Stability of the strained-layer superlattice (GaP)1/(InP)1(001)

First-principles total-energy methods have been used to study the stability of the strained monolayer superlattice (GaP${)}_1$/(InP${)}_1$ (001). We find a value of 4 mRy for the heat of formation, suggesting that this superlattice is unstable to disproportionation into its bulk constituent compounds. Upon formation of the superlattice, a small charge transfer from GaP to the more ionic InP is found. The Ga-P and In-P bond lengths in (GaP${)}_1$/(InP${)}_1$ are within 1% of their bulk theoretical values.