Tunable superstructures in hydrothermally etched iron-passivated porous silicon

Tunable superstructures were generated by hydrothermally etching silicon wafers in the solution of HF containing ferric nitrate. The structural units of these superstructures arrayed perpendicular to the surface and their shapes could be formed as cone-like, pillar-like, or crater-pit-like through changing the solution concentration of ${\mathrm{Fe}}^{\mathrm{3+}}$ in the etching process. The photoluminescence (PL) in as-prepared porous silicon was found to be independent of the microlocations chosen to carry out the PL measurements.