Enhanced photoluminescence from porous silicon formed by nonstandard preparation

Abstract

Using a nonstandard preparation procedure, porous silicon (PS) samples are grown whose overall photoluminescence (PL) intensities exceed those of standard PS samples from the same Si wafer up to 50 times, and whose PL maxima occur in the high-energy range at about 1.8 eV. The preparation includes an electrochemical etching step in a ${\mathrm{H}\mathrm{C}\mathrm{l}:\mathrm{H}\mathrm{F}:\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{OH}$ electrolyte solution with varying HCl contents. The fine structure of low-temperature PL spectra is discussed in terms of the confinement model. Crystalline silicon wires are identified as PL active structural elements, and the wire diameters are determined. At room temperature, four broad PL peaks are observed. The evolution of these peaks with varying HCl content of the electrolyte provides detailed insight into the porous structure of the samples. PL studies on laser-irradiated samples indicate that the Si wires are covered by stoichiometric silicon oxide. We conclude that the absence of Si dangling bonds, and the well-ordered wire structure, could be responsible for the enhanced PL intensity of our PS samples, as well as for their stability against exposition to air and postanodization.