Cathodoluminescence of N-doped SnO₂ nanowires and microcrystals

We present a cathodoluminescence (CL) study of the point defects in N-doped SnO₂ nanowires and microcrystals synthesized by thermal evaporation at different growth temperatures and N concentrations. SnO₂:N nanowires were grown at temperatures higher than 1150 °C with N concentrations below of about 3 at.%, while irregular microcrystals were obtained at lower temperatures increasing their N concentration gradually with the growth temperature. EELS and XPS measurements confirmed that N atoms were incorporated into the SnO₂ lattice as substitutional impurities (NO). TEM and EDS measurements revealed that the nanowires grew along the [001] direction by a self-catalyzed growth mechanism. CL measurements showed that the nanowires and microcrystals generated a broad emission composed by three components centered at about 2.05, 2.47 and 2.75 eV. CL spectra obtained at 300 and 100 K showed that the component of 2.05 eV decreased in intensity proportionally to the nitrogen content of samples. We attribute this effect to a decrease of oxygen vacancies in the SnO₂ nanowires and microcrystals, generated by the incorporation of nitrogen in their lattice.