Ab-initio and tight-binding studies of porous Si and Ge

First-principles and semi-empirical methods are employed to calculate electronic and optical properties of porous silicon and porous germanium. In order to test the parameters used in this work, the crystalline case has been taken as a starting point, where the sp³s* tight-binding and the density functional theory with the local density approximation approaches show a good agreement in the electronic band structures. For the dielectric function, the tight-binding approach demonstrates a better behavior in comparison with the experimental data. For porous systems, this tendency is preserved, showing strong quantum confinement effects.