Abstract
The plasma produced in trisilane (Si3H8) at room temperature and pressures ranging from 50to103Pa by laser-induced breakdown (LIB) has been investigated. The ultraviolet-visible-near infrared emission generated by high-power IR CO2 laser pulses in Si3H8 has been studied by means of optical emission spectroscopy. Optical breakdown threshold intensities in trisilane at 10.591μm for laser pulse lengths of 100ns have been measured as a function of gas pressure. The strong emission observed in the plasma region is mainly due to electronic relaxation of excited atomic H and Si and ionic fragments Si+, Si2+, and Si3+. An excitation temperature Texc=5600±300K was calculated by means of H atomic lines assuming local thermodynamic equilibrium. The physical processes leading to LIB of trisilane in the power density range 0.28GWcm−2<J<3.99GWcm−2 have been analyzed. From our experimental observations we can propose that, although the first electrons must appear via multiphoton ionization, electron cascade is the main mechanism responsible for the breakdown in trisilane.
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