Characterization of photonic crystals based on opal-semiconductor composites by Bragg reflection spectroscopy

The Bragg reflection spectra of photonic crystals based on the opal-semiconductor (GaP, GaN) composites are studied. An approach is developed which provides a means for characterizing the opal-like structures. The approach is based on examination of the Bragg reflection spectral features and of the conditions for multiwave Bragg diffraction. The shape of the Bragg spectra is analyzed in the context of the approximation of a periodic planar-layered medium taking into account sintering and axial compression of the a-SiO2 spheres that constitute the three-dimensional opal lattice. The diameters and the coefficient of compression of the spheres are determined with regard to the spectroscopic structural invariant suggested in the study for defining the conditions for observation of multiwave Bragg diffraction at the system of the {111} planes.