Tuned ionic mobility by Ultrafast-laser pulses in Black Silicon

TL;DR

This study uses ab-initio molecular dynamics simulations to investigate how femtosecond laser pulses affect ionic mobility in black silicon, revealing impurity concentration's role in altering atomic movement under ultrafast excitation.

Contribution

The paper provides new insights into the impact of femtosecond laser excitation on ionic impurities and atomic mobility in black silicon, a topic not previously explored in detail.

Findings

Increased impurity density weakens the crystal environment.

Ion mobility changes with impurity concentration and excitation strength.

Impurity effects are significant for semiconductor device optimization.

Abstract

Highly non-equilibrium conditions in femtosecond-laser excited solids cause a variety of ultrafast phenomena that are not accessible by thermal conditions, like sub-picosecond solid-to-liquid or solid-to-solid phase transitions. In recent years the microscopic pathways of various laser-induced crystal rearrangements could be identified and led to novel applications and/or improvements in optoelectronics, photonics, and nanotechnology. However, it remains unclear what effect a femtosecond-laser excitation has on ionic impurities within an altered crystal environment, in particular on the atomic mobility. Here, we performed ab-initio molecular dynamics (AIMD) simulations on laser-excited black silicon, a promising material for high-efficient solar cells, using the Code for Highly excIted Valence Electron Systems (CHIVES). By computing time-dependent Bragg peak intensities for doping densities of 0.16% and 2.31% we could identify the overall weakening of the crystal environment with increasing impurity density. The analysis of Si-S bond angles and lengths after different excitation densities, as well as computing interatomic forces allowed to identify a change in ion mobility with increasing impurity density and excitation strength. Our results indicate the importance of impurity concentrations for ionic mobility in laser-excited black silicon and could give significant insight for semiconductor device optimization and materials science advancement.