  Here, we compare the stabilities of different III-V crystals configurations
on stepped Si substrates, with or without anti-phase boundaries, for abrupt and
compensated interfaces, using density functional theory. Thermodynamic
stability of the different heterostructures is analyzed with an atomic scale
description of charge densities distribution and mechani-cal strain. We show
that the configuration where a III-V crystal adapts to a Si monoatomic step
through change of charge compensation at the hetero-interface is much more
stable than the configuration in which an antiphase boundary is formed. This
study thus demonstrates that antiphase boundaries commonly observed in III-V/Si
samples are not origi-nating from Si monoatomic step edges but from inevitable
kinetically driven coalescence of monophase 3D III-V islands.
