Thermal annealing and evolution of defects in neutron-irradiated cubic SiC
A careful study of neutron-irradiated cubic SiC crystals (3С-SiC(n)) has been performed using electron paramagnetic resonance (EPR) in the course of their thermal annealing within the 200…1100 °C temperature range. Several inherent temperatures have been found for annealing and transformations of pr...
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| Cite this: | Thermal annealing and evolution of defects in neutron-irradiated cubic SiC / V.Ya. Bratus’, R.S. Melnyk, B.D. Shanina, S.M. Okulov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 4. — С. 403-409. — Бібліогр.: 30 назв. — англ. |
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Bratus, V.Ya. Melnyk, R.S. Shanina, B.D. Okulov, S.M. 2017-06-13T18:05:16Z 2017-06-13T18:05:16Z 2015 Thermal annealing and evolution of defects in neutron-irradiated cubic SiC / V.Ya. Bratus’, R.S. Melnyk, B.D. Shanina, S.M. Okulov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 4. — С. 403-409. — Бібліогр.: 30 назв. — англ. 1560-8034 DOI: 10.15407/spqeo18.04.403 PACS 61.72.Bb, 61.72.Ji, 61.80.Fe, 61.82.Fk https://nasplib.isofts.kiev.ua/handle/123456789/121255 A careful study of neutron-irradiated cubic SiC crystals (3С-SiC(n)) has been performed using electron paramagnetic resonance (EPR) in the course of their thermal annealing within the 200…1100 °C temperature range. Several inherent temperatures have been found for annealing and transformations of primary defects in 3С-SiC(n) among which there are isolated negatively charged silicon vacancy VSi⁻, neutral divacancy (VSi–VC)⁰, negatively charged carbon vacancyantisite pair (VC–CSi)⁻ and neutral carbon (100) split interstitial (CC)C⁰. It has been shown that transformation of VSi⁻ into (VC–CSi)⁻ complex is among the mechanisms of silicon vacancy annealing. As it has been established on the basis of the observed hyperfine structure, the secondary T6 center is characterized by the fourfold silicon coordination and assigned to the spin S = 3/2 carbon vacancy-related pair defect. The symmetry reduction of the (VC–VSi)⁰ center is attributed to local rearrangements in the neighborhood of divacancy, and its intensity variations are assigned to changes of the Fermi-level position. Two defects with similar symmetry and close values of zero-field splitting constants D, which concentrations increase by a factor of ten after annealing at 900 °С, are tentatively attributed to the (100) split interstitial (CC)C⁰ and (NС)С⁰ pairs The authors are grateful to the Center of Shared Research Equipment of Institute of Magnetism of the National Academy Science of Ukraine for placing at their disposal the EPR spectrometer for some temperature measurements en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Thermal annealing and evolution of defects in neutron-irradiated cubic SiC Article published earlier |
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Thermal annealing and evolution of defects in neutron-irradiated cubic SiC |
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Thermal annealing and evolution of defects in neutron-irradiated cubic SiC Bratus, V.Ya. Melnyk, R.S. Shanina, B.D. Okulov, S.M. |
| title_short |
Thermal annealing and evolution of defects in neutron-irradiated cubic SiC |
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Thermal annealing and evolution of defects in neutron-irradiated cubic SiC |
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Thermal annealing and evolution of defects in neutron-irradiated cubic SiC |
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Thermal annealing and evolution of defects in neutron-irradiated cubic SiC |
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thermal annealing and evolution of defects in neutron-irradiated cubic sic |
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Bratus, V.Ya. Melnyk, R.S. Shanina, B.D. Okulov, S.M. |
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Bratus, V.Ya. Melnyk, R.S. Shanina, B.D. Okulov, S.M. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Article |
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A careful study of neutron-irradiated cubic SiC crystals (3С-SiC(n)) has been performed using electron paramagnetic resonance (EPR) in the course of their thermal annealing within the 200…1100 °C temperature range. Several inherent temperatures have been found for annealing and transformations of primary defects in 3С-SiC(n) among which there are isolated negatively charged silicon vacancy VSi⁻, neutral divacancy (VSi–VC)⁰, negatively charged carbon vacancyantisite pair (VC–CSi)⁻ and neutral carbon (100) split interstitial (CC)C⁰. It has been shown that transformation of VSi⁻ into (VC–CSi)⁻ complex is among the mechanisms of silicon vacancy annealing. As it has been established on the basis of the observed hyperfine structure, the secondary T6 center is characterized by the fourfold silicon coordination and assigned to the spin S = 3/2 carbon vacancy-related pair defect. The symmetry reduction of the (VC–VSi)⁰ center is attributed to local rearrangements in the neighborhood of divacancy, and its intensity variations are assigned to changes of the Fermi-level position. Two defects with similar symmetry and close values of zero-field splitting constants D, which concentrations increase by a factor of ten after annealing at 900 °С, are tentatively attributed to the (100) split interstitial (CC)C⁰ and (NС)С⁰ pairs
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Thermal annealing and evolution of defects in neutron-irradiated cubic SiC / V.Ya. Bratus’, R.S. Melnyk, B.D. Shanina, S.M. Okulov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 4. — С. 403-409. — Бібліогр.: 30 назв. — англ. |
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| first_indexed |
2025-11-25T23:52:48Z |
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2025-11-25T23:52:48Z |
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1850588874964729856 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 403-409.
doi: 10.15407/spqeo18.04.403
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
403
..PACS 61.72.Bb, 61.72.Ji, 61.80.Fe, 61.82.Fk
Thermal annealing and evolution of defects
in neutron-irradiated cubic SiC
V.Ya. Bratus’, R.S. Melnyk, B.D. Shanina, S.M. Okulov
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
45, prospect Nauky, 03680 Kyiv, Ukraine
e-mail: v_bratus@isp.kiev.ua, melnyk_rs@yahoo.com, shanina_bela@rambler.ru, okulov@isp.kiev.ua
Abstract. A careful study of neutron-irradiated cubic SiC crystals (3С-SiCn) has been
performed using electron paramagnetic resonance (EPR) in the course of their thermal
annealing within the 200…1100 °C temperature range. Several inherent temperatures
have been found for annealing and transformations of primary defects in 3С-SiCn
among which there are isolated negatively charged silicon vacancy VSi
, neutral
divacancy (VSi–VC)
0
, negatively charged carbon vacancyantisite pair (VC–CSi)
and
neutral carbon 100 split interstitial (CC)C
0
. It has been shown that transformation of
VSi
into (VC–CSi)
complex is among the mechanisms of silicon vacancy annealing. As
it has been established on the basis of the observed hyperfine structure, the secondary T6
center is characterized by the fourfold silicon coordination and assigned to the spin
S = 3/2 carbon vacancy-related pair defect. The symmetry reduction of the (VC–VSi)
0
center is attributed to local rearrangements in the neighborhood of divacancy, and its
intensity variations are assigned to changes of the Fermi-level position. Two defects with
similar symmetry and close values of zero-field splitting constants D, which
concentrations increase by a factor of ten after annealing at 900 °С, are tentatively
attributed to the 100 split interstitial (CC)C
0
and (NС)С
0
pairs.
Keywords: paramagnetic defect, EPR, neutron irradiation, silicon carbide, defect
annealing, zero-field splitting.
Manuscript received 02.06.15; revised version received 09.09.15; accepted for
publication 28.10.15; published online 03.12.15.
1. Introduction
The special features of silicon carbide polytypes,
namely: wide bandgap, large thermal conductivity, high
mobility of carries and breakdown electric field [1],
enable to consider them as one of the most promising
materials for high-power, high-frequency and high-
temperature electronics [2]. Application of SiC devices
for radiation-resistant and high-temperature operation
necessitates detailed knowledge of intrinsic and
irradiation damage defects and their thermal stability.
Primary defects generated by high-energy particles in
binary SiC compounds are vacancies, interstitials,
Frenkel pairs and antisites. Comprehensive information
concerning the microscopic structure of defects can be
extracted using investigations with magnetic resonance
techniques like electron paramagnetic resonance (EPR),
electron-nuclear double resonance (ENDOR) and
optically detected magnetic resonance [3]. As a general
rule, in these investigations a tentative model of a defect
is based on the analysis of its spin-Hamiltonian
parameters, mainly, the fine and hyperfine (HF)
structure of EPR spectra. As of now, to verify the
proposed model the first-principle calculations of the
spin state, symmetry and hyperfine parameters for an
assumed charge state are widely used [4].
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 403-409.
doi: 10.15407/spqeo18.04.403
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
404
Mention should be made of a renewed interest in the
high-spin defects in SiC since they can be used as solid-
state quantum bits even at room temperature along with
the nitrogen-vacancy pair center in diamond [5]. Among
the paramagnetic defects found in SiC, a great deal of
high-spin S = 1 and S = 3/2 centers have been detected
after electron as well as neutron, proton and -particle
irradiation [6-10]. For hexagonal polytypes of SiC, the
vacancy-related defects are reviewed in [11]. The
microscopic structure of isolated negatively charged sili-
con vacancy
SiV having Td symmetry has been identified
with confidence in 3C, 4H and 6H polytypes of SiC [8, 9,
12], its high spin state S = 3/2 has been determined with
additional ENDOR study [8]. The negative-U behavior
has been found for spin S = 1/2 negative carbon vacancy
(VC
−
) at both hexagonal and quasi-cubic lattice sites [13].
Almost ten spin-one defects with parameters closely
related to that of irradiated crystals have been revealed
after quenching and thermal treatment of 6H-SiC crystals
[14]. Nevertheless, the microscopic structure for many of
them is still discussed.
Considerably less information about high-spin
defects has been obtained in cubic SiC. Apart from the
spin S = 3/2 negatively charged silicon monovacancy,
the so-called T1 center, T6 and T7 centers were proposed
to be some forms of spin-one vacancy-interstitial pairs
after electron irradiation [12]. The LE1 center with the
spin S = 3/2 detected after low-temperature electron
irradiation was assigned to the Frenkel pair of silicon
vacancy VSi and the second neighbor silicon interstitial
Sii in the 3
+
charge state [15]. Noteworthy also are the
numerous theoretical studies of damage recovery in
cubic SiC that revealed various defect migration
pathways with the energy barriers lower than 1 eV (see,
e.g., [16, 17] and references therein). But there is only
little direct experimental information concerning these
aspects as yet.
Neutron irradiation attracts attention of researchers
with the potentialities for creating spin-one [7] and
extended defects [18]. In our previous study [19], it has
been shown that the T1 center and the spin-one neutral
silicon-carbon divacancy (VSi – VC)
0
, the Ky5 center, are
the dominant primary defects in relatively high-dose
neutron-irradiated 3C-SiC bulk crystals. In this work, the
results of EPR studying the thermal annealing influence
on radiation damage in these samples have been
reported. Some preliminary results of this study have
already been presented in [20].
2. Experimental
Unintentionally doped n-type cubic SiC single crystals
were grown by thermal decomposition of methyl-
trichlorosilane in hydrogen [21], the concentration of the
unavoidable nitrogen impurity was no more than
10
17
cm
–3
. The crystals were irradiated at room
temperature by reactor neutrons with the dose close to
10
19
cm
–2
, in what follows they will be designated as
3C-SiCn. Owing to high neutron penetration into SiC
[22], the distribution of generated defects may be
considered as uniform and homogeneous.
Post-irradiation isochronal thermal annealing
procedures were carried out for 10 minutes within the
200 to 1100 °C temperature range in ambient gaseous
He. The EPR study of defects was carried out within the
temperature range 77…300 K in the X-band (microwave
frequency mw 9.32…9.45 GHz). The angular varia-
tions of EPR spectra were measured for a rotation of the
magnetic field in the (1 1 0) crystal plane. The
concentration of defects was determined with EPR by
comparison with a MgO:Mn
2+
reference sample that
contained the known number of spins. To estimate
quantitatively the g-value and concentration of
irradiation-induced defects, the studied sample and
reference one were placed together into a microwave
resonator. The number of defects was determined by
comparing the double integrals of the first derivatives of
the absorption signals registered on the investigated and
reference specimens. The g-values of defects were
determined with the accuracy g = 0.0001 by using a
microwave frequency counter and calibrating the
magnetic field with a proton NMR probe.
3. Results and discussion
A. Annealing of the negatively charged silicon
monovacancy
Fig. 1 shows the EPR spectra of a 3C-SiCn sample
measured at 300 K before and after step-by-step thermal
annealing with the magnetic field direction parallel to
the 111 crystal axis. The as-irradiated unannealed
sample demonstrates an isotropic spectrum with the g-
value of 2.0029 and four sets of superhyperfine (SHF)
doublets with splitting typical to the T1 center [12]
superimposed by a broad more intense structureless
slightly anisotropic background line BG. Components of
the T1 spectrum are broadened when comparing with
those in electron-irradiated samples [12] due to a high
concentration of this and additional defects making
contribution to the BG spectrum. The total concentration
of paramagnetic defects determined by EPR is equal
to 2.7∙10
19
cm
–3
, exhibiting the high production rate
of neutron irradiation for 3C-SiC, no less than
2.7 defects/cm
3
per one neutron/cm
2
.
Annealing within the 200...500 °C interval leaves
the EPR spectra of 3C-SiCn samples unaffected,
qualitative and quantitative changes of them are
evidenced after annealing at 600 °C. From this point on,
when the total concentration of defects becomes
approximately one and a half times less mainly at the
expense of the background line, the T1 spectrum turns to
the symmetric shape (Fig. 1). The following annealing
step at 700 °C decreases the total concentration of
defects more than an order of magnitude, the T1 signal is
dramatically diminished and completely disappears after
the subsequent annealing at 800 °C. The remainder of
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 403-409.
doi: 10.15407/spqeo18.04.403
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
405
the BG line includes at least two independent spectra,
and it will no longer be discussed here. After annealing
at 700 °C, an axial spin S = 1/2 defect with the g-tensor
components g = 2.0024, g = 2.0039 and principal axis
along the 111 crystal direction, labeled Ky6 and
tentatively assigned to the negatively charged carbon
vacancycarbon antisite pair (VC–CSi)
–
[20] is observed
within the temperature range 77…200 K as the dominant
paramagnetic center (Fig. 2).
Contrary to the samples 3C-SiC irradiated with
electrons, appearance of the intense background line BG
in the 3C-SiCn samples should be related with the defect
regions formed in the result of cascade displacements.
Their first stage of annealing at 600 °C as well as
considerable decrease in the intensity of the BG spectrum
correlate with annealing of partly amorphized regions in
the 4H-SiC sample implanted with aluminum ions [23]
and theoretical calculations of defects thermal annealing
mechanisms in heavy-ion irradiated 3C-SiC [24]. Further,
the BG line gradually decreases its intensity.
Among possible mechanisms of annealing inherent
to silicon monovacancies, there theoretically considered
were Frenkel pair recombination with silicon split
interstitials and transformation of the silicon vacancy
into a carbon vacancy–antisite complex VC–CSi [16, 25].
However, any experimental confirmation was not
reported up to date. In our case, the central part of the Т1
spectrum is easily saturated even at room temperature, at
the same time lines of the HF structure are saturated at
one order higher powers. At 77 K, the central part of the
T1 spectrum is fully saturated, and only the lines of HF
structure near the lines of hyperfine structure inherent to
the Kу6 center can be registered (Fig. 2).
Fig. 1. EPR spectra of a 3C-SiCn sample before and after its
step-by-step thermal annealing observed at T = 300 K. The
magnetic field direction B0 is parallel to the [111] axis,
microwave frequency ν = 9.437 GHz.
Fig. 2. EPR spectra of a 3C-SiCn sample before annealing
(a, b) measured at T = 320 K (a), T = 77K (b), and after
annealing at 900 °C, T = 77K (c); B0 || [112], ν = 9.447 GHz.
The dashed vertical lines represent positions of some HF
structure lines of the T1 and Ky6 centers.
Contrary to the EPR spectra obtained at room
temperature after annealing of the samples at 700 °C
(Fig. 1), the decrease in the intensity of lines Kу6 + BG
at 77 K in the central part of the spectrum is
insignificant, and the intensity of the Kу6 spectrum can
be estimated with account of the intensity of lines in
the HF structure. As seen from Fig. 3, the intensity of
these lines grows doubly after annealing at 700 °C,
which can be indicative of partial transformation of the
defects T1 into the Ky6 defects. On the other hand, the
possibility of the VSi
transformation to a diamagnetic
charge state of the VC–CSi complex must not be ruled
out. According to calculations within the GW
approximations [25], the complex carries a 2
+
charge
state in the major part of the band gap of 3C-SiC.
Further, the Ky6 spectrum gradually decreases in its
intensity but keeps observable even after annealing at
1100 °C. The observed behavior of the T1 centers
during their annealing correlates with the results of
theoretical calculations performed in the works [16, 17,
25, 26]. In accord with hierarchy of annealing
mechanisms, the high mobility of interstitial C and Si
atoms, as compared to vacancies, provides their
annealing at low temperatures. Transition of silicon
vacancies from the metastable form to the stable
configuration VC–CSi requires to overcome a definite
energy barrier, that is higher annealing temperature.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 403-409.
doi: 10.15407/spqeo18.04.403
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
406
Fig. 3. EPR spectra of a 3C-SiCn sample before and after its
step-by-step annealing up to 800 °C; T = 77 K, B0 || [112],
ν = 9.256 GHz.
B. Neutral divacancy behavior with annealing
In addition to the above-listed spectra, the components of
the Ky5 center are observed with higher gain in the
extended magnetic field range (Fig. 4). The initial
concentration of this defect is found to be 3.0∙10
17
cm
–3
. In
a similar way to the T1 center, changes in the Ky5
spectrum intensity start after annealing at 600 °C. Then it
becomes hardly visible after annealing at 700 °C and
intensifies with full annealing of the silicon monovacancy
at 800 °C. It should be noted that annealing of VSi is not
accompanied by any additional growth in the intensity of
the Ky5 divacancy spectrum. Simultaneously, a new
spectrum labeled as Ky5′ emerges with a higher value of
the zero-field splitting than that for the Ky5 center, it
becomes clearly determined after annealing at 900 °C.
With the following annealing step at 1000 °C, intensities
of the Ky5 and Ky5′ centers are strongly reduced and
appearance of several additional lines with further
enhanced zero-field splitting is observed.
A considerable decrease in the intensity of the Ky5
spectrum for the sample annealed at 700 °C and its further
restoration after annealing at 800 °C can be related with
changing the Fermi level. Indeed, as it will be shown
below, after annealing at 700 °C additional lines from new
paramagnetic defects appear in the EPR spectra. Besides,
lowering the temperatures down to the helium ones, there
can be detected the EPR lines belonging to the Ky7
centers that were attributed to negatively charged
divacancies [19]. Appearance of new Kу5′ centers can be
related with mobility of divacancies at high annealing
temperatures as well as their capture by impurities that
occupy substitutional or interstitial positions in SiC lattice.
It is significant to note that the intensity of the Ky5′
spectrum grows at the expense of the Ky5 one after
annealing at 900 °C. The following “multiplication” of the
Ky5′ spectrum is probably related with capture of
divacancies by other impurities. As it was shown using
mass-spectrometry of secondary ions, beside the nitrogen
impurity in irradiated 3C-SiCn crystals, there present are
impurities of Al, P, In and some metals.
Fig. 4. EPR spectra of the Ky5 center in 3C-SiCn sample
before and after its step-by-step annealing; T = 300K,
B0 || [111], ν = 9.437 GHz.
The Ку5′ center, similar to the Ky5 one, possesses
the g-value of 2.003 and can be described by the tensor
of fine interaction with the direction of main axis along
the 111 crystal direction, however, with a little higher
value of fine interaction constant D. Simultaneously with
its appearance, one can observe lowering symmetry of
the Ky5 center, when in addition to the axial component
of crystalline field there appears the rhombic one. For
the samples annealed at temperatures higher than
800 °C, the spin Hamiltonian inherent to these centers
looks as follows:
222 )1()(ˆˆ
yxzz SSESSSDHH . (1)
Taking into account availability of magnetically
non-equivalent positions in cubic crystal, this
Hamiltonian is the matrix with the following diagonal
elements:
.)(5.0)(
,)(
,)(5.0)(
33
22
11
DHH
DH
DHH
(2)
Where the Zeeman term should be written as
)(sin)(cos)( 22
|| ggHH (3)
and splitting in the zero field
,)(sin
2
1
3
1
,1)7.54(cos3
3
1
,1)7.54(cos3
3
1
)('
2
2
2
ED
ED
ED
D (4)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 403-409.
doi: 10.15407/spqeo18.04.403
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
407
where is the energy, and the angle between direction
of the magnetic field and the crystal axis 100. The expe-
rimentally determined constants of the spin Hamiltonian
for the center Ky5 are equal to D = 471∙10
–4
cm
–1
and
E = –11∙10
–4
cm
–1
. The paramagnetic center Kу5′ is
described by slightly higher values of axial and rhombic
constants D = 489∙10
–4
cm
–1
and E = –19∙10
–4
cm
–1
. Thus,
the centers Kу5 and Kу5′ possess the similar angle
dependence of EPR spectra, and their radio-spectroscopic
parameters differ only within 5%.
We believe that this behaviour is an indication of
local rearrangement in the neighborhood of divacancy
and its intensity variations stem from a change of the
Fermi-level position. Apparently, disappearance of the
Ky5 EPR signal after annealing at 1000 and 1100 °C is
an evidence of neutral divacancy recharging, since this
defect has extremely high thermal stability in SiC [11].
С. Carbon vacancy-related complex defects
A considerable decrease in the intensity of the spectrum
inherent to the primary defect T1 after annealing at
700 °C is accompanied by appearance of new EPR
spectra that belong to secondary defects. Available
among them are lines of the known defect T6 that was
attributed to the spin-one vacancy-interstitial pair [12].
In 3C-SiCn samples, the Т6 spectrum has a much
shorter spin-lattice relaxation time and can be readily
picked out at higher level of the microwave power.
Contrary to irradiated with electrons epitaxial
monocrystalline 3C-SiC films [12], the central lines in
T6 spectra in the studied samples 3C-SiCn are
observed along with several pairs of satellite lines
(Fig. 5). Like to spectra of negatively charged carbon
vacancies VC
–
with the spin S = 1/2 in the polytype
4H-SiC [13], the ratio of intensities of satellite lines for
Si1 and Si2-4 to that of the central line reaches the values
5 and 13%, respectively. The pairs of lines with the
splitting similar to those of Si2-4 lines are also observed
both on low-field and high-field wings of the central part
in the spectrum belonging mainly to the Ky6 defect. Our
analysis of the EPR spectra showed that these pairs
cannot be related with the spectrum of the Ky6 centers.
Besides, changes in the intensity of these lines during
annealing of the samples correlate with changes in the
intensity of EPR lines related to the T6 spectrum with
account of their possible association.
Making assumption that these lines are related to the
lines of HF structure concerned with the central transition
1/2 –1/2 of the defect with the spin S = 3/2, we
performed description of the line positions for experi-
mental EPR spectra. As it was ascertained, the latter are
considerably better described by Hamiltonian (1) with the
spin S = 3/2 than with the spin S = 1 (Fig. 4) as well as
parameters g|| = 2.0021, g = 2.0044 and the principal
value of the fine interaction tensor D = 6.53 mT
(183 MHz) oriented along the 111 direction. The values
of HF splitting constants are equal for one silicon atom Si1
A|| = 1.08 mT (30.1 MHz), A = 0.85 mT (23.8 MHz) and
for three equivalent silicon atoms Si2-4 A|| = 5.88 mT
(164.8 MHz), A = 4.25 mT (119.1 MHz). In this case, the
principal axes of the HF interaction tensors are also
oriented along the 111 direction. Since the isolated
carbon vacancy has the spin S = 1/2 and as a negative-U
center is detectable only under optical excitation [13], we
should make the assumption that the T6 defect is complex
and consists of the pair VC–X with the spin S = 3/2, where
the letter Х designates still unknown atom in the vicinity
of VC
–
. As it was predicted earlier [12], it may be the atom
C or Si in the nearest tetrahedral interstitial position.
These defects possess high thermal stability. The intensity
of the T6 center EPR lines grows after annealing at
temperatures from Tann = 700 °C up to 900 °C and remains
practically unchanged after following annealing at the
temperature Tann = 1100 °C. It means that transition of the
X atom into the vacancy position is separated with a high-
energy barrier. In general, ascertaining the nature of X
atoms requires additional investigations by using ENDOR
and theoretical calculations.
D. Carbon 100 split interstitials
Simultaneously with appearance of spectra
corresponding to the T6 defect, the intensity of EPR
lines related with new anisotropic centers is considerably
increased (Fig. 6). The observed lines can be represented
as superposition of two spectra for Kу8 and Kу8′ centers
that possess the electron spin S = 1 and are characterized
by insignificant differences in the value of the fine
structure constant D. The direction of the principal axis
for the tensor of fine interaction coincides with the 100
direction in crystal lattice.
Fig. 5. a) EPR spectra of the T6 center measured at T = 77 K
and ν = 9.264 GHz for a rotation of the magnetic field in the
( 011 ) plane, θ = 0° corresponds to the [001] crystal direction.
The symbols present experimental line positions, solid and
dashed lines are calculated according to the parameters listed
in the text. b) Hyperfine lines of the high-field component of
the T6 spectrum, θ = 55°. c) Hyperfine lines attributed to the
(1/2 ↔ –1/2) transition of the spin S = 3/2 T6 center, θ = 55°.
The latter is hidden under more intense Ky6 spectrum which is
disturbed by high level of microwave power and modulation
amplitude.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 403-409.
doi: 10.15407/spqeo18.04.403
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
408
Fig. 6. Angular dependence of the Ky8 and Ky8′ spectra for a
3C-SiCn sample annealed at 900 °C, T = 77 K,
ν = 9.264 GHz. The dashed lines are calculated according to
the parameters presented in the text.
The resonance magnetic fields were found using
the following expression:
Hg
D
DfHgh
2
, , (5)
where the first term is related with Zeeman splitting,
while the second one describes fine splitting with
account of the second order correction. Being based on
calculations [27, 28] and using the spin value S = 1, the
expression for calculation of the angular dependence for
EPR lines can be simplified, and resonance positions of
the lines can be described by the formula:
42
0
2
2
0 sin2sin
8
1cos3
H
D
DHHr , (6)
where Hr is the resonance position of EPR line, H0 –
magnetic field value that corresponds to the Zeeman
term, and the second and third terms describe fine
splitting and the second order correction.
Fig. 6 shows the experimentally obtained at 77 K
angular dependence for EPR lines of the sample
annealed at the temperature 900 °C. The paramagnetic
centers Kу8/Ky8′ possess the same symmetry, g-factor
and direction of the D-tensor axis and differ only by the
values of their fine-splitting constants: g =
2.000 ± 0.010, D ≈ 589∙10
–4
cm
–1
for Kу8 and D ≈
646∙10
–4
cm
–1
for Kу8′ at Т = 77 K. These values are
close by their order to that calculated from the first
principles D-constant for the 100 carbon split
interstitial (СС)С (i.e., two carbon atoms that share one
C-site) in 3C-SiC in the neutral charge state
|D| = 670∙10
–4
cm
–1
[29]. Thus, like to the case of
divacancies Kу5/Kу5′, the spectra of Kу8/Kу8′ centers
belong to two similar defects.
When analyzing diffusion of nitrogen atoms, beside
the (СС)С defect, the authors of [30] considered the pair
of atoms (NС)С that also forms the interstitial defect split
in the direction 100. Since the D-constant value is
determined both by dipole-dipole and spin-orbital
interactions [28], and the latter is higher for nitrogen
atoms, then the Kу8 spectrum is tentatively related by us
with the pair (СС)С, while the Kу8′ spectrum with the
split interstitial (NС)С. It should be noted that the EPR
lines of Kу8/Kу8′ centers have low intensity also in
unannealed samples, which means that they are primary
defects in 3C-SiCn, they considerably grow after
annealing at Tann = 900 °C and are doubly decreased
after annealing at Tann = 1100 °C.
4. Conclusions
Thus, thermal annealing of 3С-SiCn samples enabled to
find several temperatures that provide annealing and
transformation of primary defects, i.e., VSi
, as well as
pairs (VC–CSi)
, (VSi–VC)
0
and (CC)C
0
. At Tann = 600 °С,
there takes place annealing of defects of the vacancy type
and broken bonds in the regions related with cascade
displacements and mainly conditioned by a high mobility
of interstitial atoms. Annealing of negatively charged
silicon monovacancies VSi
takes place within the
temperature interval Tann = 700…800 °C, the partial
transformation VSi
(VC – CSi)
has been registered in
this interval. Appearance of the T6 centers after annealing
within this interval is indicative of formation of pairs with
intrinsic atoms or impurities being one of the possible
ways for VC transformation in the 3C-SiCn samples.
As concerning divacancies, their detection
essentially depends on position of the Fermi level in
annealed samples, and lowering symmetry after
annealing at Tann = 800 °C can be related with capture of
these defects by impurity atoms. It should be also noted
that for all the above defects, starting from Tann =
600 °C, one can observe gradual narrowing of the EPR
lines, which is indicative of progressive ordering the
structure of irradiated samples.
Acknowledgment
The authors are grateful to the Center of Shared
Research Equipment of Institute of Magnetism of the
National Academy Science of Ukraine for placing at
their disposal the EPR spectrometer for some
temperature measurements.
References
1. Silicon Carbide: Recent Major Advances, ed. by
W.J. Choyke, H. Matsunami, G. Pensl. Springer
Berlin, Heidelberg, 2004.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 4. P. 403-409.
doi: 10.15407/spqeo18.04.403
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
409
2. Silicon Carbide, V. 2: Power Devices and Sensors,
ed. by P. Friedrichs, T. Kimoto, L. Ley, G. Pensl.
Wiley-VCH Verlag GmbH, Weinheim 2011.
3. J.M. Spaeth, J.R. Niklas, R.H. Bertram, Structural
Analysis of Point Defects in Solids. Springer Berlin,
1992.
4. V.Ya. Bratus’, T.T. Petrenko, S.M. Okulov,
T.L. Petrenko, Positively charged carbon vacancy
in three inequivalent lattice sites of 6H-SiC:
combined EPR and density functional theory study
// Phys. Rev. B, 71(12), 125202 (2005).
5. W.F. Koehl, B.B. Buckley, F.J. Heremans,
G. Calusine, D. Awschalom, Room temperature
coherent control of defect spin qubit in silicon
carbide // Nature, 479, p. 84-87 (2011).
6. L.A. de S. Balona, J.H.N. Loubser, ESR in
irradiated silicon carbide // J. Phys. C: Solid State
Phys. 3, p. 2344-2351 (1970).
7. N.M. Pavlov, M.I. Iglitsyn, M.G. Kasaganova,
V.N. Solomatin, Centers having spin 1 in silicon
carbide irradiated with neutrons and -particles //
Sov. Phys. Semiconductors, 9, p. 845-849 (1975).
8. T. Wimbauer, B.K. Meyer, A. Hofstätter,
A. Scharmann, H. Overhof, Negatively charged Si
vacancy in 4H SiC: A comparison between theory and
experiment // Phys. Rev. B, 56, p. 7384-7388 (1997).
9. H.J. von Bardeleben, J.L. Cantin, I. Vickridge,
G. Battistig, Proton-implantation-induced defects in
n-type 6H- and 4H-SiC: An electron paramagnetic
resonance study // Phys. Rev. B, 62, p. 10126-
10134 (2000).
10. H.J. von Bardeleben, J.L. Cantin, L. Henry,
M.F. Barthe, Vacancy defects in p-type 6H-SiC
created by low-energy electron irradiation // Phys.
Rev. B, 62, p. 10841-10846 (2000).
11. J. Isoya, T. Umeda, N. Mizuochi, N.T. Son, E. Jan-
zen, T. Ohshima, EPR identification of intrinsic
defects in SiC // physica status solidi (b), 245,
p. 1298-1314 (2008).
12. H. Itoh, A. Kawasuso, T. Ohshima et al., Intrinsic
defects in cubic silicon carbide // physica status solidi
(a), 162, p. 173-198 (1997).
13. X.T. Trinh, K. Szasz, T. Hornos, K. Kawahara,
J. Suda, T. Kimoto, A. Gali, E. Janzen, and
N.T. Son, Negative-U carbon vacancy in 4H-SiC:
Assessment of charge correction schemes and
identification of the negative carbon vacancy at the
quasicubic site // Phys. Rev. B, 88, 235209 (2013).
14. V.S. Vainer, V.A. Il’in, EPR of exchanged-coupled
vacancy pairs in hexagonal silicon carbide // Sov.
Phys. Solid State, 23, p. 2125-2131 (1981).
15. N.T. Son, E. Janzen, J. Isoya et al., Identification of
a Frenkel-pair defect in electron-irradiated 3C SiC //
Phys. Rev. B, 80, 125201 (2009).
16. M. Bockstedte, A. Mattausch, O. Pankratov,
Ab initio study of the migration of intrinsic defects
in 3C-SiC // Phys. Rev. B, 68, 205201 (2003).
17. M.J. Zheng, N. Swaminathan, D. Morgan, I. Szlu-
farska, Energy barriers for point-defect reactions in
3C-SiC // Phys. Rev. B, 88, 054105 (2013).
18. I.V. Ilyin, M.V. Muzafarova, E.N. Mokhov,
P.G. Baranov, Electron paramagnetic resonance
studies of multi-defect clusters in neutron irradiated
silicon carbide // Semicond. Sci. Technol. 22,
p. 270-278 (2007).
19. V.Ya. Bratus’, R.S. Melnik, S.M. Okulov,
V.N. Rodionov, B.D. Shanina, M.I. Smoliy, A new
spin one defect in cubic SiC // Physica B, 404,
p. 4739-4741 (2009).
20. V. Bratus’, R. Melnik, S. Okulov, B. Shanina,
V. Golub, I. Makeeva, An EPR study of defects in
neutron-irradiated cubic SiC crystals // Mater. Sci.
Forum, 740-742, p. 361-365 (2013).
21. S.N. Gorin, L.M. Ivanova, Cubic silicon carbide
(3C-SiC): structure and properties of single crystals
grown by thermal decomposition of methyl
trichlorosilane in hydrogen // physica status solidi
(b), 202, p. 221-245 (1997).
22. F. Maekawa, K. Ochiai, K. Shibata, Y. Kasugai,
M. Wada, Y. Morimoto, H. Takeuchi, Benchmark
experiment on silicon carbide with D–T neutrons
and validation of nuclear data libraries // Fusion
Eng. and Design, 58-59, p. 595-600 (2001).
23. Y. Zhang, W.J. Weber, W. Jiang, A. Hallén,
G. Possnert, Damage evolution and recovery on
both Si and C sublattices in Al-implanted 4H–SiC
studied by Rutherford backscattering spectroscopy
and nuclear reaction analysis // J. Appl. Phys. 91,
p. 6388 (2002).
24. D. Guo, I. Martin-Bragado, C. He, H. Zang,
P. Zhang, Modeling of long-term defect evolution
in heavy-ion irradiated 3C-SiC: Mechanism for
thermal annealing and influences of spatial
correlation // J. Appl. Phys. 116, 204901 (2014).
25. F. Bruneval, G. Roma, Energetics and metastability
of the silicon vacancy in cubic SiC // Phys. Rev. B,
83, 144116 (2011).
26. M. Bockstedte, A. Mattausch, O. Pankratov,
Ab initio study of the annealing of vacancies and
interstitials in cubic SiC: Vacancy–interstitial
recombination and aggregation of carbon
interstitials // Phys. Rev. B, 69, 235202 (2004).
27. B. Bleaney, D.J.E. Ingram, The paramagnetic
resonance spectra of two salts of manganese //
Proc. Roy. Soc. Lond. A, 205, p. 336-356 (1951).
28. А. Аbragam, B. Bleaney, Electron Paramagnetic
Resonance of Transition Ions. V. 1, M., Mir, 1972.
29. T.T. Petrenko, T.L. Petrenko, V.Ya. Bratus’, The
carbon 100 split interstitial in SiC // J. Phys.:
Condens. Matter. 14, p. 12433-12440 (2002).
30. U. Gerstmann, E. Rauls, Th. Frauenheim, and
H. Overhof, Formation and annealing of nitrogen-
related complexes in SiC // Phys. Rev. B, 67,
p. 205202 (2003).
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