Anodic Current and Temperature Dependence of Light-Emitting Properties of Porous Si.

A comprehensive study has been performed on the light-emitting properties of porous silicon (PSi) films formed by anodic etching. PSi films are investigated using photoluminescence (PL), PL excitation, and X-ray photoelectron spectroscopy (XPS). The PL emission features are strongly dependent on the anodic current density. Analysis of the PL spectrum suggests the existence of two different emission mechanisms in the PSi layers: An efficient mechanism that is usually observed at higher temperatures and one that exhibits a multiple-peak Structure and appears only at low temperatures (T ⩽ 60 K), even at an excitation energy (∼3.8 eV) far from the PL resonance band (1.5-2.4 eV). The high temperature emission can be interpreted as being due to the quantum-confinement effect, i.e., relaxation of the momentum conservation at and above the indirect absorption edge (supra-E^ID_g emission), while the lower temperature PL emission is explained by the classical configurational-coordinate model with a lattice vibronic quantum of ∼64 meV. The XPS data indicate that the short-range order is important in understanding the optical spectra not only for the amorphous substance but also for the nanocrystalline substance. [ABSTRACT FROM AUTHOR]