Abstract
We present a study of the luminescence and resonant Raman scattering (RRS) by optical phonons which are due to excitons bound to isoelectronic nitrogen impurities in GaP and in GaAs x P 1- x . The exciton bands are inhomogeneously broadened. In GaP the broadening results from nitrogen centers which are perturbed by other distant impurities (V-band). In GaAs x P 1- x , the N-bound exciton band reflects the random potential fluctuations in the alloy. Under resonant excitation at liquid He temperatures, strong Raman lines are observed involving the LO Γ, TO Γ phonons and a nitrogen-induced forbidden scattering by the zone-edge LO x phonon. The LO x RRS spectrum is shown to be determined mainly by the density of terminal states, namely, those N-bound excitons which do not tunnel to other sites within the A-B thermalization time. In GaP, this RRS shows a resonance which is strong in the V-band but is essentially missing at the peak of the A-line. This is interpreted as an indication of a fast dephasing rate within the A-line due to resonant transfer, as compared to slow tunneling between the perturbed centers.
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