  GaSbBi alloys have recently emerged as attractive materials for mid-infrared
optoelectronics owing to strong band gap reduction enabled by Bi incorporation
into the GaSb matrix. The fundamental understanding of the epitaxial process
required to demonstrate high quality crystals is in an early-developmental
phase. From this perspective, we report on the key role played by the Sb/Ga
flux ratio in controlling the structural quality and incorporation of high Bi
content (up to 14.5 %-Bi), revealing three distinct epitaxial phases. The first
phase (below stoichiometric Sb/Ga) exhibits Ga-Bi compound droplets, low
crystal quality, and reduced Bi content. At the second phase (above
stoichiometric Sb/Ga), the crystal exhibits smooth surfaces and excellent
crystallinity with efficient Bi incorporation. The last phase corresponds to
exceeding a Sb/Ga threshold that leads to reduced Bi incorporation, Bi droplets
and degraded crystallinity. This threshold value that defines the optimal
growth window is controlled by the temperature as well as the Bi/Ga ratio.
Increasing temperature increases the threshold, albeit simultaneously reducing
Bi incorporation. Conversely, increasing the Bi/Ga flux ratio increases Bi
incorporation, while narrowing down and ultimately closing the window. This
study provides a general framework enabling development of high quality GaSbBi
heterostructures for emerging mid-infrared optoelectronics.
