Tuning the reflectivity of high contrast gratings based on silicon and silica by means of wet etching with hydrofluoric acid

We report on experimental etching techniques to trim the efficiency of high-contrast gratings based on silicon and silica. We show that the resonance wavelength and hence the reflectivity can be tuned by means of selectively etching the silica grating. In order to realize a well-defined adjustment of the grating profiles the etching rates of silica layers with hydrofluoric acid were determined. Coatings deposited by different techniques such as electron-beam evaporation, ion plating and thermal oxidation are compared and the influence of structuration on the etching is investigated, as well. This work basically helps to improve the maximum reflectivity that can be realized with these high-contrast reflectors and tune the resonance to a required wavelength.