Charge characteristics of the MOS structures with oxide films containing Si nanocrystals
The processes of charge accumulation in the MOS structures with SiO₂ films containing Si nanocrystals are investigated, depending on the conditions of their formation by pulsed laser deposition. High-frequency capacity-voltage characteristics of structures with the different thicknesses of films,...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2007
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| Цитувати: | Charge characteristics of the MOS structures with oxide films containing Si nanocrystals / Е.V. Begun, O.L. Bratus', A.A. Evtukh, E.B. Kaganovich, E.G. Manoilov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 46-50. — Бібліогр.: 10 назв. — англ. |
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irk-123456789-1178922017-05-28T03:03:27Z Charge characteristics of the MOS structures with oxide films containing Si nanocrystals Begun, E.V. Bratus’, O.L. Evtukh, A.A. Kaganovich, E.B. Manoilov, E.G. The processes of charge accumulation in the MOS structures with SiO₂ films containing Si nanocrystals are investigated, depending on the conditions of their formation by pulsed laser deposition. High-frequency capacity-voltage characteristics of structures with the different thicknesses of films, sizes of Si nanocrystals, and their densities in the case of doping the films with gold and without it are measured. It is shown that the positive and negative charges are built-in, respectively, in the undoped films and those doped with gold. At the record of C-V curves, the accumulation of a positive charge is observed. The value of accumulated charge is higher in thin films and in the films doped with gold. The obtained results testify the possibility of the use of pulsed laser deposition for creation of memory structures based on the charge capture by Si nanocrystals. 2007 Article Charge characteristics of the MOS structures with oxide films containing Si nanocrystals / Е.V. Begun, O.L. Bratus', A.A. Evtukh, E.B. Kaganovich, E.G. Manoilov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 46-50. — Бібліогр.: 10 назв. — англ. 1560-8034 PACS 61.72.Tt, 84.37.+q, 85.35.Be http://dspace.nbuv.gov.ua/handle/123456789/117892 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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DSpace DC |
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English |
| description |
The processes of charge accumulation in the MOS structures with SiO₂ films
containing Si nanocrystals are investigated, depending on the conditions of their
formation by pulsed laser deposition. High-frequency capacity-voltage characteristics of
structures with the different thicknesses of films, sizes of Si nanocrystals, and their
densities in the case of doping the films with gold and without it are measured. It is
shown that the positive and negative charges are built-in, respectively, in the undoped
films and those doped with gold. At the record of C-V curves, the accumulation of a
positive charge is observed. The value of accumulated charge is higher in thin films and
in the films doped with gold. The obtained results testify the possibility of the use of
pulsed laser deposition for creation of memory structures based on the charge capture by
Si nanocrystals. |
| format |
Article |
| author |
Begun, E.V. Bratus’, O.L. Evtukh, A.A. Kaganovich, E.B. Manoilov, E.G. |
| spellingShingle |
Begun, E.V. Bratus’, O.L. Evtukh, A.A. Kaganovich, E.B. Manoilov, E.G. Charge characteristics of the MOS structures with oxide films containing Si nanocrystals Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Begun, E.V. Bratus’, O.L. Evtukh, A.A. Kaganovich, E.B. Manoilov, E.G. |
| author_sort |
Begun, E.V. |
| title |
Charge characteristics of the MOS structures with oxide films containing Si nanocrystals |
| title_short |
Charge characteristics of the MOS structures with oxide films containing Si nanocrystals |
| title_full |
Charge characteristics of the MOS structures with oxide films containing Si nanocrystals |
| title_fullStr |
Charge characteristics of the MOS structures with oxide films containing Si nanocrystals |
| title_full_unstemmed |
Charge characteristics of the MOS structures with oxide films containing Si nanocrystals |
| title_sort |
charge characteristics of the mos structures with oxide films containing si nanocrystals |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2007 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/117892 |
| citation_txt |
Charge characteristics of the MOS structures with oxide films containing Si nanocrystals / Е.V. Begun, O.L. Bratus', A.A. Evtukh, E.B. Kaganovich, E.G. Manoilov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 46-50. — Бібліогр.: 10 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT begunev chargecharacteristicsofthemosstructureswithoxidefilmscontainingsinanocrystals AT bratusol chargecharacteristicsofthemosstructureswithoxidefilmscontainingsinanocrystals AT evtukhaa chargecharacteristicsofthemosstructureswithoxidefilmscontainingsinanocrystals AT kaganovicheb chargecharacteristicsofthemosstructureswithoxidefilmscontainingsinanocrystals AT manoiloveg chargecharacteristicsofthemosstructureswithoxidefilmscontainingsinanocrystals |
| first_indexed |
2025-07-08T12:58:33Z |
| last_indexed |
2025-07-08T12:58:33Z |
| _version_ |
1837083673772425216 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 46-50.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
46
PACS 61.72.Tt, 84.37.+q, 85.35.Be
Charge characteristics of the MOS structures
with oxide films containing Si nanocrystals
Е.V. Begun, O.L. Bratus’, A.A. Evtukh, E.B. Kaganovich, E.G. Manoilov
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
41, prospect Nauky, 03028 Kyiv, Ukraine, e-mail: dept_5@isp.kiev.ua
Abstract. The processes of charge accumulation in the MOS structures with SiO2 films
containing Si nanocrystals are investigated, depending on the conditions of their
formation by pulsed laser deposition. High-frequency capacity-voltage characteristics of
structures with the different thicknesses of films, sizes of Si nanocrystals, and their
densities in the case of doping the films with gold and without it are measured. It is
shown that the positive and negative charges are built-in, respectively, in the undoped
films and those doped with gold. At the record of C-V curves, the accumulation of a
positive charge is observed. The value of accumulated charge is higher in thin films and
in the films doped with gold. The obtained results testify the possibility of the use of
pulsed laser deposition for creation of memory structures based on the charge capture by
Si nanocrystals.
Keywords: silicon, quantum dot, capacity-voltage characteristics, non-volatile memory.
Manuscript received 30.03.07; accepted for publication 24.04.07; published online 19.10.07.
1. Introduction
From the beginning of the 1990s, the intensive
researches and developments of structures on the base of
the nanocomposite system, silicon nanocrystal – silicon
dioxide (Si NC / SiO2), have been performed with the
purpose to create light emitting sources in the visible
region of spectrum, photodetectors, and memory devices
on silicon (c-Si). This nanocomposite is silicon with the
electronic system of dimension 0D (quantum dots) and is
often named nanocrystalline silicon (nc-Si). Important
information about the processes of capture of charge
carriers, the current flow, the bands diagram of the
M/nc-Si/c-Si/M structures is given by the studies of their
electric properties, in particular, capacity-voltage (C-V)
and current-voltage (I-V) characteristics. The results of
studies of the capacity properties of structures with
nanosize silicon are generalized in a review [1]. As a
rule, C-V characteristics with the shape similar to that for
the MOS structures are observed.
Interest to the charge characteristics of these
structures is related foremost to developments of devices
of memory, working on the capture of charge carriers by
sites (traps, NC). They possess the prospect of reduction
of the tunnel oxide thickness. At the creation of the
memory structures based on a floating gate with Si NC,
there are the tasks of control over Si NC sizes, their
dispersion, density, and the density of electronic states at
the interface of c-Si substrate and dielectric. Most works
concern the structures containing porous silicon (por-Si)
or layers of SiO2 with implanted silicon.
The method of pulsed laser deposition (PLD) of
films is characterized by the large technological flexi-
bility, advantages of vacuum cleanness, controllability of
the erosive torch parameters, congruence of the process,
compatibility with silicon technology, etc. It allows one
to obtain SiO2 films with quantum-size Si NC cha-
racterized by effective photoluminescence (PL) in the
visible region of the spectrum at room temperature [2].
But, to our knowledge, the charge characteristics of the
MOS structures based on these films are not practically
studied. Purpose of the present work is to investigate the
charge characteristics of M/nc-Si/p-Si/M structures with
the nc-Si films obtained by PLD in dependence on
conditions of their formation.
2. Experiment
The Al/nc-Si/p-Si structures containing nc-Si films on p-
Si substrates (ρ = 10 Ohm×cm, (001)) were formed at
the nc-Si film deposition by PLD in a vacuum chamber
with residual gas pressure 10−3 Pa for the size separation
of Si particles and the formation of films with a mirror
surface [3].
A target was single crystalline silicon with a
preliminarily deposited gold film of 100 nm in thickness
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 46-50.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
47
1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2
0
5
10
15
2
hν, eV
I P
L,
re
l.
un
its 1
Fig. 2. Time-resolved PL spectra of the films doped with
gold (1) and undoped (2).
on its surface or without it. Doping by gold atoms was
carried out for passivation of the unsaturated dangling
bonds of silicon in the film and the formation of SiO2
instead of SiOx (x < 2). Introduction of gold resulted in
the increase of the middle sizes Si NC and their
dispersion [3, 4]. The YAG:Nd3+ laser beam (wave-
length 1.06 µm, energy and duration of pulses 0.2 J and
8 ns, respectively, and frequency of their repetition
25 Hz), working in the Q-switched mode, scanned the
target. The film deposition velocity lay in the range 2-
20 nm/min, and the thicknesses of films were in the
range 50-500 nm. With removing from the erosive torch
axis, the film thickness decreased, as shown in Fig. 1.
The films grown at large distances from the torch axis
were characterized by the less sizes of Si NC and their
higher concentration (see the insertion in Fig. 1). These
regularities of formation of the SiOx films with Si NC
structure are a result of their deposition from the back
low-energy flow of erosive torch particles [3]. The
sputtering of aluminium films on the frontal and
rearward surfaces completed the formation of MOS
structures. The laser annealing provided the ohmic Al
contact to p-Si substrate.
The time-resolved PL spectra were measured in the
energy range 1.4-3.2 eV at excitation by the radiation of
a nitric laser (wavelength 337 nm, and pulse duration
8 ns) with stroboscopic registration of a signal in the
photon counting mode. The strobe width was 250 nm.
The spectra of photoluminescence, successive in time,
were measured with delay of the strobe in relation to the
pulse of a laser up to maximal times of PL relaxation –
about 20 µs.
Measurements of I-V characteristics were perfor-
med in darkness at applying the voltage changing on
increasing and falling behaviors with a step of 0.1 V.
The range of measured currents was 5×10−11…10−2 A.
-6-4-20246
0
10
20
30
40
02468101214
100
200
300
400
500
600
700
L, m m
d,
n
m
h, nm
f,
%
2
1
Fig. 1. Dependence of nc-Si film thickness on the distance
from an erosion torch. In insert: histograms of the height
distribution of surface asperities at a distance of 12 mm from
the torch (1) and nearby the torch (2). Results of Atomic Force
Microscopy [4].
The C-V characteristic measurements were fulfilled
with an AMTs-1530 C meter at a testing signal
frequency of 1 MHz and a voltage rate of 50 mV/s in the
interval from −15 to +15 V. The measurement of C-V
characteristics begins from the voltage corresponding to
the depletion or inversion of the surface semiconductor
layer (in this case of p-type semiconductor – from
positive gate voltages) to voltages corresponding to the
accumulation, and in the reverse direction. The high-
frequency signal amplitude was 20 mV.
3. Results and discussion
The PL spectra of obtained films lay in the interval of
radiation energies of 1.4-3.2 eV, and the times of PL
relaxation lay from tens of nanoseconds to tens of
microseconds. Undoped films show the PL spectra shif-
ted to the high-energy spectral region and are character-
rized by rapid, less than 250 ns, PL relaxation times. The
PL spectra of the films doped with gold are located in
the low-energy spectral region, and the slow micro-
second PL relaxation is inherent to them (Fig. 2). The
resulted PL spectra of obtained nc-Si films are typical of
the nanocomposite structures Si NC/SiO2. Their
photoluminescence properties, as was shown earlier in
[3], are caused by radiative annihilation of excitons in
quantum-size Si NC with the barrier SiO2 layer.
I-V characteristics of the investigated structures
Al/nc-Si/p-Si/Al had a rectifying character: the forward
direction of the current corresponds to a positive
potential on p-Si (Fig. 3). The forward branch of the I-V
characteristics at a bias from the parts of one volt to a
few volts with excluding the voltage drop on a ballast
resistance corresponds to the exponential dependence.
At a bias of more than 5-10 V, the saturation in the
current was observed, and the current density achieved
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 46-50.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
48
Fig. 3. Typical I-V characteristics of the MIS structure with
nanocomposite Si NC – SiO2 film (d = 173 nm). In the insert:
direct branch in the Abeles (ln(I/E) – 1/E) coordinates.
the values 10−1…10−2 A/cm2. At electric fields
E = (0.5…1)×105 V/cm, the significant parts of I-V
characteristics correspond to the direct tunnelling
mechanism between QD through the SiO2 potential
barriers, which is indicated by the linearity of I-V
characteristics in the Abeles (ln(I/E) – 1/E) coordinates
(see the insertion in Fig. 3) [5].
Fig. 4 shows the typical C-V characteristic of the
investigated structure, where the sign of voltage on the
abscissa axis corresponds to the sign of bias on the
M/nc-Si contact. The characteristic regions of high-
frequency C-V of the MOS structure are visible in the
capacity-voltage (C/C0-U) dependence. At a negative
bias, the horizontal capacity line corresponding to the
accumulation of holes in the space charge region (SCR)
of p-Si semiconductor at the interface with nc-Si is
observed. Total capacity of the structure under
accumulation is determined by the capacity of the nc-Si
layer, Cnc-Si, that is less in comparison with the
differential capacity of SCR of p-Si, CD. A growth of the
bias in the positive direction corresponds to the
subsequent realization of depletion and inversion
conditions with the observed sharp drop of capacity.
Flat band voltages VFB for structures with the
undoped nc-Si film have small negative values (about –
1 V). For structures with nc-Si films doped with gold,
the VFB values are about 0 V with lower dispersion.
Using the values of flat band voltages, the effective
built-in charge in nc-Si films was calculated by the
expression
( )FBV
S
C
Q ms
m
в −ϕ= , (1)
where ϕms is the contact difference of metal (Al) and
semiconductor (Si) potentials; S is the area of the metal
gate electrode, and Cm is the maximal capacity of the
structure.
Fig. 4. C-V characteristics of the MIS structure with nano-
composite Si NC – SiO2 film. In insert: C-V characteristic with
the capacity decreasing under accumulation.
Calculations showed that the effective built-in
charge is positive in the structures with undoped nc-Si
films, whereas it is negative in the structures with films
doped by gold (Fig. 5a). A positive charge is, usually,
connected with E′ centers (dangling silicon bonds),
which arise at the oxygen deficit in a SiO2 film, and with
the oxygen vacancies which are deep hole traps [6]. As
to a negative charge, the non-bridge oxygen, in
particular, can be a cause (O3≡Si-O− centers) [7].
Composition of the undoped nc-Si films is
characterized by the SiOx suboxides with the presence of
large concentrations of oxygen vacancies [8]. As was
shown in work [3], the doping of nc-Si films with gold
results in the effective saturation of dangling silicon
bonds on the Si NC surface and in the SiOx matrix. The
gold atoms act as catalysts for the SiOx to the SiO2
oxidization process. As a result, the concentration of
oxygen vacancies is reduced, and the concentration of
Si-O bonds is increased. These processes determine the
observed the signs of built-in charges.
The hysteresis loop was observed at recording C-V
characteristics in the forward and reverse directions. The
negative sign of flat band voltage shift (∆VFB) points out
to the accumulation of effective positive charge in the
nc-Si film (see Fig. 4). The values of this charge
calculated according to the relation
∆Q = Cm·∆VFB (2)
as functions of the thickness of nc-Si films and the
electric field strength are shown in Figs. 5b and 6,
respectively. As can be seen from Fig. 5b, the value ∆Q
is higher for the structures with thinner films. Higher
accumulation charge in thin films can be caused by less
size of NC and their higher concentration (see the insert
in Fig. 1). Growth of ∆Q in the films doped with gold
can be explained by a large content of negatively
1.0
0.8
0.6
0.4
0.2
0.0
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 46-50.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
49
Fig. 5. Built-in charge (a), accumulated charge (b), and relative
dielectric permittivity (c) vs nanocomposite film thickness: 1 –
undoped film; 2 – gold-doped film.
Fig. 6. Accumulated charge vs electric field strength (d =
100 nm): 1 – undoped film; 2 – gold-doped film.
charged defects in them caused by non-bridge oxygen.
As it was expected, the increase of the accumulated
positive charge with the electric field is observed
(Fig. 6).
Additional measurements of C-V characteristics
with variation of the amplitude of a negative (positive)
bias at a fixed value of the opposite-sign bias were
performed. With increase in the negative bias, the
considerable accumulation of positive charge took place,
while only a small negative charge was accumulated
with increase in the positive bias. Thus, the positive
charge caused by the hole injection from p-Si SCR is
accumulated in the nc-Si film. The barrier height for
holes at the nc-Si / p-Si interface is high enough (about
4.6 eV) in comparison with that of the barrier for
electrons. The direct tunneling of holes is complicated in
this case, but the mechanism of trap-assisted resonant
tunneling through traps in nc-Si is possible [9, 10]. The
current under such a mechanism by orders exceeds the
current of direct tunneling. The high-energy barrier for
holes promotes increasing the storage time of the
accumulated charge.
Reduction of capacity, sometimes with sharp
oscillations, under charge accumulation in p-Si SCR is a
characteristic feature of the measured C-V characteristics
(see the insert in Fig. 4). The Si NC charging at the
increase of a negative bias causes the given effect. It is
obvious that the electric field strength is sufficient for
the tunneling of holes from p-Si in Si NC. At the capture
of charges on Si NC, the capacity Cnc-Si is decreased,
because the number of the electronic states reactive on a
small variable signal at the C-V measurements is
diminished. At the reverse direction of the bias, a
capacity is higher than that at the direct direction, which
is caused by reduction of the negative bias and, as a
result, the release of holes from Si NC. The features of
capacity relaxation are determined by statistical
fluctuations of the potential on heterointerfaces,
dispersion of the characteristic time of defects, and the
Si NC recharging in nc-Si films.
Because the maximal capacity of the structure
under accumulation is determined by the capacity of the
nc-Si film, the relative dielectric permittivity of films
(εd) can be calculated from the relation Cm = εdε0S/d. In
the case of undoped films, the thickness-related
dispersion of εd is high enough. For the films doped with
gold, the values of εd increase with increase in the
thickness and lie in the range 3 to 5 (Fig. 5c). The large
dispersion of εd in the undoped films is explained by
considerable irregularities of the structure, and by a
higher concentration of pores. In the strongly oxidized
gold-doped films, the SiO2 phase fills many pores, and
the concentration of large Si NC is also increased with
thickness. All of these determine the increase of εd with
thickness.
Thus, the researches of C-V characteristics of the
Al/SiO2 film with Si NC/p-Si/Al structures, obtained by
pulsed laser deposition of the film on silicon, have
shown that the structures possess the hysteresis of C-V
characteristics at small voltages and reveal the capture of
the accumulated positive charge. It is established that the
accumulation of charge is determined by the injection of
holes from p-Si. Study of the influence of the formation
conditions and the parameters of nc-Si films on their
charge characteristics allows us to determine that the
positive charge is built in the undoped nc-Si films, and
the films doped with gold contain the negative charge.
Higher accumulation of charge is observed in thinner
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 46-50.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
50
films and in the films doped with gold. The results are
explained by the dependence of the capture efficiency of
holes on Si NC, their sizes and density, the influence of
gold on the Si NC density, and the defect composition of
films. On the other hand, they testify the potential
possibility for creation of non-volatile memory devices
based on structures containing a dielectric with Si
nanocrystals formed by the pulsed laser deposition
method.
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