Laser-induced thermal effects on optical and light-emitting properties of free-standing silica films containing Si nanocrystals

Leonid Khriachtchev; Markku Rasanen; Sergei Novikov

doi:10.1117/12.608280

Abstract

A Raman and photoluminescence study of a thermally annealed free-standing film of silica containing Si nanocrystals is reported with emphasis on laser-induced thermal effects. The Si-rich silica film on a Si substrate was prepared by a molecular beam deposition method and annealed at 1150 °C for 1 hour in an oven, which promoted Si nanocrystals. Then the Si substrate was partially chemically etched producing free-standing film areas with typical dimensions of 2 mm x 2 mm and thickness of 1.4 μm. For the free-standing film, we observed laser-induced (Ar⁺ laser at 488 nm) thermal effects on the light-emitting and optical properties. In fact, the light emission dramatically increases with the laser intensity, up to 4 orders of magnitude at 840 nm when the laser power increases from ~100 to 200 mW, and the absorption coefficient rises considerably as well. The anti-Stokes to Stokes Raman intensity ratio suggests a very high temperature of the free-standing silica film containing Si nanocrystals (~1200 K) upon exposure to a laser power of 100 mW focused to a ~40 μm spot, and the temperature probably rises up to ~2000 K for exposure to a laser power of 200 mW. The light emission measured at the high excitation powers is similar to blackbody radiation although some quantitative deviations occur for the temperature dependence. The Ar⁺ laser annealing strongly increases the crystalline Raman peak showing that thermal annealing at 1150 °C does not finish structural reorganization of the SiO_x material. In the waveguiding detection geometry, the spectral narrowing of the photoluminescence is observed and used to estimate the refractive index.

Citation Download Citation

Leonid Khriachtchev, Leonid Khriachtchev, Markku Rasanen, Markku Rasanen, Sergei Novikov, Sergei Novikov, } "Laser-induced thermal effects on optical and light-emitting properties of free-standing silica films containing Si nanocrystals", Proc. SPIE 5840, Photonic Materials, Devices, and Applications, (7 July 2005); doi: 10.1117/12.608280; https://doi.org/10.1117/12.608280

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