Phase Transition and Band Structure Tuned by Strains in Al1/2Ga1/2N Alloy of Complex Structure**Supported by the Fundamental Research Funds for the Central Universities under Grant No 2013QNA38.

Abstract

Phase transition and band structure tuned by uniaxial and biaxial strains are systematically investigated based on the density-functional theory for ordered Al1/2Ga1/2N alloys of complex structures. Although the structural transformations to graphite-like from wurtzite are energetically favorable for both types of strain, the phase transitions are different in nature: the second-order transition induced by uniaxial strain is jointly driven by the mechanical and dynamical instabilities and the first-order transition by biaxial strain only by the mechanical instability. The wurtzite phase always shows the direct band gap, while the band gap of the graphite-like phase is always indirect. Furthermore, the band gaps of the wurtzite phase can be reduced by both types of strain, while that of the graphite-like phase is enhanced by uniaxial strain and is suppressed by biaxial strain.