• electronic properties
• germanio
• germanium
• nanofili
• nanofilo
• nanowire
• nanowires
• semiconductor nanowire
• semiconductor nanowires
• silicio
• silicon
• strain

Nanowires are almost cylindrical structures, with diameter typically ranging from 1 to 100 nm, and lengths up to several tens of microns. They are generally grown by means of the vapor-liquid-solid (VLS) growth technique, where a catalytic gold particle acts as growth site. This method allows the production of single-crystal nanowires, permitting also to produce heterostructured wires along a given growth direction.

Nanowires are very promising both for their transport and optical properties; in the last few years, great experimental effort has been devoted to the study of their properties. Theoretical studies are however essential to support this research, in fact they can predict the behavior of nanowires as a function of different parameters as the chemical composition, the growth direction, the wire diameter, the strain conditions, etc.

In this work, we present a numerical study of the electronic structure of semiconductor nanowires made of silicon and germanium.

For this aim we have first developed a software to describe the geometrical structure of the wire (growth direction, shape) taking into account also deformation effects due to hydrostatic and uniaxial strains.

We have then adopted a semiempirical tight-binding $s p^3 d^5 s^*$ model including first neighbors, two-center integrals and spin-orbit interaction for the study of the electronic properties of the wires.

We have investigated wires with circular, square and rectangular section, grown along different directions; periodic boundary conditions have been assumed along the growth direction.

For the different wires considered we present the electronic band structure and a description of the wavefunctions in terms of the orbitals centered on the atoms of the structure. Band gaps and quantum confinement effects are analyzed as functions of the wire diameter.