Optical properties of “black silicon” formed by catalytic etching of Au/Si(100) wafers

Abstract

“Black silicon” layers were formed by catalytic etching of Au/Si(100) wafers in HF−H2O2−H2O solutions at room temperature. The structural and optical properties of the catalytic-etched Si layers were investigated by scanning electron microscopy (SEM), wettability observations, Fourier-transform infrared (FTIR) spectroscopy analysis, near-IR−UV transmittance, Raman scattering, photoluminescence (PL), PL excitation, and PL decay measurements. The SEM observation suggested that the vertically well-aligned Si nanowires can be formed in the limited synthesis conditions (H2O2 concentration, deposited Au film thickness, and etching time). FTIR and near-IR−UV transmittance spectra revealed that the catalytic-etched Si layers show optical absorbance about two orders higher in the far-IR−UV region than that for the single-crystalline Si substrate. The Raman scattering spectra were found to be clearly different from those for the bulk single-crystalline Si and were analyzed using a newly developed model. All the catalytic-etched Si samples showed efficient visible emission at ∼2 eV. This emission can be explained by the quantum-mechanical confinement effect, i.e., a relaxation of the momentum conservation at and above the indirect-absorption edge of Si (supra-EgX emission).