Optical absorption in porous silicon

The optical properties of porous silicon (p-Si) are calculated from the ele ctronic band structure obtained by means of an sp(3)s* tight-binding Hamilt onian and a supercell model, in which the pores are columns detched in crys talline silicon (c-Si). The disorder in the pore sizes and the undulation o f the silicon wires are considered by the existence of a random perturbativ e potential, which produces non-vertical interband transitions, otherwise f orbidden. A typical interval around each k-vector (optical window), where n on-vertical transitions make an important contribution, depends on the valu e of the disorder and its order of magnitude is given by l(-1), where l is the localization length. The calculated absorption spectra are compared wit h experiments, showing good agreement.