Computational modeling of the excited states of Ge nanostructures

F. A. Serrano, A. Miranda, and M. Cruz-Irisson*

ESIME-Culhuacan, Instituto Politécnico Nacional,

Av. Santa Ana 1000, 04430 México, D.F.

*e-mail: irisson@unam.mx

Recent developments of CMOS industry have demonstrated the possibility to fabricate ultimate semiconductor nanostructures MOSFET since this device represents a promising candidate due to its better electrostatic control; it then becomes relevant to develop modeling tools based on atomistic and quantum methods capable of calculating nanowire band structures. In this work the energy band gap and optical absorption of [001] oriented Ge nanowires with diverse square cross-sections are calculated by using the sp³s* semi-empirical tight-binding (TB) model with a supercell approach. Each surface dangling bond is saturated with a hydrogen atom. The results of the variation band gap are compared with those obtained by TB-sp³d⁵s*, the density functional theory, and experimental data in agreement with the quantum confinement scheme. The imaginary part of the dielectric function is calculated by using the interconnected and free standing (without interconnection) models for the Si skeleton. This microscopic supercell model predicts the low frequency tail in the absorption spectrum, which appears even without the allowance for the indirect optical transitions.

Keywords: Nanowire, germanium, tight-binding, electronic structure, optical properties

*Corresponding author contact:

Dr. Miguel Cruz-Irisson

Tel.: +5255-5624-2000 ext 73033;

Fax: +5255-5656-2058;

E-mail: irisson@unam.mx