The seeds and homogeneous nucleation of photoinduced nonthermal melting in semiconductors due to self-amplified local dynamic instability

TL;DR

This paper reveals that photoinduced nonthermal melting in semiconductors like silicon occurs through a homogeneous nucleation process driven by self-amplified local dynamic instability, challenging previous models.

Contribution

It uncovers the mechanism of ultrafast nonthermal melting via real-time density functional theory, emphasizing the role of local dynamic instability and random seed formation.

Findings

Melting occurs via homogeneous nucleation from random seeds.

Self-amplified local dynamic instability drives the process.

Charge transfer amplifies atomic displacements, initiating melting.

Abstract

Laser-induced nonthermal melting in semiconductors has been studied over the last four decades, but the underlying mechanism is still under debate. Here, by utilizing an advanced real-time time-dependent density functional theory simulation, we reveal that the photoexcitation-induced ultrafast nonthermal melting in silicon occurs via homogeneous nucleation with random seeds originating from a self-amplified local dynamic instability at the photoexcited states rather than by simultaneously breaking of all bonds, as suggested by the inertial model, phonon instability, or Coulombic repulsion mechanisms. Due to this local dynamic instability, any initial small random thermal displacements of atoms can be amplified by a charge transfer of photoexcited carriers, which in turn creates a local self-trapping center for the excited carriers and yields the random nucleation seeds. This finding provides fresh insights into photoinduced ultrafast nonthermal melting.