Phonon scattering at impurity pairs in ZnSe

Abstract

We have investigated in detail the phonon lines in the luminescence excitation spectra of donor-acceptor pairs in ZnSe as a function of crystal temperature and surface orientation. At low temperatures $T<50$ K, the phonons are emitted during the donor-acceptor pair excitation or recombination process. Besides the carrier-phonon interaction of the Fr\"ohlich type, a second interaction correlated with close donor-acceptor pairs is clearly observed. The phonon lines indicate further that the acceptor ground state is split due to interimpurity interactions. In the temperature range from 50 to 80 K, no phonon lines are detected. The lines reappear at temperatures $T>80$ K. Selection rules for first-order Raman scattering at different surfaces are observed. At $T>100$ K, the LO-phonon line grows relative to the TO due to resonant Raman scattering.