Electronic properties of porous silicon

Porous silicon (PS) has been extensively studied in recent years. The origin of its luminescence has been a subject of debate. This work attempts to give some insight towards the understanding of this phenomenon, studying the behaviour of the energy band structure of PS as a function of the pore morphology and distribution, for a given porosity. The porous structure is modeled as empty columns of different sizes and shapes, produced into an otherwise silicon perfect crystal. The columns are passivated with hydrogen atoms. A tight-binding Hamiltonian on an sp³* basis set is applied onto a supercell. Due to the simplicity of the model, morphology effects can be analyzed. The results show that the band gap and the nature of the states at the top of the valence band depend on the morphology. Furthermore, we also discuss the shift of the conduction band minimum towards the gamma point, producing an almost direct band gap, as the pore distribution changes.