posted on 2023-10-31, 19:11authored byChristopher
M. Matthews, Zachary Engel, Keisuke Motoki, W. Alan Doolittle
Phase separation
of indium-bearing III-nitrides is difficult to
control and is a major challenge in the development of these materials.
On the other hand, this same process does not occur naturally for
aluminum gallium nitride but has been leveraged to enable the synthesis
of extremely coherent superlattice structures that may lead to interesting
applications for AlGaN. This work proposes that phase separation in
III-nitride alloys can be attributed to at least four distinct surface-driven
mechanismsthermal decomposition, lateral cation segregation,
vertical cation segregation (VCS), and preferential cation incorporationmore
than bulk-diffusion-enabled spinodal decomposition. An open source,
self-consistent model has been developed to describe the evolution
of surface adlayers during the growth of these III-nitride films.
This model consists of a system of coupled differential equations
which stochastically represent physical mechanisms acting on surface
adatoms, and it is used to evaluate the influence of VCS and preferential
cation incorporation on self-assembled superlattice formation in AlGaN
to both further the understanding of phase separation and test the
validity of surface-driven phase separation. Neither preferential
incorporation nor VCS alone can explain the experimentally observed
composition profiles. However, by combining these two effects, composition
profiles similar to those of experimentally grown self-assembled superlattices
have been obtained.