  Recently, GaAsSb/GaAsN type II short-period superlattices (SLs) have been
proposed as suitable structures to be implemented in the optimal design of
monolithic multi-junction solar cells. However, due to strong surface Sb
segregation, experimental Sb composition profiles differ greatly from the
nominal square-wave design. In this work, the improvement of the interface
quality of these SLs in terms of compositional abruptness and surface roughness
has been evaluated by implementing different growth interruption times under
Sb4/As4 (soaking) and As4 (desorption) overpressure conditions before and after
the growth of GaAsSb layers, respectively. The combined effects of both
processes enhance Sb distribution, achieving squarer compositional profiles
with reduced surface roughness interfaces. It has been found that the
improvement in compositional abruptness is quantitatively much higher at the
lower interface, during soaking, than at the upper interface during desorption.
Conversely, a larger decrease in surface roughness is achieved at the upper
interface than at the lower interface. Fitting of the Sb segregation profiles
using the 3-layer kinetic fluid model has shown that the increase in Sb
incorporation rate is due to the decrease in segregation energy, presumably to
changes in the surface reconstruction of the floating layer at the surface.
