Tracing degradation mechanisms of epitaxially grown GaAsSb on InP by InSb formation at elevated temperatures

The thermal stability of GaAsSb/InP is known to be compromised by group-V volatility and intermixing at the heterojunction that adversely impact the performance of subsequently fabricated optoelectronic or high-speed devices. We interrogate the GaAsSb/InP interface and trace its degradation during extended annealing, where we observe significant intermixing and nanostructure formation. Scanning transmission electron microscopy reveals the formation of pyramidal nanostructures that extend from the epitaxial layer into the substrate. Energy-dispersive x-ray spectroscopy and geometric phase analysis show migration of Sb from the GaAsSb epilayer to the InP substrate and migration of P from the InP substrate to the epilayer. The pronounced migration of Sb and P leads to the formation of InSb-rich facets and tips of the pyramidal nanostructures. The interdiffusion also leads to InGaAsP replacing the epitaxial GaAsSb. These results are consistent with bulk characterization by high-resolution x-ray diffraction and Raman spectroscopy. The intermixing appears to be driven by simultaneous phase separation and melting of InSb that enhances atomic mobility, providing an alternative mechanism to previously proposed phase separation by spinodal decomposition.