COMPOSITIONAL DEPENDENCE OF OPTICAL-PHONON FREQUENCIES IN ALXGA1-XAS

The lattice properties of the important ternary semiconductor A1xGa1-xAs have received much attention, but substantial differences persist among reported results for the optical-phonon frequencies versus x. Some plots show kinks, whereas others are smooth. We have carefully measured the longitudinal- and transverse-optical frequencies omega(LO) and omega(TO) versus x at 300 and 80 K by Raman scattering, for (100) AlxGa1-xAs films (0 less-than-or-equal-to x less-than-or-equal-to 1) grown by molecular-beam epitaxy. The results clarify the published inconsistencies, yielding smooth quadratic dependences of frequency on x. A modified random-element-isodisplacement model gives excellent fits to the data at 300 K, and good fits at 80 K. Our analysis provides a reliable basis for Raman-based compositional analysis of AlxGa1-xAs structures, and for further theoretical study.