Effect of inhomogeneous mesoporosity and defects on the luminescent properties of slanted silicon nanowires prepared by facile metal-assisted chemical etching

Slanted silicon nanowires show an improved optical absorption and better electrical contact than the vertical silicon nanowires. High aspect ratio mesoporous slanted silicon nanowires oriented along the (100) direction are fabricated by a facile two-step metal-assisted chemical etching process. Inhomogeneous porosity with a pore diameter of 2-10 nm is identified by the analysis of transmission electron microscopy, angle dependent Raman spectroscopy, and Brunauer-Emmett-Teller measurements. Slanted silicon nanowires possess a core/shell structure, and the porosity varies from top to bottom of the slanted silicon nanowires. The presence of neutral oxygen defects, self-trapped excitons, and surface defects is identified by photoluminescence spectroscopy, and the results are correlated with Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy data. In addition to mesoporosity, defects such as self-trapped excitons, oxygen vacancies, and surface defects on Si/SiOx interface contribute to the luminescence of slanted silicon nanowires. Red shift in the photoluminescence with increasing etching time is explained using quantum confinement luminescent center model. Understanding the role of defects and porosity in slanted silicon nanowires is highly desirable to increase the efficiency of silicon nanowires based optoelectronic devices. Published by AIP Publishing