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 (E_exc) of excitation laser light is parallel to that (E_etch) of the light used during anodization, and minimum when E_exc is perpendicular to E_etch. 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. © 2002 American Institute of Physics.