12.2 Heteroepitaxy
359
Table 12.2 Number of rotational (or mirror) domains N RD for all 2D point groups of substrate (G S ) (rows) and epilayer
(G E ) (columns). When two numbers are given (x|y), the first (second) number represents the number of domains if
mirror symmetry planes of substrate and epilayer align (misalign)
G S \G E 1
m
2
2mm
3
3m
4
4 mm
6
6 mm
1
1
1
1
1
1
1
1
1
1
1
m
2
1|2
2
1|2
2
1|2
2
1|2
2
1|2
2
2
2
1
1
2
2
1
1
1
1
2 mm
4
2|4
2
1|2
4
2|4
2
1|2
2
1|2
3
3
3
3
3
1
1
3
3
1
1
3 m
6
3|6
6
3|6
2
1|2
6
3|6
2
1|2
4
4
4
2
2
4
4
1
1
2
2
4 mm
8
4|8
4
2|4
8
4|8
2
1|2
4
2|4
6
6
6
3
3
2
2
3
3
1
1
6 mm
12
6|12
6
3|6
4
2|4
6
3|6
2
1|2
Fig. 12.11 X-ray
diffraction φ-scans of
GaN(00.1)/Ge(111).
Adapted from [1141]
180
90
0
270
X-ray Intensity (arb. units)
GaN(10.1)
Ge(220)
(degree)
=8°
such surface actually exhibits two kind of terraces (1 × 2 and 2 × 1 reconstructions) and is thus itself
not homogeneous. The formation of antiphase domains can be avoided by using an off-cut of the
surface against the (001)-planes promoting double-atomic steps [1142]. In Fig. 12.12a the growth of
GaP on a Ge hemisphere with [111]-pole is depicted; spherical triangles meeting at the 100 poles can
be seen. In a similar experiment GaAs was grown in a spherical depression in Ge(001) (Fig. 12.12b),
allowing a more detailed look at the [001]-pole. Close to the it, within an approximately square area,
antiphase domains (cmp. Sect. 4.4.4) form. Along the connection lines between different 001
an antiphase domain boundary forms, microscopially broken up into domains [1129].
Details of the initial deposition steps can determine the orientation in polar materials. GaN directly
grown on c-Al 2 O 3 grows with N-face orientation (see Fig. 3.19). The high surface mobility of Ga
allows nitrogen to take its preferred position in the first atomic layer. Even under Ga-rich conditions
the N atoms can kick-off the Ga from its favorite site on the surface. If an AlN buffer is used the strong
bond between Al and oxygen leads to an Al atomic layer at the interface and subsequent GaN grows
with a Ga-face [1143]. Also for the epitaxy of ZnO on on c-Al 2 O 3 the polarity of the epilayer can be
controlled, e.g., via the details of an MgO buffer layer [1144].
12.2.5 Patterned Substrates
Using patterning of the substrate certain growth modes and crystallographic directions of the growth
front can be evoked.
359
Table 12.2 Number of rotational (or mirror) domains N RD for all 2D point groups of substrate (G S ) (rows) and epilayer
(G E ) (columns). When two numbers are given (x|y), the first (second) number represents the number of domains if
mirror symmetry planes of substrate and epilayer align (misalign)
G S \G E 1
m
2
2mm
3
3m
4
4 mm
6
6 mm
1
1
1
1
1
1
1
1
1
1
1
m
2
1|2
2
1|2
2
1|2
2
1|2
2
1|2
2
2
2
1
1
2
2
1
1
1
1
2 mm
4
2|4
2
1|2
4
2|4
2
1|2
2
1|2
3
3
3
3
3
1
1
3
3
1
1
3 m
6
3|6
6
3|6
2
1|2
6
3|6
2
1|2
4
4
4
2
2
4
4
1
1
2
2
4 mm
8
4|8
4
2|4
8
4|8
2
1|2
4
2|4
6
6
6
3
3
2
2
3
3
1
1
6 mm
12
6|12
6
3|6
4
2|4
6
3|6
2
1|2
Fig. 12.11 X-ray
diffraction φ-scans of
GaN(00.1)/Ge(111).
Adapted from [1141]
180
90
0
270
X-ray Intensity (arb. units)
GaN(10.1)
Ge(220)
(degree)
=8°
such surface actually exhibits two kind of terraces (1 × 2 and 2 × 1 reconstructions) and is thus itself
not homogeneous. The formation of antiphase domains can be avoided by using an off-cut of the
surface against the (001)-planes promoting double-atomic steps [1142]. In Fig. 12.12a the growth of
GaP on a Ge hemisphere with [111]-pole is depicted; spherical triangles meeting at the 100 poles can
be seen. In a similar experiment GaAs was grown in a spherical depression in Ge(001) (Fig. 12.12b),
allowing a more detailed look at the [001]-pole. Close to the it, within an approximately square area,
antiphase domains (cmp. Sect. 4.4.4) form. Along the connection lines between different 001
an antiphase domain boundary forms, microscopially broken up into domains [1129].
Details of the initial deposition steps can determine the orientation in polar materials. GaN directly
grown on c-Al 2 O 3 grows with N-face orientation (see Fig. 3.19). The high surface mobility of Ga
allows nitrogen to take its preferred position in the first atomic layer. Even under Ga-rich conditions
the N atoms can kick-off the Ga from its favorite site on the surface. If an AlN buffer is used the strong
bond between Al and oxygen leads to an Al atomic layer at the interface and subsequent GaN grows
with a Ga-face [1143]. Also for the epitaxy of ZnO on on c-Al 2 O 3 the polarity of the epilayer can be
controlled, e.g., via the details of an MgO buffer layer [1144].
12.2.5 Patterned Substrates
Using patterning of the substrate certain growth modes and crystallographic directions of the growth
front can be evoked.