Theoretical predictions of expanded-volume phases of GaAs

By reducing the (4;2)-connected regular three-dimensional nets of AlPO4 zeolites to simply four-connected nets of III-V semiconductors such as GaAs, we introduce a variety of expanded structures for compound semiconductors. An ab initio local-orbital quantum molecular-dynamics method is used to determine the optimized geometries, energetics, and electronic properties of the proposed structures. We specifically treat GaAs, and find that even with the 90 degrees bond angles required for these expanded structures, most of these phases remain semiconducting with band gaps ranging from slightly above that of the zinc-blende structure, to about 0.6 eV smaller than it. Two compounds with the same volume as the room pressure phase are predicted to be metallic. The total energies of the expanded phases are in the range of 0.2 eV/atom higher than the zinc-blende structure, less than or comparable to the energies of known or predicted high-pressure phases, and are energetically less favorable than analogous expanded phases of elemental semiconductors such as Si.