Crystallization of Ge in SiO2 matrix by femtosecond laser processing
(Color online) Experimental setup. (a) Optical microscope image of the laser treated Si0.2O0.5Ge0.3 surface. Each line contains identical laser marks on the surface. (b) Beam profile of the femtosecond laser beam near the focal point of the laser beam. (c) Simplified schematic of the laser treatment system. A linear stage was used to reach high speed enough (400 mm/s) to get well separated single laser marks on the surface.
(Color online) Surface profile analysis. Sloan Dektak 3030ST surface profilometer was used to measure surface profile. Swelling is observed for fluences higher than 40 mJ/cm2. (a) surface profile of the spot irradiated with 100 mJ/cm2, (b) surface profile of the spot irradiated with 115 mJ/cm2 (ablation onset). (c) Summary of all surface profile results for the all fluences. Black bars represent swelling and red bars represent ablation. Although similar results were obtained from all pulse durations used in this experiment, data from 120 fs pulses was used in this graph.
Raman spectra of the Si0.2O0.5Ge0.3 as a function of single shot laser fluence. Laser at 800 nm with 120 fs pulsewidth was used to irradiate the Germanium rich silicon dioxide film. Ge-Ge optic phonon line visible around 298 cm−1 and Si-Si optic phonon line visible around 520 cm−1. Laser fluence for best crystallization with the narrowest Raman line occurred at the laser fluence of 85 mJ/cm2.
(Color online) Ge-Ge optic phonon line Raman data. (a) Fluence vs Raman intensity, Ge optic phonon line starts to appear around 300 cm−1 at 45 mJ/cm2 and its intensity increases and linewidth decreases with increasing laser fluence. (b) Deconvolution of the experimental Raman spectrum. (c) Raman intensity vs laser fluence. Around the 55 mJ/cm2 higher pulse duration gives higher Raman intensity. (d) Linewidth of the Ge optic phonon at 300 cm−1 as a function of laser fluence provides a signature for the crystallization of Ge. Inset shows linewidth of the sample treated with 120 fs pulse duration.
(Color online) PL intensity vs wavelength for selected laser irradiated spots. PL intensity increases with increasing irradiating laser fluence up to the laser fluence of 470 mJ/cm2. inset shows maximum PL intensity vs fluence graph. Although similar results were obtained from all pulse durations used in this experiment, data from 120 fs pulses was used in this graph.
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