Al0.48In0.52As monolayers (ML) are inserted at the binary-compound interfaces of (AlAs)2 ML(InAs)2 ML short-period superlattices (SPSs) during growth on (001) InP. The insertion of Al0.48In0.52As interlayers greater than 2 ML thick tends to suppress the phase separation that normally occurs during molecular beam epitaxy of the SPS. The degree of suppression is a sensitive function of both the monolayer-scale thickness, and the intraperiod growth sequence, of the interlayers in the SPS. Given this sensitivity to monolayer-scale variations in the surface-region composition, we propose that cyclical phase transition of the reconstructed surface initiates SPS decomposition. © 2001 American Institute of Physics.