Modeling ultrafast out-of-equilibrium carrier dynamics and relaxation processes upon irradiation of hexagonal silicon carbide with femtosecond laser pulses

Abstract

We present a theoretical investigation of the yet unexplored dynamics of the produced excited carriers upon irradiation of hexagonal Silicon Carbide (6H-SiC) with femtosecond laser pulses. To describe the ultrafast behaviour of laser induced out-of-equilibrium carriers, a real time simulation based on Density Functional Theory (DFT) methodology is used to compute both the hot carrier dynamics and transient change of the optical properties. A Two-Temperature model (TTM) is also employed to derive the relaxation processes for laser pulses of wavelength 401 nm, duration 50 fs at normal incidence irradiation which indicate that surface damage on the material occurs for fluence ~1.88 Jcm -2 . This approach of linking, for the first time, real time calculations, transient optical properties and TTM modelling, has strong implications for understanding both the ultrafast dynamics and relaxation processes and providing a precise investigation of the impact of hot carrier population in surface damage mechanisms in solids.

Fluence dependent dynamics of excitons in monolayer MoSi2Z4 (Z = pnictogen)

“…To study the non-equilibrium optical properties of monolayer MoSi 2 Z 4 series, we use the td-BSE framework as implemented in the YAMBO code [51,69,70]. In our real-time simulation, we apply a pump electric field with a frequency We present the renormalization of the BE of the A and B exciton peaks with increasing pump fluence in figure 5(c).…”

The Role of Crystalline Orientation in the Formation of Surface Patterns on Solids Irradiated with Femtosecond Laser Double Pulses

“…It is noted that T c attains very high values and this could potentially influence the energy band-gap response. Certainly, a more rigorous approach (e.g., based on first principles [96]) should also be considered to estimate a possible E g variation for large T c . Nevertheless, without loss of generality, it is assumed that substantial qualitative and quantitative changes (that yields different morphological changes) do not occur if E g is considered constant.…”

Predictive modeling approaches in laser-based material processing

“…More specifically, the laser energy absorption can be described by approximate solutions 12 or through a more accurate description of the propagation of the electromagnetic wave of the laser beam 47 . Electron excitation and dynamics can be modelled through the employment of models based on Boltzmann transport equations 27 or through the use of density functional theory 48,49 while relaxation processes and transfer of the energy of the electron subsystem to the material lattice are described through well-established two temperature models 50 . Finally, phase transformation which includes either a transition from solid to the liquid phase and versa or elastic/plastic deformation of a part of the material can be described either through Navier-Stokes 12 or elastodynamics equations 25,51 , re-spectively, or from more advanced methods based on Molecular dynamics 28 (for a detailed description of the various modules of the multiscale model see 12 ).…”