Dimerization in the III-V semiconductor gallium phosphide*

We explored the high-pressure polymorphism of GaP using microdiffraction and first principles techniques. After laser heating at ~40 GPa and 1300 K we found that GaP assumes the super-Cmcm structure featuring the formation of short P-P dimers. A comparison of total energy and enthalpy suggests that the phase here proposed is more stable than earlier considered arrangements at 0K, it is therefore the best candidate high-pressure polymorph of GaP in the range ~ 20-40 GPa. The symmetry lowering is explained by the mixed nature of the bonding in the new phase.
While the polymorphism of III-V semiconductors has been considered a settled problem for more than a decade, our results show that this is not the case for all semiconductors, and, more importantly, that the metallization of GaP is associated with the formation of a range of bond types and coordination geometries in contrast with earlier consensus.