4.4 Extended Defects
89
Fig. 4.26 Micro-cracks in
a mercury indium telluride
crystal. Adapted
from [344]
4.4.2 Stacking Faults
The ideal stacking of (111) planes in the zincblende structure, ABCABC. . ., can be disturbed in various
ways and creates area defects. If one plane is missing, i.e. the stacking is ABCACABC, an intrinsic
stacking fault is present. If an additional plane is present, the defect is called an extrinsic stacking fault,
i.e. ABCABACABC. An extended stacking fault in which the order of stacking is reversed is called
a twin lamella, e.g. ABCABCB AC BABCABC. If two regions have inverted stacking order they are
called twins and their joint interface is called a twin boundary, e.g. . . .ABCABCABCBACBACBA. . .
(Fig. 4.29). The various types of stacking faults are shown in Fig. 4.27. In Fig. 4.28 a cross-sectional
image of stacking faults in GaAs on Si is shown. They block each other and thus partially annihilate
with increasing thickness.
A stacking fault is bounded by two partial dislocations (Sect. 4.3.1.5) formed by the dissociation of a
perfect dislocation. A full (or perfect) dislocation with Burger’s vector a/2[110] in a III–V compound
is dissociated into two Shockley partials according to (4.22) [348]. Since the dislocation energy is
proportional to |b|
2 , the dissociation is energetically favored (see Sect. 4.3.1.5).
The stacking-fault energy in pure silicon is γ = 47 mJ m
−2 [349]. A similar value is found for Ge,
γ = 60 mJ m
−2 [350] and undoped GaAs, γ = 45 mJ m
−2 [351]. In diamond a much larger value is
found, γ = 285 mJ m
−2 [352]. Impurity incorporation typically reduces the stacking fault energy. The
systematics of stacking fault energy for various III–V and II–VI compounds has been discussed [185,
353, 354]. It can be correlated with the s-parameter (2.11) as depicted in Fig. 4.30.
Fig. 4.27 HRTEM images
of a thin-film silicon with
intrinsic (labeled ‘ISF’)
and extrinsic (‘ESF’)
stacking faults and twin
boundary (‘Twin’). b Six
monolayer thick hexagonal
(wurtzite) CdTe layer in
cubic (zincblende) CdTe.
Stacking order (from
bottom to top) is:
ABCABABABABC. . .
Reprinted with permission
from [345]
(a)
(b)
89
Fig. 4.26 Micro-cracks in
a mercury indium telluride
crystal. Adapted
from [344]
4.4.2 Stacking Faults
The ideal stacking of (111) planes in the zincblende structure, ABCABC. . ., can be disturbed in various
ways and creates area defects. If one plane is missing, i.e. the stacking is ABCACABC, an intrinsic
stacking fault is present. If an additional plane is present, the defect is called an extrinsic stacking fault,
i.e. ABCABACABC. An extended stacking fault in which the order of stacking is reversed is called
a twin lamella, e.g. ABCABCB AC BABCABC. If two regions have inverted stacking order they are
called twins and their joint interface is called a twin boundary, e.g. . . .ABCABCABCBACBACBA. . .
(Fig. 4.29). The various types of stacking faults are shown in Fig. 4.27. In Fig. 4.28 a cross-sectional
image of stacking faults in GaAs on Si is shown. They block each other and thus partially annihilate
with increasing thickness.
A stacking fault is bounded by two partial dislocations (Sect. 4.3.1.5) formed by the dissociation of a
perfect dislocation. A full (or perfect) dislocation with Burger’s vector a/2[110] in a III–V compound
is dissociated into two Shockley partials according to (4.22) [348]. Since the dislocation energy is
proportional to |b|
2 , the dissociation is energetically favored (see Sect. 4.3.1.5).
The stacking-fault energy in pure silicon is γ = 47 mJ m
−2 [349]. A similar value is found for Ge,
γ = 60 mJ m
−2 [350] and undoped GaAs, γ = 45 mJ m
−2 [351]. In diamond a much larger value is
found, γ = 285 mJ m
−2 [352]. Impurity incorporation typically reduces the stacking fault energy. The
systematics of stacking fault energy for various III–V and II–VI compounds has been discussed [185,
353, 354]. It can be correlated with the s-parameter (2.11) as depicted in Fig. 4.30.
Fig. 4.27 HRTEM images
of a thin-film silicon with
intrinsic (labeled ‘ISF’)
and extrinsic (‘ESF’)
stacking faults and twin
boundary (‘Twin’). b Six
monolayer thick hexagonal
(wurtzite) CdTe layer in
cubic (zincblende) CdTe.
Stacking order (from
bottom to top) is:
ABCABABABABC. . .
Reprinted with permission
from [345]
(a)
(b)