(Ga, In)(N, As)-fine structure of the band gap due to nearest-neighbor configurations of the isovalent nitrogen

An intrinsic property of quaternary alloys $A_{1-y}{B}_y{C}_{1-x}{D}_x\hspace{0.5em}(x\approx 1–3\%)$ with D being an isovalent trap is reported: a set of discrete band gaps occurs due to substitution of the isovalent trap D on sites with different nearest-neighbor environments. Exemplary, this phenomenon is demonstrated for (Ga,In)(N,As) by experiment and explained by tight-binding supercell calculations. The band gap of this nitrogen-poor alloy is blueshifted by simply moving the nitrogen isovalent traps from Ga-ligand rich sites to In-ligand rich sites, without changing the alloy composition.