Depth detection and fabrication of porous silicon without the stress

Raman measurements showed that the phonon band within the etched layer shifting to lower frequencies is due to quantum confinement of phonons in the porous Si. Comparison of etched Si and bulk Si showed that etched Si exhibit much deeper detectable depth via the Raman spectrometer, presumably resulting from the pore formation. Therefore, the z-scan of Raman spectroscopy can be used to qualitatively detect the etching depth.