Optical properties of one-and two-dimensional photonic crystals based on silicon

摘要: A comparative investigation, both experimental and theoretical, of the optical properties of one-and two-dimensional photonic crystals based on silicon is presented. The samples consisted of: a)(Si/SiO2) m multilayers with m≤ 8, in the λ/4 distributed Bragg configuration, grown on SiO2 wafers by low-pressure chemical vapour deposition cycles, oxidation and wet etching steps; b) Si stripes on insulator waveguides, fabricated by electron-beam lithography and reactive ion-etching (RIE) techniques; c) macroporous Si samples with triangular lattices of holes, prepared by electrochemical etch of a prepatterned substrate. The optical response was measured in the 0.15-3 eV range by transmittance and reflectance with TE and TM polarized light at different angles of incidence θ≤ 75, and by a white-light Mach-Zehnder interferometer coupled to a Fourier-transform spectrometer. The spectra give clear evidence of the photonic band-gaps and of the quasi-guided modes of the photonic structures, and allow to obtain the photonic band dispersion. The experimental results agree well with the reflectance spectra simulated by the scattering matrix method, and with the photonic bands calculated with an expansion on the basis of plane-waves. A line-shape analysis of the structures in reflectance show that they can be associated to one-dimensional critical points; moreover, a symmetry analysis yields the selection rules for excitation of photonic modes, which can be treated like elementary excitations of the crystal.