We present an experimental and theoretical investigation of long-wavelength optical-phonon behavior in ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{As}$ alloys. We propose a model which accounts quantitatively for both phonon frequencies and Raman intensities. The transverse-optical-phonon behavior is shown to be determined by mass disorder and microscopic strains. It is shown that Raman scattering provides a means of measuring local bond distortions in mixed crystals. Coupling by the macroscopic ionic polarization is shown to determine the longitudinal optical-phonon behavior. The model accounts for the so-called anomalies of the Raman intensities and oscillator strengths observed in ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{As}.$ Our analysis is supported by a thorough 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 using different crystal orientations ([001], [110], and [111]).

• Received 22 May 1998

DOI:https://doi.org/10.1103/PhysRevB.58.10452