Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy
The main difficulty in obtaining the lateral elemental composition distribution maps of the semiconductor nanostructures by Scanning Auger Microscopy is the thermal drift of the analyzed area, arising from its local heating with the electron probe and subsequent shift. Therefore, the main goal of...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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irk-123456789-1216512017-06-16T03:02:30Z Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy Ponomaryov, S.S. Yukhymchuk, V.O. Valakh, M.Ya. The main difficulty in obtaining the lateral elemental composition distribution maps of the semiconductor nanostructures by Scanning Auger Microscopy is the thermal drift of the analyzed area, arising from its local heating with the electron probe and subsequent shift. Therefore, the main goal of the study was the development of the effective thermal drift correction procedure. The measurements were carried out on GeSi/Si nanoislands obtained with molecular beam epitaxy by means of Ge deposition on Si(100) substrate. Use of the thermal drift correction procedure made it possible to get the lateral elemental composition distribution maps of Si and Ge for various types of GeSi/Si nanoislands. The presence of the germanium core and silicon shell in both the dome GeSi/Si nanoislands and pyramid ones was established. In the authors’ opinion, this type of elemental distribution is a result of the completeness of the interdiffusion processes course in the island/wetting layer/substrate system, which play the key role in the nucleation, evolution and growth of GeSi/Si nanoislands. The proposed procedure of the thermal drift correction of the analyzed area allows direct determination of the lateral composition distribution of the GeSi/Si nanoislands with the size of the structural elements down to 10 nm. 2016 Article Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy / S.S. Ponomaryov, V.O. Yukhymchuk, M.Ya. Valakh // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 4. — С. 321-327. — Бібліогр.: 28 назв. — англ. 1560-8034 DOI: 10.15407/spqeo19.04.321 PACS 81.07.Ta, 68.65.Hb, 68.37.Xy http://dspace.nbuv.gov.ua/handle/123456789/121651 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 |
The main difficulty in obtaining the lateral elemental composition distribution
maps of the semiconductor nanostructures by Scanning Auger Microscopy is the thermal
drift of the analyzed area, arising from its local heating with the electron probe and
subsequent shift. Therefore, the main goal of the study was the development of the
effective thermal drift correction procedure. The measurements were carried out on
GeSi/Si nanoislands obtained with molecular beam epitaxy by means of Ge deposition on
Si(100) substrate. Use of the thermal drift correction procedure made it possible to get
the lateral elemental composition distribution maps of Si and Ge for various types of
GeSi/Si nanoislands. The presence of the germanium core and silicon shell in both the
dome GeSi/Si nanoislands and pyramid ones was established. In the authors’ opinion,
this type of elemental distribution is a result of the completeness of the interdiffusion
processes course in the island/wetting layer/substrate system, which play the key role in
the nucleation, evolution and growth of GeSi/Si nanoislands. The proposed procedure of
the thermal drift correction of the analyzed area allows direct determination of the lateral
composition distribution of the GeSi/Si nanoislands with the size of the structural
elements down to 10 nm. |
| format |
Article |
| author |
Ponomaryov, S.S. Yukhymchuk, V.O. Valakh, M.Ya. |
| spellingShingle |
Ponomaryov, S.S. Yukhymchuk, V.O. Valakh, M.Ya. Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Ponomaryov, S.S. Yukhymchuk, V.O. Valakh, M.Ya. |
| author_sort |
Ponomaryov, S.S. |
| title |
Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy |
| title_short |
Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy |
| title_full |
Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy |
| title_fullStr |
Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy |
| title_full_unstemmed |
Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy |
| title_sort |
drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning auger microscopy |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2016 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/121651 |
| citation_txt |
Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy / S.S. Ponomaryov, V.O. Yukhymchuk, M.Ya. Valakh // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 4. — С. 321-327. — Бібліогр.: 28 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T20:17:02Z |
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2025-07-08T20:17:02Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 321-327.
doi: https://doi.org/10.15407/spqeo19.04.321
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
321
PACS 81.07.Ta, 68.65.Hb, 68.37.Xy
Drift correction of the analyzed area during the study
of the lateral elemental composition distribution in single
semiconductor nanostructures by scanning Auger microscopy
S.S. Ponomaryov*, V.O. Yukhymchuk, M.Ya. Valakh
V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
*Correspondence e-mail: s.s.ponomaryov@gmail.com; phone: +38(095)-457-02-28
Abstract. The main difficulty in obtaining the lateral elemental composition distribution
maps of the semiconductor nanostructures by Scanning Auger Microscopy is the thermal
drift of the analyzed area, arising from its local heating with the electron probe and
subsequent shift. Therefore, the main goal of the study was the development of the
effective thermal drift correction procedure. The measurements were carried out on
GeSi/Si nanoislands obtained with molecular beam epitaxy by means of Ge deposition on
Si(100) substrate. Use of the thermal drift correction procedure made it possible to get
the lateral elemental composition distribution maps of Si and Ge for various types of
GeSi/Si nanoislands. The presence of the germanium core and silicon shell in both the
dome GeSi/Si nanoislands and pyramid ones was established. In the authors’ opinion,
this type of elemental distribution is a result of the completeness of the interdiffusion
processes course in the island/wetting layer/substrate system, which play the key role in
the nucleation, evolution and growth of GeSi/Si nanoislands. The proposed procedure of
the thermal drift correction of the analyzed area allows direct determination of the lateral
composition distribution of the GeSi/Si nanoislands with the size of the structural
elements down to 10 nm.
Keywords: thermal drift correction, GeSi/Si nanoislands, lateral composition distribution.
Manuscript received 01.06.16; revised version received 14.09.16; accepted for
publication 16.11.16; published online 05.12.16.
1. Introduction
In recent decades, nanoobjects with charge carriers
subjected to three-dimensional confinement attract
considerable interest of researchers. Spatial confinement
of charge carriers leads to the splitting of the system
energy levels, providing atomic properties of such objects
(quantum dots or nanoislands). Shape, size, elemental
composition and elastic stress field distribution in
nanoislands’ bulk define their energy spectrum.
Control of both individual and group quantum dots
characteristics opens new horizons of possibilities for
their practical applications in lasers, communication
systems, quantum informatics (computations) and
photonics [1-4]. Also, it should be noted that GeSi/Si
nanoislands are easily compatible with already existing
and widespread silicon technology, which allows easy
integration of quantum dots in micro- and optoelectronic
components.
Understanding the nucleation and evolution nature
of the quantum dots is of fundamental importance from
the viewpoint of quantum mechanics and materials
science.
It is important to control the values of the discrete
energy levels of individual GeSi/Si nanostructures for
the successful practical application of quantum dots in
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 321-327.
doi: https://doi.org/10.15407/spqeo19.04.321
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
322
different industrial sectors. It is known that the elastic
stress distribution in the defect-free nanoislands depends
exceptionally on chemical composition distribution.
Therefore, the detailed study of this characteristic is a
first-priority for understanding the atomic properties of
investigated nanostructures.
The significant amount of methods for the study of
structural parameters and nanostructures chemical
composition, including a combination of microscopic,
spectroscopic, diffraction methods, and sometimes
chemical etching is used nowadays [5]. Despite the great
variety of methods, each of them has a number of
advantages and drawbacks, as a result, the data obtained
by these methods has a contradictory character [6-8].
Raman spectroscopy [9-11], X-ray diffraction [12],
X-ray photoelectron spectroscopy and Auger electron
spectroscopy (AES) are widely used for characterization
of the nanoislands, however, they have a low locality
and provide averaged information over a statistical
ensemble of the nanostructures. Transmission electron
microscopy (TEM) in combination with electron energy
loss spectroscopy (EELS) or energy-dispersive X-ray
spectroscopy (EDX) provides high spatial resolution
[13]. However, EELS and EDX require a long period of
spectra registration. On the other hand, the sample
preparation process for TEM measurements is protracted
and complicated. The surface sample area suitable for
analysis is sufficiently small for reliable statistical
results and data obtained in the process of the chemical
composition analysis by TEM are averaged along the
vertical axis (axis of the probe). Another drawback of
the technique is the uncertainty of the foil surface area
position for analysis relatively to the nanoislands growth
axis. All of the above-mentioned drawbacks in the
sample preparation procedure are also inherent to
scanning tunneling microscopy, which determines the
crystal lattice distortion at the atomic level. At the same
time, determination of the elemental composition using
the elastic stress fields distribution in the cluster’s bulk
is not trivial. Another interesting technique is a
combination of atomic force microscopy and selective
chemical etching [14-17]. Alternate etching procedure
and sample scanning give the representation of the
surfaces with the identical chemical composition.
However, the presence of the strong elastic stress fields
distorts the quantum dot surface geometry, on the one
hand, and affects the selective etching rate, on the other
hand.
2. Materials and methods
Use of scanning Auger microscopy (SAM) for studying
the individual nanoislands composition is promising due
to high locality of the technique [18]. The lateral size of
analyzed area can reach down to 3…5 nm, and Auger-
electron escape depth is about 1 nm [19]. The pioneering
works in application of SAM to study the elemental
composition of individual GeSi/Si nanoislands were
performed by Maximov et al. [20]. However, the low
spatial resolution of the used instrument has allowed
working only with objects having the lateral sizes from
125 up to 600 nm, which is much higher than that of
nanostructures sizes being of practical interest. It’s
inevitable to have a deal with the problem of analyzed
area drift during long-time registration of the Auger
spectra and at reducing the size of investigation objects.
Effective compensation of this shift is a key problem
when registering the lateral elemental composition
distribution on the sample surface containing GeSi/Si
nanoislands.
Objects of investigation in this study are arrays of
GeSi nanoislands formed under the self-induced
Stranski–Krastanov growth mode using “BALZERS”
molecular beam unit under the residual atmospheric
pressure of 10–7 – 10–8 Pa [21].
The study was performed using two samples. А1
sample was obtained by Ge deposition on Si (100)
substrate at the temperature 700 °С and deposition rate
0.07 Å/s. The nominal thickness of the Ge layer was 8.7
monolayers (ML). The buffer layer containing 10 at.%
of Ge with the 10-nm thickness was grown on the
Si (100) substrate on А2 specimen before Ge deposition.
Germanium film with the nominal thickness of 8 ML
was deposited on the buffer layer with the same rate and
at the same temperature as in the case of A1 specimen.
The investigation was performed on the scanning
Auger microprobe JAMP-9500F of JEOL production
(Japan) with the spatial resolution in the secondary
electron image mode of 3 nm. The instrument is
equipped with the hemispherical Auger electrons
analyzer with the energy resolution ΔE/E of 0.05 to
0.6% and the ion gun for the layer-by-layer analysis with
Ar+ ion accelerating voltage of 10 to 4000 V. The
diameter of ion beam is about 120 μm, and the vacuum
of the specimen chamber was better than 5·10–7 Pa.
3. Results
The main goal of the study is to obtain high spatial
resolution maps of the elemental composition
distribution on the GeSi/Si nanoislands and wetting layer
surface [22]. Based on the above-mentioned maps, it is
possible to determine the character of Ge and Si
distribution in the cluster bulk and evaluate the scale and
role of the interdiffusion in the process of nucleation,
evolution, and growth of GeSi/Si nanostructures.
The nanoislands’ lateral sizes of practical interest
lie within the range from 5 to 100 nm. The study of such
objects requires the use of high spatial resolution
operation modes.
It is necessary to use the minimal diameter of the
electron probe in the above-mentioned modes, which can
be only achieved by reducing its current. On the other
hand, decreasing the probe current leads to disastrous
declining of the Auger signal intensity, and it is vital
significantly to increase the signal registration time
(from 3 to 15 hours) to obtain the acceptable signal-to-
noise ratio during Auger spectra and maps registration.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 321-327.
doi: https://doi.org/10.15407/spqeo19.04.321
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
323
Fig. 1. The series of three successive secondary electron images of the analyzed sample area registered with an interval of 90 s.
The drift of the analyzed area during the measurement
process
The drift of the analyzed area during the measurement
process is the critical problem in operation modes with
high locality. The sequence of the GeSi/Si nanoislands
pictures in the secondary electron mode recorded for the
intervals of 90 s is shown in Fig. 1. As seen from this
figure, the investigated section of the sample surface
moves smoothly, chaotically wandering around the initial
position. According to our observations, the diameter of
such wandering region can be up to 100 nm and
displacement velocity of the analyzed object – up to
20 nm/s. It follows from the aforesaid that the
measurement time for which the investigated object
haven’t enough time to shift by a significant distance (e.g.,
0.1 of the analyzed object diameter) should not exceed
25…30 s. It is obvious that the stated time is insufficient
for significant Auger signal accumulation at the low probe
current required to obtain the high-resolution image. Thus,
the Auger signal registration of such objects is possible
only in the case of its accumulation in the series of a large
number of short successive measurements in combination
with correction of the analyzed object position each time
after every this measurement.
The proposed correction procedure removes
aftereffects of the analyzed area drift and does not
eliminate its reasons. So, the issue of clarifying the
nature of the effect is not essential for us. Nevertheless,
let’s say a few words regarding this issue. It is widely
believed that the drift of the analyzed area under the
electron probe is caused by electric charge [20]. In other
words, it is believed that accumulation of the negative
charge on the sample surface due to its low electrical
conductivity creates an electric field that can shift the
high-energy electrons of the primary beam (30 keV)
from their initial trajectory. According to our
observations, the charging effect begins to appear first
on the low-energy electrons. In the case of charging, the
Auger peaks were primarily shifted from their standard
energy positions and then the whole Auger spectrum was
deformed starting with the low-energy range. Further
intensification of charging leads to a change in the
brightness of the secondary electron image: brightness
spontaneously and gradually rises to a certain level and
then comes to its dramatic disruption. Numerous bands
of the abrupt image shift appear on the secondary
electron image under strong charging that are
accompanied by spontaneous modulation of the
brightness. The above-mentioned attributes of charging
are not observed in our case. Moreover, the ability of the
charging neutralization of the dielectric samples by
irradiation of them with the low-energy Ar+ ion beam is
provided in the Auger microprobe JAMP 9500F. The
use of the specified procedure to the Ge/Si samples did
not influence the observed character of the analyzed area
drift. All these facts do not testify in favor of the
electrical nature of the drift. We tend to consider that the
analyzed area drift has a thermal nature. Local heating
the analyzed sample site with following thermal
expansion occurs due to the low thermal conductivity of
the sample under the electron probe, which leads to the
smooth drift of the analyzed area. It should be added for
completeness of this issue that the drift effect is
practically absent (hardly observed) on the copper
samples with high electrical and thermal conductivity
characteristics.
The procedure of the thermal drift correction
The principle of the successive comparison at regular
time intervals of the analyzed area initial image and the
current one subjected to the drift with its subsequent
compensation was the basis for the developed procedure
of thermal drift correction. This correction was
performed every 10–15 s. A single raster line of the
Auger map was recorded for this time, and the array of
GeSi/Si nanoislands exactly does not shift to a distance
more than 10 nm. The positioning accuracy during
matching these two images was ±3.5 nm. The ultimate
spatial resolution of the registered Auger maps was
practically defined by the above-mentioned parameters.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 321-327.
doi: https://doi.org/10.15407/spqeo19.04.321
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
324
Fig. 2. Ge (a) and Si (b) Auger maps of the analyzed surface section of A1 sample under magnification 50 000 without thermal
drift correction.
Fig. 3. Ge (a) and Si (b) Auger maps of the same analyzed surface section of A1 sample under magnification 50 000 with thermal
drift correction.
Let us illustrate the effect of thermal drift
procedure application. The Auger maps of germanium
(a) and silicon (b) registered on the same surface section
of A1 sample containing GeSi/Si nanostructures at
magnification ×50 000 without thermal drift correction
are shown in Fig. 2. The analytical Auger peaks of
GeLMM with the energy 1147 eV and SiLVV with the
energy 92 eV were used for registration of the specified
maps. Each map consisted of 256 lines, and each line
contains 256 pixels. The single line of the germanium
Auger map was recorded for the total time of 100 s due
to the low intensity of the GeLMM peak, while the single
line registration time of intensive SiLVV peak was only
20 s. Thus, the total acquisition time for the obtained
Auger maps for Ge and Si was ~7 and 1.5 hours,
respectively. In Fig. 2, as further for all Auger maps, hot
color corresponds to a high content of the analyzed
element, while a cold color – to its low content.
Ge (a) and Si (b) Auger maps of the same surface
section of A1 sample, as in Fig. 2, registered using
thermal drift correction are shown in Fig. 3. The single
line registration time of Ge Auger map was 10 s, which
prevented the shift of the GeSi/Si nanoislands array to
the significant distance. Immediately thereafter, the
above-described procedure of image drift correction was
performed for 11 s. The specified line registration time
was not enough for accumulation of acceptable signal-
to-noise ratio of the Auger map. Therefore, 9 additional
passes through the same raster with subsequent
summation were performed to improve this ratio during
map registration. Thus, the total acquisition time of the
single line signal reached the same 100 s as in the case
of Fig. 2a. As a result, the total registration time of the
Ge Auger map, including signal acquisition time and
image drift correction, was ~15 hours. The same
operation mode was used for Si Auger map registration
(Fig. 3b). Image drift correction was performed after
each line registration, which lasted 10 s. In this case,
two passes through the raster were enough to achieve
the acceptable signal-to-noise ratio. As a result, the
total analysis time of the single line was 20 s, as in the
case of Fig. 2b, and the total registration time of the Si
Auger map was ~3 hours. Comparison of the Auger
maps quality shown in Figs. 2 and 3 leads to a
conclusion about the efficiency of using the proposed
image drift correction procedure for the elemental
composition distribution investigation of structures with
nanometric sizes.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 321-327.
doi: https://doi.org/10.15407/spqeo19.04.321
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
325
Fig. 4. Secondary electron images of the surface sections of A1 (a) and A2 (d) samples and corresponding to them Auger maps of
Ge and Si in A1 (b, c) and A2 (e, f) samples, respectively.
The developed procedure was used to study the
nature of the lateral elemental composition distribution
on the sample surface containing GeSi/Si nanoislands
and for understanding the relationship between this
distribution and morphological features of the studied
nanostructures.
The secondary electron image of A1 sample
surface containing GeSi/Si nanoislands is shown in
Fig. 4a. Auger maps of Ge and Si distribution registered
from the same area of A1 sample are shown in Figs. 4b
and 4c, respectively. The similar image (d) and
corresponding to it Auger maps of Ge (e) and Si (f) were
obtained for A2 sample. All of the above-mentioned
pictures were registered at magnification 100 000.
4. Discussion
The analysis of secondary electron image of A1 sample
shows the presence of two known types of GeSi/Si
nanoislands on its surface. One of them has pyramidal
faceting (p-clusters) and the other – dome-like faceting
(d-clusters) [23, 24]. It is easy to see that dome-like
faceting type in Fig. 4a prevails over the pyramidal
faceting one, and lateral sizes of all formed nanoislands
lay within the range from 40 up to 80 nm. The contours
of the structures that appeared in the Auger maps of A1
sample (b, c) have the sharp boundaries and correspond
to contours of GeSi/Si nanoislands presented in Fig. 4a.
The maximum content of Ge corresponds to the central
part of the nanoislands, and decrease of its concentration
is observed on their periphery, which follows from
Fig. 4b. It should be noted that the level of Ge content in
the central part of the d-clusters on average is
considerably higher than the level of its concentration in
the central part of the p-clusters. The minimum
concentration of Ge corresponds to the wetting layer.
Lateral distribution of Si (c) is complementary to Ge
distribution (b): sections enriched with germanium
correspond to those with silicon depletion and vice
versa. Thus, the maximum Si content corresponds to the
wetting layer, and the minimum – to the central part of
the nanoislands. The nanostructures of the d-type contain
less silicon than the p-type structures.
It is easy to see on the surface section of A 2
sample shown in Fig. 4d that pyramidal faceting of the
nanoislands prevails over dome-like faceting. The lateral
sizes of all nanoislands vary within the range from 80 up
to 150 nm. As in the case of A1 sample, the central parts
of both nanoclusters types are enriched with Ge and the
nanoislands of d-type have a higher concentration of Ge
than the nanoislands of p-type. Also, from Fig. 4e it
follows that the minimum Ge concentration at the
surface of A2 sample corresponds to the wetting layer.
The character of Si lateral distribution (Fig. 4f) is
complementary to Ge Auger map of A2 sample. The
minimum silicon content falls on the central parts of the
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 321-327.
doi: https://doi.org/10.15407/spqeo19.04.321
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
326
d-type clusters. The p-type clusters contain more silicon,
whereas the maximum concentration of Si corresponds
to the wetting layer. It should be noted that the surface of
A2 sample contains carbon as a contaminant. The
presence of the thin carbon film on the studied surface
critically influences on the intensity of the low-energy
SiLVV Auger peak. This fact explains inhomogeneity of
Si distribution on the wetting layer surface of A2 sample
on the registered Auger map.
Analyzing the data shown in Fig. 4(a-f), it is easy
to make the conclusion that dome-like and pyramidal
nanoislands have Ge core surrounded with Si shell on
both samples [25, 26]. The Ge content in the core of d-
type clusters is always considerably higher than its
content in the core of p-type clusters of the studied
samples.
The formation of the cluster Si shell can be easily
explained by the intensive interdiffusion development of
Ge into the substrate and Si into the nanoisland on its
surface [27, 28]. The bulk diffusion of Ge is slower than
its surface one. Thus, the enrichment of the cluster core
and the depletion of its shell by Ge occur. It is known
that d-clusters due to the greater height are less stressed
than p-clusters. The greater distances to the substrate and
the lower gradients of stresses lead to a higher Ge
content in the core of the domes.
Analyzing the lateral distribution of Si on the
surface of A1 sample, it is easy to draw the conclusion
that the interdiffusion process takes place the most
intensively in the wetting layer. The wetting layer
consists of pure Ge at the early stages of the planar film
growth. The minimum concentration of Ge (Fig. 4b) and
the maximum concentration of Si (Fig. 4c) are contained
on the surface of the wetting layer after nucleation and in
the process of the consequent nanoislands growth.
Some differences of the structural and
morphological characteristics of the nanoislands in A1
and A2 samples should be noted. The presence of
Si0.9Ge0.1 buffer layer in A2 sample has led to the
increase of surface density and lateral sizes of the
clusters. It is easily seen from Fig. 4d that pyramidal
faceting of the clusters prevails over the dome-like
faceting and the dispersion of nanoislands sizes is
insignificant. This fact indicates that clusters were
nucleated massively within a single generation in A2
sample. The nucleation process of nanoislands in A1
sample progressed slowly within several generations
forming clusters of different facets and sizes in contrast
to the previous case.
5. Conclusions
The use of AES and high-resolution SEM in
combination with the developed procedure of the
thermal drift correction is an effective instrument for
analyzing the lateral elemental composition distribution
on GeSi/Si nanoislands surface. The proposed method
allows analyzing the clusters with the size of the
structural elements down to 8…10 nm.
Overcoming the problem of thermal drift plays a
key role in determining the lateral chemical composition
distribution of GeSi/Si nanoclusters during operation at
large magnifications in high spatial resolution mode. The
long duration of the Auger maps registration procedure
and weak removal of the heat released in the sample
under the electron probe due to the low thermal
conductivity of the sample are the factors contributing to
the appearance of the thermal drift.
It was found that both the pyramidal and dome-like
nanoclusters have the germanium core and the silicon
enriched shell on the studied samples. Cores of dome-
like nanoislands contain more Ge than cores of
pyramidal nanoislands for all the samples. Such
elemental composition distribution indicates an
important role of surface interdiffusion of Ge into the
substrate and Si into the cluster in the process of its
nucleation and growth. The high concentration of Ge in
the d-cluster core is a result of its greater sizes compared
to the p-cluster. Germanium containing in the d-cluster
core should overcome the greater diffusion path to the Si
substrate. The Ge core of dome is closer to the
equilibrium state as compared with the pyramid core due
to the lower level of stresses in the d-cluster.
The presence of the Si0.9Ge0.1 buffer layer led to the
increase of the lateral sizes and the surface density of the
nanoclusters. In this case the nucleation of the
nanoislands occurs massively and rapidly. The small size
dispersion indicates this fact. The nucleation process,
apparently, passes slowly and over several generations,
forming the nanoislands with different faceting and sizes
in absence of the buffer layer.
References
1. D. Bimberg, N. Ledentsov, Quantum dots: Lasers
and Amplifiers // J. Phys.: Condens. Matter, 15, p.
R1063-R1076 (2003).
2. G. Masini, L. Colace, G. Assanto, Si based
optoelectronics for communications // Mater. Sci.
and Eng. B, 89, p. 2-9 (2002).
3. E. Knill, R. Laflamme, G.J. Milburn, A scheme for
efficient quantum computation with linear optics //
Nature, 409, p. 46-52 (2001).
4. Z. Yuan, B.E. Kardynal, R.M. Stevenson,
A.J. Shields, C.J. Lobo, K. Cooper, N.S. Beattie,
D.A. Ritchie, M. Pepper, Electrically driven single-
photon source // Science, 295, p. 102-105 (2002).
5. F. Ratto, G. Costantini, A. Rastelli, O.G. Schmidt,
K. Kern, F. Rosei, Alloying of self-organized
semiconductor 3D islands // J. Experim. Nanosci.
1, p. 279-305 (2006).
6. J. Zhang, M. Brehm, M. Grydlikac, O.G. Schmidt,
Evolution of epitaxial semiconductor nanodots and
nanowires from supersaturated wetting layers //
Chem. Soc. Rev. 44, p. 26-39 (2015).
7. J.-N. Aqua, I. Berbezier, L. Favre, T. Frisch,
A. Ronda, Growth and self-organization of SiGe
nanostructures // Phys. Repts. 522, p. 59-189 (2013).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 321-327.
doi: https://doi.org/10.15407/spqeo19.04.321
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
327
8. G. Biasiol, S. Heun, Compositional mapping of
semiconductor quantum dots and rings // Physics
Reports 500, p. 117-173 (2011).
9. Z.F. Krasil’nik, P.M. Lytvyn, D.N. Lobanov,
N. Mestres, A.V. Novikov, J. Pascual,
M.Ya. Valakh, V.A. Yukhymchuk, Microscopic and
optical investigation of Ge nanoislands on silicon
substrates // Nanotechnology, 13, p. 81-85 (2002).
10. M.Ya. Valakh, V.O. Yukhymchuk, V.M. Dzhagan,
O.S. Lytvyn, A.G. Milekhin, A.I. Nikiforov,
O.P. Pchelyakov, F. Alsina, J. Pascual, Raman
study of self-assembled SiGe nanoislands grown at
low temperatures // Nanotechnology, 16, p. 1464-
1468 (2005).
11. M.Ya. Valakh, P.M. Lytvyn, A.S. Nikolenko,
V.V. Strelchuk, Z.F. Krasilnik, D.N. Lobanov,
A.V. Novikov, Gigantic uphill diffusion during
self-assembled growth of Ge quantum dots // Appl.
Phys. Lett. 96, 141909 (2010).
12. J. Stangl, A. Daniel, V. Holý, T. Roch, G. Bauer,
I. Kegel, T.H. Metzger, Th. Wiebach, O.G. Schmidt,
K. Eberl, Strain and composition distribution in
uncapped SiGe islands from X-ray diffraction //
Appl. Phys. Lett. 79, p. 1474-1476 (2001).
13. M. Valvo, C. Bongiorno, F. Giannazzo, A. Terrasi,
Localized Si enrichment in coherent self-assembled
Ge islands grown by molecular beam epitaxy on
(001)Si single crystal // J. Appl. Phys. 113, 033513
(2013).
14. U. Denker, M. Stoffel, O.G. Schmidt, Probing the
lateral composition profile of self-assembled
islands // Phys. Rev. Lett. 90, 196102 (2003).
15. M.I. Alonso, M. Calle, J.O. Ossó, M. Garriga,
A.R. Goñi, Strain and composition profiles of self-
assembled Ge/Si (001) islands // J. Appl. Phys. 98,
033530 (2005).
16. G. Katsaros, G. Costantini, M. Stoffel, R. Esteban,
A.M. Bittner, A. Rastelli, U. Denker,
O.G. Schmidt, K. Kern, Kinetic origin of island
intermixing during the growth of Ge on Si (001) //
Phys. Rev. B 72, 195320 (2005).
17. O.G. Schmidt, U. Denker, S. Christiansen, F. Ernst,
Composition of self-assembled Ge/Si islands in
single and multiple layers // Appl. Phys. Lett. 81, p.
2614-2616 (2002).
18. S.S. Ponomaryov, V.O. Yukhymchuk, P.M. Lytvyn,
M.Ya. Valakh, Direct determination of 3D
distribution of elemental composition in single
semiconductor nanoislands by scanning Auger
microscopy // Nanoscale Res. Lett. 11, p. 103
(2016).
19. D. Briggs, M.P. Seah, Practical Surface Analysis:
Auger and X-ray Photoelectron Spectroscopy, 1.
Chichester, John Wiley & Sons Inc., 1990.
20. G.A. Maximov, Z.F. Krasil’nik, A.V. Novikov,
V.G. Shengurov, D.O. Filatov, D.E. Nikolitchev,
V.F. Dryakhlushin, K.P. Gaikovich, Composition
Analysis of Single GeSi/Si Nanoclusters by
Scanning Auger Microscopy, Ch. 3, in:
Nanophysics, Nanoclusters and Nanodevices, Ed.
K.S. Gehar, p. 87-123. New York, Nova Science
Publishers, 2006.
21. P. Frigeri, L. Seravalli, G. Trevisi, S. Franchi,
Molecular Beam Epitaxy: An Overview, in:
Comprehensive Semiconductor Science and
Technology, Eds. P. Bhattacharya, R. Fornari,
H. Kamimura, p. 480-522. Amsterdam, Elsevier, 2011.
22. M. Brehm, F. Montalenti, M. Grydlik, G. Vastola,
H. Lichtenberger, N Hrauda, M.J. Beck,
T. Fromherz, F. Schäffler, L. Miglio, G. Bauer, Key
role of the wetting layer in revealing the hidden path
of Ge/Si(001) Stranski–Krastanow growth onset //
Phys. Rev. B, 80, pp. 205321 (2009).
23. G. Medeiros-Ribeiro, A.M. Bratkovski,
T.I. Kamins, D.A.A. Ohlberg, R.S. Williams,
Shape transition of germanium nanocrystals on a
silicon (001) surface from pyramids to domes //
Science, 279, p. 353-355 (1998).
24. A. Rastelli, M. Stoffel, G. Katsaros, J. Tersoff,
U. Denker, T. Merdzhanova, G.S. Kar,
G. Costantini, K. Kern, H. Kanel, O.G. Schmidt,
Reading the footprints of strained islands //
Microelectron. J. 37, p. 1471-1476 (2006).
25. M.S. Leite, A. Malachias, S.W. Kycia, T.I. Kamins,
R.S. Williams, G. Medeiros-Ribeiro, Evolution of
thermodynamic potentials in closed and open
nanocrystalline systems: Ge-Si:Si(001) islands //
Phys. Rev. Lett. 100, 226101 (2008).
26. G. Medeiros-Ribeiro, R.S. Williams, Thermo-
dynamics of coherently-strained GexSi1-x nano-
crystals on Si(001): Alloy composition and island
formation // Nano Lett. 7, p. 223-226 (2007).
27. R. Magalhaes-Paniago, G. Medeiros-Ribeiro,
A. Malachias, S. Kycia, T.I. Kamins,
R.S. Williams, Direct evaluation of composition
profile, strain relaxation, and elastic energy of
Ge:Si(001) self-assembled islands by anomalous
x-ray scattering // Phys. Rev. B, 66, 245312 (2002).
28. T.I. Kamins, G. Medeiros-Ribeiro, D.A.A. Ohlberg,
R.S. Williams, Evolution of Ge islands on Si(001)
during annealing // J. Appl. Phys. 85, p. 1159-1171
(1999).
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