Oxidation of sub-50 nm Si columns for light emission study

Abstract

Understanding the optical and electrical properties of Si nanostructures is essential for exploring the potential of using structural quantum confinement to induce light emission from crystalline Si. To this end, sub-50 nm Si columns were fabricated with high resolution electron beam lithography and anisotropic reactive ion etching. The dimensions of the Si nanostructures were further reduced by thermal oxidation. A novel transmission electron microscopy technique was developed to monitor the oxidation progress without removing the oxide structural support. Images of sub-5 nm crystalline Si cores were obtained. The oxidation rates of the Si nanostructures were characterized. Among the various interesting oxidation phenomena are the nonmonotonic oxidation rate with respect to the column size and an unexpectedly slow change of the outer diameters of the oxidized columns. Several likely mechanisms, including the stress retardation of oxidation for a small radius of curvature, the stress induced generation and diffusion of Si interstitials, the stress induced radial strain in the Si core, and SiO sublimation during oxidation, were proposed to explain the unusual oxidation phenomena. Although not thoroughly understood, a photoluminescence spectrum was also obtained for a sample with a large patterned area.