DENSE TETRAHEDRAL STRUCTURES OF COMPOUND SEMICONDUCTOR

Dense tetrahedral forms of the elemental semiconductors silicon and germanium can be synthesised as metastable phases by depressurisation from metallic modifications. These structures are denoted as BC8 (body-centred: 8 atoms per cell) and ST12 (simple-tetragonal: 12 atoms per cell). Despite having similar metallic phases, the III-V compounds have never been formed in the diatomic equivalent of the BC8 or ST12 structures. We report the results of our ab initio total energy calculations which suggest that the diatomic analogue of the BC8 structure, (the SC16 structure: simple cubic: 16 atoms per cell) is a stable high-pressure polymorph of several III-V compounds. We suggest that kinetic factors rather than energetics inhibit its formation. In light of the recent discovery of the pressure-induced formation of the SC16 structure in I-VII compounds, it now seems that the energetics of high-pressure phase transitions in tetrahedral semiconductors are much more similar than they once appeared to be and that the transition mechanisms are much more involved.