Nanostructures in lightly doped silicon carbide crystals with polytypic defects
In this work, photoluminescence spectra of lightly doped SiC crystals with ingrown original defects are reported. Undoped SiC single crystals with the impurity concentration of ND – NA ~ (2…8)*10¹⁶ cm⁻³, NA ~ (2…8)*10¹⁷ cm⁻³, and ND – NA ~ (1…5)*10¹⁷ cm⁻³, ND = 10¹⁸ cm⁻³ were investigated. The...
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Vlaskina, S.I. Mishinova, G.N. Vlaskin, L.V. Rodionov, V.E. Svechnikov, G.S. 2017-05-30T05:57:20Z 2017-05-30T05:57:20Z 2014 Nanostructures in lightly doped silicon carbide crystals with polytypic defects / S.I. Vlaskina, G.N. Mishinova, L.V. Vlaskin, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 2. — С. 155-159. — Бібліогр.: 23 назв. — англ. 1560-8034 PACS 64.70.K-, 78.60.Lc https://nasplib.isofts.kiev.ua/handle/123456789/118364 In this work, photoluminescence spectra of lightly doped SiC crystals with ingrown original defects are reported. Undoped SiC single crystals with the impurity concentration of ND – NA ~ (2…8)*10¹⁶ cm⁻³, NA ~ (2…8)*10¹⁷ cm⁻³, and ND – NA ~ (1…5)*10¹⁷ cm⁻³, ND = 10¹⁸ cm⁻³ were investigated. The analysis of absorption, excitation and low temperature photoluminescence spectra suggests formation of a new micro-phase during the growth process and appearance of the deep-level (DL) spectra. The complex spectra of the crystals can be decomposed into the so-called DLi (i = 1, 2, 3, 4) spectra. The appearance of the DLi spectrum is associated with formation of new nano-phases. Data of photoluminescence, excitation and absorption spectra show the uniformity of different DLi spectra. Structurally, the general complexity of the DLi spectra correlated with the degree of disorder of the crystal and was connected with onedimensional disorder, the same as in the case of the stacking fault (SFi) spectra. The DLi spectra differ from SFi spectra and have other principles of construction and behavior. The DLi spectra are placed on a broad donor-acceptor pairs emission band in crystals with higher concentrations of non-compensated impurities. The excitation spectra for the DLi and SFi spectra coincide and indicate formation of nanostructures 14H₁<4334>, 10H₂<55>, 14H₂<77>, 8H<44> en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Nanostructures in lightly doped silicon carbide crystals with polytypic defects Article published earlier |
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| title |
Nanostructures in lightly doped silicon carbide crystals with polytypic defects |
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Nanostructures in lightly doped silicon carbide crystals with polytypic defects Vlaskina, S.I. Mishinova, G.N. Vlaskin, L.V. Rodionov, V.E. Svechnikov, G.S. |
| title_short |
Nanostructures in lightly doped silicon carbide crystals with polytypic defects |
| title_full |
Nanostructures in lightly doped silicon carbide crystals with polytypic defects |
| title_fullStr |
Nanostructures in lightly doped silicon carbide crystals with polytypic defects |
| title_full_unstemmed |
Nanostructures in lightly doped silicon carbide crystals with polytypic defects |
| title_sort |
nanostructures in lightly doped silicon carbide crystals with polytypic defects |
| author |
Vlaskina, S.I. Mishinova, G.N. Vlaskin, L.V. Rodionov, V.E. Svechnikov, G.S. |
| author_facet |
Vlaskina, S.I. Mishinova, G.N. Vlaskin, L.V. Rodionov, V.E. Svechnikov, G.S. |
| publishDate |
2014 |
| language |
English |
| container_title |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| format |
Article |
| description |
In this work, photoluminescence spectra of lightly doped SiC crystals with ingrown
original defects are reported. Undoped SiC single crystals with the impurity
concentration of ND – NA ~ (2…8)*10¹⁶ cm⁻³, NA ~ (2…8)*10¹⁷ cm⁻³, and ND – NA ~
(1…5)*10¹⁷ cm⁻³, ND = 10¹⁸ cm⁻³ were investigated. The analysis of absorption,
excitation and low temperature photoluminescence spectra suggests formation of a new
micro-phase during the growth process and appearance of the deep-level (DL) spectra.
The complex spectra of the crystals can be decomposed into the so-called DLi (i = 1, 2,
3, 4) spectra. The appearance of the DLi spectrum is associated with formation of new
nano-phases. Data of photoluminescence, excitation and absorption spectra show the
uniformity of different DLi spectra. Structurally, the general complexity of the DLi
spectra correlated with the degree of disorder of the crystal and was connected with onedimensional
disorder, the same as in the case of the stacking fault (SFi) spectra. The DLi
spectra differ from SFi spectra and have other principles of construction and behavior.
The DLi spectra are placed on a broad donor-acceptor pairs emission band in crystals
with higher concentrations of non-compensated impurities. The excitation spectra for the
DLi and SFi spectra coincide and indicate formation of nanostructures 14H₁<4334>,
10H₂<55>, 14H₂<77>, 8H<44>
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118364 |
| citation_txt |
Nanostructures in lightly doped silicon carbide crystals with polytypic defects / S.I. Vlaskina, G.N. Mishinova, L.V. Vlaskin, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 2. — С. 155-159. — Бібліогр.: 23 назв. — англ. |
| work_keys_str_mv |
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| first_indexed |
2025-11-27T00:35:42Z |
| last_indexed |
2025-11-27T00:35:42Z |
| _version_ |
1850781640196882432 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 155-159.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
155
PACS 64.70.K-, 78.60.Lc
Nanostructures in lightly doped silicon carbide crystals
with polytypic defects
S.I. Vlaskina1,2, G.N. Mishinova3, L.V. Vlaskin4, V.E. Rodionov2, G.S. Svechnikov2
1Yeoju Institute of Technology (Yeoju University),
338 Sejong-ro, Yeoju-eup, Yeoju-gun, Gyeonggi-do, 469-705 Korea
2V. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine; e-mail: businkaa@mail.ru
3Taras Shevchenko Kyiv National University, 64, Volodymyrs’ka str., 01033 Kyiv, Ukraine
4Sensartech, 2540 Lobelia Dr., Oxnard, 93036 California, USA
Abstract. In this work, photoluminescence spectra of lightly doped SiC crystals with in-
grown original defects are reported. Undoped SiC single crystals with the impurity
concentration of ND – NA ~ (2…8)1016 cm–3, NA ~ (2…8)1017 cm–3, and ND – NA ~
(1…5)1017 cm–3, ND 11018 cm–3 were investigated. The analysis of absorption,
excitation and low temperature photoluminescence spectra suggests formation of a new
micro-phase during the growth process and appearance of the deep-level (DL) spectra.
The complex spectra of the crystals can be decomposed into the so-called DLi (i = 1, 2,
3, 4) spectra. The appearance of the DLi spectrum is associated with formation of new
nano-phases. Data of photoluminescence, excitation and absorption spectra show the
uniformity of different DLi spectra. Structurally, the general complexity of the DLi
spectra correlated with the degree of disorder of the crystal and was connected with one-
dimensional disorder, the same as in the case of the stacking fault (SFi) spectra. The DLi
spectra differ from SFi spectra and have other principles of construction and behavior.
The DLi spectra are placed on a broad donor-acceptor pairs emission band in crystals
with higher concentrations of non-compensated impurities. The excitation spectra for the
DLi and SFi spectra coincide and indicate formation of nanostructures 14H14334,
10H255, 14H277, 8H44.
Keywords: silicon carbide, polytype, stacking fault, photoluminescence spectra,
nanostructure.
Manuscript received 15.01.14; revised version received 29.04.14; accepted for
publication 12.06.14; published online 30.06.14.
1. Introduction
Silicon carbide (SiC) is material widely used in several
industrial applications such as high power electronics,
light emitting diodes, as well as in researches such as
photo-voltaic and quantum technologies. Silicon carbide
exists as several different polytypes according to the
stacking sequence of SiC atomic double layers in the
crystal lattice. Great advances were reported in growing a
single crystalline polytype by controlled sublimation and
chemical vapor deposition [1–3]. Polytypic transformation
in SiC was investigated by many authors [4–19].
The phase transformation in highly doped by
nitrogen 6H – SiC crystal and the mechanism of solid-
phase transition through formation of multilayer
polytypes has been studied [5, 14]. Syntax coalescence
becomes a very important characteristic of α-polytype
SiC crystals – the intergrowth of two or more polytypes
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 155-159.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
156
when not only the major axis c but also the axis a
coincide in the hexagonal structures. It happens because
of the “layer-by-layer” crystal growth and the existence
of different types of errors in the layers sequence (SF)
along the axis c. The layers with in-grown one
dimensional disorder in the original α-SiC crystals are
called D-layers. D-layers have a clear crisp coalescence
boundary with the neighboring blocks of the structurally
perfect 6H – SiC along the (0001) plane.
However, single crystals with multiple nucleations
also exist. The interaction of the growth fronts produces
incoherent boundaries (the so-called “mosaic”). In this
case, all kinds of in-grown dislocations and properties of
“border inconsistencies” play a crucial role. To stabilize
the appropriate polytype structure, it is essential to
consider the influence of different factors:
thermodynamic, kinetic, impurity, and dislocation
nucleation mechanisms. Any fluctuation of the
stabilization parameters can lead to errors in structure
formation. It also contributes to a very small stacking
fault energy in silicon carbide (2–9 mJ/m2).
Photoluminescence (PL) is one of the most widely
used experimental techniques for the physical
characterization of semiconductors. The complex
research of the low temperature photoluminescence
(LTPL) spectra under different conditions of registration
and at various temperatures is one among the most
widely used experimental techniques for the physical
characterization of the crystals [3, 6, 17]. The
simultanious control of the phase state and structural
imperfactions showed defect formation as a result of
polytypes reorganization in the process of crystal
growth.
Investigated in the paper [5] have been defects in
heavily doped with nitrogen single crystals by using
photoluminescence. However, correspondence between
the PL spectra and mechanism of phase transformation
has not been investigated. The nature of the PL spectra
depends on the concentration of impurities. Spectroscopy
of defects in pure perfect crystal SiC has already been
described in the works of Refs. [6, 16, 20–22].
In this report, LTPL studies of lightly doped α-SiC
single crystals have been presented. This work is the
continuation of the spectroscopic diagnosis of defects
created by the unstable growth conditions in lightly
doped α-SiC single crystals.
2. Experimental
The method of optical spectroscopy LTFL was used in
this work, as it is very sensitive to structural changes.
The group of single crystalline α-SiC crystals
grown by using Lely’s (Tairov’s) method [3] was
selected for the research. Undoped SiC single crystals
with the impurity concentration of ND – NA ~
(2…8)1016 cm–3, NA ~ (2…8)1017 cm–3, and ND – NA ~
(1…5)1017 cm–3, ND 11018 cm–3 were investigated. In
perfect 6H – SiC crystals, the donor impurity (N) and the
acceptor impurity (Al) in low-temperature
recombination show well-known blue radiation of
donor-acceptor pairs (DAP). This type of recombination
usually dominates [3].
We selected samples with LTPL (77 K) in the
turquoise green spectrum area. We will call these
samples deep level (DL) samples. The turquoise green
luminescence was observed within the whole crystal
volume as well as only in some parts of the crystal. For
example, in the block from one side of the (0001) SiC
crystal, the DL luminescence was observed while the
other part of the crystal produced the DAP (6H – SiC)
luminescence. These blocks were separated from the rest
of the crystal by using layer-by-layer polishing and were
selected for further structural analysis.
The X-ray (Laue’s method) and electron diffraction
methods were used to detect symmetrical and layering
parameters of the crystals. Moreover, in some cases, to
analyze structural peculiarities of the allocated blocks,
the transmission electron microscopy technique (TEM)
(15 000) was used. The metallographic method was
used for evaluating the crystal face surface in the starting
growth state.
LTPL spectra were registered by the ДФС-12
spectrograph with the photodetector (ФЭУ-79). In
photoluminescence (PL) experiments, a nitrogen ЛГИ-21,
λ = 337 nm (3.68 eV) or helium-cadmium ЛГ-70, λ =
441.6 nm (2.807 eV) laser, respectively, were used. Also,
a mercury ultrahigh pressure lamp СВДШ-1000 with
УФ-2 filter and xenon lamp ДКСШ-1000 were used.
The PL spectra were measured using the samples
contained in a liquid helium or nitrogen cryostat, which
provided temperatures ranging from 1.5 to 330 K.
3. Results and discussions
SF related luminescence dominates in pure SiC crystals
[22]. After full extinction of the SFi luminescence
described in [23] at the temperature of 35-40 K, a weak
(in its intensity) and wide background band of radiation
remained. This luminescence was more or less clearly
pronounced and had a rich structure depending on the
features and degree of the one-dimensional disorder of
the samples.
The spectra of this type (DLi) differ from SFi
spectra and have other principles of construction and
behavior. The DLi spectra are localized on the
background of the broad DAP spectral band of crystals
with higher concentrations of non-compensated
impurities. Originally, these spectra were found and
investigated in defective crystals (1DL, 2DL samples in
Fig. 1) with a higher concentration of the main impurity.
In these samples, the DL spectrum was much more
intensive, whereas the SF spectrum (which was also
present) even at 4.2 K was poorly pronounced, or
practically was not fixed.
The dependence of the intensity of the DLi spectra
on the impurity concentration is shown in Fig. 1.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 155-159.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
157
Fig. 2 shows absorption spectra of DLi samples.
Samples with DL1 spectra have a more or less
pronounced sharp absorption edge (typical for 6H – SiC
crystals) that transforms into a long-wave smooth tail,
testifying to the existence of absorption in the
transparency region of this phase. There are no evidence
that this absorption is related with the impurity
concentration (ND – NA ~ (3…8) 1016 cm–3) in the
samples.
Fig. 1. Intensity of the DLi spectra (i = 1) (T = 77 K) at
2.4…2.5 V vs. the impurity concentration for different samples
(of the SFi and DLi series). Shaded area – the SFi spectra from
the ref. [22]. (a) Most pure samples with only SF spectra,
ND – NA ~ (4…9)1016 cm–3, (1…5)1016 cm–3, ND < 11017 cm–3,
NA ~ (1…3)1016 cm–3 from the ref. [22]. (b) Pure samples with
the SFi and DLi series, ND – NA ~ (2…8)1016 cm–3, NA ~
(2…8)1017 cm–3. (c) Samples with only DLi spectra, ND –
NA ~ (2…7)1017 cm–3, ND < 11018 cm–3.
6
10
2.8
2
3.0 3.22.6
x
x
x
x
x
x
x
x
x
x
x
x
Egx
21R
Egx
8H
Egx
6H
TA
LO
TA
1DL
4DL
3DL
9DL
T=77K
K
1/
2 ,
cm
-1
/2
E,eV
6
10
2.8
2
3.0 3.22.6
x
x
x
x
x
x
x
x
x
x
x
x
Egx
21R
Egx
8H
Egx
6H
TA
LO
TA
1DL
4DL
3DL
9DL
T=77K
K
1/
2 ,
cm
-1
/2
E,eV
Fig. 2. Absorption spectra of DL samples.
However, the shift to the longwave area and
absorption coefficient fully correlate with the degree and
character of structural defects in the samples. The
absorption area is located far away in the longwave side
in relation to the exciton absorption edge (Egx) of
6H – SiC. It rather strongly suggests formation of
structures with a higher percentage of cubic α-SiC than
6H – SiC. The peculiarities of the absorption spectra are
also in good agreement with those for the DLi excitation
spectra. The absorption at the energy E < Egx 6H – SiC
can be attributed to the absorption of the new matrix of
micro- or nano-phases, as noted in the analysis/study of
the SFi spectra [22].
The PL spectra (77 K) and corresponding
excitation low temperature photoluminescence spectra
(ELTPLS) of these DL samples are shown in Fig. 3.
There is correlation between the energy shift of
longwave edges of the excitation low temperature PL
spectra and the corresponding DLi spectra.
Consequently, it is possible to eliminate completely
shorter wavelength DLi spectra from the total complex
panorama of the DLi spectra (for example as it is shown
for 9DL sample) by choosing suitable photon energy of
the exciting radiation. It was done using monochromatic
light and various lasers.
Structurally, the total complexity of the DLi spectra
correlated with the degree of disorder of the crystal and
was related with peculiarities of defect characteristics
performance (as in the case of the SFi spectra [22]) and,
above all, with such its manifestations as one-
dimensional disordering. The complex spectrum of the
crystals can be decomposed into the so-called DLi (i = 1,
2, 3, 4) spectra.
As it is shown in Fig. 3, the PL spectra of the 1DL
and 8DL samples are represented mainly by only one DL1
and DL2 spectra, respectively, while the sample 9DL
includes more than one DL3, DL4 spectra, which
corresponds to an even higher degree of the structural
disordering of the crystals.
Fig. 3. DLi spectra (I) and corresponding photoluminescence
excitation spectra (η) at T = 77 K. The longwave edge of the
photoluminescence excitation spectra for the DLi and SFi types
is the same (i = 1 → Egx (21R), i = 2 → Egx (10H2), i = 3 → Egx
(14H2), ..., i = 6 → Egx (8H).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 155-159.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
158
a)
b)
Photo 1. Laue pattern of SiC crystals with DL luminescence
spectra: a) sample 4DL, b) sample 9DL.
Comparison of Laue patterns (Photo 1) shows that
the crystal 9DL looks like “morphological freak”.
Following changes in DL-luminescence in this crystal
with layer-by-layer grinding of the (0001) face (along
the axis c), it was possible to trace transformation of the
structure during the growth process. The spectrum from
the base surface of one of the faces of the crystal in the
original state of the sample 9DL is dominated by DL3 and
weaker DL2 and DL1 spectra, then with the grinding of
the defect layers, DL2 luminescence was mainly
observed, and from the other natural face DL1
luminescence took place. Thus, the luminescence within
one sample reflects distribution of the corresponding
luminescence centers during the growth process and
indicates the independence of each of the DLi spectra.
Comparison of the longwave edge of these samples
with the longwave edges of the SFi type samples (pure
crystals) (Fig. 4) [21, 22] shows evidence that the
ELTPLS for DLi type spectra and ELTPLS for SFi type
coincide:
i = 1 Egx (14H1) 4334,
i = 2 Egx (10H2) 55,
i = 3 Egx (14H2) 77,
i = 4 Egx (N/A),
i = 5 Egx (33R) (3332)3,
i = 6 Egx (8H) 44.
Fig. 4. SFi spectra and corresponding photoluminescence
excitation spectra (ELTFLS) at T = 4.6 K. The longwave edge
of ELTFLS for DLi and SFi types is the same (i = 1 → Egx
(14H1), i = 2 → Egx (10H2), i = 3 → Egx (14H2). Arrows (↓,↑)
indicate the areas of the PL spectra for which the excitation
spectra were recorded.
Thus, the analysis of the excitation spectra of the
DLi luminescence leads to the conclusion that the spectra
are in qualitative agreement with the excitation spectrum
of ELTPLS luminescence for the appropriate type SFi
(ELTPLS DL1 → ELTPLS SF1, ELTPLS DL2 →
ELTPLS SF2). Consequently, DL luminescence is
related to formation of a new micro-phase during the
growth, and DL spectra are also indicators of the
corresponding motif forming [23] the main phase
adjustment.
4. Conclusion
In this work, photoluminescence spectra of lightly doped
SiC crystals with in-grown original defects are reported.
Undoped SiC single crystals with the impurity
concentration of ND – NA ~ (2…8)1016 cm–3, NA ~
(2…8)1017 cm–3, and ND – NA ~ (1…5)1017 cm–3,
ND 11018 cm–3 were investigated. The analysis of
absorption, excitation and low temperature
photoluminescence spectra of lightly doped SiC crystals
with in-grown original defects suggests formation of a
new micro-phase during the growth process and
appearance of the deep-level (DL) spectra. The complex
spectra of the crystals can be decomposed into the so-
called DLi (i = 1, 2, 3, 4) spectra. The appearance of the
DLi spectrum is associated with formation of new nano-
phases. Data of photoluminescence, excitation and
absorption spectra show the uniformity of different DLi
spectra. Structurally, the general complexity of the DLi
spectra correlated with the degree of disorder of the
crystal and was connected with one-dimensional
disorder, the same as in the case of the stacking fault
(SFi) spectra. The DLi spectra differ from SFi spectra
and have other principles of construction and behavior.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 155-159.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
159
The DLi spectra are placed on a broad donor-acceptor
pairs emission band in crystals with higher
concentrations of non-compensated impurities. The
excitation spectra for the DLi and SFi spectra coincide
and indicate formation of nanostructures 14H14334,
10H255, 14H277, 8H44.
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between 3C- and 6H-silicon carbide at high
pressure and high temperature // J. Amer. Cer. Soc.
84(12), p. 3013-3016 (2001).
14. S.I. Vlaskina, Mechanism of 6H-3C transformation
in SiC // Semiconductor Physics, Quantum
Electronics and Optoelectronics, 5(2), p. 252-255
(2002).
15. M. Durandurdu, An initio simulations of the
structural phase transformation of 2H-SiC at high
pressure // Phys. Rev. B, 75, 235204 (2007).
16. S.W. Lee, S.I. Vlaskina, V.I. Vlaskin, I.V.
Zaharchenko, V.A. Gubanov, G.N. Mishinova,
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).
17. C. Raffy, Furthmüller and Beshtedt, Properties of
interface between cubic and hexagonal polytypes in
silicon carbide // J. Phys.: Condens. Matter, 14,
p. 12725-12731 (2002).
16. F. Shimojo, I. Ebbsjö, 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. S. Juillaguet, T. Robert, J. Camassel, Optical
investigation of stacking faults in 4H-SiC epitaxial
layers: Comparison of 3C and 8H polytypes //
Mater. Sci. and Eng. B, 165, p. 5-8 (2009).
18. S. Shinozaki, K.R. Kisman, Aspects of “one
dimensional disorder” in silicon carbide // Acta
Metallurgica, 26, p. 769-776 (1978).
19. L.U. Ogbuji, T.E. Mitchell, A.H. Heuer, The β→α
transformation in polycrystalline SiC: The
thickening of α plates // J. Amer. Ceram. Soc.
64(2), p. 91-99 (1981).
20. S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, V.E.
Rodionov, G.S. Svechnikov, 6H-3C transformation
in heated cubic silicon carbide 3C-SiC //
Semiconductor Physics, Quantum Electronics and
Optoelectronics, 14(4), p. 432-437 (2013).
21. S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, G.S.
Svechnikov, V.E. Rodionov, S.W. Lee, Silicon
carbide phase transition in as-grown 3C-6H –
polytypes junction // Semiconductor Physics,
Quantum Electronics and Optoelectronics, 16(2),
p. 132-136 (2013).
22. S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, V.E.
Rodionov, G.S. Svechnikov, 8H-, 10H-, 14H-SiC
formation in 6H-3C silicon carbide phase
transitions // Semiconductor Physics, Quantum
Electronics and Optoelectronics, 16(3), p. 272-278
(2013).
23. Kozuaki Kobayashi, Shojiro Komatsu. First-
principle study of 8H-, 10H-, 12H-, ND 18H-SiC
polytypes // J. Phys. Soc. Jpn. Appl. 024714 (2012).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 155-159.
PACS 64.70.K-, 78.60.Lc
Nanostructures in lightly doped silicon carbide crystals
with polytypic defects
S.I. Vlaskina1,2, G.N. Mishinova3, L.V. Vlaskin4, V.E. Rodionov2, G.S. Svechnikov2
1Yeoju Institute of Technology (Yeoju University),
338 Sejong-ro, Yeoju-eup, Yeoju-gun, Gyeonggi-do, 469-705 Korea
2V. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine; e-mail: businkaa@mail.ru
3Taras Shevchenko Kyiv National University, 64, Volodymyrs’ka str., 01033 Kyiv, Ukraine
4Sensartech, 2540 Lobelia Dr., Oxnard, 93036 California, USA
Abstract. In this work, photoluminescence spectra of lightly doped SiC crystals with in-grown original defects are reported. Undoped SiC single crystals with the impurity concentration of ND – NA ~ (2…8)(1016 cm–3, NA ~ (2…8)(1017 cm–3, and ND – NA ~ (1…5)(1017 cm–3, ND ( 1(1018 cm–3 were investigated. The analysis of absorption, excitation and low temperature photoluminescence spectra suggests formation of a new micro-phase during the growth process and appearance of the deep-level (DL) spectra. The complex spectra of the crystals can be decomposed into the so-called DLi (i = 1, 2, 3, 4) spectra. The appearance of the DLi spectrum is associated with formation of new nano-phases. Data of photoluminescence, excitation and absorption spectra show the uniformity of different DLi spectra. Structurally, the general complexity of the DLi spectra correlated with the degree of disorder of the crystal and was connected with one-dimensional disorder, the same as in the case of the stacking fault (SFi) spectra. The DLi spectra differ from SFi spectra and have other principles of construction and behavior. The DLi spectra are placed on a broad donor-acceptor pairs emission band in crystals with higher concentrations of non-compensated impurities. The excitation spectra for the DLi and SFi spectra coincide and indicate formation of nanostructures 14H1(4334(, 10H2(55(, 14H2(77(, 8H(44(.
Keywords: silicon carbide, polytype, stacking fault, photoluminescence spectra, nanostructure.
Manuscript received 15.01.14; revised version received 29.04.14; accepted for publication 12.06.14; published online 30.06.14.
1. Introduction
Silicon carbide (SiC) is material widely used in several industrial applications such as high power electronics, light emitting diodes, as well as in researches such as photo-voltaic and quantum technologies. Silicon carbide exists as several different polytypes according to the stacking sequence of SiC atomic double layers in the crystal lattice. Great advances were reported in growing a single crystalline polytype by controlled sublimation and chemical vapor deposition [1–3]. Polytypic transformation in SiC was investigated by many authors [4–19].
The phase transformation in highly doped by nitrogen 6H – SiC crystal and the mechanism of solid-phase transition through formation of multilayer polytypes has been studied [5, 14]. Syntax coalescence becomes a very important characteristic of α-polytype SiC crystals – the intergrowth of two or more polytypes when not only the major axis c but also the axis a coincide in the hexagonal structures. It happens because of the “layer-by-layer” crystal growth and the existence of different types of errors in the layers sequence (SF) along the axis c. The layers with in-grown one dimensional disorder in the original α-SiC crystals are called D-layers. D-layers have a clear crisp coalescence boundary with the neighboring blocks of the structurally perfect 6H – SiC along the (0001) plane.
However, single crystals with multiple nucleations also exist. The interaction of the growth fronts produces incoherent boundaries (the so-called “mosaic”). In this case, all kinds of in-grown dislocations and properties of “border inconsistencies” play a crucial role. To stabilize the appropriate polytype structure, it is essential to consider the influence of different factors: thermodynamic, kinetic, impurity, and dislocation nucleation mechanisms. Any fluctuation of the stabilization parameters can lead to errors in structure formation. It also contributes to a very small stacking fault energy in silicon carbide (2–9 mJ/m2).
Photoluminescence (PL) is one of the most widely used experimental techniques for the physical characterization of semiconductors. The complex research of the low temperature photoluminescence (LTPL) spectra under different conditions of registration and at various temperatures is one among the most widely used experimental techniques for the physical characterization of the crystals [3, 6, 17]. The simultanious control of the phase state and structural imperfactions showed defect formation as a result of polytypes reorganization in the process of crystal growth.
Investigated in the paper [5] have been defects in heavily doped with nitrogen single crystals by using photoluminescence. However, correspondence between the PL spectra and mechanism of phase transformation has not been investigated. The nature of the PL spectra depends on the concentration of impurities. Spectroscopy of defects in pure perfect crystal SiC has already been described in the works of Refs. [6, 16, 20–22].
In this report, LTPL studies of lightly doped α-SiC single crystals have been presented. This work is the continuation of the spectroscopic diagnosis of defects created by the unstable growth conditions in lightly doped α-SiC single crystals.
2. Experimental
The method of optical spectroscopy LTFL was used in this work, as it is very sensitive to structural changes.
The group of single crystalline α-SiC crystals grown by using Lely’s (Tairov’s) method [3] was selected for the research. Undoped SiC single crystals with the impurity concentration of ND – NA ~ (2…8)(1016 cm–3, NA ~ (2…8)(1017 cm–3, and ND – NA ~ (1…5)(1017 cm–3, ND ( 1(1018 cm–3 were investigated. In perfect 6H – SiC crystals, the donor impurity (N) and the acceptor impurity (Al) in low-temperature recombination show well-known blue radiation of donor-acceptor pairs (DAP). This type of recombination usually dominates [3].
We selected samples with LTPL (77 K) in the turquoise green spectrum area. We will call these samples deep level (DL) samples. The turquoise green luminescence was observed within the whole crystal volume as well as only in some parts of the crystal. For example, in the block from one side of the (0001) SiC crystal, the DL luminescence was observed while the other part of the crystal produced the DAP (6H – SiC) luminescence. These blocks were separated from the rest of the crystal by using layer-by-layer polishing and were selected for further structural analysis.
The X-ray (Laue’s method) and electron diffraction methods were used to detect symmetrical and layering parameters of the crystals. Moreover, in some cases, to analyze structural peculiarities of the allocated blocks, the transmission electron microscopy technique (TEM) ((15 000) was used. The metallographic method was used for evaluating the crystal face surface in the starting growth state.
LTPL spectra were registered by the ДФС-12 spectrograph with the photodetector (ФЭУ-79). In photoluminescence (PL) experiments, a nitrogen ЛГИ-21, λ = 337 nm (3.68 eV) or helium-cadmium ЛГ-70, λ = 441.6 nm (2.807 eV) laser, respectively, were used. Also, a mercury ultrahigh pressure lamp СВДШ-1000 with УФ-2 filter and xenon lamp ДКСШ-1000 were used.
The PL spectra were measured using the samples contained in a liquid helium or nitrogen cryostat, which provided temperatures ranging from 1.5 to 330 K.
3. Results and discussions
SF related luminescence dominates in pure SiC crystals [22]. After full extinction of the SFi luminescence described in [23] at the temperature of 35-40 K, a weak (in its intensity) and wide background band of radiation remained. This luminescence was more or less clearly pronounced and had a rich structure depending on the features and degree of the one-dimensional disorder of the samples.
The spectra of this type (DLi) differ from SFi spectra and have other principles of construction and behavior. The DLi spectra are localized on the background of the broad DAP spectral band of crystals with higher concentrations of non-compensated impurities. Originally, these spectra were found and investigated in defective crystals (1DL, 2DL samples in Fig. 1) with a higher concentration of the main impurity. In these samples, the DL spectrum was much more intensive, whereas the SF spectrum (which was also present) even at 4.2 K was poorly pronounced, or practically was not fixed.
The dependence of the intensity of the DLi spectra on the impurity concentration is shown in Fig. 1.
Fig. 2 shows absorption spectra of DLi samples. Samples with DL1 spectra have a more or less pronounced sharp absorption edge (typical for 6H – SiC crystals) that transforms into a long-wave smooth tail, testifying to the existence of absorption in the transparency region of this phase. There are no evidence that this absorption is related with the impurity concentration (ND – NA ~ (3…8) ( 1016 cm–3) in the samples.
Fig. 1. Intensity of the DLi spectra (i = 1) (T = 77 K) at 2.4…2.5 V vs. the impurity concentration for different samples (of the SFi and DLi series). Shaded area – the SFi spectra from the ref. [22]. (a) Most pure samples with only SF spectra,
ND – NA ~ (4…9)(1016 cm–3, (1…5)(1016 cm–3, ND < 1(1017 cm–3, NA ~ (1…3)(1016 cm–3 from the ref. [22]. (b) Pure samples with the SFi and DLi series, ND – NA ~ (2…8)(1016 cm–3, NA ~ (2…8)(1017 cm–3. (c) Samples with only DLi spectra, ND – NA ~ (2…7)(1017 cm–3, ND < 1(1018 cm–3.
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Fig. 2. Absorption spectra of DL samples.
However, the shift to the longwave area and absorption coefficient fully correlate with the degree and character of structural defects in the samples. The absorption area is located far away in the longwave side in relation to the exciton absorption edge (Egx) of
6H – SiC. It rather strongly suggests formation of structures with a higher percentage of cubic α-SiC than 6H – SiC. The peculiarities of the absorption spectra are also in good agreement with those for the DLi excitation spectra. The absorption at the energy E < Egx 6H – SiC can be attributed to the absorption of the new matrix of micro- or nano-phases, as noted in the analysis/study of the SFi spectra [22].
The PL spectra (77 K) and corresponding excitation low temperature photoluminescence spectra (ELTPLS) of these DL samples are shown in Fig. 3.
There is correlation between the energy shift of longwave edges of the excitation low temperature PL spectra and the corresponding DLi spectra. Consequently, it is possible to eliminate completely shorter wavelength DLi spectra from the total complex panorama of the DLi spectra (for example as it is shown for 9DL sample) by choosing suitable photon energy of the exciting radiation. It was done using monochromatic light and various lasers.
Structurally, the total complexity of the DLi spectra correlated with the degree of disorder of the crystal and was related with peculiarities of defect characteristics performance (as in the case of the SFi spectra [22]) and, above all, with such its manifestations as one-dimensional disordering. The complex spectrum of the crystals can be decomposed into the so-called DLi (i = 1, 2, 3, 4) spectra.
As it is shown in Fig. 3, the PL spectra of the 1DL and 8DL samples are represented mainly by only one DL1 and DL2 spectra, respectively, while the sample 9DL includes more than one DL3, DL4 spectra, which corresponds to an even higher degree of the structural disordering of the crystals.
Fig. 3. DLi spectra (I) and corresponding photoluminescence excitation spectra (η) at T = 77 K. The longwave edge of the photoluminescence excitation spectra for the DLi and SFi types is the same (i = 1 → Egx (21R), i = 2 → Egx (10H2), i = 3 → Egx (14H2), ..., i = 6 → Egx (8H).
a)
b)
Photo 1. Laue pattern of SiC crystals with DL luminescence spectra: a) sample 4DL, b) sample 9DL.
Comparison of Laue patterns (Photo 1) shows that the crystal 9DL looks like “morphological freak”. Following changes in DL-luminescence in this crystal with layer-by-layer grinding of the (0001) face (along the axis c), it was possible to trace transformation of the structure during the growth process. The spectrum from the base surface of one of the faces of the crystal in the original state of the sample 9DL is dominated by DL3 and weaker DL2 and DL1 spectra, then with the grinding of the defect layers, DL2 luminescence was mainly observed, and from the other natural face DL1 luminescence took place. Thus, the luminescence within one sample reflects distribution of the corresponding luminescence centers during the growth process and indicates the independence of each of the DLi spectra.
Comparison of the longwave edge of these samples with the longwave edges of the SFi type samples (pure crystals) (Fig. 4) [21, 22] shows evidence that the ELTPLS for DLi type spectra and ELTPLS for SFi type coincide:
i = 1 ( Egx (14H1) (4334(,
i = 2 ( Egx (10H2) (55(,
i = 3 ( Egx (14H2) (77(,
i = 4 ( Egx (N/A),
i = 5 ( Egx (33R) ((3332)3(,
i = 6 ( Egx (8H) (44(.
Fig. 4. SFi spectra and corresponding photoluminescence excitation spectra (ELTFLS) at T = 4.6 K. The longwave edge of ELTFLS for DLi and SFi types is the same (i = 1 → Egx (14H1), i = 2 → Egx (10H2), i = 3 → Egx (14H2). Arrows (↓,↑) indicate the areas of the PL spectra for which the excitation spectra were recorded.
Thus, the analysis of the excitation spectra of the DLi luminescence leads to the conclusion that the spectra are in qualitative agreement with the excitation spectrum of ELTPLS luminescence for the appropriate type SFi (ELTPLS DL1 → ELTPLS SF1, ELTPLS DL2 → ELTPLS SF2). Consequently, DL luminescence is related to formation of a new micro-phase during the growth, and DL spectra are also indicators of the corresponding motif forming [23] the main phase adjustment.
4. Conclusion
In this work, photoluminescence spectra of lightly doped SiC crystals with in-grown original defects are reported. Undoped SiC single crystals with the impurity concentration of ND – NA ~ (2…8)(1016 cm–3, NA ~ (2…8)(1017 cm–3, and ND – NA ~ (1…5)(1017 cm–3, ND ( 1(1018 cm–3 were investigated. The analysis of absorption, excitation and low temperature photoluminescence spectra of lightly doped SiC crystals with in-grown original defects suggests formation of a new micro-phase during the growth process and appearance of the deep-level (DL) spectra. The complex spectra of the crystals can be decomposed into the so-called DLi (i = 1, 2, 3, 4) spectra. The appearance of the DLi spectrum is associated with formation of new nano-phases. Data of photoluminescence, excitation and absorption spectra show the uniformity of different DLi spectra. Structurally, the general complexity of the DLi spectra correlated with the degree of disorder of the crystal and was connected with one-dimensional disorder, the same as in the case of the stacking fault (SFi) spectra. The DLi spectra differ from SFi spectra and have other principles of construction and behavior. The DLi spectra are placed on a broad donor-acceptor pairs emission band in crystals with higher concentrations of non-compensated impurities. The excitation spectra for the DLi and SFi spectra coincide and indicate formation of nanostructures 14H1(4334(, 10H2(55(, 14H2(77(, 8H(44(.
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S.I. Vlaskina, Mechanism of 6H-3C transformation in SiC // Semiconductor Physics, Quantum Electronics and Optoelectronics, 5(2), p. 252-255 (2002).
15.
M. Durandurdu, An initio simulations of the structural phase transformation of 2H-SiC at high pressure // Phys. Rev. B, 75, 235204 (2007).
16.
S.W. Lee, S.I. Vlaskina, V.I. Vlaskin, I.V. Zaharchenko, V.A. Gubanov, G.N. Mishinova, 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).
17.
C. Raffy, Furthmüller and Beshtedt, Properties of interface between cubic and hexagonal polytypes in silicon carbide // J. Phys.: Condens. Matter, 14, p. 12725-12731 (2002).
16.
F. Shimojo, I. Ebbsjö, 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.
S. Juillaguet, T. Robert, J. Camassel, Optical investigation of stacking faults in 4H-SiC epitaxial layers: Comparison of 3C and 8H polytypes // Mater. Sci. and Eng. B, 165, p. 5-8 (2009).
18.
S. Shinozaki, K.R. Kisman, Aspects of “one dimensional disorder” in silicon carbide // Acta Metallurgica, 26, p. 769-776 (1978).
19.
L.U. Ogbuji, T.E. Mitchell, A.H. Heuer, The β→α transformation in polycrystalline SiC: The thickening of α plates // J. Amer. Ceram. Soc. 64(2), p. 91-99 (1981).
20.
S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, V.E. Rodionov, G.S. Svechnikov, 6H-3C transformation in heated cubic silicon carbide 3C-SiC // Semiconductor Physics, Quantum Electronics and Optoelectronics, 14(4), p. 432-437 (2013).
21.
S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, G.S. Svechnikov, V.E. Rodionov, S.W. Lee, Silicon carbide phase transition in as-grown 3C-6H – polytypes junction // Semiconductor Physics, Quantum Electronics and Optoelectronics, 16(2), p. 132-136 (2013).
22.
S.I. Vlaskina, G.N. Mishinova, V.I. Vlaskin, V.E. Rodionov, G.S. Svechnikov, 8H-, 10H-, 14H-SiC formation in 6H-3C silicon carbide phase transitions // Semiconductor Physics, Quantum Electronics and Optoelectronics, 16(3), p. 272-278 (2013).
23.
Kozuaki Kobayashi, Shojiro Komatsu. First-principle study of 8H-, 10H-, 12H-, ND 18H-SiC polytypes // J. Phys. Soc. Jpn. Appl. 024714 (2012).
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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