Chemistry Reference
In-Depth Information
Fig. 10.12
RHEED patterns of GaSb nanodots formed by codeposition (
a
)of15MLGaSbat
300
◦
Cand(
b
) of 30ML GaSb at 450
◦
C. (
c
)and(
d
) STM images corresponding to (
a
)and
(
b
), respectively. (
e
) Temperature dependence of densities of the formed nanodots (
solid circles
)
and nanodot density estimated from Ga diffusion length on ultrathin SiO
2
surface (
open circles
).
(
f
) Raman spectrum from the nanodots in (
d
)
With a decrease in the codeposition temperature, the spot patterns in RHEED
became obscure as shown in Fig.
10.12
a, b, indicating degradation in nanodot crys-
tallinity. On the other hand, when the codeposition temperature was reduced, the
nanodot density continuously increased to 3
10
11
cm
−
2
at 300
◦
C and the ultra-
×
10
12
cm
−
2
) at 200
◦
C as shown in Fig.
10.12
e. Figure
10.12
fis
Raman spectra for GaSb nanodots corresponding to Fig.
10.12
b, d. The sharp peak
related to Si crystal phonons near 520 cm
−
1
and the broad peak around 400 cm
−
1
also appeared for the Si substrates without GaSb nanodots, indicating that the sharp
peak at 223 cm
−
1
is related to GaSb nanodots. This peak at 223 cm
−
1
was assigned
to the transverse optical (TO) mode in GaSb nanodots from the TO mode in the
GaSb bulk (223.6 cm
−
1
)[
51
]. The peak positions were independent of the amount
of GaSb nanodots deposited in our experiment. The close peak positions of the nan-
odots and the bulk indicate that the lattice mismatch strains with Si almost relaxed
in the nanodots. This was also confirmed by comparing RHEED spot spacings in
Fig.
10.12
b with those of homoepitaxial Si nanodots [
14
].
high density (
∼
1
×
