THE COLLECTIVE EXCITATIONS OF SEMICONDUCTING FILMS; OPTICAL PHONONS AND PLASMONS

Macroscopic dielectric theory provides a simple and widely used description of the principal long wavelength collective excitations of ionic or doped semiconductors. Recent experiments, however, show that the eigenvectors associated with standing wave normal modes of thin films produced by dielectric theory are qualitatively incorrect. This issue is reviewed, and recent theories which produce results in accord with the data are described.