Multiple-peak structure in porous Si photoluminescence

Abstract

Photoluminescence (PL) measurements have been carried out on anodic porous silicon (PSi) at temperatures between T=20 and 300 K. He–Ne laser (1.96 eV), green laser diode (2.33 eV), and He–Cd laser (3.81 eV) are used as excitation light sources. Low-temperature (T≤250 K) PL spectra show a multiple-peak structure even when laser excitation is far from resonance with the red PL band. The configurational-coordinate model explains such unique multiple-peak structure very well. Fourier transform (FT) technique is used for the analysis of the measured multiple-peak structure. The FT frequency is determined to be ∼64 meV, which is in exact agreement with the bulk long-wavelength optical phonon energy in crystalline Si. Although the origin of the multiple-peak structure is bulk-related, its strength is very sensitive to the presence of surface oxide.