Silicon Nanocrystal Nucleation as a Function of the Annealing Temperature in SiO x Films
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Silicon Nanocrystal Nucleation as a Function of the Annealing Temperature in SiOx Films N. Daldosso, 1 G. Das1, G. Dalba, 1 S. Larcheri, 1 R. Grisenti, 1 G. Mariotto,1 L. Pavesi,1 F. Rocca, 2 F. Priolo,3 G. Franzò,3 A. Irrera,3 M. Miritello,3 D. Pacifici3 and F. Iacona 4 1
INFM-Dipartimento di Fisica, Università di Trento, via Sommarive 14, I-38050 Povo (Trento) CNR-IFN, Sezione "CeFSA" di Trento, I-38050 Povo (Trento), Italy 3 INFM-Dipartimento di Fisica, Università di Catania, Via S. Sofia 64, I-95123 Catania, Italy 4 CNR-IMM, Sezione di Catania, Stradale Primosole 50, I-95121 Catania, Italy 2
ABSTRACT Si nanocrystals (Si-nc) embedded in amorphous silica matrix have been obtained by thermal annealing of substoichiometric SiOx films, deposited by PECVD (plasma enhanced chemical vapour deposition) technique with different amount of Si concentrations (42 and 46 at.%). Both nucleation and evolution of Si-nc together with the changes of the amorphous matrix have been studied as a function of the annealing temperature. The comparison of x-ray absorption measurements in Total Electron Yield (TEY) mode at the Si k-edge with photoluminescence (PL), FTIR and Raman spectra, allowed clarifying the processes of Si-nc formation and structural evolution as a function of the annealing temperature and Si content. INTRODUCTION The research of Si-based light emitting systems has increased due to the high luminescence efficiency, stability and robustness of silicon nanocrystals (Si-nc) embedded in amorphous silica (a-SiO2 ) [1,2,3,4,5], and more recently to experimental evidences of optical gain [6,7]. However, because of the various techniques and experimental conditions used to prepare Si-nc, the interpretation of the light emission mechanism given by different authors is often controversial. It is fundamental a comprehensive characterization of the Si-nc and the embedding matrix about the amount of Si atoms segregated in the Si-nc, the evaluation of size and distribution of the clusters, and the chemical composition and structure of the host matrix. In this work, we report on x-ray absorption measurements performed on a set of plasma enhanced chemical vapour deposition (PECVD) grown Si-nc samples and on FTIR, Raman, and photoluminescence (PL) measurements, whose comparison yields to a better comprehension of the embedding amorphous matrix and the evolution of Si-nc with the annealing temperature. EXPERIMENTAL Silicon nanocrystals dispersed in an amorphous matrix have been produced by hightemperature annealing of substoichiometric silicon oxide (SiOx ) films prepared by PECVD. The SiO x films thickness ranges from 200 to 1000 nm. The substrates were 5 in. (100) Czochralski
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silicon (1.5-4 Ω cm) or quartz wafers. Due to the use of N 2 O as one of the gaseous precursors, the amo
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