Localized states in mixedGaPzAs1−zcrystals

The vibrational properties of a diatomic $A{B}_z{C}_{1-z}$ in which the mass $m_B$ and $m_C$ are randomly distributed have been investigated. The calculation has been performed in the short-range-forces approximation. A nonlinear Lagrangian which describes the vibrational properties is obtained by averaging over the random mass. The mass disorder creates a region of continuous localized states near the edge and the center of the averaged crystal Brillouin zone. Experimentally $\mathrm{Ga}{\mathrm{P}}_z{\mathrm{As}}_{1-z}$ has been studied by means of Raman scattering; the predicted behavior has been observed which explains the existence of a two-mode behavior in the acoustical region, as well as the appearance of a new peak with LO symmetry in the range of optical frequencies.