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.

Depth distribution of luminescent Si nanocrystals in Si implanted SiO2 films on Si

“…[1][2][3][4] Forming Si nanocrystals by means of Si ion implantation into SiO 2 followed by precipitation has been extensively studied [5][6][7][8][9][10] and SiO 2 has proven to be a robust matrix that provides good chemical and electrical passivation of the nanocrystals. Previously, we have demonstrated that SiO 2 films containing Si nanocrystals made by ion implantation show photoluminescence in the visible and near-infrared that can be attributed to two distinct sources.…”

The Structural and Electrical Characteristics of Silicon-Implanted Borosilicate Glass

“…11) Such materials exhibit strong photo-and electroluminescence (PL and EL) in visible and near-infrared wavelengths, which attracts much attention due to the potential applications in electronic and optoelectronic devices. [12][13][14][15] Most of the studies on these materials discuss light-emitting properties of the metal-oxide-semiconductor (MOS) structure with Si nanocrystals buried in the surface oxide layer on the silicon substrate. The combined carrier transport effects of the conventional MOS diode, the implanted Si-related defects, and the buried Si nanocrystals in the SiO 2 layer on Si substrate are thus complicated.…”