Professor James Galligan
Department of Metallurgy and Materials Engineering,

When ultraviolet light (UV) is shone on ordinary silicon, then it re-emits light in the near-infrared region.  When suitably etched silicon emits light in the visible region.  The mechanism(s) for this can be either a chemical transformation of the surface or a quantum confinement of the electrons and holes, introduced by the UV, in the nanoscale structure formed by the chemical treatment.  We have examined this problem through scanning probe microscopy (SPM), x-ray photoelectron spectroscopy (XPS), and secondary ion emission spectrometry, (SIMS).  These experiments show that the surface is initially hydrogen passivated, and SPM studies show that this surface contains nanoscale wires with nodule size in the range of 1-7 nm.  In Situ SPM images, taken during UV excitation, show a decrease in feature width and an increase in feature height between the non-luminescing and the luminescing porous silicon images.  This corresponds to an increase in tunneling current, and, therefore, and increase in the number of available charge carriers in the wires.  The photoluminescence originates, as such, from quantum confinement of charges within the wires.
Further studies of the reduction in hydrogen passivation, and the associated Ph shifts will be discussed.