Optical response of one-dimensional (Si/SiO2)m photonic crystals

One-dimensional photonic crystals made of (Si/SiO2)m multilayers with m = 2,8 have been grown on SiO2 4-in. wafers by repeated polysilicon low-pressure chemical vapor deposition, oxidation, and wet etching steps. The poly-Si and SiO2 layers were about 220 and 660 nm thick, respectively, thus realizing /4 distributed Bragg reflectors. Spectroscopic ellipsometry in the 1.4–5 eV range was used to determine the dielectric function of poly-Si and the actual layer thicknesses, as well as to check the structural and compositional homogeneity of the structures. In order to measure the photonic crystal properties, specular reflectance and transmittance measurements were performed from 0.2 to 6 eV at different angles of incidence 50° and for transverse electric and transverse magnetic polarizations. The stop-bands characteristic of Bragg reflector multilayers appear up to the fifth order and become more pronounced with increasing m, reaching almost complete rejection for m = 4 periods. The experimental spectra were fitted by the transfer-matrix method, both versus and m. Moreover, the experimental stop bands of the finite multilayers matched the calculated photonic band gaps of an infinite one-dimensional photonic crystal very well.