Multi‐phonon processes in C _6V ⁴ (P6 ₃ mc) hexagonal semiconductors: GaN, ZnO, ZnS, BeO, CdS, and Al ₂ O ₃ – sapphire: D _3d ⁶ (R3c)

Abstract

The vibrational states of crystals are classified according to appropriate irreducible representations (irrps) of wave vector space groups. Based on the irrps of the C 6v 4 space group the selection rules for one -twoand three -phonon processes are derived. Experimentally, we have performed inelastic light scattering experiments on several different GaN samples as well as ZnO. Some multi -phonon transitions present on our spectra have been verified by the derived multi -phonon selection rules.