SKM 2023 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 17: Optical Analysis of Thin Films III

DS 17.3: Hauptvortrag

Donnerstag, 30. März 2023, 17:15–17:45, SCH A 316

Spectroscopic ellipsometry studies of optical constants in highly excited semiconductors — •Stefan Zollner — New Mexico State University, Las Cruces, NM, USA

Spectroscopic ellipsometry is an optical reflection technique with polarized light. Most commonly, it is used to measure the thicknesses of thin-film layers, such as SiO₂ on Si. But it can also be used to study the energies and broadenings of elementary excitations in solids, such as electrons (band gaps, transport), infrared active phonons, and their interactions. We previously reported precision measurements of the complex refractive index of germanium near the direct band gap, which allowed us to compare our results quantitatively with theoretical predictions from Fermi’s Golden Rule, based on k.p theory and including the excitonic interaction between electrons and holes. Going further, we can investigate how many-body effects impact the properties of electrons in highly excited semiconductors. Large carrier concentrations can be achieved through doping, thermal excitation of electron-hole pairs in small band-gap semiconductors, or optical excitation with ultrafast lasers. In this talk, I will report recent ellipsometry results for the temperature-dependent dielectric function of InSb near the direct band gap and the transient dielectric function of Ge near the E₁ and E₁+Δ₁ transitions from femtosecond pump-probe ellipsometry. I will also point out the theoretical approach needed to explain these data sets.