Up to fifth-order Raman scattering of InP under nonresonant conditions

We present Raman spectra of InP measured under nonresonant conditions revealing multiphonon processes up to fifth order. Using an incident photon energy in the absorption region of the compound but far from any of its interband transitions, nonresonant multiphonon processes of order higher than two, which have not been reported so far in a zinc-blende-type semiconductor, have been observed in indium phosphide. In this way it has been possible to detect contributions not only from the longitudinal optical phonons but also from the transverse optical phonons in the higher-order peaks. We find a very good agreement between multiples of the TO- and LO-phonon frequencies at the zone center and the higher-order phonons measured in the experiments. The trend of strong intensity reductions observed when passing from first to second as well as from second to third order is not maintained when going from third to fourth, and from fourth to fifth order