# Regensburg 2002 – wissenschaftliches Programm

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# HL: Halbleiterphysik

## HL 38: Poster 2

### HL 38.9: Poster

### Donnerstag, 14. März 2002, 16:30–19:00, Poster A

**Ab initio study of anharmonic properties in semiconductors: The Grüneisen tensor** — •Gerd Birner, Gernot Deinzer, Pasquale Pavone, and Dieter Strauch — Institut für Theoretische Physik, Universität Regensburg, Germany

The Grüneisen tensor describes the relative change of frequencies in
solids, if a macroscopic strain is applied.
For homogeneous deformations of crystals with cubic symmetry, it is
possible
to gain the volume dependence of the frequencies on the variation of
the lattice parameter [1].
In the general case of arbitrary deformations,
perturbation theory to first order in the anharmonic potential allows
to express the Grüneisen tensor in terms of harmonic and anharmonic
force constants [2].
In this work, we present an *ab initio* study of the complete
Grüneisen tensor of the tetrahedral semiconductors Si, Ge, and GaAs.
Within the harmonic approximation, interatomic force constants are
calculated using density-functional perturbation theory. Anharmonic
coefficients of third order are derived by application of the
2*n*+1 theorem to the density-functional formalism.
The volume mode-Grüneisen parameters obtained by our approach are
very similar to those derived by the
standard—quasi-harmonic—approximation. However, our method allows to
extract in a direct way the off-diagonal elements of the Grüneisen
tensor, which are less efficiently obtained by the standard approach.

[1] P. Pavone *et al.*, Phys. Rev. B **48**, 3156 (1993).

[2] A. P. Mayer and R. K. Wehner, phys. stat. sol. (b) **126**,
91 (1984).