Structural and optical properties of vapour-etching based porous silicon

Abstract

The structural and optical properties of porous silicon (PS) layers prepared by Vapour-Etching (VE) of moderately and heavily boron-doped Si substrates are investigated. The VE technique produces rough PS layers that are essentially formed of interconnected cluster-like structures. Optical investigations indicate that this surface roughness enables the PS layers to be used as antireflection coatings in silicon based devices. These optical characteristics are investigated by optical reflectivity and light scattering. The local chemical state and the microstructure of the PS layers are studied by electron energy loss spectroscopy (EELS) in transmission electron microscopy (TEM), and are correlated to the red photoluminescence (PL). TEM studies point out that the cluster-like interconnected structures are composed of luminescent nanocrystallites. PL measurements display that both quantum confinement and surface passivation determine the electronic states of the silicon nanocrystallites. The complex dielectric function is calculated from the experimental single-scattering distribution spectrum using a Kramers Kronig analysis. The first resonance peak in the imaginary part is observed at 2.3eV; two other broadened features appear at 4.7 and 8.8 eV. The latter is generally related to an interface plasmon resulting from the silicon-silicon oxide interface. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.