Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure
In this work, the growth properties of Ge₁₋xSix epitaxial films grown on Ge substrates were investigated. The structural perfection of the films was controlled by electron diffraction, electron microscopic and X-ray diffraction methods. It has been established that the surface structure of the sa...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2009
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| Цитувати: | Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure / Sh.M. Abbasov, G.T. Aghaverdiyeva, Z.A. Ibrahimov, U.F. Farajova, R.A. Ibrahimova, Heyder Mehdevi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 4. — С. 357-361. — Бібліогр.: 13 назв. — англ. |
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irk-123456789-1188362017-06-01T03:06:24Z Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure Abbasov, Sh.M. Aghaverdiyeva, G.T. Ibrahimov, Z.A. Farajova, U.F. Ibrahimova, R.A. Mehdevi, Heyder In this work, the growth properties of Ge₁₋xSix epitaxial films grown on Ge substrates were investigated. The structural perfection of the films was controlled by electron diffraction, electron microscopic and X-ray diffraction methods. It has been established that the surface structure of the sample Ge/Ge₁₋xSix changes after irradiation by accelerated electrons Ф = 5×1016 cm⁻², and generated are surface defects which play the role of traps for change carriers. 2009 Article Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure / Sh.M. Abbasov, G.T. Aghaverdiyeva, Z.A. Ibrahimov, U.F. Farajova, R.A. Ibrahimova, Heyder Mehdevi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 4. — С. 357-361. — Бібліогр.: 13 назв. — англ. 1560-8034 PACS 42.25.Bs, 78.40.-q, 81.15.-z http://dspace.nbuv.gov.ua/handle/123456789/118836 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 |
| description |
In this work, the growth properties of Ge₁₋xSix epitaxial films grown on Ge
substrates were investigated. The structural perfection of the films was controlled by
electron diffraction, electron microscopic and X-ray diffraction methods. It has been
established that the surface structure of the sample Ge/Ge₁₋xSix changes after irradiation by
accelerated electrons Ф = 5×1016 cm⁻², and generated are surface defects which play the
role of traps for change carriers. |
| format |
Article |
| author |
Abbasov, Sh.M. Aghaverdiyeva, G.T. Ibrahimov, Z.A. Farajova, U.F. Ibrahimova, R.A. Mehdevi, Heyder |
| spellingShingle |
Abbasov, Sh.M. Aghaverdiyeva, G.T. Ibrahimov, Z.A. Farajova, U.F. Ibrahimova, R.A. Mehdevi, Heyder Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Abbasov, Sh.M. Aghaverdiyeva, G.T. Ibrahimov, Z.A. Farajova, U.F. Ibrahimova, R.A. Mehdevi, Heyder |
| author_sort |
Abbasov, Sh.M. |
| title |
Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure |
| title_short |
Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure |
| title_full |
Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure |
| title_fullStr |
Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure |
| title_full_unstemmed |
Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure |
| title_sort |
influence of electron irradiation on spectra of light electroreflection from the surface of ge/ge₁₋xsix heterostructure |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2009 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118836 |
| citation_txt |
Influence of electron irradiation on spectra of light electroreflection from the surface of Ge/Ge₁₋xSix heterostructure / Sh.M. Abbasov, G.T. Aghaverdiyeva, Z.A. Ibrahimov, U.F. Farajova, R.A. Ibrahimova, Heyder Mehdevi // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 4. — С. 357-361. — Бібліогр.: 13 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
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2025-07-08T14:45:20Z |
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2025-07-08T14:45:20Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 4. P. 357-361.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
357
PACS 42.25.Bs, 78.40.-q, 81.15.-z
Influence of electron irradiation on spectra of light electroreflection
from the surface of Ge/Ge1-xSix heterostructure
Sh.M. Abbasov1, G.T. Aghaverdiyeva1, Z.A. Ibrahimov2, U.F. Farajova1, R.A. Ibrahimova3, Heyder Mehdevi1
1Institute of Radiation Problems, Azerbaijan National Academy of Sciences
2Institute of Physics, Azerbaijan National Academy of Sciences
3Institute of Cybernetics, Azerbaijan National Academy of Sciences
Phone: (+99412) 393-391; fax. (+99412) 398-318; e-mail: shabbasov@rambler.ru
Abstract. In this work, the growth properties of Ge1-xSix epitaxial films grown on Ge
substrates were investigated. The structural perfection of the films was controlled by
electron diffraction, electron microscopic and X-ray diffraction methods. It has been
established that the surface structure of the sample Ge/Ge1-xSix changes after irradiation by
accelerated electrons Ф = 51016 cm-2, and generated are surface defects which play the
role of traps for change carriers.
Keywords: germanium-silicon alloy, epitaxial film, heterostructure, optical absorption,
electroreflection.
Manuscript received 26.01.09; accepted for publication 10.09.09; published online 30.10.09.
1. Introduction
Recently interest in periodical structures based on Ge
and Si:Ge/Ge1-xSix [1, 2] has increased. These structures
referred to a class of superlattices with strained layers
allow to essentially expand the opportunities of initial
materials [3] traditionally used in practice as well as are
of interest, in particular for detectors of infrared [4] and
millimeter ranges of wavelengths. Besides, the
possibility to observe quantum size effects with their
perspectives in electronics is now widely discussed [5]
and can be pronounced in the structures with hyperfine
layers at low temperatures.
2. Experimental
In this work, the singularities of the growth of Ge1-xSix
epitaxial films grown on Ge (111) substrates by the
method of molecular-beam condensation in vacuum
10-4 Pa and preparation of photosensitive p-n junctions
on their basis are investigated.
With this aim, optimal conditions were developed
to obtain structurally perfect (W1/2 = 90…100 arc sec –
half-width of the rocking curve in X-ray diffraction)
epitaxial films Ge1-xSix possessing p- and n-types of
conductivity with the thickness 0.5…1 m,
concentration ((n, p77 К) = 11016…11017 cm-3) and
charge carrier mobility (n,p(77 К) =
(2.5…3)104 cm2/Vs). The epitaxial films were grown
on Ge (111) substrates at the condensation rate υc =
8…10 Å/s and temperature of the substrates Тs =
653…673 К.
The thickness of separate layers in the superlattice
was 2 to 20 nm in comparison with its total thickness 2
to 4 m, the content of Si in alloy layers was 5…15 %.
Structural perfection of the films was controlled
by electron diffraction, electron microscopic and X-ray
diffraction methods (Fig. 1). For the purpose of
obtaining the films with n- and p-type conductivity,
perfect structure and necessary electrophysical
parameters, an additional compensating vapor from a Sb
source was used in the growth process [3].
One of the methods to reduce the density of surface
defects is preparation of active elements in the same
technological cycle. By this way, p-n homostructures
were obtained as intersecting bands in one technological
cycle without vacuum deterioration. After deposition of
the first system of bands p-Ge1-xSix, the baffler was
closed, and in a certain time after establishment of the
necessary temperature conditions and mask
displacement, the baffler was opened again, and the
second system of n-Ge1-xSix bands was deposited.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 4. P. 357-361.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
358
Fig. 1. Microphotos and electron diffraction patterns of the
films Ge1-xSix (х = 0.15), d = 100 nm; Тs = 490 K (а),
500 K (b), 530 K (c). Magnification ×3500.
3. Results and discussion
The explanation of the effects observed during the
experiments [5] as well as creation of fundamentally
new devices based on the obtained structures demands a
reliable control of the parameters of deposited layers and
development of methods for determining the
characteristics of electron gas in them. One of the
suitable methods for the superlattice Ge1-xSix grown on
Ge substrates to investigate periodic potential and
electron energy band spectrum, which requires no
application of complicated apparatus, is the method of
light electroreflection from the surface of
semiconductor [6].
The samples were irradiated using a linear electron
accelerator of ELA-6 type with the nominal output
energy 4.5 MeV. The accelerator operated with the
frequency 50 Hz and pulse duration 2.5 ms. Besides, the
average current of the accelerated electrons, by which
the sample was irradiated, equaled to 2 A. The sample
was irradiated via a cryostat window covered by a
beryllium foil with the thickness 100 m.
In this work, the spectra of light elecroreflection
from the surface of periodic semiconductor structures
Ge/Ge1-xSix with various periods were measured in the
near IR spectral range and analyzed. Their distinctive
features were revealed in comparison with the spectra of
light electroreflection from thick layers of solid solution
Ge1-xSix. The possibility to use this method for
diagnostics of separate parameters of the superlattice
was shown. An essential difference in the characters of
the spectra of light electroreflection from the structure
with tunnel transparent and opaque potential barriers
was found out.
Some parameters of the obtained structures are
summarized in Table. The mean concentration of Si in
the superlattice (xsl) and amplitude of Si content
variations in neighboring layers (x) were determined
by the method of X-ray diffraction analysis. The
measurement procedure of the spectra of light
electroreflection from the surface of the samples differed
from that applied before in the work [7] according to the
use of ditch with capillary layer of electrolyte. It made
possible to carry out measurements in the neighborhood
of lower bound of fundamental absorption band. In the
near IR spectral region (0.7…1.2 eV), the depth of light
penetration into crystal was of the order of several tens
of micrometer in comparison with a visible frequency
band [8], which allows determining the properties of the
superlattice as a whole.
Let’s assume that this periodic system is
characterized by sufficiently perfect boundaries of
heterojunctions Ge/Ge1-xSix (the thickness of the
transition region is much smaller than that of a separate
layer). Then the potential relief can be approximated by
alternate rectangular wells separated by sufficiently thick
barriers excluding the effect of tunneling. It’s evident
that the spectra of light electroreflection from such a
system should possess the properties inherent to the
spectra of electroreflection from the separate layers Ge
and Ge1-xSix. Let us analyze how this model agrees with
the experimental results obtained for the specific
structures with thick enough layers (Fig. 2). The spectra
of light electroreflection from the structures 1 and 4
possess series of well-allowed (broadening parameter is
close to 10 meV) resonance peaks relatively shifted from
one another. The resonance peak Е01 is connected with
direct (at a point к = 0) transitions in the layers Ge, the
peak Е02 – in the layers Ge1-xSix. The spectra of light
electroreflection from the surface of the superlattice on
the surface of thick (4 to 8 m) alloy layers Ge1-xSix
(Fig. 3) differ from each other by a total number and
relative position of resonance peaks.
Table. Composition and parameters of the samples
S
am
pl
e
P
er
ce
nt
ag
e
S
i
(a
t.%
)
In
it
ia
l c
on
ce
nt
ra
ti
on
of
th
e
ca
rr
ie
rs
a
t
77
K
(
cm
-3
)
M
ob
ili
ty
0
, c
m
2 /V
·s
d,
n
m
S
pe
ci
fi
c
re
si
st
an
ce
(O
hm
c
m
)
at
T
=
2
93
K
1
2
3
4
0
5
10
15
1.431015
11016
1.371016
1.01017
3·104
2.75·104
2.62·104
2.5·104
135
132
130
120
1.38
1.45
3.0
6.45
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 4. P. 357-361.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
359
The comparison of the curves in Figs 2 and 3
shows that elastic stress present in the layers of the
periodic structure shifts the position of the resonance
peaks. The low-energy boundary of absorption region
caused by direct electron transitions in Ge layers is
shifted to much more shortwave spectral region.
The spectra of reflection of Ge-Si were investigated
in the works [3, 9, 10]. The analysis shows that the first
maximum for Ge lies in the region 2.0 to 2.3 eV, and for
Si – in the vicinity of 3.3 eV. The first maximum in the
solid solution Ge-Si is between these maxima, in
dependence on the content of Si.
In the work [11], it has been shown that the
effective mass of current carriers determined using
infrared reflection spectra in the solid solution Ge-Si
doesn’t depend on the concentration of the carriers as a
concentration function and corresponds to the absolute
values of the electron effective mass in Si, which agrees
with the character of the band structure for the solid
solutions Ge-Si.
The thin structure of the spectra of light
electroreflection from the surface of the samples 1, 4
(Fig. 2а; the spectrum for the sample 4 is similar to that
for the sample 1), apparently, is connected with splitting
of degenerate states of the valence band at the point
к = 0 under the action of deformation breaking the
symmetry of crystal lattice in a separate layer. The
splitting value of the peaks Е01-Е01 (Е02-Е02) in the
spectra of light electroreflection (Fig. 2а, d) for the
investigated samples varies within the range of several
hundreds of electron-volt, which corresponds to elastic
stress values in the layers 108…109 Pa [10].
Fig. 2. Spectra of electroreflection for heterostructures Ge/Ge1-
xSix before and after irradiation. Solid line before irradiation.
1 – х = 0; 2 – х = 0.05; 3 – х = 0.10; 4 – х = 0.15; Ф =
(1…5)1016 cm-2.
Fig. 3. Spectra of electroreflection of Ge1-xSix alloy samples
before and after irradiation. Solid line – before irradiation. Ф =
(1…5)1016 cm-2.
The reduction of the superlattice period without
change of Si content in the layers leads to broadening the
peaks in the electroreflection spectra in consequence of
relative increase of the role of reflected light from
transition regions. The thin structure of the resonant
peaks Е01 (2) in spectral curves may vanish (Fig. 2с).
The rise of Si concentration in the layers Ge1-xSix
(compare the curve d in Fig. 2 with the ones а, с)
displaces the resonant peak Е02 to the side of high
energies, increases the broadening parameter and the
size of valence band splitting at the point к = 0, which
result in rise of the number of resonant peaks in spectral
curves. For the simplicity of comparison, the amplitudes
of separate peaks were multiplied by the correspondent
factor in the dependences R()/R(). Shown in Fig. 2b
is the spectrum of light electroreflection from the sample
2 differing by a higher Si content but a low amplitude of
its variation (x 2 %) in the neighboring layers. An
essential broadening (up to 50 meV) the resonance peaks
is apparently conditioned by considerable (in
comparison with d) rise of transition regions’ sizes. It’s
evident that deviation from periodicity of the system
should lead to broadening the spectral maxima, too.
Thus, in a general case the quality and some
electron characteristics of the obtained structures can be
determined using the spectra data of light
electroreflection and the value of the broadening
parameter for resonant bands. Besides, the difference of
peaks’ positions Е02-Е01 allows evaluating the total (for
conductivity band and valence band) amplitude U of
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 4. P. 357-361.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
360
the potential relief taking into account the stress in the
structures. It equals to U 0.02…0.03 eV for the
structures 1, 3 and U 0.1 eV for the structure 4. The
value of the potential amplitude in the spectra of light
electroreflection in the visible spectral range gives the
same order of magnitude at sequential etching the
layers [7].
The negative differential conductivity in current-
voltage characteristics of this periodic structure at
current flowing along the layers of the superlattice can
also occur as a result of transversal diffusion of charge
carriers from Ge layers with a high mobility to the
neighboring alloy layers with a low mobility [3]. In the
reverse situation (the main charge carriers are
concentrated in the layers of solid solution), a
superlinear current-voltage characteristics appears.
Superlinearity or sublinearity of the current-voltage
characteristics is connected with electron transitions
between split bands when heating as a consequence of
elastic stress in the system, and it can be one of the
probable reasons for high nonlinearity occurrence in the
high-frequency characteristics observed in the
experiments [10].
The measurement has shown that there is an
absorption band for pure germanium in the vicinity of
λ = 24.2 m (Fig. 4). Absorption bands close to 21.0,
20.8 and 20.6 m are correspondingly revealed for the
samples with 5, 10 and 15 atomic percents of silicon. As
it is evident, the absorption peaks for the solutions with
different contents of silicon are very close. The
absorption spectrum shifts in the direction of short
wavelengths with rise in the content of silicon. A
significant increase of the absorption coefficient in thin
films in the range of short wavelengths in comparison
with pure germanium apparently indicates a cluster
nature of the vibrational spectrum [11].
Fig. 4. Dependence of lattice absorption coefficient on the light
wavelength: 1 – for pure germanium; 2, 3, 4 – for solid
solution with 5, 10 and 15 at.% of silicon, accordingly.
In the works [8, 11-13], absorption within the range
9 to 48 m was studied. In the alloy Ge-Si, besides
absorption inherent to pure germanium and silicon, new
absorption bands 214 and 508 cm-1 that are less sensitive
to changes of the alloy content, but demonstrate some
changes observed in their shape and height (Fig. 4).
4. Conclusions
Investigation of electroreflection spectra for thin
epitaxial Ge-Si layers shows that the number of peaks
and their amplitude change as a result of electron
irradiation of the samples. These changes can be
explained by appearance of surface structural defects in
the course of irradiation, which serve as traps for charge
carriers.
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 4. P. 357-361.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
361
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