Photonic and polaritonic band gaps in 2D macroporous silicon structures

Abstract

Out-of-plane optical transmission spectra of 2D photonic macroporous silicon structures are investigated. By the plane wave expansion method all possible 2D lattice symmetries are considered and analyzed both in general case and for p-, s-polarizations. Sharp increase of absorption and formation of photonic band gaps is measured for wavelengths between one and two optical periods of macroporous silicon structure. Thus, for periodic structures one photonic band gap is formed, and some narrow peaks of density of states are formed for structure with the arbitrary macropore distribution. Theoretically unpredicted reduction in the transmittance of electromagnetic radiation and the step formation are observed for wavelengths less than optical period of macropores. Transmission spectra of macroporous silicon as well as steps were explained by a model of directed and decay optical modes formed by macroporous silicon as a short wave-guide structure. Prevalence of absorption over reflection of light, dependence of photoconductivity on incidence angle of the electromagnetic radiation testify to formation of the polaritonic type band formation.