Interface electronic properties of eterojunctions based on nanocrystalline silicon
For investigations of electronic properties of heterojunctions nanocrystalline Si film (nc-Si)/ monocrystalline Si (c-Si) the technique of temperature dependencies of surface photovoltage was used. Two types of samples fabricated by laser ablation of c-Si target with deposition of nc-Si films onto s...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
1999
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| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Цитувати: | Interface electronic properties of eterojunctions based on nanocrystalline silicon / E.B. Kaganovich, S.I. Kirillova, E.G. Manoilov, V.E. Primachenko, S.V. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 2. — С. 11-14. — Бібліогр.: 14 назв. — англ. |
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irk-123456789-1191072017-06-05T03:03:04Z Interface electronic properties of eterojunctions based on nanocrystalline silicon Kaganovich, E.B. Kirillova, S.I. Manoilov, E.G. Primachenko, V.E. Svechnikov, S.V. For investigations of electronic properties of heterojunctions nanocrystalline Si film (nc-Si)/ monocrystalline Si (c-Si) the technique of temperature dependencies of surface photovoltage was used. Two types of samples fabricated by laser ablation of c-Si target with deposition of nc-Si films onto substrates situated at a distance from the target and onto the plane of target were studied. The temperature dependencies of concentration of charge carriers captured in the traps in the heterojunction interface, and of distribution of density of surface electron states on energy were calculated. The connections between conditions of heterojunction fabrication and their electronic properties are clarified. 1999 Article Interface electronic properties of eterojunctions based on nanocrystalline silicon / E.B. Kaganovich, S.I. Kirillova, E.G. Manoilov, V.E. Primachenko, S.V. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 2. — С. 11-14. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS 73.20.D, 81.15.F http://dspace.nbuv.gov.ua/handle/123456789/119107 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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For investigations of electronic properties of heterojunctions nanocrystalline Si film (nc-Si)/ monocrystalline Si (c-Si) the technique of temperature dependencies of surface photovoltage was used. Two types of samples fabricated by laser ablation of c-Si target with deposition of nc-Si films onto substrates situated at a distance from the target and onto the plane of target were studied. The temperature dependencies of concentration of charge carriers captured in the traps in the heterojunction interface, and of distribution of density of surface electron states on energy were calculated. The connections between conditions of heterojunction fabrication and their electronic properties are clarified. |
| format |
Article |
| author |
Kaganovich, E.B. Kirillova, S.I. Manoilov, E.G. Primachenko, V.E. Svechnikov, S.V. |
| spellingShingle |
Kaganovich, E.B. Kirillova, S.I. Manoilov, E.G. Primachenko, V.E. Svechnikov, S.V. Interface electronic properties of eterojunctions based on nanocrystalline silicon Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Kaganovich, E.B. Kirillova, S.I. Manoilov, E.G. Primachenko, V.E. Svechnikov, S.V. |
| author_sort |
Kaganovich, E.B. |
| title |
Interface electronic properties of eterojunctions based on nanocrystalline silicon |
| title_short |
Interface electronic properties of eterojunctions based on nanocrystalline silicon |
| title_full |
Interface electronic properties of eterojunctions based on nanocrystalline silicon |
| title_fullStr |
Interface electronic properties of eterojunctions based on nanocrystalline silicon |
| title_full_unstemmed |
Interface electronic properties of eterojunctions based on nanocrystalline silicon |
| title_sort |
interface electronic properties of eterojunctions based on nanocrystalline silicon |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
1999 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/119107 |
| citation_txt |
Interface electronic properties of eterojunctions based on nanocrystalline silicon / E.B. Kaganovich, S.I. Kirillova, E.G. Manoilov, V.E. Primachenko, S.V. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 2. — С. 11-14. — Бібліогр.: 14 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T15:14:10Z |
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2025-07-08T15:14:10Z |
| _version_ |
1837092203771461632 |
| fulltext |
11© 1999, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Semiconductor Physics, Quantum Electronics & Optoelectronics. 1999. V. 2, N 2. P. 11-14.
1. Introduction
The interest to electronic properties of interfaces between
nanocrystalline silicon (nc-Si) and monocrystalline silicon
(c-Si) is explained by the possibility of creation of light sourc-
es in visible region of the spectrum on the basis of nc-Si/c-
Si heterostructures. The design of such sources are in initial
stage [1-5]. It is suggested that in the structures nc-Si/c-Si
the heterojunction is formed between the wide-bandgap nc-
Si and narrow-bandgap c-Si, and the expanded bandgap of
nc-Si is related to the quantum limitation of the charge car-
riers in the Si nanocrystals. Nanocrystalline silicon has the
nanocomposite structure, containing Si nanocrystals in the
matrices of oxide, nitride, silicon carbide, amorphous sili-
con, etc. Their nearest relative is the porous silicon (por-Si)
representing a three-phase nanocomposite structure contain-
ing low-dimensional Si nanocrystals in the matrix of the
porous silicon oxide. Recently some information about elec-
tronic properties of por-Si/c-Si structures were obtained
during photovoltage studies [6-8]. To the best of our knowl-
edge, the data about the electronic properties of the nc-Si/c-
Si structures are absent in literature. But such information
are necessary for understanding the properties of these het-
PACS 73.20.D, 81.15.F
Interface electronic properties of heterojunctions
based on nanocrystalline silicon
E.B. Kaganovich, S.I. Kirillova, E.G. Manoilov, V.E. Primachenko, S.V. Svechnikov
Institute of Semiconductor Physics of NASU, 45, prospect Nauki, 252028 Kiev, Ukraine
Abstract. For investigations of electronic properties of heterojunctions nanocrystalline Si film (nc-Si)/
monocrystalline Si (c-Si) the technique of temperature dependencies of surface photovoltage was used.
Two types of samples fabricated by laser ablation of c-Si target with deposition of nc-Si films onto
substrates situated at a distance from the target and onto the plane of target were studied. The tempera-
ture dependencies of concentration of charge carriers captured in the traps in the heterojunction inter-
face, and of distribution of density of surface electron states on energy were calculated. The connections
between conditions of heterojunction fabrication and their electronic properties are clarified.
Keywords: silicon, nanocomposite, boundary electronic states, surface photovoltage.
Paper received 01.06.99; revised manuscript received 05.07.99; accepted for publication 12.07.99.
erojunctions and the designing of optoelectronic devices on
their basis.
The objective of this paper is to investigate, using the
technique of temperature dependencies of pulse photovolt-
age, the nc-Si/c-Si structures fabricated by pulse laser abla-
tion of nc-Si thin films onto c-Si substrates. Since the bound-
ary potential of the c-Si surface, ϕs, plays an important role
in operation of the nc-Si/c-Si structures, in this work the
features of the temperature dependencies of ϕs in the nc-Si/
c-Si structures formed at different conditions of deposition
of thin nc-Si film onto the c-Si substrate of p-type conduc-
tivity (p-Si) are investigated.
2. Samples and experimental technique
The boundary potential of the c-Si surface ϕs (the bending
of energy bands at the surface) was determined using the
technique of capacitance photovoltage at high levels of
generation charge carriers flattening the band bending at the
silicon surface. For the measurements the capacitor was con-
structed: investigated sample nc-Si/c-Si - mica plate with
deposited conductive layer of SnO2. Thin aluminum films
deposited on the edges of the p-Si surface provided Ohmic
E.B. Kaganovich et al.: Interface electronic properties of heterojunctions...
12 SQO, 2(2), 1999
low-noise contacts at low temperatures. The sample was
formed by the deposition onto the c-Si substrate of nc-Si
film by the laser ablation technique using the set-up con-
structed on the basis of the standard vacuum post with re-
sidual pressure 10�3 Pa and pulse solid-state laser YAG: Nd+3
operating in the regime of modulated quality with the irradi-
ation wavelength of 1.06 mm, energy in the pulse 0.2 J, pulse
duration 10 nsec and repetition frequency 25 Hz [9]. As a
target p-Si (KDB-10) and n-Si (KEF-4.5) and substrates of
p-Si (100) were used. Deposition was carried out onto sub-
strates separated from the target, from the direct flow of
particles of erosion flame and to the substrate situated in the
plane of the target, from the reverse flow of particles, being
turned back as a result of collisions with gas molecules in
the chamber [10]. Sputtering was performed in the atmo-
sphere of inert (helium, argon) or reactive (oxygen) gas vary-
ing its pressure from 10�2 Pa to 5·102 Pa. After chemical
and mechanical polishing, the substrates were treated in 49%
solution of HF with subsequent rinsing in distilled water.
The thickness of nc-Si films were about 100 nm.
When the capacitor was illuminated by light flashes of
the ISSh-100 flash lamp with 10 msec duration, repetition
frequency 1Hz and intensity 1021 quanta·cm-2·sec-1, the pho-
tovoltage signal Vph appeared, which was recorded using
the memory oscilloscope. The measurements of Vph were
carried out in the cryostat (pressure 10�4 Pa) when reducing
the temperature T from 300 to 100 K. In order to obtain the
magnitude of ϕs the circuit calibration was done using the
testing electrical pulse. The high intensity of the used light
allowed to rectify the energy bands of c-Si during irradia-
tion [11]. In several cases the magnitude of the photovolt-
age measured during the action of the first pulse of light was
different from that at the second or any subsequent pulse
due to a capture of non-equilibrium charge carriers at the
surface traps during the first pulse. Because of this the sam-
ple after each measurement was heated to the temperature
at which the release of these traps took place and then again
was cooled in the darkness to the temperature of new mea-
surements of Vph first and second values [12].
3. Results and Discussion
Below, the results of measuring temperature dependencies
of interface potential ϕs (T) for two sample sets (Fig. a, c)
and results of calculating their interface electron states and
traps capturing the charge carriers concentration (Fig. b, d)
are presented. The first set of samples was fabricated using
the direct flow of particles, and the second set was formed
using the reverse one.
In the Figure (a) the temperature dependencies of the
interface potential ϕs (T) are shown for three structures from
the first set, obtained by the ablation of p-Si target with dep-
osition onto p-Si substrates. The structures differ by condi-
tions of fabrication. The first one was formed in the helium
atmosphere at the pressure ~ 10�1 Pa, the second one was
fabricated at the residual pressure of the air in the vacuum
chamber, i.e. in the vacuum ~10�3 Pa, the third one was fab-
ricated in the oxygen atmosphere at the pressure 6 Pa. The
first and second nc-Si films did not show the photolumine-
scense (PL) in the visible part of spectrum, but in the third
one the PL with a broad maximum in the range 400-800 nm
was observed. As our previous measurements of absorption
spectra have shown [9], the size of the nanocrystals only in
the third film were less than 3 nm. The numbers of the curves
in the Figure (a) correspond to the types of structures. In the
same Figure (a) the dependence of ϕs (T) for p-Si substrate
before the deposition of nc-Si film was shown (curve 4).
It is seen from the Figure (a) that, as it is usually ob-
served in the p-type samples, the sign of photovoltage is
positive, the depletion of the p-Si surface takes place for the
majority carriers, holes, i.e. the energy bands are bent down.
With decreasing temperature the value of ϕs increases for
all curves 1 to 4, which is related to filling interface electron
states (IES) of the substrate by holes when the Fermi level
in p-Si is displaced to the valence band with temperature
variation. From plots ϕs (Ò) it is possible to calculate the den-
sity of IES in the probed by the Fermi level section of the
bandgap in the surface of p-Si [13]. It was found that for free
p-Si substrate the maximum concentration of IES, equal to
Ns max = 8·1011 cm�2 eV�1 is situated by 0.18 eV below the
middle of the bandgap Ei (Ei � 0.18 eV). For the structure of
the third type Ns max = 4·1011 cm�2eV�1 at Ei � 0.20 eV. For
the first and second structures, it is characteristic that in these
structures the position of the Fermi level in the interface is
practically unchanged with changing temperature. It is fixed
near Ei by high concentration of IES (Ns >1012 cm�2 eV�1).
The dependencies ϕs (Ò) measured during the second
pulse of light (curves 1I to 4I) at Ò < 180 � 200 Ê are below
the curves measured during the first pulse. Such a differ-
ence is due to the capture of non-equilibrium electrons in
the interface traps during the illumination by the first pulse,
which forms the photomemory of potential ϕs [12]. Note
that the most prominent effect is observed for the structures
of the first and second types, which are characterized also
by the greatest magnitudes of ϕs. From the data of the ob-
served photomemory effect the temperature dependencies
of the number of trapped electrons N(T) (Figure (b)) are
calculated [14]. Since the traps are completely filled by elec-
trons just during the first pulse of light, the dependencies
N(T) represent also the temperature dependencies of trap
concentration. The increase of N with decreasing tempera-
ture is related to involvement of more shallow traps, located
closer to the conduction band. It is seen from Figure (b) that
at low temperatures the structures of the first and second
types are characterized by the greatest capture of electrons
(~ 4·1010 cm�2) at shallow traps.
In Figure (c) are presented the dependencies ϕs (T) for
five structures of the second set of samples, obtained by
ablation of p- and n-type Si targets (curves 2, 3, 4 and curves
1, 5, respectively) with deposition onto p-Si substrates of
nc-Si films in the atmosphere of He (curves 1, 2) and Ar
(curves 3-5) at pressures 3·102 Pa and 3·101 Pa, respective-
ly. Thicknesses of all films, except 4, are 100 nm, and the
thickness of the film 4 is 10 nm. All nc-Si films had visible
PL. As it is seen from the Figure (c), this set of samples is
characterized by small values of ϕs (-50 ÷ 150 mV), both
positive, and negative, and by the absence of photomemory
E.B. Kaganovich et al.: Interface electronic properties of heterojunctions...
13SQO, 2(2), 1999
Table. Interface electronic properties of heterojunctions nanocrystalline silicon/ monosilicon
Samples Density of IES Concentration of traps
Ns, cm�2 eV�1 Nmax, cm�2
1st set (p)nc-Si/p-Si
1. He, 10�1 Pa >1012 (Ei) 3·1010
2. 10�3 Pa >1012 (Ei) 4·1010
3. Î2, 6 Pa 4·1011 ( Ei � 0.2 eV) 1·1010
2nd set p(n)nc-Si/ð-Si
1. n, He 2·10 11 (Ei � 0.45 eV) �
2. p, He 1·1011 (Ei � 0.38 eV) �
3. p, Ar 3·1011 (Ei � 0.35 eV) �
4. p, Ar (10nm) 4·1011 (Ei � 0.4 eV) �
5. n, Ar 7·1011 (Ei � 0.35 eV) �
Note. Deposition for the first set of samples was performed from the direct particle flow in the flame, for the second set it was from
the reverse flow. The number of the sample (number of the curve in the figure), type of conductivity of the target, gas in the laser ablation
chamber are indicated.
Figure. Temperature dependencies of interface potential ϕ
s
of p-Si for the first (a) and second (c) set of samples nc-Si/p-Si, and for the first set of
samples the dependence of concentration N of interface electron traps on temperature (b) and for the second set the dependence of IES density on energy
E below the middle of the bandgap (d). The first set of samples: 1- He, 10–1 Pa; 2 - vacuum, 10–3 Pa; 3 - oxygen, 6 Pa. The second set of samples for (n,p)
nc-Si films on p-Si: 1 - n, He; 2 - p, He; 3 - p, Ar; 4 - p, Ar, 10 nm; 5 - n, Ar.
100 140 180 220 260 300
100
200
300
400
500
600
à
3'
2'
3
4'
1'
4
2
1
T, K
ϕ
s
, mV
1
a
100 140 180 220 260 300
-50
0
50
100
150
â
5 s
2
4
1
3
T, K
ϕ
s
, mV
5
c
100 140 180 220
0
1
2
3
4
á
1
2
3
4
T, K
b
N, 1010 cm-2
-0,5 -0,4 -0,3
0
2
4
6ã
5
s
4
3
2
1
E, eV
d
Ns, 1011 cm-2 eV-1
E.B. Kaganovich et al.: Interface electronic properties of heterojunctions...
14 SQO, 2(2), 1999
effect. The calculation of energy distribution of the IES den-
sity below the midgap is presented in Figure (d). It showed
at the level Ei � (0.3�0.5) eV the dependence of the IES
density on the type of sputtered c-Si target (curves 1,2), on
the type of inert gas Ar or He (curves 2, 3 and 1, 5), and on
the thickness of deposited film (curves 3, 4). The maximum
densities of IES reach the values Ns max = (1�7) 1011 cm�
2eV�1.
The obtained results are summarized in the Table. It can
be seen from the Table that the interface electron properties
of heterojunctions nanocrystalline silicon/monocryctalline
silicon, formed by the laser ablation are sensitive to the con-
ditions of fabrication. The measurement of temperature de-
pendencies of the interface potential, calculation of densi-
ties of interface electron states and interface traps, captur-
ing the nonequilibrium charge carriers make it possible to
conclude the following. The highest (>1012 cm�2eV�1) den-
sity of IES is observed in the structures the films of which
are fabricated during the deposition from the direct particle
flow of the erosion flame in vacuum or in the inert gas at
low pressures. Under the same conditions of film fabrica-
tion the highest (~4·1010 cm�2) density of traps capturing
the nonequilibrium charge carriers is generated. It is seen
from Figure (b) that these traps are mostly shallow, captur-
ing the nonequilibrium carriers at lower temperatures. Dur-
ing the particle deposition from the direct flow at higher
pressure in the oxygen atmosphere both IES density and
concentration of shallow traps is reduced. This reduction is
related to the interaction of particles sputtered by the laser
beam with the oxygen molecules, as a result, their energy
becomes lower and formation of the nc-Si film on the p-Si
substrate takes place in conditions of creation of lesser num-
ber of defects in the substrate. Besides, oxidation of the sub-
strate and of deposited particles may play a definite role in
reduction of IES density.
The electron microscopy confirmed that nc-Si films fab-
ricated in deposition from the reverse particle flow in the
inert ambient are more uniform as compared to the films
obtained in the direct particle flow. In the reverse flow their
energy is greatly reduced due to interaction with the gas
molecules. This results in the formation of nc-Si films with
slightly poorer adhesion to the surface, but more uniform
and with lower defect concentration in the film-substrate
interface. This is confirmed by the data obtained in the sec-
ond set of samples. It is seen from the Table, that the IES
density for nc-Si film formation in the reverse particle flow
is as a rule lower than that for the films from the direct flow
at lower gas pressures. Besides, in formation of the nc-Si/p-
Si systems from the reverse particle flow the traps for non-
equilibrium charge carriers are not created. It should be not-
ed that in the second set of samples the IES density is lower
for structure fabrication at higher pressure of inert gas (heli-
um as compared to argon), and also is lower for the struc-
tures obtained at other equal conditions for the use of iso-
type targets and substrates.
These results are used for the control by the spectrum of
local states of heterojunctions fabricated on the basis of
nanocrystalline silicon and for revealing of their role in elec-
tron, photoelectron, electroluminescense properties of these
heterojunctions.
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