Orientation-dependent phase separation of GaAsSb epilayers grown by gas-source molecular-beam epitaxy

This work describes a regular solution model that considers the free energy of the surface monolayer to explain the orientation-dependent phase separation in GaAsSb. In the proposed model, only the interaction between the second nearest-neighboring atoms sitting on the same monolayer contributes to the interaction parameter. Consequently, the parameter reduces to Ω/2 and Ω/3 for (111)B GaAsSb and (100) GaAsSb, where Ω denotes the parameter of bulk GaAsSb. By including the strain effect, the proposed model thoroughly elucidates the immiscibility behavior of (111)B GaAsSb and (100) GaAsSb.

► (111)B GaAsSb exhibits severe phase separation than (100) GaAsSb.
► We propose a model to calculate the monolayer free energy of different planes.
► Monolayer model suggests that (111)B GaAsSb has larger interaction parameter.
► Monolayer model including strain well explains the immiscibility of GaAsSb.