Theory of the optical properties of resonant states in nitrogen-doped semiconductor alloys

The optical properties of N-doped semiconductor alloys, such as GaAs-P and In-GaP, are investigated theoretically in the range of compositions, near the direct-indirect crossover, in which the discrete electronic state associated with the nitrogen trap is degenerate with the conduction-band continuum near the center of the Brillouin zone. The resolvent-operator formalism is applied to obtain the density of states and the optical absorption and emission spectra, by approximating the short-range impurity potential by a Koster-Slater interaction and using a simple parametrized description of the density of states of the host alloy. The presence of the discrete autoionizing trap state is shown to produce a characteristic Fano resonance-antiresonance line shape, in agreement with recent experimental observations, and in contrast to earlier theoretical predicitons of a sharp and resonantly enhanced emission spectrum.