STABILITY AND ELECTRONIC-STRUCTURE OF THE CINNABAR PHASE IN GAAS

We have performed nb initio pseudopotential calculations to investigat e the pressure-induced phase transitions in GaAs in the light of the r ecent experimental observation of a stable cinnabar structure. We find that a cinnabar structure is metastable with respect to other candida te structures, although extremely close to stability for pressures in the region of 16 GPa. This is in good agreement with experiment, where it has been observed to coexist with the zinc-blende and Cmcm phases in this pressure regime. It had been suggested that the cinnabar struc ture is the only known semiconducting high-pressure phase in a III-V c ompound. We perform band-structure calculations on this high-pressure structure and confirm that the material is semiconducting.