The role of a thin amorphous silicon layer in the fabrication of micro-pored silicon

Micro-pored silicon formed by electrochemical anodization of a p-type (100) Si wafer with a thin amorphous Si (a-Si) layer showed green colored photoluminescence (PL) at room temperature. The a-Si thin films were deposited on an Si(100) wafer by rf magnetron sputtering. The wafers with and without a-Si layer were electrochemically anodized and annealed by a rapid thermal process at 800 °C for 10 min. A strong green PL signal peaked at 543 nm appeared in the samples fabricated with a-Si thin film, while normally processed porous Si samples showed only a typical PL signal at 681 nm. From scanning electron microscopy, Auger electron spectroscopy, and Fourier transformed infra-red spectroscopy, it is suggested that the a-Si layer has the role of a mesh for the smooth and fine Si porosity which prevents oxidation during the anodization of the Si substrate.