film, i.e. M/Si/nematic/ITO structures, possess more
extended functional possibilities because, in this case, a
surface conductivity of silicon can be additionally modu-
lated: 1) by electric field of ion cloud, which can be local-
ized very close to silicon surface and 2) by means of cur-
rent leakage through Si/LC interface. Such structures
being exploited as OA SLMs, for example, can separate
moving and stop images [7]. Such type of structures al-
lows to easily realize an ion �quasi� electrode concep-
tion when the locally accumulated charge within liquid
crystal layer plays a role of the field electrode [7]. Using
a field effect in silicon induced by ion charges [8], there is
a possibility to study the ion processes taking place in
liquid crystals.
Meantime, the charges flowing through Si/LC inter-
face can cause the modification of silicon surface. One of
the most probable process could be gone on silicon sur-
face under the action of DC (as well AC) voltage is a
passivation of silicon surface by dielectric film.
The aim of the present work was to reveal a passivation
effect on silicon surface in a prototype of liquid crystal
device under the action of DC voltage. In the work, se-
veral independent methods were used to confirm a pas-
sivation effect.
2. Experimental and results
The structure performed on the base of n-type conductiv-
ity monocrystalline silicon (see Fig.1) and specific resis-
tivity of 4.5 Ω×cm was used in order to reveal the pas-
sivation effect of silicon surface in M/Si/nematic/ITO
structures. The upper electrodes were performed as ITO
stripes. Before assembling the structure the silicon sur-
face was etched in HF solution and then rinsed in distil-
late water. Liquid crystal 5CB layer thickness was 20 µm.
After this the DC voltage equal to 4.4 V with polarity +U
M.I. Gritsenko et al.: Passivation of silicon surface by ultrathin dielectric film ...
155SQO, 7(2), 2004
on silicon substrate was applied to structure for 5 minu-
tes. The current density was equal to ~ 1 µA/cm2. Then
the structure was disassembled, and the silicon surface is
cleaned only by organic dissolvent: dimetilformamide
and hexane (so SiO2 was not etched).
The investigation of silicon surface with optical mi-
croscope showed that both �A� and �B� silicon surfaces
that lie opposite the stripes (Fig.1) are optically identi-
cal. (�A� and �B� surfaces lie opposite the stripes on
which the voltage U was applied and not applied, respec-
tively).
The �A� and �B� surfaces are well detected by means
of a water dew condensation and evaporation. From �A�
surface a dew evaporates slower than from �B� surface,
what is well seen by the naked eye. This means that the
roughness of �A� surface is large than roughness of �B�
surface. Taking into account that �A� and �B� surfaces
are optically identical, the difference between their rough-
ness must be at a nanoscale level.
�A� and �B� surfaces were examined by the atomic
force microscope (AFM, Digital Instruments NanoScope
IIIa in tapping mode) in scanning areas of 1×1 µm. The
surface topography in points �A� and �B� is shown as
height maps in Fig. 2. As it is well seen, the morphology
of these fragments of �A� and �B� surfaces are different.
On �A� surface the round pores (Fig.2a, black small spots)
are observed. A typical profile of single pore on �A� sur-
face is presented in Fig. 2c. The depth of pore is approxi-
mately equal to several nanometers and its diameter is ~
40 nanometers, respectively. We suppose that the pores
have been appeared on �A� surface by the following way.
It is well known [6] that in the course of anode oxidizing
the silicon surface contacting with electrolyte, silicon ox-
ide film grows. Varying electrolyte mixture the oxide film
having required porosity can be obtained. In our case a
liquid crystal 5CB plays a role of weak electrolyte [9].
Therefore, when an external voltage with +U polarity on
silicon is applied to Al/Si/5CB/ITO structure, a dielec-
tric film grows on silicon surface. We believe that this
dielectric film is silicon oxide. Taking into account that
the radius of AFM tip is equal to ~ 5�10 nm, we assume
also that the minimal value of silicon oxide film thick-
ness is equal approximately to depth of a pore, i.e. 3�4 nm.
It should be noted from the results of AFM examina-
tion of silicon surface it is followed that both �A� and
�B� surfaces are clean, i.e. there are no any contamina-
tion which could influence on the alignment of liquid crys-
tals in the following experiments.
On the base of above investigated silicon sample con-
taining �A� and �B� surfaces the Al/Si/5CB/ITO struc-
ture was assembled in the way where the upper ITO elec-
trode was unbroken. In order to obtain perfect homoge-
neous planar alignment of 5CB liquid crystal on whole
surface of ITO electrode, the surface was covered by
rubbed polyimide film. Liquid crystal thickness was
20 µm. Fig. 3 shows the fragment of Al/Si/5CB/ITO struc-
A B
+U
�U
LCITO
Si
Al
S
Fig. 1. The cross-section of investigated Al/Si/5CB/ITO struc-
ture. S denotes a spacer.
200nm
200nm
Fig. 2. AFM images of Si surface in points �A� (a) and �B� (b)
shown in Fig. 1 after removing of liquid crystal; (c) � the profile
of pore on surface (a).
a b
c
0 50 100 150 200
�0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Horiz. distance, nm
V
e
r
t.
d
is
ta
n
ce
,
n
m
Fig. 3. Image of �A� and �B� fragments of silicon surface in
Al/Si/5CB/ITO structure with polarized light.
156
SQO, 7(2), 2004
M.I. Gritsenko et al.: Passivation of silicon surface by ultrathin dielectric film ...
ture with silicon surface includes �A� and �B� regions.
As seen, a liquid crystal layer well decorates �A� and
�B� surfaces, respectively. It means that there takes place
the difference of liquid crystal alignment on �A� and �B�
surfaces (taking into account that the molecules are ho-
mogeneously oriented on upper ITO electrode).
Then we studied a photosensitivity of the Al/Si/5CB/
ITO structure in �A� and �B� areas. The photosensiti-
vity of structure is determined by the reaction (yes/no) of
liquid crystal on He-Ne laser illumination of correspon-
ding area of silicon surface. When external ÀÑ voltage is
applied to Al/Si/nematic/ITO structure the surface dep-
letion layer in silicon may be produced and almost whole
voltage drops across depleted layer. Within a laser spot
a liquid crystal reorients because depleted layer in sili-
con is not formed and the total voltage applied to struc-
ture drops across liquid the crystal layer. In the case of n-
type silicon, a depletion of silicon surface takes place
when the polarity of AC voltage is +U on silicon. Be-
cause of a liquid crystal layer, in general case, is not
isolated by dielectric film, a surface density of major car-
riers in silicon depends strongly on the current leakage J
through Si/LC interface. In order to obtain a silicon sur-
face depletion (in other words a structure photosensitiv-
ity), it is required that the major carriers flow from sur-
face into bulk induced by external electric field must be
larger than the total current consisting of the current leak-
age J and the current due to thermo- and light-generated
non-equilibrium carriers. Obviously, the ultrathin dielec-
tric film on silicon surface can influence on value of cur-
rent leakage J and therefore on the structure photosensi-
tivity.
Figure 4 shows the dependence of the threshold volt-
age of structure photosensitivity appearance on the fre-
quency of the applied voltage. As seen, the frequency of
structure photosensitivity appearance in �A� area (ar-
row on A curve) is more than an order of magnitude lower
than the frequency of structure photosensitivity appear-
ance in �B� area (arrow on B curve). It means that the
current leakage J through Si/LC interface in �A� surface
of silicon is limited by a dielectric film grown on silicon
surface.
3. Conclusions
In summary, we have found a passivation effect in the
liquid crystal structure as a prototype of OA SLM. When
the external voltage with polarity +U on Si is applied to
Al/Si/5CB/ITO structure a silicon surface, prior etched
in HF solution, is passivated by an ultrathin dielectric
film. The passivating film changes an initial alignment
of liquid crystal and limits the transfer of carriers through
Si/LC interface that promotes the formation of depleted
surface layer in silicon under the action of AC voltage
within more wide range of frequency.
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ford Press, New York (1997).
T
h
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es
h
o
ld
o
f
p
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o
to
se
n
si
ti
v
it
y
,
V
10
2
10
3
10
4
10
5
2
4
6
8
10
12
14
A B
Frequency, Hz
Fig. 4. Frequency dependence of threshold voltage applied to
Al/Si/5CB/ITO when a structure photo-sensitivity appears. Illu-
mination by He-Ne laser (0.63 µm, Ð ~ 2 mW).
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