  In strained heteroepitaxy, two-dimensional (2D) layers can exhibit a critical
thickness at which three-dimensional (3D) islands self-assemble, relieving
misfit strain at the cost of an increased surface area. Here we show that such
a morphological phase transition can be induced on-demand using surfactants. We
explore Bi as a surfactant in the growth of InAs on GaAs(110), and find that
the presence of surface Bi induces Stranski-Krastanov growth of 3D islands,
while growth without Bi always favors 2D layer formation. Exposing a static two
monolayer thick InAs layer to Bi rapidly transforms the layer into 3D islands.
Density functional theory calculations reveal that Bi reduces the energetic
cost of 3D island formation by modifying surface energies. These 3D
nanostructures behave as optically active quantum dots. This work illustrates
how surfactants can enable quantum dot self-assembly where it otherwise would
not occur.
