COMPOSITIONAL DEPENDENCE OF OPTICAL-PHONON FREQUENCIES IN ALXGA1-XAS

The lattice properties of the important ternary semiconductor A1xGa1-x As have received much attention, but substantial differences persist a mong reported results for the optical-phonon frequencies versus x. Som e plots show kinks, whereas others are smooth. We have carefully measu red the longitudinal- and transverse-optical frequencies omega(LO) and omega(TO) versus x at 300 and 80 K by Raman scattering, for (100) Alx Ga1-xAs films (0 less-than-or-equal-to x less-than-or-equal-to 1) grow n by molecular-beam epitaxy. The results clarify the published inconsi stencies, yielding smooth quadratic dependences of frequency on x. A m odified random-element-isodisplacement model gives excellent fits to t he data at 300 K, and good fits at 80 K. Our analysis provides a relia ble basis for Raman-based compositional analysis of AlxGa1-xAs structu res, and for further theoretical study.