Influence of Electrochemical Etching Current Density on Porous Si Luminescence Properties and Microstructure

A porous silicon layer (PSL) was prepared on single-crystal p-type Si (100) wafers with electrochemical etching in HF solutions at different current densities to explore the effect of current density on the PSL luminescence properties and microstructure. Luminesence was evaluated by measuring photoluminescence (PL) spectra. The microstructure was observed using FE-SEM, TEM, and CLSM. The surface composition was determined using FT-IR analysis. The PL intensity emitted by the PSL increased with increasing electrochemical etching current density. TEM images indicated that the PSL prepared on a Si specimen with a specific resistivity of 1kΩm consisted of dispersed ultrafine Si particles with a diameter of 2∼5nm. The structure of the PSL prepared on a Si specimen with a specifis resistivity of 0.1Ωm was coarse and columnar. The PSL microstructure (0.1Ωm) became fine and granular with increasing current density. FT-IR spectra showed that the surface SiHx concentration of PSL decreased with increasing current density. From these results, we concluded that the quantum confinement effect is operative on the visible luminescence from the PSL, and the surface compound consisting of SiHx forms surface states reducing the luminescence intensity. The electronic band models of the SiHx/PSL/p-Si substrate are proposed to explain the visible PL mechanism.