Fine Structure of Porous Si with Visible Photoluminescence

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Abstract
Porous Si formed by anodization is studied by means of high-resolution scanning electron microscopy, optical microscopy, microphotoluminescence spectroscopy and micro-Raman spectroscopy. Surface morphologies of porous Si films are varied by changing the anodization conditions. High-resolution scanning electron microscopy measurements show that in all these films, porous Si fine structures of visible photoluminescent regions, which are confirmed with optical microscopy and micro-photoluminescence spectroscopy, are composed of particlelike structure of various sizes from several nm to several tens of nm. The peak of the Raman spectrum from the particlelike structure is shifted to lower energy and is wider than that for bulk Si, possibly due to lattice expansion around large surface fractions. Visible photoluminescence in porous Si is not due to carrier confinement in quantum wires, but is probably due to carrier confinement in this structure.