Perturbation analysis on large band gap bowing of dilute nitride semiconductors

Contrary to the conventional empirical law, band gap of the dilute nitride semiconductors decreases with increasing nitrogen concentration. In spite of a number of investigations, the origin of this “large band gap bowing” is still under debate. In order to elucidate this phenomenon, we investigate change of the band edge energy of GaNxAs1−xGaNxAs1−x due to nitrogen by using the perturbation theory. We found that energy shift of the conduction band edge is arising from intervalley mixing between the ΓΓ- and L-states and/or ΓΓ- and X-states mainly induced by displacement of Ga atoms around nitrogen. The valence band edge state shows upward shift in spite of negative potential of nitrogen. These results are well understood from symmetry of the wavefunctions and the perturbation potential.