Quaternary MgSiN2-GaN alloy semiconductors for deep UV applications

Ultra-wide direct band gap semiconductors have been investigated extensively for their potential in deep ultraviolet optoelectronic applications. In this work, we investigate two octet-rule preserving structures of the MgSiN2-GaN alloys in 50 % mixing -- namely, Pmn21 and P1n1 space groups -- as candidates for these applications. Although the MgSiN2 has an indirect band gap of ~0.4 eV below its direct band gap of ~6.5 eV, the alloy structures we present here are nearly direct gaps in the sense that the indirect gap is less than 0.1 eV lower than the direct gap of ~4.7 eV, calculated by the quasiparticle self-consistent QSGW method. The positive mixing energies of 8 (31) meV/atom for Pmn21 (P1n1) show only a small driving force toward phase separation. Moreover, the different sign lattice mismatch in two basal plane directions between MgSiN2 and GaN could avoid the tensile strain, which is a known problem in Al_xGa_(1-x)N. Besides band structures, we also present effective masses and symmetry analysis of the valence band splitting which affects the band gap optical transition polarizations.