Photoluminescence behavior of Si nanocrystals as a function of the implantation temperature and excitation power density

Abstract

In this work we present a study of photoluminescence (PL) on Si nanocrystals (NC) produced by ion implantation on SiO2 targets at temperatures ranging between room temperature and 800°C and subsequently annealed in N2 atmosphere. The PL measurements were performed at low excitation power density (20mW∕cm2) in order to avoid nonlinear effects. Broad PL spectra were obtained, presenting a line-shape structure that can be reproduced by two superimposed peaks at around 780 and 950nm. We have observed that both PL intensity and line-shape change by varying the annealing as well as the implantation temperatures. Implantations performed at 400°C or higher produce a remarkable effect in the PL line shape, evidenced by a strong redshift, and a striking intensity increase of the peak located at the long-wavelength side of the PL spectrum. In addition we have studied the PL dependence on the excitation power density (from 0.002to15W∕cm2). The samples with broad NC size distribution containing large grains, as revealed by transmission electron microscopy observations presented a PL spectrum whose line shape was strongly dependent on the excitation power density. While high excitation power densities (saturation regime) induce only the short-wavelength part of the PL spectrum, low excitation power densities bring out the appearance of the hidden long-wavelength part of the emission. The present results are explained by current models.