Modelling of electronic and phononic states of Ge nanostructures

Abstract

The electronic band structure of ordered porous germanium (PGe) and germanium nanowires (GeNW) are studied by means of an sp 3 s* tight-binding approach. Within the linear response theory, a local bond-polarization model based on the displacement–displacement Green's function and the Born potential including central and non-central interatomic forces are used to investigate the Raman response and the phonon band structure of PGe and GeNW. This study is carried out by means of a supercell model, in which along the [0 0 1] direction empty-column pores and nanowires are constructed preserving the crystalline Ge atomic structure. An advantage of this model is the interconnection between Ge nanocrystals in PGe and then, all the electronic and phononic states are delocalized. However, the results of both elementary excitations show a clear quantum confinement signature. Moreover, the highest-energy Raman peak in both PGe and GeNW shows a shift towards lower frequencies with respect to that of bulk crystalline Ge, in good agreement with the experimental data.