Influence of Point Defects on Laser-Induced Excitation in Silicon

TL;DR

This study investigates how point defects like oxygen interstitials and silicon vacancies affect laser excitation in silicon, revealing defect-induced changes in absorption and potential detection methods via high-harmonics generation.

Contribution

The paper demonstrates how defect states alter silicon's optical properties under laser excitation, highlighting the role of defect density and type in absorption efficiency and harmonic generation.

Findings

Defect density increases photoabsorption efficiency.

Defects relax selection rules, changing indirect to direct gap.

Saturable absorption reduces photoabsorption in silicon vacancies.

Abstract

We studied the influence of defect states on the laser excitation process in silicon using time-dependent density functional theory. We assumed two types of point defects: interstitial oxygen and silicon vacancies. We found that the photoabsorption efficiency increased with defect density in both cases owing to the color center. These defects distorted the crystal structure, thereby relaxing the selection rules and changing the indirect gap to direct. At low laser intensities, the defect states dominated the absorption process. However, as the laser intensity increased, the excitation efficiency approached that of crystalline silicon. In addition, we observed that the excitation efficiency did not scale linearly with the pulse length. Notably, in the case of Si vacancies, saturable absorption significantly reduced photoabsorption. Our results suggest that the existence of a defect and its density could be detected by even-order high-harmonics generation.