Crystallinity and Photoluminescence in Stain‐Etched Porous Si

Si thin films were deposited by low pressure chemical vapor deposition on quartz and oxidized Si substrates at temperatures ranging from 540 to 640°C. X‐ray diffraction (XRD) indicates that films deposited ≥ 590°C are increasingly polycrystalline with a '220' orientation, while films deposited ≤580°C are amorphous. After deposition, the Si films were rendered porous by stain‐etching in . XRD and Raman spectroscopy indicate that initially polycrystalline films retain their crystallinity after becoming porous. PoSi films deposited ≥590°C exhibit visible (∼650–670 nm) photoluminescence (PL) at room temperature under UV excitation. Films deposited ≤580°C do not luminesce, even after a very long etch time which produces a significant increase in the surface pore area density. The XRD signal of the Si films and the corresponding PL intensity exhibit a qualitatively similar dependence on deposition temperature. A certain degree of crystallinity in the material appears to be a necessary condition for photoluminescence.