Two-Phonon Absorption Spectra of III–V Compound Semiconductors

Abstract

High-resolution, two-phonon absorption spectra of GaAs and InAs were measured with a far-infrared Fourier transform spectrometer. Prominent Van Hove singularities on the GaAs two-phonon spectrum were identified with the aid of two-phonon density-of-states spectra and energy contour plots on symmetry planes. These were calculated using a shell model, with parameters derived from neutron diffraction experiments, in a manner similar to that employed in the investigation of the two-phonon absorption spectrum of InSb. There were strikingly similar features in the spectra of GaAs, InAs and InSb. In the case of GaAs and InSb, energy contour analysis confirmed that similar features were produced by phonon combinations of the same type and from the same Brillouin zone location. This permitted a tentative assignment of features of the InAs spectrum in the absence of experimental phonon dispersion curves. The interpretation of the two-phonon spectra of these materials demonstrates that not all of the strong peaks are due to phonon combinations at the high symmetry points of the Brillouin zone as previously assumed. Many result from two-phonon processes occurring on the hexagonal face of the fcc Brillouin zone and at other locations in the interior of the zone.