Non‐isodisplacement of P atoms in long‐wavelength optical phonons in In_1–<i>x</i>Ga_<i>x</i>P

Abstract

Abstract A study on long‐wavelength optical phonon modes in In 1– x Ga x P is carried out by infrared reflection and Raman scattering. The oscillator strengths of the single reststrahlen band (one‐mode behaviour) and of the additional band between the TO and LO mode are determined by classical dispersion analysis. The origin of the additional structure is explained by non‐isodisplacement motions of the P atoms in the long‐wavelength phonon modes arising from changes in the nearest‐neighbour force constants with the kind of surrounding atoms. Compositional dependences of the mode frequencies and oscillator strengths are calculated using a virtual crystal model with five types of basic units.