Münster 1997 – scientific programme
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HL: Halbleiterphysik
HL 28: Gitterdynamik
HL 28.6: Talk
Thursday, March 20, 1997, 11:45–12:00, H4
Theoretical Investigation of Isotope Effects on the Lattice Dynamics of Elemental Semiconductors — •P. Pavone1, K. Karch1, A.P. Mayer1, B. Steininger1, H. Sterner1, D. Strauch1, and S. Baroni2 — 1Theoretische Physik, Universität Regensburg — 2SISSA & INFM, Trieste, Italy; CECAM, Lyon, France
Crystals with different isotopic composition have not only a different average mass, but also show isotopic disorder-induced effects. Both these effects lead to small but appreciable variations of several static and lattice-dynamical properties of crystals. Due to the increase of experimental resolution and availability of samples, many experiments have been performed in the last years to determine these changes. The purpose of this work is to present results of a very accurate theoretical study of isotope effects in tetrahedral elemental semiconductors based on ab initio methods such as the density-functional and density-functional perturbation theory. The dependence of the lattice parameter and elastic constants upon the isotopic composition has been determined within the virtual-crystal approximation, neglecting disorder effects. Full inclusion of isotopic disorder-induced effects on the first-order Raman scattering has been obtained calculating phonons in big supercells with random distribution of isotopes at given composition. Furthermore, we have calculated the one-phonon density of states, frequency shifts, and line-shape broadenings including disorder effects within the coherent-potential approximation. Our results agree very nicely with the available experiments.