Stable ultraviolet photoluminescence of nanoporous silicon

In this paper, we report for the first time the observation from porous silicon (PS) the intense, narrow (similar to 0.12 eV) line of ultraviolet (UV) (375 nm) photoluminescence (PL) that in air is long-duration stable (at least few month). The intense UV line is created after exposure of PS sample in ambient air for 6 month at room temperature. The PS layers were fabricated by electrochemical etching in standard (HF-ethanol) electrolyte on high resistivity (similar to 3 k Omega cm) (111)-oriented FZ wafer. Moreover boron-doped CZ-(100) wafer with 7-10 Omega cm was used for PS preparation in standard electrolyte with direct added of HCl acid (in the rage from 20 to 30%). After draining in these samples two emission bands with high intensity of PL which are centered at blue (similar to 415 nm) and red (similar to 650 nm) regions for the first time were observed. Image of PS surface obtained by atomic force microscopy (AFM) demonstrate that surface with UV emission in contrast to red ones has multilayer structure of strip-type resonators with gap at least below of 2 nm. The Raman spectra (around 5 19 cm(-1)) that are associated with crystalline silicon for UV and red layers have shown that their intensity large in approximately five times than signal from a bulk substrate. (c) 2007 Elsevier B.V. All rights reserved.