Boron, aluminum, nitrogen, oxygen impurities in silicon carbide
Diffusion of boron, aluminum, and oxygen was conducted at temperatures 1600 – 1700°C. Very pure original n-SiC crystal (6H-SiC) specially grown by the Lely method annealed in oxygen during 2 h at 1700 °C, in argon during 2 h at 1700 °C, with aluminum and silicon oxide powder during 2 h, and with...
Gespeichert in:
| Veröffentlicht in: | Semiconductor Physics Quantum Electronics & Optoelectronics |
|---|---|
| Datum: | 2007 |
| Hauptverfasser: | , , , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2007
|
| Online Zugang: | https://nasplib.isofts.kiev.ua/handle/123456789/117865 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | Boron, aluminum, nitrogen, oxygen impurities in silicon carbide / S.I. Vlaskina, V.I. Vlaskin, S.A. Podlasov, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 21-25. — Бібліогр.: 24 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
nasplib_isofts_kiev_ua-123456789-117865 |
|---|---|
| record_format |
dspace |
| spelling |
Vlaskina, S.I. Vlaskin, V.I. Podlasov, S.A. Rodionov, V.E. Svechnikov, G.S. 2017-05-27T09:48:47Z 2017-05-27T09:48:47Z 2007 Boron, aluminum, nitrogen, oxygen impurities in silicon carbide / S.I. Vlaskina, V.I. Vlaskin, S.A. Podlasov, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 21-25. — Бібліогр.: 24 назв. — англ. 1560-8034 PACS 85.60.Y https://nasplib.isofts.kiev.ua/handle/123456789/117865 Diffusion of boron, aluminum, and oxygen was conducted at temperatures 1600 – 1700°C. Very pure original n-SiC crystal (6H-SiC) specially grown by the Lely method annealed in oxygen during 2 h at 1700 °C, in argon during 2 h at 1700 °C, with aluminum and silicon oxide powder during 2 h, and with boron oxide and aluminum during 0.5 h. Electrical characterization of the silicon carbide samples was done by the Hall effect measurements using the square van der Pauw method to determine the sheet resistance, mobility, and free carrier concentration. The model of deep donor level as a complex of nitrogen atom replacing carbon with adjacent silicon vacancy is suggested. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Boron, aluminum, nitrogen, oxygen impurities in silicon carbide Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Boron, aluminum, nitrogen, oxygen impurities in silicon carbide |
| spellingShingle |
Boron, aluminum, nitrogen, oxygen impurities in silicon carbide Vlaskina, S.I. Vlaskin, V.I. Podlasov, S.A. Rodionov, V.E. Svechnikov, G.S. |
| title_short |
Boron, aluminum, nitrogen, oxygen impurities in silicon carbide |
| title_full |
Boron, aluminum, nitrogen, oxygen impurities in silicon carbide |
| title_fullStr |
Boron, aluminum, nitrogen, oxygen impurities in silicon carbide |
| title_full_unstemmed |
Boron, aluminum, nitrogen, oxygen impurities in silicon carbide |
| title_sort |
boron, aluminum, nitrogen, oxygen impurities in silicon carbide |
| author |
Vlaskina, S.I. Vlaskin, V.I. Podlasov, S.A. Rodionov, V.E. Svechnikov, G.S. |
| author_facet |
Vlaskina, S.I. Vlaskin, V.I. Podlasov, S.A. Rodionov, V.E. Svechnikov, G.S. |
| publishDate |
2007 |
| language |
English |
| container_title |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| format |
Article |
| description |
Diffusion of boron, aluminum, and oxygen was conducted at temperatures
1600 – 1700°C. Very pure original n-SiC crystal (6H-SiC) specially grown by the Lely
method annealed in oxygen during 2 h at 1700 °C, in argon during 2 h at 1700 °C, with
aluminum and silicon oxide powder during 2 h, and with boron oxide and aluminum
during 0.5 h. Electrical characterization of the silicon carbide samples was done by the
Hall effect measurements using the square van der Pauw method to determine the sheet
resistance, mobility, and free carrier concentration. The model of deep donor level as a
complex of nitrogen atom replacing carbon with adjacent silicon vacancy is suggested.
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/117865 |
| citation_txt |
Boron, aluminum, nitrogen, oxygen impurities in silicon carbide / S.I. Vlaskina, V.I. Vlaskin, S.A. Podlasov, V.E. Rodionov, G.S. Svechnikov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2007. — Т. 10, № 2. — С. 21-25. — Бібліогр.: 24 назв. — англ. |
| work_keys_str_mv |
AT vlaskinasi boronaluminumnitrogenoxygenimpuritiesinsiliconcarbide AT vlaskinvi boronaluminumnitrogenoxygenimpuritiesinsiliconcarbide AT podlasovsa boronaluminumnitrogenoxygenimpuritiesinsiliconcarbide AT rodionovve boronaluminumnitrogenoxygenimpuritiesinsiliconcarbide AT svechnikovgs boronaluminumnitrogenoxygenimpuritiesinsiliconcarbide |
| first_indexed |
2025-11-27T01:28:35Z |
| last_indexed |
2025-11-27T01:28:35Z |
| _version_ |
1850790982745849856 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 21-25.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
21
PACS 85.60.Y
Boron, aluminum, nitrogen, and oxygen impurities in silicon carbide
S.I. Vlaskina1, V.I. Vlaskin2, S.A. Podlasov2, V.E. Rodionov2, G.S. Svechnikov2
1Dong Seoul College, 461-714, 423,
Bokjung-Dong, Sungnam-city, Kyonggi-do, Korea
Phone: 82 (031) 7202141, fax 82(031) 7202261; e-mail: svitlana@haksan.dsc.ac.kr
2V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
45, prospect Nauky, 03028 Kyiv, Ukraine
Phone: 380(44) 5253792, fax 380 (44) 5258342; e-mail: businkaa@mail.ru
Abstract. Diffusion of boron, aluminum, and oxygen was conducted at temperatures
1600 – 1700 oC. Very pure original n-SiC crystal (6H-SiC) specially grown by the Lely
method annealed in oxygen during 2 h at 1700 °C, in argon during 2 h at 1700 °C, with
aluminum and silicon oxide powder during 2 h, and with boron oxide and aluminum
during 0.5 h. Electrical characterization of the silicon carbide samples was done by the
Hall effect measurements using the square van der Pauw method to determine the sheet
resistance, mobility, and free carrier concentration. The model of deep donor level as a
complex of nitrogen atom replacing carbon with adjacent silicon vacancy is suggested.
Keywords: silicon carbide, diffusion, p-n junction.
Manuscript received 09.02.07; accepted for publication 24.04.07; published online 19.10.07.
1. Introduction
Silicon carbide devices have important applications in
motor drives, in power transmission systems, in
information systems, in field effect devices (MOSFET,
MESFET, JFET, BJT), in the Shottky barrier diodes
(SBDs), in switch elements, and in all cases where
silicon-based semiconductor electronics cannot operate
[1-3].
Such impurities as boron, oxygen, and aluminum
are used in fabrication of all devices for the formation of
junctions, contacts, and the Shottky barriers [4, 5].
Diffusion of such impurities takes place in the process
of fabrication of a junction or in the process of post-
implantation annealing. The diffusion experiment had
been performed with boron in 4H- and 6H-SiC at
temperatures between 1700 and 2000 °C.
Boron depth profiles had been measured with
secondary ion mass spectroscopy on implantation and
recovery annealing [6] and well described on the basis
of the kick-out mechanism giving evidence for the
significant role of Si self-interstitials in boron diffusion
[7, 8].
Silicon carbide 6H-SiC crystals with a boron
impurity on a silicon site [9] and the role of intrinsic
point defects are in focus of the theoretical studies and
industrial researches [10, 11]. Even the process of self-
diffusion of silicon in SiC is not investigated well until
now [12, 13] and a lot of fundamental questions are
under investigation.
Diffusion of boron, aluminum, and oxygen had
been used in the fabrication of various devices of
optoelectronics [14]. The best crystals for SiC LEDs
were doped by nitrogen (1018…1019 cm−3): 6H-SiC,
15R-SIC, 33R-SiC. In these crystals, p-n junction had
been made by diffusion of aluminum with oxygen (from
SiO powder) or boron with aluminum. Diffusion of Al
with O was carried out for 2 h at 1700 ºC. Boron and
aluminum were diffused for 15 min at 1600 ºC. The
sources for oxygen, aluminum, and boron were SiO,
99.99 % Al, and B2O3, respectively. The optimal depth
(1 µm) of p-n junctions had been obtained with the
crystals heavily doped by nitrogen. But the mechanism
of doping had not been yet understood.
The main goal of this article is the better under-
standing of the diffusion of boron and aluminum in SiC.
2. Experiment
Diffusion experiments with boron, aluminum, and
oxygen were conducted at temperatures from 1600 to
1700 °C. Very pure original n-SiC crystal (6H-SiC)
specially grown by the Lely method was cut into several
pieces. One piece of this crystal was annealed in oxygen
during 2 h at 1700 °C. Another piece was annealed in
argon during 2 h at 1700 °C. The next one was annealed
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 21-25.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
22
with aluminum and silicon oxide powder for 2 h for
aluminum to be diffused. Later on, the same piece was
annealed with boron oxide and aluminum for diffusion of
boron.
Electrical characteristics of silicon carbide samples
was obtained by the Hall effect measurements using the
square van der Pauw samples to determine the sheet
resistance, mobility, and concentration of free carrier.
According to the equation for space charge
neutrality, the electron concentration at equilibrium for
two different temperatures is given by:
1
1
1
11 )(
)( kT
E
c
ad
a eTN
nNN
Nnn ∆−
β=
−−
+ , (1)
2
2
2
22 )(
)( kT
E
c
ad
a eTN
nNN
Nnn ∆−
β=
−−
+ . (2)
Noncompensated impurities (Nd − Na) can be
determined from the extrinsic part of the carrier
concentration as a function of temperature. Namely,
(Nd − Na) is virtually constant with variation in
temperature, until the concentration of intrinsic carriers
becomes comparable with that of extrinsic carriers.
The division of Eqs. (1) and (2) gives
Nc(T) ∼ A·T 3/2 . (3)
Then, writing the equation for space charge
neutrality for the third temperature T3 ,
3
3
3
33 )(
)( kT
E
c
ad
a eTN
nNN
Nnn ∆−
β=
−−
+ , (4)
we obtain
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
∆
−
1
1
kT
E
a efBN , ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
∆
−
2
2
kT
E
a efBN , (5)
which allows us to determine ∆E.
Very pure single crystal n-SiC specially grown
with a concentration of about 1017…1016 cm-3 (at 300 K)
and µ = 90 cm2/Vs was cut into pieces which were
annealed in oxygen for 2 h at 1700 °C, in argon under
the same condition, in oxygen with aluminum (99.9999)
during 2 h, and with boron and aluminum in oxygen for
0.5 h.
The temperature dependence of the free carrier
concentration is shown in Fig. 1.
Very pure initial (NCO-7) crystal was more
compensated and had steeper (a steeper slope) behavior
of the plot log n = f (1/T) than others (Fig. 1a), the
concentration Nd − Na = l.5⋅1017 cm−3, and only one donor
level at 0.15 eV was working.
After annealing in argon, the concentration of
acceptors was decreased, (Nd − Na) was increased, but
the plot log n = f (1/T) became not so steep (Fig. 1b) and
the mobility was increased by two times (Fig. 2b as
compared with Fig. 2a). This can occur if the impurity
distribution became more uniform. The less fold of the
dependence µ(T) at low temperatures gives us an
additional evidence for this fact. It can be only if the
concentration of Si vacancies is decreased after
annealing in argon. We suggest that Si vacancies have
acceptor character.
After annealing in oxygen, (Nd − Na) for the
nitrogen level was 2.5⋅1017 at 0.15 eV. But a new deep
noncompensated donor level at 0.35 eV appeared
(Fig. 1c). This level appears only after annealing in
oxygen. The concentration of this level is about
1.06⋅1017 (nearby the nitrogen concentration at the zero
level of compensation).
It can be only if, at first version, oxygen is
responsible for this donor level. In the second version,
because the crystal surface is covered by the silicon
oxide layer, some amount of Si diffuses to the surface
creating new Si vacancies. These vacancies bind nitro-
gen and create complexes which have donor character.
The concentration of noncompensated donors was
increased after annealing with aluminum in oxygen (at a
level of 0.15 eV it became 4⋅1017, and 1.5⋅1017 at
0.35 eV) as shown in Fig. 1d. It seems unusual since the
nitrogen concentration should be decreased when we add
acceptor (aluminum).
But, if aluminum occupies Si vacancies, the
concentration of Si vacancies will be decreased due to
aluminum, some part of nitrogen will be electrically
active again, and, just in this case, we can explain the
increase in the free carrier concentration. The plot in
Fig. 1d allows us to calculate a new deep level at
0.35 eV.
After annealing in the presence of boron, a deeper
level appears (but we failed to calculate the level’s
energy from these data), and the compensation was
increased, as usual: see Fig. 1e.
Mobility increases, in common, after annealing, but
only annealing in argon leads to the increase in the
mobility by two times (Fig. 2a, b). In another cases, the
mobility was not so increased because we added
additional scattering centers.
3. Discussion
A substitution atom of the elements of group III
normally acts as an acceptor in SiC since there is a
deficit of one valence electron to complete the normal
tetrahedral bonding.
A substitution atom of the elements of group V acts
as a donor in SiC. It was discovered that B creates a
shallow, as well as a deep, acceptor level.
Nitrogen creates a shallow (six levels depending on
the hexagonal-like or cubic-like position) donor’s levels.
The activation energies of impurities in cubic-like sites
are larger than those in hexagonal-like sites.
But can nitrogen create a deep, as well as shallow,
donor level?
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 21-25.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
23
A model of deep acceptor level created by boron
was suggested in [15, 16]. The model of Al and Ga in
deep acceptor states seems to be the “element of group
III − vacancy” pair.
Like the case of oxygen in silicon or nitrogen in
diamond and in silicon [17, 18], there exists a
mechanism for SiC which drives some impu-
rities off the nominal substitutional sites. Acceptor
Al and Ga atoms occupy the Si-substitutional
on-center position and B and Be do the off-center
position. Nitrogen atoms occupy the C-substitution
position.
a b c
d e
Fig. 1.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 21-25.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
24
a
b
Fig. 2.
We suggest a model of deep donor level created by
nitrogen. The model of N in a deep donor state seems to
be the “element of group V − vacancy” pair as NC (like
BSi) [16] with the complex which consists of a nitrogen
atom replacing a carbon atom (adjacent to a silicon
vacancy (VSi) and acts as deep donor (NC − VSi))
similarly to the complex which consists of a boron atom
replacing a silicon atom (adjacent to a carbon vacancy
(VC)) and acts as a deep acceptor in the (BSi − VC) in
model [15, 16]
In this case, all our experiments can be explained
from this point of view.
In particular, bright-yellow luminescence arises due
to a deep probably aluminum-related acceptor [21]
rather than due to the recombination involving a deep
boron center and N donors or conduction electrons
[19, 20]. We suggest that the characteristic high-
temperature bright-yellow luminescence in annealed 6H-
SiC [22], 4H-SiC [23], and heavy doped 6H-SiC [13] is
due to the recombination involving a deep nitrogen
center as the complex consisting of a nitrogen atom
replacing carbon with adjacent silicon vacancies (VSi)
and acting as a deep donor as well. In annealed crystals,
deep donors and deep acceptors exist together. The
chemical nature and structure of D- and Z-centers, and
the acceptor or donor character of deep levels [22, 24]
are else open questions.
We mention also another possible model, in which
nitrogen replacing Si with adjacent carbon vacancies
(VC) (if B can occupy a C-site, why cannot N occupy a
Si-site?) creates a deep donor level. For example, a
nitrogen atom responsible for 0.35 eV replaces carbon
with adjacent silicon vacancies (VSi) responsible for
0.74 eV or vice versa. But this looks not so reasonable.
A nitrogen atom replacing carbon with adjacent silicon
vacancies (VSi) and acting as a deep donor seems more
suitable.
4. Conclusion
So, we can see that all these data of the experiments with
very pure SiC crystals (1017…1016 cm−3) can be
explained only on one base by the participation of
vacancies in the diffusion process. A nitrogen atom
replacing a carbon atom creates the “element of group V
− vacancy” pair (NC with adjacent silicon vacancies −
VSi) and acts as a deep donor (NC − VSi) similarly to the
complex consisting of a boron atom replacing a silicon
atom with adjacent carbon vacancies (VC).
References
1. http://www.grc.nasa.gov/www/SiC (internet infor-
mation).
2. S.C. Kim, W. Bahng, N.K. Kim, E.D. Kim, T.
Ayalew, T. Grasser and S. Selberherr // Materials
Science Forum 483-485, p. 793-796 (2005).
3. S.I. Vlaskina, Silicon carbide LED //
Semiconductor Physics, Quantum Electronics &
Optoelectronics, 5(l), p. 71-75 (2002).
4. Simulation, devices, and process technology in
silicon carbide, research project of the department
of microelectronics and information technology,
http://www.imit.kth.se//forskningsprojekt-
detalj.html?projektid=2
5. Dallas Morisette, Mitch McGlothlin, J.A. Cooper,
Jr., M.R. Meloch, SiC Shottky barrier diodes deve-
lopment at Purdue // http:/www.enc.purdue.edu/
WBG/Device-research/Shottky-Diodes/index.html
6. Diffusion in bulk crystals and heterostructures of
compound semiconductors. http://www.uni-
muenster.de/Rectorat/Forschungsberichte2000/foll
gd03.htm
7. H. Bracht, N.A. Stolwijk, M. Laube, G. Pensl,
Diffusion of boron in silicon carbide: Evidence for
the kick-out mechanism // Appl. Phys. Lett. 77,
p. 3188-3190 (2000).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2007. V. 10, N 2. P. 21-25.
© 2007, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
25
8. H. Bracht, N.A. Stolwijk, M. Laube, G. Pensl,
Modelling of boron diffusion in silicon carbide //
Mater. Sci. Forum 353-356, p. 327-333 (2001).
9. Doping issues in wide band-gap semiconductors,
Exeter, United Kingdom, 21-23 March, 2001.
http://widegap2001.ex.ac.uk/sic.html.
10. M. Bockstedte, A. Mattausch, and O. Pankratov,
Boron diffusion in SiC: the role of intrinsic point
defects. http://psi-k.dl.ac.uk/psi-
k2000/abstracts/MichelBockstedte.html.
11. Peter Deak, Materials characterization and
modeling of SiC in Europe – From the viewpoint of
a theorist // Mater. Sci. Forum 483-485, p. 457-464
(2005).
12. Birnie, P. Dunbar, A model for silicon self
diffusion in silicon carbide: anti-cite defect motion
// J. Amer. Ceram. Soc. 69, p. 33-35 (1986)
(http://www.mse.arizona.edu/faculty/birnie/abs860
1.html).
13. S.I. Vlaskina, D.H. Shin, Effect of annealing on the
impurities of 6H-SiC single crystals // Jpn J. Appl.
Phys. Part 2 -Letters, 38, p. L861-L863 (1999).
14. S.L. Vlaskina, K.W. Kim, Y.S. Kim, Y.P. Lee,
G.S. Svechnikov, Optoelectronics devices on
silicon carbide // J. Korean Phys. Soc. 30 (910),
p. 117-121 (1997).
15. P.G. Baranov, I.V. Ilyn and E.N. Mokhov // Solid
State Communs 100, p. 371 (1996).
16. A.V. Duijn-Arnold, T. Ikoma, O.G. Poluektov,
P.G. Baranov, E.N. Mokhov and J. Schmidt //
Phys. Rev. B 57(3), p. 1607 (1998).
17. G. Bachelet, G.A. Baraff and M. Schulter // Phys.
Rev. B 22, p. 2842 (1980).
18. S.T. Pantelides, W.A. Harrison and F. Indurain //
Phys. Rev. B 34, p. 6038 (1986).
19. H. Kuwabara and S. Yamada // Phys. status solidi
(a) 30, p. 739 (1975).
20. M. Ikeda, H. Matsunami and T. Tanaka // Phys.
Rev. B 22, p. 2842 (1980).
21. E.N. Kalabuhova, S.N. Lukin, E.N. Mokhov, J.
Reinke, S. Greulich-Weber and J.M. Spaeth // Inst.
Phys. Conf. Ser. 142, p. 333-335 (1996).
22. W. Suttrop, G. Pensl and P. Lanig // Appl. Phys. A
51, p. 231-237 (1990).
23. T. Troffer, Ch. Habler, G. Pensl, K. Holzlein, H.
Mitlhner, J. Volki // Inst. Phys. Conf. Ser. 142,
p. 281-284 (1996).
24. P.G. Baranov and E.N. Mokhov // Inst. Phys. Conf.
Ser. 142, p. 293-296 (1996).
|