OPTICAL-PHONON BEHAVIOR IN GA1-XINXAS - THE ROLE OF MICROSCOPIC STRAINS AND IONIC PLASMON COUPLING

We present an experimental and theoretical investigation of long-wavel ength optical-phonon behavior in Ga1-xInxAs alloys. We propose a model which accounts quantitatively for both phonon frequencies and Raman i ntensities. The transverse-optical-phonon behavior is shown to be dete rmined by mass disorder and microscopic strains. It is shown that Rama n scattering provides a means of measuring local bond distortions in m ixed crystals. Coupling by the macroscopic ionic polarization is shown to determine the longitudinal optical phonon behavior. The model acco unts for the so-called anomalies of the Raman intensities and oscillat or strengths observed in Ga1-xInxAs. Our analysis is supported by a th orough Raman-scattering study. The frequencies, Raman intensities and symmetries of both the transverse- and longitudinal-optical modes have been determined accurately over the whole compositional range, by usi ng different crystal orientations ([001], [110], and [111]). [S0163-18 29(98)07540-7].