Resonant Raman scattering induced by excitons bound to nitrogen impurities in GaP:N

A study of the resonant Raman scattering (RRS) by optical phonons that is induced by excitons bound to isoelectronic nitrogen impurities in GaP is presented. Strong Raman lines are observed under resonant excitation into the inhomogeneously broadened 1S exciton band, at liquid He temperatures. They involve the ${\mathrm{LO}}_{\mathrm{\Gamma }}$,${\mathrm{TO}}_{\mathrm{\Gamma }}$ phonons and a nitrogen-induced, forbidden scattering by the zone-edge ${\mathrm{LO}}_{\mathit{X}}$ phonon. The ${\mathrm{LO}}_{\mathit{X}}$ RRS profile is shown to be a sum of contributions from the J=1 state of all N-bound excitons weighted by their density and damping factors. The RRS is dominated by those N-bound excitons which are perturbed by distant background impurities. A model based on the measured density of N-bound exciton states and on the energy-dependent damping factor is presented and is found to account well for the observed ${\mathrm{LO}}_{\mathit{X}}$ RRS profile. The main damping processes are due to tunneling between the various N-bound exciton states. The resonant enhancement of the ${\mathrm{LO}}_{\mathrm{\Gamma }}$-phonon scattering by the N-bound excitons is measured as ${10}^9$ times that of the pure GaP crystal.