8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions
In this paper the results of photoluminescence researches devoted to phase
 transitions in 6H-3C-SiC have been presented. High pure 6H-SiC crystals grown by
 Tairov’s method with and without polytype joint before and after plastic deformation at
 high temperature annealing we...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2013
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| Cite this: | 8H-, 10H-, 14H-SiC formation
 in 6H-3C silicon carbide phase transitions / S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 3. — С. 273-279. — Бібліогр.: 26 назв. — англ. |
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| author | Vlaskina, S.I. Mishinova, G.N. Vlaskin, V.I. Rodionov, V.E. Svechnikov, G.S. |
| author_facet | Vlaskina, S.I. Mishinova, G.N. Vlaskin, V.I. Rodionov, V.E. Svechnikov, G.S. |
| citation_txt | 8H-, 10H-, 14H-SiC formation
 in 6H-3C silicon carbide phase transitions / S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 3. — С. 273-279. — Бібліогр.: 26 назв. — англ. |
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| container_title | Semiconductor Physics Quantum Electronics & Optoelectronics |
| description | In this paper the results of photoluminescence researches devoted to phase
transitions in 6H-3C-SiC have been presented. High pure 6H-SiC crystals grown by
Tairov’s method with and without polytype joint before and after plastic deformation at
high temperature annealing were investigated using optical spectroscopy. Low
temperature photoluminescence changes in the transition phase of SiC crystal represented
with the stalking fault spectra within the temperature range 4.2 to 35 K. The stalking
fault spectra indicate formation of metastable nanostructures in SiC crystals (14H₁
<4334>, 10H₂ <55>, 14H₂ <77>). The phononless part of each stalking fault spectrum
consists of two components of radiative recombination that are responsible for hexagonal
and cubic arrangement of atoms. Each of radiative recombination components in the
stalking fault spectrum has the width of entire band 34 meV and shifts relative to each
other by 26 meV. The overlap area of those components equals to 8 meV. The super-fine
structure of the recombination components in spectrum is observed, and it is related to
different Si – Si or C – C and Si – C bonds. Behavior of all the stalking fault spectra is
similar (temperature, decay of luminescence). The processes of the phase transition are
explained by the mechanism of interfacial rearrangements in the SiC crystals.
|
| first_indexed | 2025-12-07T18:01:58Z |
| format | Article |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 3. P. 273-279.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
273
PACS 64.70.K-, 78.60.Lc
8H-, 10H-, 14H-SiC formation
in 6H-3C silicon carbide phase transitions
S.I. Vlaskina1,2, G.N. Mishinova3, V.I. Vlaskin4, V.E. Rodionov1, G.S. Svechnikov1
1Institute of Semiconductor Physics, National Academy of Science of Ukraine
45, prospect Nauky, 03028 Kyiv, Ukraine; e-mail: businkaa@mail.ru
2Yeoju Institute of Technology, 200 Myeongseong-ro, Gyeonggi-do, 469-705 Korea
3Taras Shevchenko Kyiv National University, 64, Volodymyrska str., Kyiv 03033, Ukraine
4Sensartech, 2540 Lobelia Dr., Oxnard, 93036 California, USA
Abstract. In this paper the results of photoluminescence researches devoted to phase
transitions in 6H-3C-SiC have been presented. High pure 6H-SiC crystals grown by
Tairov’s method with and without polytype joint before and after plastic deformation at
high temperature annealing were investigated using optical spectroscopy. Low
temperature photoluminescence changes in the transition phase of SiC crystal represented
with the stalking fault spectra within the temperature range 4.2 to 35 K. The stalking
fault spectra indicate formation of metastable nanostructures in SiC crystals (14H1
4334, 10H2 55, 14H2 77). The phononless part of each stalking fault spectrum
consists of two components of radiative recombination that are responsible for hexagonal
and cubic arrangement of atoms. Each of radiative recombination components in the
stalking fault spectrum has the width of entire band 34 meV and shifts relative to each
other by 26 meV. The overlap area of those components equals to 8 meV. The super-fine
structure of the recombination components in spectrum is observed, and it is related to
different Si – Si or C – C and Si – C bonds. Behavior of all the stalking fault spectra is
similar (temperature, decay of luminescence). The processes of the phase transition are
explained by the mechanism of interfacial rearrangements in the SiC crystals.
Keywords: silicon carbide, polytype, stacking fault, nanoparticle, phase transitions.
Manuscript received 10.06.13; revised version received 26.07.13; accepted for
publication 19.09.13; published online 30.09.13.
1. Introduction
Researches associated with formation of polytype
structures are a staple of modern condensed matter
physics of nanostructures. The phenomenon of
polytypism is inherent to single crystals, films, powders,
polycrystalline compact materials, and nanostructures.
Polytypes of SiC differ fundamentally only by the number
and the sequence of position of the atomic Si – C bilayers
relative to the adjacent (neighboring) bilayers in a cubic
(c) or hexagonal (h) arrangements. Replacement of any
layer in the cubic setting on a hexagonal (or vice versa)
can be viewed as a stacking fault (SF) of the polytype,
which has a strictly defined motif of alternating atomic
planes, the so-called zig-zag chains. Regular input of h-
layers in a cubic structure 3C-SiC (β-phase) can give
structure of the α-phase (H or R).
In terms of the dislocation, the transition
mechanism of the cubic structure to the hexagonal
structure is discussed in the articles [1-7]. In terms of
formation of the multilayers polytypes, transition of the
hexagonal structure to the cubic one is discussed in [8-
13]. The interface interactions between 3C-SiC and 2H-
SiC have been also investigated [14]. The mechanism of
this transition is the object of various simulations
[15, 16].
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 3. P. 273-279.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
274
Also, SiC polytypes can be described by different
stacking of Si – C layers that are perpendicular to the
direction of the SiC closed-packed plane. SF play the
main role in the process of structure transformation
[11, 13]. SF dimension of a few SiC lattices is a
quantum well 3C-SiC within wider band-gap α-SiC. The
structure leads to appearance of the quantum effects and
SiC actually becomes a direct band gap semiconductor,
which results in intense photoluminescence in the blue
part of the spectrum. A new type of heterostructure can
be created using SiC, namely: heterostructure not
between different materials but between different
modifications of the same material [17]. Degradation of
the electrical characteristics of bipolar SiC devices is
explained by the presence of SF in crystal bulk [18, 19].
Formation of different polytypes under the same
thermodynamic conditions can be understood when
using optical spectroscopy analysis [1, 20].
This work is aimed at properties of high purity 6H-
SiC crystals (before and after plastic deformation and
high temperature annealing treatment) and disordered
grown layers in the crystals of α-SiC (mainly 6H-SiC)
by using optical spectroscopy such as low temperature
photoluminescence (LTPL), Photoluminescence
excitation spectra (PES) and absorption spectra have
been analyzed.
2. Experiment
The luminescence spectra were obtained using excitation
by the mercury lamp (λ = 365 nm), and by lasers:
nitrogen laser (λ = 337 nm); He-Cd laser (λ = 441.6 nm);
Ar-laser (λ = 488 nm).
Crystals were grown by sublimation (Lely method),
were selected according to the phase composition (α- or
β-phase) and the degree of structural disorder (control,
twinning, and one-dimensional disorder). Crystal
structural researches were carried out using X-ray
diffraction (Laue method) and electron diffraction
methods. Thermal treatment of crystals (high-
temperature annealing) was performed in a resistance
furnace with a graphite heater in argon atmosphere at
T = 2000…2100 °C for 1 to 10 hours. Plastic
deformation of the samples was carried out in a
resistance furnace at the argon atmosphere by three
points bending at 2000 °C for 15…30 min.
2.1. 6H-SiC perfect crystals
High purity crystals with a very low concentration of
impurities have been selected for the spectroscopic
investigation of the phase transition 6H-3C SiC. Laue
diffraction patterns indicated a single-phase crystal
composition. Normally, only in such perfect crystals of
6H-SiC observed is the well known spectrum of
exciton impurity (nitrogen) complexes (as known as
PRS) together with ABC-spectra associated with
titanium. The spectra of LTPL of the crystal (at 4.2 K)
with the non-compensated nitrogen concentration
ND – NA ~ (6…7) 1016 cm–3 were investigated. The
change of the LTPL spectra had been observed after
plastic deformation at the temperature from 2000 up to
2100 °C for 30 min in argon atmosphere. A fine
spectrum structure of the SiC appeared. Similar results
in SiC crystal after annealing were demonstrated and
specified as SF in Refs. [1, 9, 13].
The intensity of the PRS and ABC maxima is
considerably reduced after applying the force to the
crystals. The plastic deformation stimulates an
emergence of the so-called L-spectrum, which is
associated with presence of vacancies, and it was
previously obtained only by the ion bombardment of
crystals. This confirms a possibility of vacancies
formation during the process.
2.2. Grown polytype’s transformations in SiC crystals
For better understanding the process of transformation
the pure SiC crystals (ND – NA ~ (4…9) 1016 cm–3) with
natural inter-grown SiC polytype’s joints were specially
selected. The crystals have been studied in detail for the
presence of similar spectra. Crystal structure of
disordered layers was determined by diffuse smearing of
reflections in Laue pattern. The “twin plates” of the β-
phase in SiC (10…100 Å lamellae) and the basic
structures of the α-phase: 6H-SiC, 15R-SiC, 21R-SiC
were investigated. Fig. 1 shows LTPL of various
samples of the inter-grown polytypes at T =4.2 K. The
overall spectral pattern of each sample represents a
specific series of spectra SF1 (Fig. 1a), SF2 (Fig. 1a, c),
SF3 (Fig. 1a, b), SF4 (Fig. 1b) which look like spectra of
the 6H-SiC crystal after applying the force.
Fig. 1. LTPL at 4.2 K of the inter-grown polytypes joint in
different samples: (a) sample N5; (b) sample N6;
(c) sample N7.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 3. P. 273-279.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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Fig. 2. SF1 spectrum of SiC at 4.2 K: (a) reconstituted
phononless part of SF1 spectrum; (b) phonons in SiC involved
in SF1 spectrum.
The difference is that all the SF fine spectra are
located at the different energy scale with different
intensities of the spectra. But a comprehensive
spectroscopic analysis showed that all SF spectra have
the same characteristics and principle of their
construction regardless of placement in the common
energy scale. Transcript structure of the spectrum SFi
(where i = 1, 2, 3, 4) is made with the spectrum SF1 that
is most frequently observed. Transcripts of another SFi
fine spectrum are the same. Other SFi spectra are located
in different energy region compare with SF1 fine spectra.
The entire structure of the spectrum SF (Fig. 2a)
can be obtained by summing together additive phonon
replicas to some phononless part of the spectrum
(Fig. 2b).
Phonons of extended edge Brillouin zone of the
silicon carbide (ETA = 46 meV, ELA = 77 meV, ETO =
95 meV, ELO = 104 meV) are involved in the emission.
Adding the phonon replicas spectrum to the proposed
phononless structure spectrum gives the
photoluminescence spectrum (LTPL) (Fig. 2a). By the
way, a specific feature is that the phononless part itself is
not observed. The phononless part of fine spectra was
created in accordance with the structure of TA-replica
and its transitions as a whole to higher energies by the
energy of TA phonon (46 meV). Fig. 3 shows that the
phononless spectrum of SF1 is located within the energy
region (2.853…2.793 eV) with the width of the entire
band 60 meV. The energy region for SF – I spectrum is
2.853…2.819 eV and for SF – II spectrum is
2.827…2.793 eV, accordingly.
It turns out that, after determining the position of
the phononless part of SF1 in the energy scale, the
energy of the short-wave spectrum SF1 is the same as the
exciton band gap of the SiC-polytype 21R-SiC at T =
4.2 K, and equal to 2.853 eV [1]. The energy of inserting
a 2H(3C) crystal in a 3C(2H) matrix had been calculated
and is 68.4 meV/atom for (2H), and 66.9 meV/atom for
(3C) [14]. Both calculated energy values are about the
same as the energy obtained from a width of the entire
band of SFi spectra (60 meV).
Careful investigation of phononless part of the SF1
showed that the spectrum by itself consists of two
components are SF – I (2.853…2.819 eV) and SF – II
(2.827…2.793 eV). Each of them has the width of the
entire band 34 meV. Maximums of SF – I and SF – II
are shifted relatively to each other by 26 meV (Fig. 4).
The overlap spectrum area equals to 8 meV.
Two parts of the SFi (SF – I and SF – II) spectrum
also have super-fine structure. Resolution of the super-
fine structure SF – I and SF – II is different in the case of
different natural inter-grown SiC crystal polytypes. The
smallest width at half maximum of the fine structure
SF – I and SF – II components is 1.5 meV. According to
Ref. [14], the process of interface formation in the SiC
crystal requires energy 0.151 eV/Å 2. This energy induces
distortion of tetrahedrons and generates compressed
Si – Si and stretched C – C bonds. So, the super-fine
structures of SF – I and SF – II can be caused by the
arrangement of each atom.
Fig. 3. The phononless part of the SF1 spectrum.
Fig. 4. Scheme of the phononless spectrum SF1.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 3. P. 273-279.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
276
3. Discussion
Silicon carbide is a covalent crystal in which atoms have
sp3-type hybridization. The covalent bonds between
atoms with sp3-type of hybridization can explain
polytypism in SiC. If a cubic crystal to orient along the
crystallographic direction (111) and hexagonal and
rhombohedra crystals along the (0001), the crystal of
silicon carbide can be considered as a layered macro-
molecular one (like cyclohexane).
Cubic crystal 3C-SiC is characterized by the
interlayer structures like “N”. Hexagonal 2H polytype
layers are linked like “V” structures. The structure of
another hexagonal and rhombohedra polytypes is
determined by sequence of “N” and “V” structures along
the (0001) direction. The difference of a crystal structure
of the silicon carbide polytypes is only in a nature of the
interlayer bond, but structure of each layer is exactly the
same.
From the fact that the energy of bonds between
atoms in the cubic 3C-SiC (cubic arrangement) are not
identical to the energy of bonds between atoms in
hexagonal 2H-SiC (hexagonal arrangement), it implies
the assumption why SFi spectrum has two parts SF – I
and SF – II. Namely, the difference in the interlayer
bond’s energies at the exactly same structure of each
layer gives appearance of the super-fine structure of
SF – I and SF – II parts in every spectrum.
These differences of the energy scale of SF – I and
SF – II should be attributed to particular inter-atomic
bonds. The phononless part of the SF – I spectrum
consists of the components of radiative recombination,
which is responsible for hexagonal and in the case of
SF – II for cubic arrangements of atoms.
The same character of all the SFi spectra is
confirmed by the same temperature behavior. Both of
the SFi spectra are observed at the temperatures 4.2 up to
35 K (Fig. 5). The parts SF – I are observed at
4.2…18 K (Fig. 5a), and SF – II – at 4.2…35 K,
accordingly (Fig. 5a, b). Fig. 5a illustrates the sequence
decay of short-wave maximums for SF – I and SF – II
(shown above in Fig. 3). At the temperatures higher than
18 K, the sequence decay of short-wave maximums
associated with SF – II remains only (Fig. 5c). The
thermal activation energy of the SF – I and SF – II parts
is different and equal meV5.3T
aE and
meV5.7T
aE , accordingly (Fig. 5b).
The dependence of PL intensity with the intensity
of exciting light has sub-linear character, namely:
IPL = Iexc.light, α = 0.7. At the same time, significant
duration of the PL decay is observed. The PL intensity
of the SF1 spectra is registered after switching-off the
excitation and has the delay time s103 3 herewith
IPL = 0.02I0. The intensity of the SF – I part decays
rapidly. All these allow to make an assumption of
possibility that there is a saturation effect of the radiation
centers as well as the fact that recombined electrons and
holes are significantly separated in space with the weak
overlap of wave functions. High-temperature annealing
(T = 2000 C, t = 5 h) of pure SiC crystals (with SF)
leads to a weakening the short-wave SFi maximums.
In the beginning SF – I component disappears in all
SFi spectra (Fig. 3, curves 1 to 5), then the SF – II one
disappears (Fig. 3, curves 7 to 10). After the high-
temperature annealing for more than 5 hours, the SF – I
components of spectra completely disappear. For better
understanding the location of SF – I in the PL spectrum
one, needs to study the overlap in PL spectra for SiC
before (Fig. 6a, curve 1) and after deformation (Fig. 6a,
curve 2).
Fig. 5. Temperature behavior of the SF1 spectrum for the
sample N5: (a) SF1 spectrum at various temperatures;
(b) dependence of the PL intensity for the fine structure with
inverse temperature; (c) temperature dependence of the PL
intensity of the fine structure.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 3. P. 273-279.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
277
The phononless part of SF1 spectra was obtained by
calculation and is located between 2.793 and 2.852 eV
(Fig. 6a). Variation of changes in the distribution of
intensities inherent to the phononless part of the fine SiC
spectra is shown in Fig. 6b. The curves 1 and 2 in Fig. 6b
show the spectroscopic features of the two different
samples of SiC growth polytype’s joint. After plastic
deformation of the non-defect SiC crystal (Fig. 6a, curve 1)
by applying the force along c-axis, the SF – I spectrum
appears (Fig. 6b, curve 3). The appearance of the SF – I
spectrum due to various external influences on the crystal is
as follows: curve 4 (for the high force), curve 5 (for the low
force), curve 6 (for additional applied forces). Curve 7 is the
intensity distribution of β → transformation in the β-SiC
after the high temperature annealing at T = 2000…2100 C.
All these spectra emphasizes the complex structure of the
SF – I spectrum and confirm the association with the
peculiarities of structural states of the crystals. The super-
fine structure of SF – I component is related with the bond
length between atoms in polytypes and depends on the
crystallographic direction [21].
In order to understand the origin of super-fine
structure in the spectrum, it needs to review the faulted-
arrangement structure properties of different hexagonal
layers in the SiC polytypes.
SiC polytypes have varying degrees of
hexagonality, and the numeric value of which is defined
as a ratio of amount of the atoms in the hexagonal
arrangement and total amount of atoms in the polytype’s
cell. Similar phenomena were obtained in diamond and
have a linear character of dependence of the interlayer
distances with the degree of hexagonality [22]. The
relationship of the degree of hexagonality and optical
band gap in the SiC polytypes is linear [1]. By plotting
the short-wave edge of each SFi spectra on the energy
scale and the corresponding excitation spectra in the
dependence of the percentage hexagonality in the
different polytypes, percentage of new hexagonality
nanostructures can be obtained. The metastable form of
nano-structures appear either in the growth process or
after plastic deformation.
Short-wave edge location of the phononless part for
each of the SFi spectra is an indicator of the
nanopolytype junction [23]. The locations of the
spectrum the phononless parts of SFi in the energy scale
are summarized in Table.
Fig. 6. LTPL spectra of SiC crystals: (a) pure 6H SiC before and after plastic deformation; (b) intensity of the fine structure
SF-I component in SFi spectra of as-grown crystal polytype’s joint and after plastic deformation by pressure.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 3. P. 273-279.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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Table. The phononless part of SF as indicator of formation
of metastable intermediate phase.
After determining the position of the spectrum for
the SF1 phononless part in the energy scale, it turned out
that the short-wave part of the spectrum is the same to
the position of the exciton band gap polytype 21R at T =
4.2 K, i.e. 2.853 eV.
The study of the excitation spectra gives better
understanding the total complex panorama of the PL
spectrum (SFs). Each SFs has its own spectrum of
excitation. The total excitation spectrum repeats the
absorption spectra. The linear dependence of the exciton
band gap (Egx) with a percentage of hexagonality of
polytypes indicates occurrence of a nanostructure.
If the initial polytypes were 15R (23)3 and 6H
33, then the spectrum of SF5 was observed. Due to the
overlap with the other spectra, the SF4 spectrum is
difficult to determine. SF4 corresponds to the unknown
polytypes with lower percentage of hexagonality (up to
7%). The SF6 had overlap with another spectrum and
may correspond to the polytype 8H 44.
The possibility of occuring such new nano-phase
with the percentage hexagonality less than 25% (both in
the growth and in the result of solid state
transformations) was confirmed by high-resolution
electron microscopy [24, 25] and by first-principle study
of 8H-, 10H-, 12H-, 18H-SiC polytypes [26].
For example, the different percentage of
hexagonality (h) for structures 10H2 55 and 10H1
3223 is shown in Fig. 7.
Fig. 7. Calculation of the hexagonality percentage for 10H –
SiC.
Moreover, the motif of the metastable nano-scale
building structures 10H1 3223 (with 40% hexagonality)
corresponds to the motive of building structure
15R (32)3, which takes place in stable conditions. The
motif of 14H1 4334 (28.5% h) corresponds to the
known stable polytype 21R (34)3.
4. Conclusion
LTPL of pure α-SiC crystals and pure crystals of β-SiC
are represented by the similar spectra of SFs, which are
indicators of formation of the metastable nanostructures,
namely: 14H1 4334, 10H2 55, 14H2 77,
33R (3332)3, 8H 44.
Comprehensive spectroscopic studies revealed the
same principle of construction and the same behavior of
each of the SFs spectra under various external influences
on the crystals. The difference in interlayer bond’s
energies for the exactly same structure of each layer
gives appearance of the super-fine SF – I and SF – II
parts of every SFs spectrum. All SFs spectra are
observed within the temperature range 4.2 to 35 K (SF –
I at 4.2…15 K, SF – II at 4.2…35 K). SF – I
corresponds to radiation caused by atoms creating the V
(hexagonal) bonds between layers, SF – II corresponds
to radiation of atoms creating the N (cubic) bonds
between layers. Spectroscopic data have shown the same
principle and the same behavior of the construction of
each SFs spectrum under different external influences on
the crystals.
The results of this work have shown the mechanism
of interfacial rearrangements, which allows monitoring
the processes of transforming the energy states in the
crystal.
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G.S. Svechnikov, V.E. Rodionov, S.A. Podlasov,
Silicon carbide defects and luminescence centers in
current heated 6H-SiC // Semiconductor Physics,
Quantum Electronics and Optoelectronics, 13(1),
p. 24-29 (2010).
14. C. Raffy, J. Furthmuller, F. Bechstedt, Properties of
interfaces between cubic and hexagonal polytypes
of silicon carbide // J. Phys.: Condens. Matter,
14(48), p. 12725-12731 (2002).
15. A. Romano, J. Li, S. Yip, Atomistic simulation of
rapid compression of fractured silicon carbide // J.
Nucl. Mater. 352, p. 22-28 (2006).
16. F. Shimojo, I. Ebbsjo, R.K. Kalia, A. Nakano,
J.P. Rino, and P. Vashishta, Molecular-dynamics
simulation of structural transformation in silicon
carbide under pressure // Phys. Rev. Lett. 84,
p. 3338-3341 (2000).
17. F. Bechstedt, P. Kackell // Phys. Rev. Lett. 75,
p. 2180 (1995).
18. J.Q. Liu, M. Skowronski, C. Hallin, R. Soderholm
and H. Lendenmann, Structure of recombination-
induced stacking faults in high voltage SiC p-n
junctions // Appl. Phys. Lett. 80, p. 749 (2002).
19. M.S. Miao, S. Limpijumnong and W.R. Lambrecht,
Stacking fault band structure in 4H SiC and its
impact on electronic devices // Appl. Phys. Lett. 79,
p. 4360-4362 (2001).
20. S. Juillaguet, T. Robert, J. Camassel Optical
investigation of stacking faults in 4H-SiC epitaxial
layers: Comparison of 3C and 8H polytypes //
Mater. Sci. Eng. B – Solid State Mater. Adv.
Technol., 165, p. 5-8 (2009).
21. A. Bauer, P. Reischauer, J. Kräusslich, N. Schell,
W. Matz and K. Goetz, Structure refinement of the
silicon carbide polytypes 4H and 6H: unambiguous
determination of the refinement parameters // Acta
Cryst. A, 57, p. 60-67 (2001).
22. B. Wen, J. Zhao, M. Bucknum, P. Yao, T. Li, First
principles studies of diamond polytypes // Diamond
Relat. Mater. 17, p. 356-364 (2008).
23. F. Herman, J.P. van Duke, R.L. Kortum, Electronic
structure and spectrum of silicon carbide // Mater.
Res. Bull. 4, p. S167-S178 (1969).
24. S. Shinozaki, K.R. Kisman, Aspects of “one
dimensional disorder” in silicon carbide // J. Acta
Metallurgica, 26, p. 769-776 (1978).
25. L.U. Ogbuji, T.E. Mitchell, A.H. Heuer, The
transformation in polycrystalline SiC // J. Amer.
Ceram. Soc. 64(12), p. 91-99 (1981).
26. Kazuaki Kobayashi, Shojiro Komatsu, First-
principles study of 8H-, 10H-, 12H-, and 18H-SiC
polytypes // J. Phys. Soc. Jpn. Appl. 024714 (2012).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 3. P. 273-279.
PACS 64.70.K-, 78.60.Lc
8H-, 10H-, 14H-SiC formation
in 6H-3C silicon carbide phase transitions
S.I. Vlaskina1,2, G.N. Mishinova3, V.I. Vlaskin4, V.E. Rodionov1, G.S. Svechnikov1
1Institute of Semiconductor Physics, National Academy of Science of Ukraine
45, prospect Nauky, 03028 Kyiv, Ukraine; e-mail: businkaa@mail.ru
2Yeoju Institute of Technology, 200 Myeongseong-ro, Gyeonggi-do, 469-705 Korea
3Taras Shevchenko Kyiv National University, 64, Volodymyrska str., Kyiv 03033, Ukraine
4Sensartech, 2540 Lobelia Dr., Oxnard, 93036 California, USA
Abstract. In this paper the results of photoluminescence researches devoted to phase transitions in 6H-3C-SiC have been presented. High pure 6H-SiC crystals grown by Tairov’s method with and without polytype joint before and after plastic deformation at high temperature annealing were investigated using optical spectroscopy. Low temperature photoluminescence changes in the transition phase of SiC crystal represented with the stalking fault spectra within the temperature range 4.2 to 35 K. The stalking fault spectra indicate formation of metastable nanostructures in SiC crystals (14H1 (4334(, 10H2 (55(, 14H2 (77(). The phononless part of each stalking fault spectrum consists of two components of radiative recombination that are responsible for hexagonal and cubic arrangement of atoms. Each of radiative recombination components in the stalking fault spectrum has the width of entire band 34 meV and shifts relative to each other by 26 meV. The overlap area of those components equals to 8 meV. The super-fine structure of the recombination components in spectrum is observed, and it is related to different Si – Si or C – C and Si – C bonds. Behavior of all the stalking fault spectra is similar (temperature, decay of luminescence). The processes of the phase transition are explained by the mechanism of interfacial rearrangements in the SiC crystals.
Keywords: silicon carbide, polytype, stacking fault, nanoparticle, phase transitions.
Manuscript received 10.06.13; revised version received 26.07.13; accepted for publication 19.09.13; published online 30.09.13.
1. Introduction
Researches associated with formation of polytype structures are a staple of modern condensed matter physics of nanostructures. The phenomenon of polytypism is inherent to single crystals, films, powders, polycrystalline compact materials, and nanostructures. Polytypes of SiC differ fundamentally only by the number and the sequence of position of the atomic Si – C bilayers relative to the adjacent (neighboring) bilayers in a cubic (c) or hexagonal (h) arrangements. Replacement of any layer in the cubic setting on a hexagonal (or vice versa) can be viewed as a stacking fault (SF) of the polytype, which has a strictly defined motif of alternating atomic planes, the so-called zig-zag chains. Regular input of h-layers in a cubic structure 3C-SiC (β-phase) can give structure of the α-phase (H or R).
In terms of the dislocation, the transition mechanism of the cubic structure to the hexagonal structure is discussed in the articles [1-7]. In terms of formation of the multilayers polytypes, transition of the hexagonal structure to the cubic one is discussed in [8-13]. The interface interactions between 3C-SiC and 2H-SiC have been also investigated [14]. The mechanism of this transition is the object of various simulations [15, 16].
Also, SiC polytypes can be described by different stacking of Si – C layers that are perpendicular to the direction of the SiC closed-packed plane. SF play the main role in the process of structure transformation [11, 13]. SF dimension of a few SiC lattices is a quantum well 3C-SiC within wider band-gap α-SiC. The structure leads to appearance of the quantum effects and SiC actually becomes a direct band gap semiconductor, which results in intense photoluminescence in the blue part of the spectrum. A new type of heterostructure can be created using SiC, namely: heterostructure not between different materials but between different modifications of the same material [17]. Degradation of the electrical characteristics of bipolar SiC devices is explained by the presence of SF in crystal bulk [18, 19]. Formation of different polytypes under the same thermodynamic conditions can be understood when using optical spectroscopy analysis [1, 20].
This work is aimed at properties of high purity 6H-SiC crystals (before and after plastic deformation and high temperature annealing treatment) and disordered grown layers in the crystals of α-SiC (mainly 6H-SiC) by using optical spectroscopy such as low temperature photoluminescence (LTPL), Photoluminescence excitation spectra (PES) and absorption spectra have been analyzed.
2. Experiment
The luminescence spectra were obtained using excitation by the mercury lamp (λ = 365 nm), and by lasers: nitrogen laser (λ = 337 nm); He-Cd laser (λ = 441.6 nm); Ar-laser (λ = 488 nm).
Crystals were grown by sublimation (Lely method), were selected according to the phase composition (α- or β-phase) and the degree of structural disorder (control, twinning, and one-dimensional disorder). Crystal structural researches were carried out using X-ray diffraction (Laue method) and electron diffraction methods. Thermal treatment of crystals (high-temperature annealing) was performed in a resistance furnace with a graphite heater in argon atmosphere at T = 2000…2100 °C for 1 to 10 hours. Plastic deformation of the samples was carried out in a resistance furnace at the argon atmosphere by three points bending at 2000 °C for 15…30 min.
2.1. 6H-SiC perfect crystals
High purity crystals with a very low concentration of impurities have been selected for the spectroscopic investigation of the phase transition 6H-3C SiC. Laue diffraction patterns indicated a single-phase crystal composition. Normally, only in such perfect crystals of 6H-SiC observed is the well known spectrum of exciton impurity (nitrogen) complexes (as known as PRS) together with ABC-spectra associated with titanium. The spectra of LTPL of the crystal (at 4.2 K) with the non-compensated nitrogen concentration
ND – NA ~ (6…7) (1016 cm–3 were investigated. The change of the LTPL spectra had been observed after plastic deformation at the temperature from 2000 up to 2100 °C for 30 min in argon atmosphere. A fine spectrum structure of the SiC appeared. Similar results in SiC crystal after annealing were demonstrated and specified as SF in Refs. [1, 9, 13].
The intensity of the PRS and ABC maxima is considerably reduced after applying the force to the crystals. The plastic deformation stimulates an emergence of the so-called L-spectrum, which is associated with presence of vacancies, and it was previously obtained only by the ion bombardment of crystals. This confirms a possibility of vacancies formation during the process.
2.2. Grown polytype’s transformations in SiC crystals
For better understanding the process of transformation the pure SiC crystals (ND – NA ~ (4…9) (1016 cm–3) with natural inter-grown SiC polytype’s joints were specially selected. The crystals have been studied in detail for the presence of similar spectra. Crystal structure of disordered layers was determined by diffuse smearing of reflections in Laue pattern. The “twin plates” of the β-phase in SiC (10…100 Å lamellae) and the basic structures of the α-phase: 6H-SiC, 15R-SiC, 21R-SiC were investigated. Fig. 1 shows LTPL of various samples of the inter-grown polytypes at T =4.2 K. The overall spectral pattern of each sample represents a specific series of spectra SF1 (Fig. 1a), SF2 (Fig. 1a, c), SF3 (Fig. 1a, b), SF4 (Fig. 1b) which look like spectra of the 6H-SiC crystal after applying the force.
Fig. 1. LTPL at 4.2 K of the inter-grown polytypes joint in different samples: (a) sample N5; (b) sample N6; (c) sample N7.
Fig. 2. SF1 spectrum of SiC at 4.2 K: (a) reconstituted phononless part of SF1 spectrum; (b) phonons in SiC involved in SF1 spectrum.
The difference is that all the SF fine spectra are located at the different energy scale with different intensities of the spectra. But a comprehensive spectroscopic analysis showed that all SF spectra have the same characteristics and principle of their construction regardless of placement in the common energy scale. Transcript structure of the spectrum SFi (where i = 1, 2, 3, 4) is made with the spectrum SF1 that is most frequently observed. Transcripts of another SFi fine spectrum are the same. Other SFi spectra are located in different energy region compare with SF1 fine spectra.
The entire structure of the spectrum SF (Fig. 2a) can be obtained by summing together additive phonon replicas to some phononless part of the spectrum (Fig. 2b).
Phonons of extended edge Brillouin zone of the silicon carbide (ETA = 46 meV, ELA = 77 meV, ETO = 95 meV, ELO = 104 meV) are involved in the emission. Adding the phonon replicas spectrum to the proposed phononless structure spectrum gives the photoluminescence spectrum (LTPL) (Fig. 2a). By the way, a specific feature is that the phononless part itself is not observed. The phononless part of fine spectra was created in accordance with the structure of TA-replica and its transitions as a whole to higher energies by the energy of TA phonon (46 meV). Fig. 3 shows that the phononless spectrum of SF1 is located within the energy region (2.853…2.793 eV) with the width of the entire band 60 meV. The energy region for SF – I spectrum is 2.853…2.819 eV and for SF – II spectrum is 2.827…2.793 eV, accordingly.
It turns out that, after determining the position of the phononless part of SF1 in the energy scale, the energy of the short-wave spectrum SF1 is the same as the exciton band gap of the SiC-polytype 21R-SiC at T = 4.2 K, and equal to 2.853 eV [1]. The energy of inserting a 2H(3C) crystal in a 3C(2H) matrix had been calculated and is 68.4 meV/atom for (2H), and 66.9 meV/atom for (3C) [14]. Both calculated energy values are about the same as the energy obtained from a width of the entire band of SFi spectra (60 meV).
Careful investigation of phononless part of the SF1 showed that the spectrum by itself consists of two components are SF – I (2.853…2.819 eV) and SF – II (2.827…2.793 eV). Each of them has the width of the entire band 34 meV. Maximums of SF – I and SF – II are shifted relatively to each other by 26 meV (Fig. 4). The overlap spectrum area equals to 8 meV.
Two parts of the SFi (SF – I and SF – II) spectrum also have super-fine structure. Resolution of the super-fine structure SF – I and SF – II is different in the case of different natural inter-grown SiC crystal polytypes. The smallest width at half maximum of the fine structure SF – I and SF – II components is 1.5 meV. According to Ref. [14], the process of interface formation in the SiC crystal requires energy 0.151 eV/Å2. This energy induces distortion of tetrahedrons and generates compressed
Si – Si and stretched C – C bonds. So, the super-fine structures of SF – I and SF – II can be caused by the arrangement of each atom.
Fig. 3. The phononless part of the SF1 spectrum.
Fig. 4. Scheme of the phononless spectrum SF1.
3. Discussion
Silicon carbide is a covalent crystal in which atoms have sp3-type hybridization. The covalent bonds between atoms with sp3-type of hybridization can explain polytypism in SiC. If a cubic crystal to orient along the crystallographic direction (111) and hexagonal and rhombohedra crystals along the (0001), the crystal of silicon carbide can be considered as a layered macro-molecular one (like cyclohexane).
Cubic crystal 3C-SiC is characterized by the interlayer structures like “N”. Hexagonal 2H polytype layers are linked like “V” structures. The structure of another hexagonal and rhombohedra polytypes is determined by sequence of “N” and “V” structures along the (0001) direction. The difference of a crystal structure of the silicon carbide polytypes is only in a nature of the interlayer bond, but structure of each layer is exactly the same.
From the fact that the energy of bonds between atoms in the cubic 3C-SiC (cubic arrangement) are not identical to the energy of bonds between atoms in hexagonal 2H-SiC (hexagonal arrangement), it implies the assumption why SFi spectrum has two parts SF – I and SF – II. Namely, the difference in the interlayer bond’s energies at the exactly same structure of each layer gives appearance of the super-fine structure of SF – I and SF – II parts in every spectrum.
These differences of the energy scale of SF – I and SF – II should be attributed to particular inter-atomic bonds. The phononless part of the SF – I spectrum consists of the components of radiative recombination, which is responsible for hexagonal and in the case of SF – II for cubic arrangements of atoms.
The same character of all the SFi spectra is confirmed by the same temperature behavior. Both of the SFi spectra are observed at the temperatures 4.2 up to 35 K (Fig. 5). The parts SF – I are observed at 4.2…18 K (Fig. 5a), and SF – II – at 4.2…35 K, accordingly (Fig. 5a, b). Fig. 5a illustrates the sequence decay of short-wave maximums for SF – I and SF – II (shown above in Fig. 3). At the temperatures higher than 18 K, the sequence decay of short-wave maximums associated with SF – II remains only (Fig. 5c). The thermal activation energy of the SF – I and SF – II parts is different and equal
meV
5
.
3
»
T
a
E
and
meV
5
.
7
»
T
a
E
, accordingly (Fig. 5b).
The dependence of PL intensity with the intensity of exciting light has sub-linear character, namely: IPL = I(exc.light, α = 0.7. At the same time, significant duration of the PL decay is observed. The PL intensity of the SF1 spectra is registered after switching-off the excitation and has the delay time
s
10
3
3
-
×
herewith IPL = 0.02I0. The intensity of the SF – I part decays rapidly. All these allow to make an assumption of possibility that there is a saturation effect of the radiation centers as well as the fact that recombined electrons and holes are significantly separated in space with the weak overlap of wave functions. High-temperature annealing (T = 2000 (C, t = 5 h) of pure SiC crystals (with SF) leads to a weakening the short-wave SFi maximums.
In the beginning SF – I component disappears in all SFi spectra (Fig. 3, curves 1 to 5), then the SF – II one disappears (Fig. 3, curves 7 to 10). After the high-temperature annealing for more than 5 hours, the SF – I components of spectra completely disappear. For better understanding the location of SF – I in the PL spectrum one, needs to study the overlap in PL spectra for SiC before (Fig. 6a, curve 1) and after deformation (Fig. 6a, curve 2).
Fig. 5. Temperature behavior of the SF1 spectrum for the sample N5: (a) SF1 spectrum at various temperatures; (b) dependence of the PL intensity for the fine structure with inverse temperature; (c) temperature dependence of the PL intensity of the fine structure.
The phononless part of SF1 spectra was obtained by calculation and is located between 2.793 and 2.852 eV (Fig. 6a). Variation of changes in the distribution of intensities inherent to the phononless part of the fine SiC spectra is shown in Fig. 6b. The curves 1 and 2 in Fig. 6b show the spectroscopic features of the two different samples of SiC growth polytype’s joint. After plastic deformation of the non-defect SiC crystal (Fig. 6a, curve 1) by applying the force along c-axis, the SF – I spectrum appears (Fig. 6b, curve 3). The appearance of the SF – I spectrum due to various external influences on the crystal is as follows: curve 4 (for the high force), curve 5 (for the low force), curve 6 (for additional applied forces). Curve 7 is the intensity distribution of β → ( transformation in the β-SiC after the high temperature annealing at T = 2000…2100 (C. All these spectra emphasizes the complex structure of the SF – I spectrum and confirm the association with the peculiarities of structural states of the crystals. The super-fine structure of SF – I component is related with the bond length between atoms in polytypes and depends on the crystallographic direction [21].
In order to understand the origin of super-fine structure in the spectrum, it needs to review the faulted-arrangement structure properties of different hexagonal layers in the SiC polytypes.
SiC polytypes have varying degrees of hexagonality, and the numeric value of which is defined as a ratio of amount of the atoms in the hexagonal arrangement and total amount of atoms in the polytype’s cell. Similar phenomena were obtained in diamond and have a linear character of dependence of the interlayer distances with the degree of hexagonality [22]. The relationship of the degree of hexagonality and optical band gap in the SiC polytypes is linear [1]. By plotting the short-wave edge of each SFi spectra on the energy scale and the corresponding excitation spectra in the dependence of the percentage hexagonality in the different polytypes, percentage of new hexagonality nanostructures can be obtained. The metastable form of nano-structures appear either in the growth process or after plastic deformation.
Short-wave edge location of the phononless part for each of the SFi spectra is an indicator of the nanopolytype junction [23]. The locations of the spectrum the phononless parts of SFi in the energy scale are summarized in Table.
Table. The phononless part of SF as indicator of formation of metastable intermediate phase.
Stacking fault
Locations
(eV)
Polytype
Hexagonality
(%)
SF1
2.853
14 H1 (4334(
28.5
SF2
2.712
10H2 (55(
20
SF3
2.611
14Н2 (77(
14.3
SF4
2.515
N/A
7
SF5
3.002
33R ((3332)3(
37
SF6
2.78
8H (44(
25
After determining the position of the spectrum for the SF1 phononless part in the energy scale, it turned out that the short-wave part of the spectrum is the same to the position of the exciton band gap polytype 21R at T = 4.2 K, i.e. 2.853 eV.
The study of the excitation spectra gives better understanding the total complex panorama of the PL spectrum (SFs). Each SFs has its own spectrum of excitation. The total excitation spectrum repeats the absorption spectra. The linear dependence of the exciton band gap (Egx) with a percentage of hexagonality of polytypes indicates occurrence of a nanostructure.
If the initial polytypes were 15R ((23)3( and 6H (33(, then the spectrum of SF5 was observed. Due to the overlap with the other spectra, the SF4 spectrum is difficult to determine. SF4 corresponds to the unknown polytypes with lower percentage of hexagonality (up to 7%). The SF6 had overlap with another spectrum and may correspond to the polytype 8H (44(.
The possibility of occuring such new nano-phase with the percentage hexagonality less than 25% (both in the growth and in the result of solid state transformations) was confirmed by high-resolution electron microscopy [24, 25] and by first-principle study of 8H-, 10H-, 12H-, 18H-SiC polytypes [26].
For example, the different percentage of hexagonality (h) for structures 10H2 (55( and 10H1 (3223( is shown in Fig. 7.
Fig. 7. Calculation of the hexagonality percentage for 10H – SiC.
Moreover, the motif of the metastable nano-scale building structures 10H1 (3223( (with 40% hexagonality) corresponds to the motive of building structure 15R ((32)3(, which takes place in stable conditions. The motif of 14H1 (4334( (28.5% h) corresponds to the known stable polytype 21R ((34)3(.
4. Conclusion
LTPL of pure α-SiC crystals and pure crystals of β-SiC are represented by the similar spectra of SFs, which are indicators of formation of the metastable nanostructures, namely: 14H1 (4334(, 10H2 (55(, 14H2 (77(, 33R ((3332)3(, 8H (44(.
Comprehensive spectroscopic studies revealed the same principle of construction and the same behavior of each of the SFs spectra under various external influences on the crystals. The difference in interlayer bond’s energies for the exactly same structure of each layer gives appearance of the super-fine SF – I and SF – II parts of every SFs spectrum. All SFs spectra are observed within the temperature range 4.2 to 35 K (SF – I at 4.2…15 K, SF – II at 4.2…35 K). SF – I corresponds to radiation caused by atoms creating the V (hexagonal) bonds between layers, SF – II corresponds to radiation of atoms creating the N (cubic) bonds between layers. Spectroscopic data have shown the same principle and the same behavior of the construction of each SFs spectrum under different external influences on the crystals.
The results of this work have shown the mechanism of interfacial rearrangements, which allows monitoring the processes of transforming the energy states in the crystal.
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�
�
Fig. 6. LTPL spectra of SiC crystals: (a) pure 6H SiC before and after plastic deformation; (b) intensity of the fine structure SF-I component in SFi spectra of as-grown crystal polytype’s joint and after plastic deformation by pressure.
© 2013, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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| record_format | dspace |
| spelling | Vlaskina, S.I. Mishinova, G.N. Vlaskin, V.I. Rodionov, V.E. Svechnikov, G.S. 2017-05-26T13:45:10Z 2017-05-26T13:45:10Z 2013 8H-, 10H-, 14H-SiC formation
 in 6H-3C silicon carbide phase transitions / S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2013. — Т. 16, № 3. — С. 273-279. — Бібліогр.: 26 назв. — англ. 1560-8034 PACS 64.70.K-, 78.60.Lc https://nasplib.isofts.kiev.ua/handle/123456789/117728 In this paper the results of photoluminescence researches devoted to phase
 transitions in 6H-3C-SiC have been presented. High pure 6H-SiC crystals grown by
 Tairov’s method with and without polytype joint before and after plastic deformation at
 high temperature annealing were investigated using optical spectroscopy. Low
 temperature photoluminescence changes in the transition phase of SiC crystal represented
 with the stalking fault spectra within the temperature range 4.2 to 35 K. The stalking
 fault spectra indicate formation of metastable nanostructures in SiC crystals (14H₁
 <4334>, 10H₂ <55>, 14H₂ <77>). The phononless part of each stalking fault spectrum
 consists of two components of radiative recombination that are responsible for hexagonal
 and cubic arrangement of atoms. Each of radiative recombination components in the
 stalking fault spectrum has the width of entire band 34 meV and shifts relative to each
 other by 26 meV. The overlap area of those components equals to 8 meV. The super-fine
 structure of the recombination components in spectrum is observed, and it is related to
 different Si – Si or C – C and Si – C bonds. Behavior of all the stalking fault spectra is
 similar (temperature, decay of luminescence). The processes of the phase transition are
 explained by the mechanism of interfacial rearrangements in the SiC crystals. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions Article published earlier |
| spellingShingle | 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions Vlaskina, S.I. Mishinova, G.N. Vlaskin, V.I. Rodionov, V.E. Svechnikov, G.S. |
| title | 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions |
| title_full | 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions |
| title_fullStr | 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions |
| title_full_unstemmed | 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions |
| title_short | 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions |
| title_sort | 8h-, 10h-, 14h-sic formation in 6h-3c silicon carbide phase transitions |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/117728 |
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