Unusual reentrant step-flow morphology in low-temperature MBE-grown GaSb(100) enabled by bismuth surfactancy

This study reports the discovery of reentrant step-flow growth behavior in homoepitaxial GaSb(100) films grown via molecular beam epitaxy under bismuth surfactancy. Using ex situ atomic force microscopy, we observe a superposition of short-scale mound and large-scale step-flow morphologies at temperatures significantly below the conventional threshold for step-flow growth. The findings suggest that bismuth surfactant atoms facilitate long-range adatom kinetics, enabling step-flowlike features despite reduced thermal energy. This behavior diverges from traditional epitaxial growth models and aligns with previously reported reentrant phenomena in other material systems. The implications for surface morphology control and device fabrication are discussed, highlighting the role of surfactants in enabling nonequilibrium growth pathways.