XCVI Congresso Nazionale SIF, Bologna 20-24 Settembre 2010
Nucleation of Ge(Si) quantum dots
on Si(001) vicinal surfaces
Adalberto Balzarotti
Dipartimento di Fisica, Università di Roma II, Tor Vergata
Outline
Heteroepitaxy of Ge on Si(100)
•
Ge on flat (singular) Si(001) surfaces:
1) From WL to 3D pyramids and domes
• Ge on vicinal Si(001) surfaces:
1) From WL relaxation to 3D islands formation.
2) Islands’ shape evolution vs miscut angle.
3) The special case of the (1 1 10)-8°-miscut surface.
4) Elastic pair interaction and local ordering on vicinal substrates
5) Conclusions
Si on Si (111) hepitaxy
2000 nm
Si flux: 0.018 ML/min
T=500°C
Stranski-Krastanow growth mode
Mismatched (pseudomorphic) growth
• The lattice mismatch is the cause of the
aGe  aSi

deformation
aSi
• The deformation is partially compensated by
the tetragonal distortion (Poisson ratio)
• The elastic energy (per unit area) of a
strained film is proportional to the film
thickness d
• Above a critical thickness 3D islands are
formed (SK coherent growth)
Tension
Compression
v
ESK coh  R

 //
E 2
 d   3D
1 
//

Steps
Vicinal Surfaces: Basic definitions
[001]
q
[-110]
j
[110]
•θ: polar miscut angle
• j: azimuthal angle
0<θ<8°, j=0°
Steps on the clean flat Si(001) surface
SA
SB
[110]
[110]
L. Persichetti, A. Sgarlata, M. Fanfoni, M. Bernardi, and A. Balzarotti, PRB 80, 075315
(2009).
Steps on clean vicinal Si(001) surfaces
2°
6°
4°
8°
Steps on clean vicinal Si(001) surfaces
nS q   2nD q  a
l 
8 tanq
<q>
<L> (nm)
0.2°
94.3 ± 0.3
2°
6.80 ± 0.2
4°
3.23 ± 0.09
6°
2.5
8°
1.36 ± 0.02
± 0.05
L.Persichetti, A.Sgarlata,M.Fanfoni, M.Bernardi, and A.Balzarotti, Phys.Rev.B 80, 075315 (2009)
Wetting layer evolution on the
flat Si(001) surface
FLUX=0.1 ML/min
T=600°C
Dimer Vacancy Lines - Dimer Row Vacancies- 2D Islands
D
V
L
0.6 ML
D
R
V
1.9 ML
WL relaxation on the flat Si(001) surface
2.7
3.1
2.6
2.8
3.0
2.4
2.5
1.7
2.1
2.9
ML
2.2
2.3
0.7ML
ML
3.2
2.0
1.9
ML
3Dformation
island
(2xN)
reconstruction
(MxN)
reconstruction
2DFirst
island
The 2D-to-3D transition on
the flat Si(001) surface
The 2D-to-3D transition on the flat Si(001) surface
3.0<Θ<3.5 ML
P. D. Szkutnik, A. Sgarlata, S. Nufris, N. Motta, and A. Balzarotti, PRB 69, 201309 (2004)
Ge pre-pyramids on the flat Si(001) surface
25 nm x25 nm
Ge pre-pyramids on the flat Si(001) surface
4.0 ML
3D island’s shape evolution vs miscut angle
0° miscut
{105} facets
[110]
50 x 50 nm2
From WL towards 3D islands:
the growth evolution
on vicinal Si(001) substrates
Wetting layer evolution on the vicinal Si(001)
surfaces
2°-miscut
[110]
Clean
Wetting layer evolution on the vicinal Si(001)
surfaces
2°-miscut
0.8 ML
2.3 ML
[110]
Wetting layer evolution on the vicinal Si(001)
surfaces
2°-miscut
3.0 ML
[110]
Wetting layer evolution on vicinal Si(001) surfaces
4°-miscut
Clean
10 nm
[110]
10 nm
0.3 ML
Wetting layer evolution on the vicinal Si(001)
surfaces
4°-miscut
2.0 ML
18 nm
8 nm
Early stages of Ge growth on the vicinal Si(001) surfaces
6°-miscut
[110]
Clean
1.4 ML
Wetting layer evolution on the vicinal Si(001)
surfaces
3 ML
6°-miscut
Pyramid’s shape evolution on
vicinal surfaces
Pyramid shape evolution vs miscut angle
1.5°-miscut
[110]
175 x 175 nm2
150 x 150 nm2
0°
6
Pyramid shape evolution vs miscut angle
2°-miscut
145 x 145
nm2
0°
[110]
200 x 200 nm2
6°
Pyramid shape evolution vs miscut angle
4°-miscut
130 x 130
nm2
0°
[110]
230 x 230 nm2
6°
3D island’s shape evolution vs miscut angle
6°-miscut
25 x 25
[110]
nm2
0°
100 x 100 nm2
6°
Pyramid shape evolution vs miscut angle
Calculated vs experimental Lm LM ratio
as a function of the miscut angle
L. Persichetti, A. Sgarlata, M. Fanfoni, and A. Balzarotti, PRL 104, 036104 (2010)
The 8°-miscut surface:
a special case
WL evolution on the 8° vicinal surface
8°-miscut
Clean
[110]
WL evolution on the 8° vicinal surface
8°-miscut
50 x 50 nm2
15 x 15 nm2
P.D.Szutnik, A.Sgarlata, A. Ronda,I. Berbezier, N. Motta,A. Balzarotti, PRB 75, 033305(2007)
WL evolution on the 8° vicinal surface
8°-miscut
2 ML
50 x 50 nm2
15 x 15 nm2
The 8°-miscut: a special case
4.0 ML
The 8°-miscut: a special case
Calculated elastic energy density as a
function of the miscut angle
L. Persichetti, A. Sgarlata, M. Fanfoni, and A. Balzarotti, PRL 104, 036104 (2010)
The 8°-miscut: a special case
4.0 ML
6.0 ML
The 8°-miscut: a special case
150x150 nm2
350x350 nm2
10.0 ML
Sb surfactant effect(AFM images)
q=8°
Pyramid-to-dome transition on
flat surfaces
Pyramid-to-dome transition on the flat Si(001)
surface
6.0 ML
Pyramid-to-dome transition on the flat Si(001)
surface
6.0 ML
F. Montalenti, P. Raiteri, D. B. Migas, H. von Känel, A. Rastelli, et al., PRL 93, 216102 (2004),
Ripple-to-dome transition
on the 8°-miscut surface
Ripple-to-dome transition on the 8°-miscut Si(001) surface
4.0 ML
L.Persichetti, A.Sgarlata, M.Fanfoni, and A.Balzarotti ,PRB 82, xx, (2010)
Ripple-to-dome transition on the 8°-miscut Si(001) surface
4.0 ML + 10 min annealing @
993 K
or
4.0 ML +1 ML
L.Persichetti, A.Sgarlata, M.Fanfoni, and A.Balzarotti , PRB 82, xx, (2010)
.
Ripple-to-dome transition on the 8°-miscut Si(001) surface
Etot  erelaxV  esurf V 2 / 3
N
esurf 

i 1
 i  i  Si   0S0 V 2 / 3
 q    cosq    sinq 
0
0
Evolution of dome morphology with
miscut angle
Morphology of domes vs miscut angle
0°
0 (105)
α (113)
β (15 3 23)
L.Persichetti, A.Sgarlata, M.Fanfoni, and A.Balzarotti , PRB-Rapid Comm, 82, xx, (2010)
.
Morphology of domes vs miscut angle
4°
0 (105)
α (113)
β (15 3 23)
Morphology of domes vs miscut angle
6°
0 (105)
α (113)
β (15 3 23)
Morphology of domes vs miscut angle
8°
0 (105)
α (113)
β (15 3 23)
Morphology of domes vs miscut angle
10°
0 (105)
α (113)
β (15 3 23)
Morphology of domes vs miscut angle
Elastic pair interaction and local
ordering on vicinal substrates
Elastic Pair interaction vs miscut angle
Flat surface
L.Persichetti, A.Sgarlata, M.Fanfoni, and A.Balzarotti , PRB 81, 113409 (2010)
.
Elastic Pair interaction vs miscut angle
6°-miscut surface
Elastic Pair interaction vs miscut angle
8°-miscut surface
WL relaxation vs coverage
dome morphology vs q
pyramid morphology vs q
Ripple-dome transition
pyramid spatial distribution vs q
THE NANOLAB GROUP
Roma Tor Vergata
Anna Sgarlata
Massimo Fanfoni
Luca Persichetti
SIF Bologna Sept.2010