Facet-Dependent Doping and Dopant-Dependent Faceting in Si-Doped GaAsSb Nanowires

In this work, we correlate the spatial distributions
of Si, Sb,
and rotational twins in Si-doped GaAs1–xSbx nanowires. GaAs1–xSbx nanowires were grown
epitaxially on Si(111) substrates by tuning process conditions to
achieve repeated nucleation of rotational twins and growth along the
[111]B direction; dilute Sb and Si fluxes were chosen to create a
sufficient twin density to achieve a high yield while avoiding the
growth of the wurtzite phase. While the impact of Si and Sb on twin
density and nanowire growth rate has been previously reported, the
facet-dependent incorporation of these species has not been established.
Scanning transmission electron microscopy was used to confirm that
Sb incorporates preferentially on the (111)B facets relative to {1̅1̅0} facets prior to
nucleation of
a rotational twin. With periodic twinning, this facet dependence leads
to alternating regions of enriched and depleted Sb concentrations
attributed to a growth rate-dependent Sb–As-exchange mechanism.
Atom probe tomography measurements establish that while Si doping
is not perturbed by twinning on (111)B facets, Si and Sb concentrations
are anticorrelated for growth on non-(111)B facets. Density functional
theory calculations underpin a thermodynamic model that explains the
observed anisotropies in the dopant incorporation.