Brongersma, M. L. and Polman, A. and Min, K. S. and Atwater, H. A. (1999) Depth distribution of luminescent Si nanocrystals in Si implanted SiO2 films on Si. Journal of Applied Physics, 86 (2). pp. 759-763. ISSN 0021-8979. http://resolver.caltech.edu/CaltechAUTHORS:BROjap99
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Depth-resolved measurements of the photoluminescence of Si implanted and annealed SiO2 films on Si have been performed to determine the depth distribution of luminescent Si nanocrystals. Si nanocrystals with diameters ranging from ~ 2 to 5 nm were formed by implantation of 35 keV Si ions into a 110-nm-thick thermally grown SiO2 film on Si(100) at a fluence of 6 × 1016 Si/cm2, followed by a thermal anneal at 1100 °C for 10 min. The photoluminescence spectrum is broad, peaks at lambda =790 nm, and contains contributions from both recombination of quantum confined excitons in the nanocrystals and ion-implantation-induced defects. By chemical etching through the SiO2 film in steps and analyzing the changes in the photoluminescence spectrum after each etch step, the depth from which each of the two luminescence features originate is determined. The etch rate of the oxide, as derived from Rutherford backscattering spectrometry data, varies from 1.3 nm/s in the regions of small excess Si to 0.6 nm/s at the peak of the concentration profile (15 at. % excess Si). It is found that the defect luminescence originates from an ~ 15-nm-thick near-surface region. Large nanocrystals luminescing at long wavelengths (lambda =900 nm) are mainly located in the center of the film, where the Si concentration is highest (48 at. %). This is corroborated by transmission electron microscopy that shows a high density of Si nanocrystals in the size range of 2–5 nm in the center of the film. The largest density of small luminescent nanocrystals (lambda =700 nm), not detectable by electron microscopy is found near the SiO2 surface and the SiO2/Si interface. This is attributed to either the fact that the surface and the SiO2/Si interface affect the Si nanocrystal nucleation kinetics in such a way that small nanocrystals are preferentially formed in these regions, or an optical interaction between nanocrystals of different sizes that quenches the luminescence of small nanocrystals in the center of the film.
|Additional Information:||©1999 American Institute of Physics. (Received 11 December 1998; accepted 6 April 1999) This work is part of the research program of the "Stichting voor Fundamenteel Onderzoek der Materie (FOM)," which is financially supported by the "Nederlandse Organisatie voor Wetenschappelijke Onderzoek (NWO)," and the ESPRIT program of the European Community. Jan van der Elsken is acknowledged for discussions and Michiel de Dood is acknowledged for the calculation of optical mode densities.|
|Subject Keywords:||photoluminescence; excitons; transmission electron microscopy; Rutherford backscattering; silicon compounds; silicon; nanostructured materials; elemental semiconductors; semiconductor-insulator boundaries; ion implantation; annealing; doping profiles; etching; insulating thin films|
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|Deposited On:||05 Mar 2006|
|Last Modified:||26 Dec 2012 08:47|
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