Non-resonant Raman scattering of wurtzite GaAs and InP nanowires

It is now possible to synthesize the wurtzite crystal phase of most III-V semiconductors in the form of nanowires. This sparks interest for fundamental research and adds extra degrees of freedom for designing novel devices. However, the understanding of many properties, such as phonon dispersion, of these wurtzite semiconductors is not yet complete, despite the extensive number of studies published. The E 2L and E 2H phonon modes exist in the wurtzite crystal phase only (not in zinc blende) where the E 2H mode has been already experimentally observed in Ga and In arsenides and phosphides, while the E 2L mode has been observed in GaP, but not in GaAs or InP. In order to determine the energy of E 2L in wurtzite GaAs and InP, we performed Raman scattering measurements on wurtzite GaAs and InP nanowires. We found clear evidence of the E 2L phonon mode at 64 cm -1 and 54 cm -1 , respectively. Polarization-dependent experiments revealed similar selection rules for both the E 2L and the E 2H phonon modes (as expected) where the intensity peaked with excitation and detection polarization being perpendicular to the [0001] crystallographic direction. We further find that the splitting between the E 1 (TO) and A 1 (TO) modes is around 2 cm -1 in wurtzite GaAs and below 1 cm -1 in wurtzite InP. We believe these results will be useful for a better understanding of phonons in wurtzite crystal phase of III-V semiconductors as well as for testing and improving phonon dispersion calculations.