Papers by Author: Miguel Cruz-Irisson

Abstract: The effects on the electronic band structure of hydrogenated cubic silicon carbide (-SiC) nanowires of changes in the diameter and morphology are studied using a semiempirical sp3s* tight-binding approach applied to a supercell model. The results of the calculation of the electronic band structure and electronic density of states obtained are compared with those calculated by density functional theory within local density approximation only for the bulk of -SiC. As boundary conditions, we passivated all the Si and C dangling bonds with hydrogen atoms. The results show that although surface morphology modifies the band gap, the change is more systematic with the thickness variation. The energy band gap increases with decreasing diameter in all cases because of quantum confinement, but the scaling is dependent on the morphology (cross-section) of the -SiC nanowires. Finally, the calculations show a consistent asymptotical behavior to the crystalline limit when the width of the wires enlarges.

Abstract: For ordered porous silicon, the Born potential and phonon Green’s functions are used to investigate its Raman response, while the electronic band structure and dielectric function are studied by means of a sp3s* tight-binding supercell model, in which periodical pores are produced by removing columns of atoms along [001] direction from a crystalline Si structure and the pores surfaces are passivated by hydrogen atoms for the electronic band structure calculations. This supercell model emphasizes the interconnection between silicon nanocrystals, delocalizing the electronic and phononic states. However, the results of both elementary excitations show a clear quantum confinement signature, which is contrasted with that of nanowire systems. In addition, ab-initio calculations of small supercells are performed in order to verify the tight-binding results. The calculated dielectric function is compared with experimental data. Finally, a shift of the highest-frequency Raman peak towards lower energy is observed, in agreement with the experimental data.