Investigation of the glassy layer formed at the top of porous silicon films

The surface properties of porous silicon (PS) play a vital role in its applications in optoelectronic devices and PS-based chemical/biological sensory devices. We have investigated the effects of reactive ion etching (RIE) treatment on the surface structures, optical properties and internal stresses of the PS films. Experimental results show that there is a thin layer of glassy, mirror-like material covered on the top of the PS films and the main composites of this layer are silicon oxides. When removing away this layer, the photoluminescence (PL) intensities decrease sharply, micro-Raman resonant peaks (near 516 cm/sup -1/) shift slightly and the intensities reduce significantly. The functions of the top layer and mechanisms of interaction with PS films will be discussed in this paper.