Strain-induced structural, band-structure and piezoelectric evolutions in Al_(0.5)Ga_(0.5)N alloy

摘要

Structural phase transition, band structure, and piezoelectric response of Al_(0.5)Ga_(0.5)N alloy under uniaxial and biaxial strains are systematically investigated using first-principle calculations. The main findings are summarized as follows: (Ⅰ) Although the wurtzite structure transforms to an intermediate graphite-like structure for both uniaxial and biaxial strains, the second-order phase transition is found for uniaxial strain and the first-order transition for biaxial strain. The transition is driven by the mechanical and dynamical instabilities for uniaxial strain, and by the mechanical instability for biaxial strain. (Ⅱ) The wurtzite phase always remains the direct band structure, whereas the band gap of graphite-like phase is always indirect. The band gaps of wurtzite and graphite-like phases are greatly reduced by internal strains. (Ⅲ) The drastic enhancements in piezoelectric response are observed near phase transition, which is attributed to the flat and shallow local energy minima associated with two different phases. Our calculated results are compared with the available experimental and other theoretical data, and good agreements are obtained.