FABRICATION AND PROPERTIES OF VISIBLE-LIGHT SUBWAVELENGTH AMORPHOUS-SILICON TRANSMISSION GRATINGS

We present the first fabrication and investigation of visible-light su bwavelength transmission gratings in high refractive index materials ( e.g., amorphous silicon) on silica substrates. The gratings have perio ds ranging from 100 to 800 nm in 50 nm increments, a thickness of 180 nm (very thin), and they were fabricated using electron-beam lithograp hy and reactive ion etching. Because of the high index, we have observ ed, for the first time, strong polarization dependence in light transm ittance. The polarization effect was found to greatly depend on the ra tio of grating period to wavelength, having the largest variation when the period is near half of the wavelength. The largest transmission d ifference for the polarization parallel and perpendicular to the grati ng fingers was found to be 12 dB. This observation contradicts the beh avior manifested in subwavelength transmission gratings in low index m aterials, where the transmittance is essentially independent of the li ght polarization and the grating period. Rigorous electromagnetic theo ry has been used to model the gratings and agrees with experiments. (C ) 1995 American Vacuum Society.