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–
10] direction
(Fig. 7c and d). The formation of wires is often re-
ported for weakly strained systems11 and reflects the
typical adatom surface diffusion anisotropy on ar-
senic-stabilized surfaces.
12
The positive enthalpy of mixing ∆Hm= x(1–x)Ω
(interaction parameter Ω = 3600 cal/mol)13 for the
InxAl1–xAs alloy increases when the indium content
varies from 33% to 52% and goes against the alloying
between the InAs deposit and the InAlAs buffer layer.
As a result, for small In contents, the alloying limits
the growth of the islands on the InAlAs buffer despite
the large lattice mismatch. On the other hand, for
larger In contents in the InAlAs buffer, the mismatch
is lower but alloying is limited and larger islands can
develop. The surface of the metamorphic InAlAs
sample (Fig. 7c) and the lattice matched InAlAs
sample (Fig. 7d) covered with InAs are similar. The
main difference between these two last structures is
a rougher surface due to the relaxation of mismatch
strain in the metamorphic buffer, with resulting strain
and composition modulations. These modulations can
play a role in the self-assembling process of the
nanostructures as observed for the growth of InAs on
thick InGaAs layer on GaAs which results in island
accumulation at the top of the ridges of the cross-
hatched surface.
14 This is also the case for the growth
of InAs on lateral composition modulated InAs/GaAs
short-period superlattices, for which larger islands
with enhanced dot-dot interactions lead to the self-
equalization of dot size.
15 The interaction parameter
Ω for InGaAs is lower (Ω = 2490 cal/mol)13 as compared
with InAlAs and then a more important alloying can
explain the results obtained with InGaAs. Our results
show that due to reduced alloying effects between
InAs and the InAlAs with 52% In content, similar
nanostructures can be grown on the metamorphic
template as compared with the lattice matched tem-
plate despite the textured surface and the residual
strain in the metamorphic layer. A stronger modula-
tion at the surface of InAlAs would be necessary to
achieve a noticeable change in the dot formation as
confirmed by the realization of InAs dots on InAlAs
islands grown on AlGaAs/GaAs layers.
16 Due to the