Ternary silicon germanium nitrides: A class of tunable band gap materials

Ternary silicon germanium nitrides with compositions of both Si1-xGexN and (Si1-xGex)(3)N-4 are predicted to have a band gap that decreases as the germanium: silicon ratio increases. The band gap is indirect for the silicon-rich compounds but becomes direct as the germanium content increases, due to greater mixing of s and p states in the conduction band. This effect of band gap tunability has recently been reported for (Si1-xGex)(3)N-4 in the spinel structure [Boyko et al., Phys. Rev. B 81, 155207 (2010)]. Our results suggest that this is a more general effect and that ternary group-14 nitrides should form a class of semiconducting materials for which the band gap can be tuned by controlling the composition.