Origin of the nitrogen-induced optical transitions inGaAs1−xNx

Abstract

The temperature and concentration dependence of optical transitions in ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ $(<3.8\mathrm{eV})$ are studied by electromodulated reflectance. These studies suggest that the ${E}_{+}$ transition involves the valence-band maximum at $\ensuremath{\Gamma}$ 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 ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ 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.