Effects of terminated atoms, porosity and drilling orientations on the band structure of porous silicon

We designed different models of nano porous silicon terminated by hydrogen or oxygen atoms, and analyzed their band gap structure and density of states by means of first-principles density functional theory calculation. For the hydrogen-atom-passivation porous silicon in the [100] direction, with the increase of porosity, the band gap increased. When the porosity is 64%, a direct band gap is obtained. The theoretical results were confirmed by our experiments. For the oxygen-atom-passivation porous silicon in the [100] direction, half-metallic behavior and ferromagnetism appear when the porosity is 64%, which is due to the Si 3p band affected by O 2p and H 1s orbitals. For the oxygen-atom-passivation porous silicon in the [1 1 0] direction, a direct band gap occurs when the porosity is 49%. Passivation atom, porosity and hollowed-out direction are key factors affecting the band gap structure and density of states of porous silicon. These results would have significant impacts on design of complex porous silicon structures for silicon band-gap engineering in the area of optoelectronics. (C) 2017 Elsevier B.V. All rights reserved.