Tunable characteristics of porous silicon optical microcavities by energetic N ion beams interactions

The present study demonstrates the tuning of optical characteristics of porous silicon (PSi) based microcavities by N ion beams interactions. These optical microcavities prepared using electrochemical etching of heavily doped p+-type Si. The PSi microcavities were exposed to N ions of 200 keV and 1 MeV at an optimized ion fluence of 1 x 1015 ions/cm2 . A significant red-shifting of 32~60 nm resonance cavity mode was observed due to ion interaction. The experimental spectral data are in good agreement with the transfer matrix simulations. A substantial modification of PSi microcavity surface states are visualised through the Raman and X-ray photoelectron spectroscopies (XPS). The Raman spectral results show modifications from crystalline Si (c-Si) to nanostructured Si (n-Si) and subsequently to amorphous Si (a-Si). The XPS indicates the modification of Si–Si and Si–O bonds and the formation of new Si–N bonds implying the presence of Si3N4. These experimental observations along with analytical simulations and cavity modelling conclusively show the realization of cavity tunability and substantial modification in the optical field intensity and photon confinement within the spacer layer of the microcavity. These results suggest that ion beams are the effective tools to produce wider tunable optical properties in microcavity with highly stable designer optical structures suitable for photonic applications.