Mechanism of 6H-3C transformation in SiC
Heavily doped by nitrogen single crystals of 6H-SiC were completely transformed into 3C-SiC ones by annealing in vacuum at presence of Si vapor for 1 hour at 2180 K or 4 hours at 2080 K. Mechanism of solid-to-solid transformation have been studied. Calculated nitrogen concentration from the Hall eff...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2002
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| Zitieren: | Mechanism of 6H-3C transformation in SiC / S.I. Vlaskina // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 152-155. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-1211882017-06-14T03:06:38Z Mechanism of 6H-3C transformation in SiC Vlaskina, S.I. Heavily doped by nitrogen single crystals of 6H-SiC were completely transformed into 3C-SiC ones by annealing in vacuum at presence of Si vapor for 1 hour at 2180 K or 4 hours at 2080 K. Mechanism of solid-to-solid transformation have been studied. Calculated nitrogen concentration from the Hall effect and EPR spectra for transformed crystals show its decreasing value in 3C-SiC. Data show appearance of new defects - donors and acceptors - that make nitrogen optically and electrically non-active. These defects accompany the process of transformation. 2002 Article Mechanism of 6H-3C transformation in SiC / S.I. Vlaskina // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 152-155. — Бібліогр.: 5 назв. — англ. 1560-8034 PACS: 77.84.B http://dspace.nbuv.gov.ua/handle/123456789/121188 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Heavily doped by nitrogen single crystals of 6H-SiC were completely transformed into 3C-SiC ones by annealing in vacuum at presence of Si vapor for 1 hour at 2180 K or 4 hours at 2080 K. Mechanism of solid-to-solid transformation have been studied. Calculated nitrogen concentration from the Hall effect and EPR spectra for transformed crystals show its decreasing value in 3C-SiC. Data show appearance of new defects - donors and acceptors - that make nitrogen optically and electrically non-active. These defects accompany the process of transformation. |
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Vlaskina, S.I. |
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Vlaskina, S.I. Mechanism of 6H-3C transformation in SiC Semiconductor Physics Quantum Electronics & Optoelectronics |
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Vlaskina, S.I. |
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Vlaskina, S.I. |
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Mechanism of 6H-3C transformation in SiC |
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Mechanism of 6H-3C transformation in SiC |
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Mechanism of 6H-3C transformation in SiC |
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Mechanism of 6H-3C transformation in SiC |
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Mechanism of 6H-3C transformation in SiC |
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mechanism of 6h-3c transformation in sic |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2002 |
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http://dspace.nbuv.gov.ua/handle/123456789/121188 |
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Mechanism of 6H-3C transformation in SiC / S.I. Vlaskina // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 152-155. — Бібліогр.: 5 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT vlaskinasi mechanismof6h3ctransformationinsic |
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2025-07-08T19:22:02Z |
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Semiconductor Physics, Quantum Electronics & Optoelectronics. 2002. V. 5, N 2. P. 152-155.
© 2002, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine152
PACS: 77.84.B
Mechanism of 6H-3C transformation in SiC
S.I. Vlaskina
Institute of Semiconductor Physics, NAS of Ukraine, 45 prospect Nauky, 03028 Kiev, Ukraine
Phone: +380(44) 269 3792; fax +380(44) 265 8342; e-mail:businkaa@mail.ru
Dong Seoul College, 461-714, 423,
Bokjung-Dong, Sungnam- city, Kyonggi-do, Korea
Phone: 82(031)7202141; fax 82(0342)7202261; e-mail:svitlana@haksan.dsc.ac.kr
Abstract. Heavily doped by nitrogen single crystals of 6H-SiC were completely transformed
into 3C-SiC ones by annealing in vacuum at presence of Si vapor for 1 hour at 2180 K or 4
hours at 2080 K. Mechanism of solid-to-solid transformation have been studied. Calculated
nitrogen concentration from the Hall effect and EPR spectra for transformed crystals show its
decreasing value in 3C-SiC. Data show appearance of new defects � donors and acceptors �
that make nitrogen optically and electrically non-active. These defects accompany the process
of transformation.
Keywords: silicon carbide, phase transformation.
Paper received 11.02.02; revised manuscript received 28.05.02; accepted for publication 25.06.02.
1. Introduction
Many attempts have been made to explain polytypism in
SiC, ZnS, CdJ2. The transformation from one polytype
to another takes place in gas phase [1-2] or in solid state
[3-4] and can be considered both from thermodynamic
and kinetic points of view. In most experiments dealing
with polytypism, β-SiC (cubic phase) has been reported
to transform to α-SiC (hexagonal phase), in particular
the 6H phase, by high-temperature annealing. Many
authors have studied these β→α transformations in SiC.
In general, the 6H polytype is stable at high tempera-
tures, while 3C-SiC at low ones. A few reports of the
�reverse� transformation, i.e., 6H→3C, confirmed their
realization even at high temperatures. A number of these
transformations have been made under high nitrogen pres-
sures and at high temperatures in hard nitrogen doped
Lely crystals. The authors concluded that nitrogen sta-
bilized the 3C polytype at high temperatures. In general
impurities are believed to have an important influence on
the stability of different polytypes of SiC. Acceptor im-
purities, such as B or Al, are reported to stabilize layers
in a hexagonal environment, while donor impurities, such
as N or P, stabilize layers in a cubic environment. Actual
mechanism of polytypic transformation in solid state as
a kinetic problem has been considered both as diffusive
process and dislocation processes. The present paper dis-
cusses some possibilities of 6H-3C transformation and
transformation mechanism.
2. Experimental results and discussion
Hard dark green heavily nitrogen doped 6H-SiC sam-
ples (concentration of donors nitrogen Nd-Na about
1019cm�3) with thickness about 500 µm were transformed
partly or fully at 3C-SiC by the method described in [5].
Heavily nitrogen doped 6H-SiC crystals were exposed to
1500-2500 K temperature at the presence of Si vapor in
vacuum crucible. After the transformation process, crys-
tals became yellow, thinner (100-200 µm) and not trans-
formed part of initial 6H-SiC that became white or even
slightly violet. The crystals are completely transformed
into 3C-SiC when 6H-SiC is annealed for 1 hour at 2180
K or 4 hours at 2080 K. The quantity of transformed
6H→3C SiC was calculated using phase-contrast micro-
scope for crystals annealed for various times at different
temperatures. Fig. 1a shows the content of 3C-SiC in 6H-
SiC phase (η) versus temperature. The content of 3C-SiC
(in %) was calculated as a ratio of transformed area to
common area using photos of crystals heated at different
temperatures for the same time (t = 1 hour).
S.I. Vlaskina: Mechanism of 6H-3C transformations in SiC
153SQO, 5(2), 2002
According with Avraami-Kolmogorov equation:
( ).exp1 nkt−−=η . (1)
Usually �n� value shows a mechanism of transforma-
tion. From the kinetic of transformation (Fig. 2b) �n� is
close to 3 (n=3) in our case.
⋅⋅−−= 33
3
1
exp1 grcr VVt
π
η (2)
Vcr � velocity of nuclear creation,
Vgr � velocity of nuclear growth.
20
40
60
80
100
1800 1900
a )
h
, %
T,
O
C
2,0 3,1 3,5 3,9 4,2
-2,1
-1,6
-1,1
-0,6
-0,1
lg t
lg
lg
(1
-
)
h
-1
t = 1910
t = 81 10
t = 8 81 0
t = 8 61 0
b )
10 /T, K
4 -17
8
9
4,5 4,6 4,7 4,8
ñ)
ln
[
/
ln
]
t
T
·
(1
-
h
)
1
/3
1
/3
Fig. 1. a � Temperature dependence of 3C-SiC content in 6H-
SiC phase, b � calculation of �n�, c - activation energy.
Creation of crystallization centers is necessary for a
crystallization process.
The velocity of this creation is as follows:
.1
kT
W
eccrV
−
⋅= (3)
where:
W � activation energy for new nucleus creation,
k � the Boltzmann constant,
T � temperature.
The velocity of new phase creation is constant.
The velocity of a new phase growth is:
,2
kT
U
ecgrV
−
⋅⋅= ν (4)
U � average activation energy of self-diffusion of new
and old phases.
Characteristic frequency:
,33
3
1
exp1exp1
⋅⋅−−=
−−= grVcrVtnkt
π
η (5)
⋅⋅⋅⋅−−=
−− 3
3
exp1 teeTC kT
U
kT
W
η . (6)
⋅⋅⋅⋅−=−
−−
kT
U
kT
W
eetTC
3
3exp1 η . (7)
( ) ,
3
expexp1ln 3
−⋅
−⋅⋅⋅−=−
kT
U
kT
W
tTCη (8)
( )
3
3
expexp1ln
t
TC
kT
U
kT
W
=
⋅
⋅⋅−− η
. (9)
Transformation activation energy was calculated ac-
cording:
( )[ ]
kT
U
W
TBt
+
⋅⋅−−⋅=
− 3
exp1ln 3
1
3
1
η , (10)
( )
−−
=
+
3
1
1ln
ln
3
ηB
t
kT
W
U
(11)
From Fig. 1c:
./20140
3
molKcal
W
U ±=
+ (12)
This calculated activation energy is very close to the
energy of sublimation.
154 SQO, 5(2), 2002
S.I. Vlaskina: Mechanism of 6H-3C transformations in SiC
This calculation was based on the assumption of crea-
tion of new centers providing both crystallization and
growing processes of these centers. It means that it is
based on solid-state transformation going on with new
phase-disordered 6H-SiC structure and through forma-
tion of an intermediate multilayer structure. Fact of clos-
ing this energy to the gas transformation energy shows
the similar nature of both processes.
A possible model of this transformation is a site chang-
ing according to A→B, B→C or C→A and changing
stacking sequence ABCACB (6H-SiC) to ACB (3C-SiC)
followed by final 6H→3C conversion through formation
of an intermediate multilayer structure. It can be both a
diffusion process and the dislocation one.
As seen from the Hall effect measurements, free car-
rier concentration at T = 300 K (noncompensated im-
purities � Nd�Na) became 1015 cm�3, that is decreased
by three orders of magnitude. The mobility was in-
creased. In some very small transformed 3C crystals,
mobility was 790 cm2/V·s, free carrier concentration
6.1·1016 cm�3, conductivity 7.75 ohm�1·cm�1. Some sam-
ples had mobility 960 cm2/V·s.
Several samples had very high resistivity (conductivity
about 6·10�3 ohm�1·cm�1 and less), and we could not make
measurements.
In general, it is necessary to do the Hall measure-
ments only at one plane of originally grown 3C-SiC crys-
tals because the concentration and all parameters are
different at available planes due to differing velocities of
the crystal growth in various directions and at different
nitrogen doping. But we could not make such measure-
ments using transformed crystals. In Fig. 2, shown are
the results of Hall measurements in transformed crystals
(temperature dependences of the free carrier concentra-
tion).
Temperature dependence of mobility is shown in Fig.
3. Some deep donor levels at 0.35±0.1 eV and 0.74±0.04
eV appear in the crystal. Usual nitrogen levels are about
0.1 eV. In Fig. 2 black points are experimental, and an-
other ones theoretically calculated for a two-level sys-
tem. Lines 1 and 2 are indicative of this fact. Deep level
0.35 eV appears at low temperatures only. At tempera-
tures close to 400 K this level is exhausted, and free car-
rier concentration is 2·1017 cm�3. Compensation of this
level is very small (about 1% as it was calculated accord-
ingly to equation for doped and compensated semicon-
ductors). New deep levels (0.74 eV) appear at 400K. The
concentration of these levels is very high. The tempera-
ture dependence of mobility (Fig. 3) shows some mate-
rial property improvement and argues in favour of ab-
sence of new scattering centers. But, in general, the mo-
bility is increased.
The nitrogen concentration calculated from EPR spec-
tra for transformed crystals shows a decreasing nitrogen
concentration in 3C-SiC.
All these data show appearance of new defects - do-
nors and acceptors that make nitrogen optically and elec-
trically non-active. These can be vacancies (Si-vacancy -
as an acceptor, C-vacancy -as a donor or more compli-
13
14
15
16
17
18
19
20
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
lg
(C
a
rr
ie
r
ñ
o
n
c
e
n
tr
a
ti
o
n
,
c
m
-
3
)
10 / T(K )
3 -1
0.90
1.10
1.30
1.50
2.40 2.48 2.56 2.64
lg
(M
o
b
il
it
y,
c
m
/
V
·s
)
-3
lg T(K)
cated complexes, namely: nitrogen-vacancy, vacancy-
vacancy, or some impurities play more important role in
these processes). Nature of these defects has to be under-
stood later � now we don�t know it exactly. But these
defects accompany processes of transformation.
3. Conclusion
So, 6H→3C transformation in SiC was investigated as a
solid-state transformation. Tight proximity of meanings
valid for the transformation and sublimation energies as
well as for the gas phase transformation one enabled us
to consider this 6H→3C conversion as accompanied by
Fig. 2. Temperature dependence of the free electron concen-
tration.
Fig. 3. Temperature dependence of the free electron mobility.
S.I. Vlaskina: Mechanism of 6H-3C transformations in SiC
155SQO, 5(2), 2002
some reconstruction processes. At the same time, it is clear
that some new defects participate in these processes. Prob-
ably, these defects are complexes of doping elements with
silicon and carbon vacancies. And vacancies play an im-
portant role in the transformation process. Some electri-
cal properties were investigated, too.
References
1. A.J. Verma, P.Krishna, Polymorphism and Polytypism in Crys-
tals, Wiley, New York, (1966).
2. P.Krishna., R.C. Marshall, Direct transformation from the
2H to the 6H-structure in single crystal SiC// J.Cryst.Growth,
9, pp.310-327 (1971).
3. H.Yagodzinsky, Polytypism in SiC crystals// Acta crystals, 7,
pp.300-307 (1954).
4. J.W. Yang, P.Pirous, The aÞb polytypic transformation in
high-temperature indented SiC// J.Mater.Res, 8 (11),
pp.2902-2906 (1993).
5. Vlaskina S., Shin D.H. 6H to 3C Polytype transformation in
Silicon Carbide// Jpn.J.AppI.Phys. 38(1A), pp.L27-L29
(1999).
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