JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Hole Concentration [cm -3 ]
10 15
Mechanisms of Changes of Hole Concentration in
Al-doped 6H-SiC by Electron Irradiation and Annealing
H. Matsuura a) , H. Yanagisawa a) , K. Nishino a) , Y. Myojin a) , T. Nojiri a) , Y. Matsuyama a) ,
S. Onoda b) and T. Ohshima b)
a) Dept. of Electric and Electronic Engineering, Osaka Electro-Communication University,
b) Environment and Industrial Materials Research Division, QuBS, JAEA
By comparing electron-radiation damage in p-type
4H-SiC with that in p-type Si, 1, 2) it was found that the
reduction in the temperature-dependent hole concentration
p(T) in Al-doped p-type 4H-SiC by electron irradiation was
much larger than in Al-doped p-type Si. From p(T) for
lightly Al-doped 6H-SiC epilayers, an acceptor species with
E V+0.2 eV, which is ascribed to an Al atom at a Si
sublattice site, was observed. In heavily Al-implanted
p-type 6H-SiC layers, the removal cross section of Al
acceptors (κ Al) for 1 MeV electron irradiation was
determined to be 6.4 × 10-18 cm 2, 3) .
A 4.9 μm-thick lightly Al-doped p-type 6H-SiC epilayer
on n-type 6H-SiC (resistivity: 0.027 Ωcm) was cut to a
1 × 1 cm2 size. The sample was irradiated with 200 keV
electrons with total fluences (Φ) of 0, 1.0, 2.0, and 3.0 ×
10 16 cm -2 at room temperature. The value of p(T) were
obtained by Hall-effect measurements. Since the p(T) at Φ
of 3.0 × 1016 cm -2 could not be obtained, the sample was
annealed at 500 °C for 2 min in an Ar atmosphere. The
densities and energy levels of acceptors were determined by
free carrier concentration spectroscopy (FCCS) 1-4) from
p(T).
Figure 1 shows the experimental p(T) before irradiation
(○) and after irradiation with 200 keV electrons with Φ of
1.0 × 1016 cm -2 (▲) and 2.0 × 1016 cm -2 (□). The value of
p(T) in the annealed sample is denoted by + in Fig. 1.
Using p(T), the densities (N Al and N DA) and levels (E Al and
E DA) of Al and deep acceptors were determined by FCCS.
200 keV electrons
Fluence [cm -2 ]
: 0
: 1x10 16
: 2x10 16
: 3x10 16 and
500 o C annealing for 2 min
1000/T [K -1 10
1 2 3 4 5
]
13
10 14
Fig. 1 Temperature dependence of hole concentration for
Al-doped p-type 6H-SiC before and after irradiation
with three difference Φ of 200 keV electrons. The
p(T) for the annealed sample was shown by +. The
solid lines represent p(T) simulations with N Al, E Al,
N DA, E DA, and N comp obtained by FCCS.
JAEA-Review 2010-065
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Since each p(T) simulation (solid line) with the obtained
values is in good agreement with the corresponding
experimental p(T), the values obtained by FCCS are
reliable.
Figure 2 shows the dependence of N Al and N DA on Φ,
denoted by ○ and Δ, respectively. At Φ of 3.0 × 1016 cm -2 ,
N Al and N DA in the 500 °C-annealed sample were shown by
● and ▲, respectively. Although N Al and N DA in the
sample irradiated with Φ of 3 × 1016 cm -2 could not be
determined, they are expected to be 4.3 × 1013 and
2.1 × 1015 cm -3 , respectively, by simulation 4) with κ Al of
1 × 10-16 cm 2 and κ DA of 9 × 10-18 cm 2 . The simulations of
the dependence of N Al and N DA on Φ represent the solid and
broken lines in Fig. 2, respectively. After annealing the
sample at 500 °C for 2 min, N Al and N DA could be
determined to be 4.0 × 1014 and 1.5 × 10 15 cm -3 , respectively.
By annealing at 500 °C, N Al is increased, and N DA is
decreased. From Fig. 2, furthermore, the increment of N Al
is nearly equal to the decrement of N DA. These suggest
that the 500 °C annealing transforms the deep acceptors into
the Al acceptors.
References
1) H. Matsuura et al., Jpn. J. Appl. Phys. 45 (2006) 2648.
2) H. Matsuura et al., Physica B 376-377 (2006) 342.
3) H. Matsuura et al., Jpn. J. Appl. Phys. 47 (2008) 5355.
4) H. Matsuura et al., J. Appl. Phys 104 (2008) 043702.
Density [x10 15 cm -3 ]
3
2
1
N A2
N A1
After 773 K
annealing
for 2 min
Fluence of 200 keV electrons [x10 16 cm -2 0 1 2 3
]
Fig. 2 Dependence of N Al and N DA on Φ of 200 keV
electrons. Since NAl and N DA in the sample irradiated
at Φ of 3 × 1016 cm -2 could not be obtained, the sample
was annealed at 500 °C for 2 min. N Al and N DA in the
annealed sample are denoted by ● and ▲, respectively.
The dependence of N Al and N DA on Φ, simulated with
κ Al of 1 × 10-16 cm 2 and κ DA of 9 × 10 -18 cm 2 , are shown
by solid and broken lines, respectively.