Direct structural evidence of the change in N-III bonding in (GaIn)(NAs) before and after thermal annealing

The blueshift of the fundamental energy gap of (GaIn)(NAs) upon thermal treatment is well established. However, the physical reason is still controversially discussed in literature. In the present paper we give direct structural evidence using transmission electron microscopy in combination with structure factor calculation that this blueshift—for the metal organic vapor phase epitaxy grown samples investigated here—results solely from a change in the local environment of nitrogen. N is bound to Ga upon growth and moves into an In-rich environment upon annealing to minimize the strain energy of the crystal. The technique presented here can be used to unambiguously determine the reason for the blueshift of differently grown and annealed dilute nitride materials.