Tailoring the Optical Properties of Si Nanocrystals In SiO₂: Materials Issues And Nanocrystal Laser Perspectives

Abstract

Si nanocrystals (diameter 2 - 5 nm) were formed by 35 keV Si⁺ implantation at a fluence of 6×10¹⁶ Si/cm² into a 100 nm thick thermally grown SiO₂ film on Si (100), followed by thermal annealing at 1100 °C for 10 min. The nanocrystals show a broad photoluminescence spectrum, peaking at 880 nm, attributed to the recombination of quantum confined excitons. Rutherford backscattering spectrometry and transmission electron microscopy show that annealing these samples in flowing O₂ at 1000 °C for times up to 30 min. results in oxidation of the Si nanocrystals, first close to the SiO₂ film surface and later at greater depths. Upon oxidation for 30 min. the photoluminescence peak wavelength blue-shifts by more than 200 nm. This blueshift is attributed to a quantum size effect in which a reduction of the average nanocrystal size leads to emission at shorter wavelengths. The fabrication of a laser based on SiO₂ waveguides doped with Si nanocrystals seems possible, if the nanocrystal size distribution can be narrowed down into the percent range.