Relationship of Processing Parameters to Photoluminescence Intensity and Mechanical Failure in Thick Porous Silicon Layers

Abstract

The surface passivation of porous silicon has received much attention. While nuclear magnetic resonance may be able to provide insight into the surface passivation of porous silicon, relatively thick (>40 μm) layers are desired. However, mechanically stable layers could only be produced within identifiable ranges of HF concentration, current density, and anodization time. This information allowed sample preparation for nuclear magnetic resonance characterization of porous silicon. In addition, an inverse correlation between mechanical stability and photoluminescence intensity was observed. In a pairwise comparison, similar porosity and surface passivation were maintained as anodization time increased under otherwise constant conditions. However, at the longer anodization time, photoluminescence intensity and surface area increased. To account for these observations, we hypothesize that the thickness of the silicon wall between pores decreases as electrochemical etching proceeds. Decreasing wall thickness could lead to both mechanical failure and increase the probability of creating regions of quantum confinement. A larger number of quantum confined regions, having the same surface passivation, could account for the observed increased photoluminescence intensity.