ENHANCED PHOTOLUMINESCENCE FROM POROUS SILICON FORMED BY NONSTANDARD PREPARATION

Using a nonstandard preparation procedure, porous silicon (PS) samples are grown whose overall photoluminescence (PL) intensities exceed tho se of standard PS samples from the same Si wafer up to 50 times, and w hose PL maxima occur In the high-energy range at about 1.8 eV. The pre paration includes an electrochemical etching step in a HCl:HF:C2H5OH e lectrolyte solution with varying HCl contents. The fine structure of l ow-temperature PL spectra is discussed in terms of the confinement mod el. Crystalline silicon wires are identified as PL active structural e lements, and the wire diameters are determined. At room temperature, f our broad PL peaks are observed. The evolution of these peaks with var ying HCl content of the electrolyte provides detailed insight into the porous structure of the samples. PL studies on laser-irradiated sampl es indicate that the Si wires are covered by stoichiometric silicon ox ide. We conclude that the absence of Si dangling bands, and the well-o rdered wire structure, could be responsible for the enhanced PL intens ity of our PS samples, as well as for their stability against expositi on to air and postanodization. [S0163-1829(97)08139-3].