Lattice-constant dependence of the dynamical effective charge in AlAs and GaAs

We have used Raman spectroscopy to study the lattice-constant dependence of the optical-phonon frequencies in AlAs and GaAs. From these studies, we deduce the dynamical effective charge for AlAs to be eT*=2.20±0.01-(5. 8±0.1)(-Δa/a0). For GaAs we find a dynamical effective charge eT*= 2.18±0.01-(4.8±0.7)(-Δa/a0)-(28±16)(- Δa/a0)2. First-principles calculations, recently confirmed by experiment, indicate that the interatomic force constants (related to the second derivative of the interatomic potential) are virtually identical for GaAs and AlAs. The results reported in this paper indicate that higher-order derivatives of the interatomic potential are also remarkably similar for these two materials.