Porous Si has been fabricated from amorphous and polycrystalline Si films by stain‐etching in . Infrared transmission measurements have revealed an absorption peak at 880–890 cm −1 only in crystalline porous Si samples. This peak is probably due to an bending mode in the presence of oxygen. Similarly, only crystalline films exhibit visible (∼650–670 nm) photoluminescence under UV excitation. Amorphous samples do not luminesce even after very long etch times, in spite of greatly increased porosity. Therefore, it appears that there exists a unique correlation between the presence of crystallinity in the starting Si film and the presence of surface oxyhydrides and photoluminescence after stain‐etching.
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Steckl et al. (1995) studied this question.