Spontaneous Raman scattering in [100], [110], and [11-2] directional GaP waveguides

Spontaneous Raman scattering in GaP waveguides with micrometer size cross s ections has been investigated for [100], [110], and [11-2] directions. For backward scattering, the result is the same as for the GaP bulk crystals, w hich depends exactly on the Raman selection rule. However, it is found that mode changes from longitudinal optical (LO) phonon to transverse optical ( TO) phonon mode and TO phonon to LO phonon mode occur when the waveguide cr oss section is of micrometer size for forward scattering. The mode change i s determined by the relationship of the waveguide width, thickness and wave vector of phonons. The Raman scattering intensity ratios for different wav eguide directions as well as for different light polarization directions ob tained from the forward scattering experiments show good agreement with the calculations for this waveguide effect. In particular, the highest LO inte nsity is obtained for forward scattering in a [11-2] directional waveguide. This effect should be taken into account for the design of semiconductor R aman amplifiers and lasers with micrometer size waveguides. (C) 2001 Americ an Institute of Physics.