Atomic topology and optical properties of amorphous porous silicon, ap-Si

Porous silicon has been studied extensively due to the interesting luminous properties that it displays. However, amorphous porous silicon, ap-Si, is an elusive material difficult to produce and study. Since ap-Si can be visualized as highly defective a-Si we have applied our new thermal process, based on an ab initio molecular dynamics method that uses the Harris functional, to generate samples of ap-Si with 50% porosity starting with a cubic periodic supercell of 216 atoms, from which a porous cell was carved out. The randomizing process was done using a 7.5 fs time step and after the various structures were obtained, their optical gaps were determined. We find that the gaps increase monotonically with the randomness of the structure from 0.004 to 0.580 eV.