Generalized thermo-elastodynamics for semiconductor material subject to ultrafast laser heating. Part I: Model description and validation

A generalized thermo-elastodynamic formulation applicable to the investigation of coupled thermomechanical responses of a silicon thin structure excited by ultrafast laser pulses is presented. Hyperbolic energy transport equations with two relaxation times is incorporated along with the relaxation-time approximation of the Boltzmann equation and a set of balance equations that consider temperature-dependent multi-phonons, free-carrier absorptions, and the recombination and impact ionization processes. A staggered-grid finite difference scheme allows the coupled equations system that govern the transport dynamics in silicon wafer to be solved without having to be concerned with non-physical numerical oscillations. The time evolution of carrier density and the non-thermal melting fluence level at which damages are inflicted in response to a given pulse duration are examined and compared favorably with experimental data. The feasibility of using the model formulation in describing near-field, short time scale thermal–mechanical responses induced by ultrafast laser pulses is thus validated.