Tailoring the Optical Properties of Si Nanocrystals In SiO 2 : Materials Issues And Nanocrystal Laser Perspectives
- PDF / 1,047,571 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 20 Downloads / 204 Views
ABSTRACT Si nanocrystals (diameter 2 - 5 nm) were formed by 35 keV Si÷ implantation at a fluence of 6x1016 Si/cm 2 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 02 at 1000 'C for times up to 30 min. results in oxidation of the Si nanocrystals, first close to the SiO 2 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 Si0 2 waveguides doped with Si nanocrystals seems possible, if the nanocrystal size distribution can be narrowed down into the percent range.
INTRODUCTION The recent discovery of visible light emission from nanocrystalline group IV materials has stimulated considerable experimental effort to understand its origin and utilize it to fabricate Sibased opto-electronic devices [1-4]. The process of making Si nanocrystals by Si ion implantation into thermal Si0 2 films on Si, followed by precipitation [5-7], is fully compatible with standard integrated circuit technology and the SiO 2 matrix is a robust host that provides good passivation for the Si 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. One luminescence feature is related to ion irradiation induced defects in the Si0 2 matrix and can be quenched by introducing H or D into the film [6]. The other has been attributed to radiative recombination of quantum-confined excitons in the Si nanocrystals. We have also shown that the nanocrystal luminescence intensity can be increased by as much as a factor of 10 by annealing a deuterated sample at 400 'C, which is attributed to the passivation of dangling bonds at the nanocrystal/Si0 2 interface [6]. In this letter, we demonstrate that the photoluminescence (PL) peak wavelength from Si nanocrystals embedded in an SiO 2 film can be blue-shifted by more than 200 nm by thermal oxidation at 1000 *C. Transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) measurements show the oxidation of Si particles starts near the surface of the Si0 2 film and as time progresses, an oxidation front moves deeper into the film. The PL blueshift is attributed to a decrease in the average nanocrystal size as the oxidation progresses, in agreement with quantum confinement theory.
213
Mat. Res. Soc. Symp. Proc. Vol. 486 0 1998 Materials Research Society
EXPERIMENTAL Si0 2 films (100 nm thick) grown by wet thermal oxidation of lightly p-dop
Data Loading...
