Transient dielectric functions of Ge, Si, and InP from femtosecond pump-probe ellipsometry

• Published in: Applied physics letters Vol. 115; no. 5
• Main Authors: Espinoza, Shirly, Richter, Steffen, Rebarz, Mateusz, Herrfurth, Oliver, Schmidt-Grund, Rüdiger, Andreasson, Jakob, Zollner, Stefan
• Format: Journal Article
• Language: English
• Published: 29.07.2019
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.5109927

Transient dielectric functions with a 120 fs time resolution of Ge, Si, and InP were acquired from 1.7 to 3.5 eV with a femtosecond pump-probe rotating-compensator ellipsometer. The intensity of the pump laser (with 1.55, 3.10, or 4.65 eV photon energy) was adjusted to create an initial near-surface carrier density of 1020 cm−3. In Ge, there is a significant (∼15%) decrease in the E1 and E1 + Δ1 critical point absorption and a Kramers–Kronig consistent change in the refractive index because photoexcited electrons at L block these transitions and reduce their amplitudes. Only a small redshift of the E1 critical point is observed, which we attribute to lattice heating and exchange-correlation effects. Minimal changes were found for Si and InP, where electrons near Δ and Γ do not participate in interband transitions between 1.7 and 3.5 eV.