Carrier band-to-band recombination in Mn-passivated porous silicon

Abstract

Porous silicon (PS) was in situ passivated by Mn2+ and covered by a layer of MnO2 using a hydrothermal technique. A 370 nm photoluminescence (PL) band, showing carrier `band edge' recombination features, was observed, which agrees well with the inter-band transition of 3.4 eV detected by optical absorption measurements. Silicon nanocrystallites several nanometres in size were able to cause conduction band splitting; then an inter-band transition of 3.4 eV was observed due to the carrier transition between the sub-conduction band to the valence band (A1). A high potential layer of manganese oxide on the surface of the silicon nanocrystallites prevents excited carrier diffusion from the core of Si to neighbouring defects from nonradiative decay, and as a result enhances carrier band-to-band recombination, resulting in the ultraviolet PL (370 nm).