Theory of High Pressure Phases of Group-IV and III-V Semiconductors

Under high pressure the open, covalent structure of group-IV and III–V semiconductors collapses to a denser metallic crystal structure. On further pressure increase a range of behaviours is seen. There has been an enormous amout of theoretical and experimental work recently on these phases, and this paper draws together the underlying themes and trends to give the theoretical interpretations of the system, from generic ball and stick thermodynamics, which explains the collapse from diamond to the β-tin and Imma phases, through free electron theory which explains some of the trends in c/a ratios of the various structures, on to accurate electronic structure calculations of specific systems which can determine which of closely related structures have lowest free energy. Also, the observation and causes of disorder and metastability are discussed, and the prospects for high-pressure synthesis in making new materials.