3.7 Alloys
67
Fig. 3.46 CuPt-ordered
ternary alloy In 0.5 Ga 0.5 P;
the lattice symmetry is
reduced from T d to C 3v
In
Ga
P
T d
C 3v
(a)
(b)
Fig. 3.47 (a) Cross-sectional transmission electron microscope image along the [110] zone axis of a Cd 0.68 Zn 0.32 Te
epilayer on GaAs showing ordered domains having a doublet periodicity on the {111} and {001} lattice planes. Two
different {111} variants are labeled ‘a’ and ‘b’. The doublet periodicity in the [001] is seen in the ‘c’ region. (b) Selectedarea diffraction pattern along the [110] zone. Strong peaks are fundamental peaks of the zincblende crystal, weak peaks
are due to CuPt ordering, labeled A and B, and CuAu-I ordering, labeled C and D. The latter are the weakest due to a
small volume fraction of CuAu-ordered domains. Adapted from [259]
Therefore physical properties connected to u, such as the spontaneous polarization, will exhibit a
bowing.
3.7.5 Ordering
Some alloys have the tendency for the formation of a superstructure [258]. Growth kinetics at the
surface can lead to specific adatom incorporation leading to ordering. For example, in In 0.5 Ga 0.5 P the
In and Ga atoms can be ordered in subsequent (111) planes (CuPt structure) instead of being randomly
mixed (Fig. 3.46). This impacts fundamental properties such as the phonon spectrum or the band gap.
CuPt ordering on (111) and ( ¯
1 ¯
11) planes is called CuPt A , on ( ¯
111) and (1 ¯
11) planes CuPt B ordering. In
67
Fig. 3.46 CuPt-ordered
ternary alloy In 0.5 Ga 0.5 P;
the lattice symmetry is
reduced from T d to C 3v
In
Ga
P
T d
C 3v
(a)
(b)
Fig. 3.47 (a) Cross-sectional transmission electron microscope image along the [110] zone axis of a Cd 0.68 Zn 0.32 Te
epilayer on GaAs showing ordered domains having a doublet periodicity on the {111} and {001} lattice planes. Two
different {111} variants are labeled ‘a’ and ‘b’. The doublet periodicity in the [001] is seen in the ‘c’ region. (b) Selectedarea diffraction pattern along the [110] zone. Strong peaks are fundamental peaks of the zincblende crystal, weak peaks
are due to CuPt ordering, labeled A and B, and CuAu-I ordering, labeled C and D. The latter are the weakest due to a
small volume fraction of CuAu-ordered domains. Adapted from [259]
Therefore physical properties connected to u, such as the spontaneous polarization, will exhibit a
bowing.
3.7.5 Ordering
Some alloys have the tendency for the formation of a superstructure [258]. Growth kinetics at the
surface can lead to specific adatom incorporation leading to ordering. For example, in In 0.5 Ga 0.5 P the
In and Ga atoms can be ordered in subsequent (111) planes (CuPt structure) instead of being randomly
mixed (Fig. 3.46). This impacts fundamental properties such as the phonon spectrum or the band gap.
CuPt ordering on (111) and ( ¯
1 ¯
11) planes is called CuPt A , on ( ¯
111) and (1 ¯
11) planes CuPt B ordering. In