Influence of point defects on laser-induced excitation in silicon

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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mi>Si</a:mi></a:math> vacancies, saturable absorption reduced photoabsorption significantly. Our results suggest that the existence of a defect induces the even-order high-harmonics generation. The enhancement of even-order high-harmonics generation by the silicon vacancy is larger than the interstitial oxygen. Published by the American Physical Society 2024