Quantum mechanical effects in (Ga,In)(As,N) alloys

A large supercell pseudopotential technique is used to predict optical and electronic properties of (Ga1-yIny)(As1-xNx) alloys-with small x and y comp ositions-that are either in their disordered form or exhibiting a particula r atomic ordering, namely one-dimensional nitrogen chains. In addition to t he previously reported quantum couplings between electronic states with dif ferent reciprocal k points, another mechanism is found to participate in th e strong decrease of the band gap of (Ga1-yIny)(As1-xNx) alloys with respec t to GaAs. This mechanism only involves the reciprocal Gamma point, and is a nitrogen-induced shift of the conduction band minimum of GaAs. The existe nce of these two effects-quantum couplings and nitrogen-induced shift-can b e easily understood within the framework of perturbation theory. Furthermor e, atomic ordering in (Ga1-yIny)(As1-xNx) alloys is found to strongly alter the band-gap and wave-function localization, by modifying the quantum coup lings.