The Cmcm structure as a stable phase of binary compounds: Application to GaAs-II

We have studied the orthorhombic high-pressure phase II of GaAs. We find that the structure previously suggested for this phase is unstable and leads to the same Cmcm structure which was recently found in high-pressure studies of ZnTe and CdTe. We have investigated the mechanism for the distortion leading to Cmcm. Our calculations show that Cmcm GaAs becomes thermodynamically stable at 120 kbar in agreement with experimental data for GaAs-II. The available experimental structural parameters are consistent with this Cmcm structure, which may be common among II-VI and III-V compounds.