Different behavior of photoluminescence anisotropy in porous silicon layers made by polarized-light-assisted electrochemical etching

Luminescent porous silicon (PSi) layers have been made on n-type Si wafers by anodization in a HF solution under illumination with linearly polarized light. It is observed that the photoluminescence from samples anodized at a current density of 30 mA/cm2 and slightly oxidized electrochemically for passivation exhibits a significant anisotropy in polarization memory (PM): the degree of PM becomes maximum when the vector electric field (Eexc) of excitation laser light is parallel to that (Eetch) of the light used during anodization, and minimum when Eexc is perpendicular to Eetch. These maxima and minima are in totally different directions from those reported previously. In addition, the anisotropy is found to be weak at low anodization current density of 2.3 mA/cm2. These experimental results are discussed based on the electrochemical, rather than photochemical, thinning of Si-nanocrystal assemblies in PSi layers.