SINGULARITIES OF CYCLOTRON-PHONON ABSORPTION IN SEMICONDUCTING FILMS.

The cyclotron-phonon absorption coefficient in a thin semiconducting plate placed in an external magnetic field perpendicular to the plate surface is considered. The absorption is found to have a resonant character regardless of the polarization of the electromagnetic waves, and the absorption peaks are much narrower than the analogous peaks in a bulky sample. It is shown that the presence of the magnetic field makes the size-effect phonon absorption also resonant. In addition, an additional series of absorption lines, which are not present in either ordinary cyclotron-phonon or in size-effect phonon absorption, is observed.