Electronic mechanism of ion expulsion under UV nanosecond laser excitation of silicon: Experiment and modeling

TL;DR

This study combines experiments and modeling to understand ion expulsion mechanisms during UV nanosecond laser ablation of silicon, revealing non-thermal desorption and Coulomb explosion effects at low fluences.

Contribution

It introduces a new approach to analyze plume dynamics and models the electronic excitation and charge transport in silicon during laser irradiation.

Findings

Non-thermal ion desorption occurs below melting threshold.

High concentration of non-thermal ions during ablation.

Coulomb explosion mechanism explains ion origin.

Abstract

We present experimental and modeling studies of UV nanosecond pulsed laser desorption and ablation of (111) bulk silicon. The results involve a new approach to the analysis of plume formation dynamics under high-energy photon irradiation of the semiconductor surface. Non-thermal, photo-induced desorption has been observed at low laser fluence, well below the melting threshold. Under ablation conditions, the non-thermal ions have also a high concentration. The origin of these ions is discussed on the basis of electronic excitation of Si surface states associated with the Coulomb explosion mechanism. We present a model describing dynamics of silicon target excitation, heating and harge-carrier transport.