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77LP-PS-1
Determination of surface modification and nonlinear absorption thresholds of silicon using mid-infrared ultrashort laser pulses
J. Sladek1,2,I. Mirza1, A.V. Bulgakov1-3, Y. Levy1, W. Marine1, B. Csanakova1,4, L. Roskot1,4, O. Novak1, N.M. Bulgakova1, M. Smrz1
1HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, Dolni Brezany, Czech Republic
2Faculty of Nuclear Sciences and Physical Engineering- Czech Technical University in Prague, Department of Solid State Engineering, Prague, Czech Republic 3S.S. Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russian Federation 4Faculty of Nuclear Sciences and Physical Engineering- Czech Technical University in Prague, Department of Physical Electronics, Prague, Czech Republic
During last decades, there has been a growing interest in surface and volumetric modification of semiconductor materials using ultrashort laser pulses for application in microelectronics, optoelectronics and photovoltaics [1, 2]. The action of conventional near-IR ultrashort laser pulses on silicon and germanium is limited to surface modification, since these semiconductors are opaque in this spectral region. Experiments have been performed to demonstrate that, by tightly focusing mid-IR ultrashort laser pulses [3, 4] inside Si, local nonlinear optical absorption can be initiated [5, 6]. The laser-generated free carrier density leads to optical breakdown and can potentially induce volumetric structural modification. However, laser beam focusing inside the material bulk is accompanied by processes connected to nonlinear beam propagation, such as the Kerr effect and light scattering by free electron plasma, which overlap with nonlinear absorption. For obtaining knowledge on absorption nonlinearity of semiconductor materials at a certain wavelength, it is essential to study absorption behavior by placing a precise focal spot on the material surface, to determine the intensities corresponding to surface modification threshold and to derive the absorption order. In this work, we have performed a systematic study of surface modification and nonlinear absorption of Si using 1.6 and 3.2 p,m, few ps long laser pulses. The transmission signal was measured as a function of pulse intensity using a light collection setup. The correlation results between surface modification and multiphoton excitation in semiconductor materials will be presented and discussed.
References
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