Phonons in ternary group-III nitride alloys

Abstract

The lattice dynamics of random $A_x{B}_{1-x}\mathrm{N}$ alloys $(A,B=\mathrm{A}\mathrm{l},\mathrm{}\mathrm{G}\mathrm{a},\mathrm{}\mathrm{In})$ is studied with a method based on the modified random-element isodisplacement (MREI) and a rigid-ion model. The MREI description is generalized so that no additional force constants are needed but all lattice vibrations can be considered. Phonon frequencies and spectral weights are studied versus composition x for zinc-blende and wurtzite mixed crystals. The one- and two-mode behavior of the zone-center optical phonons is discussed in the light of the interplay of elastic and electric forces as well as of the atomic masses. The results are compared with data from recent Raman and IR measurements.