FIRST-PRINCIPLES PSEUDOPOTENTIAL STUDY OF THE PHASE-STABILITY OF THE III-V SEMICONDUCTORS GAAS AND ALAS

A first-principles pseudopotential study of the phase stability of the III-V semiconductors GaAs and AlAs is reported. For both compounds we study the zinc-blende, wurtzite, NaCl, CsCl, beta-tin, NiAs, and sc16 structures, the latter being the binary analog of the metastable bc8 structure observed in Si and Ge. For GaAs we have also considered a structure of orthorhombic symmetry with four atoms per unit cell. This structure is the same as that recently discovered for ZnTe III [Phys. Rev. Lett. 73, 1805 (1994)], and includes as a special case the Pmm2 structure which had previously been suggested as the structure of GaAs II. Comparison is made with the experimental transition pressures, equations of state, and internal parameters of these compounds. We investigate the recent suggestion that the sc16 structure is very low in energy in III-V compounds. We find that sc16 GaAs is thermodynamically stable to all the other phases studied in a very small range of pressures, but sc16 AlAs is not thermodynamically stable at any pressure. For both GaAs and AlAs we find that the CsCl structure is thermodynamically stable at very high pressures.