Optical properties of two-dimensional photonic-bandgap crystals characterized by spectral ellipsometry

In this paper, we demonstrate a simple and non-destructive measuring method for both TE and TM bandgaps of two-dimensional (2D) silicon photonic bandgap (PBG) structures by using reflected spectral ellipsometry. Although this method measures the reflected light from samples, the transmitted signal of PBG layer can be measured by using reflecting signals. With large incident angles, planar PBG modulation effects and bandgap information can be obtained. To verify this method, we fabricated silicon arrays for 2D PBG by using electron-beam lithography. From SEM images, we can verify the geometry especially the radius of the cells, which is related to the bandgaps. With a specific set of radii and dielectric constants, we can get the band diagram with plane-wave expansion method. There are several bandgaps of both TE and TM modes, which can be used to detect multiple bandgaps by spectral ellipsometry.