PLANAR VIBRATIONAL-MODES IN SEMICONDUCTORS - A SIMPLE-MODEL

A macroscopic continuum model for optical phonon modes is applied to o btain the planar vibrational modes of a monoatomic layer embedded in a homogeneous material. The differences in optical force constants and reduced masses across the atomic plane are considered within the theor y as a fundamental factor to describe the modes localized at the inter face. We have derived analytical expressions for the phonon spectrum, as well as for the vector displacement and electric potential as a fun ction of coordinates. An analysis of the infrared and Raman activity f or the obtained modes is given together with a comparison with recent experimental data.