The temperature and concentration dependence of optical transitions in ${\mathrm{GaAs}}_{1-x}{\mathrm{N}}_x$ $(<\mathrm{}3.8\mathrm{}\mathrm{eV})$ are studied by electromodulated reflectance. These studies suggest that the $E_{+}$ transition involves the valence-band maximum at $\Gamma$ and a singlet state originating from the splitting of the quadruply degenerate conduction band at L. Such a transition, forbidden in pure GaAs, becomes allowed in ${\mathrm{GaAs}}_{1-x}{\mathrm{N}}_x$ due to the strong perturbation of nitrogen doping to the band structure. A similar analysis applied to the transition $E_{*}$ suggests that it is related either to resonant states evolving from the level created by a single isolated nitrogen impurity in GaAs, or to the splitting of the triplet originating from the L conduction band, induced by a further reduction in symmetry associated with nitrogen pairs.

• Received 25 April 2003

DOI:https://doi.org/10.1103/PhysRevB.68.075207