Dresden 2026 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 21: Optical Analysis of Thin Films

DS 21.7: Vortrag

Freitag, 13. März 2026, 11:30–11:45, REC/C213

Refining the Tanguy dispersion model for strong direct interband interactions — •Beáta Hroncová and Stefan Zollner — New Mexico State University, Las Cruces, NM, USA

In semiconductors, absorption near the band gap energy is dominated by electron valence-to-conduction band transitions. Exciton formation effectively reduces the band gap and enhances the absorption coefficient. A sharp excitonic peak corresponding to this bound state is observed in the spectral function, especially at low temperatures and low carrier concentrations [1]. At higher temperatures, the bound state is broadened and the peak disappears, but the Sommerfeld enhancement of the absorption persists.

A dispersion model of Wannier–Mott excitons with a screened Coulomb potential was derived by Tanguy [2]. However, if the band gap is small, the interactions between the conduction and valence bands are more prominent. This leads to deviations from the parabolic band curvature, and the effective mass approximation used for the calculation of the excitonic spectra is no longer accurate.

We study the dielectric response of InAs and InSb near the band edge measured by spectroscopic ellipsometry in a wide range of temperatures 50-800 K. With the use of k· p theory, we find the non-parabolicity of the electronic band structure, and describe how to include it in the Tanguy model. Herewith we achieve a better agreement between the theory and the experimental data.

[1] Schweizer et. al., Phys. Rev. Lett. 51, (1983)

[2] Tanguy, Phys. Rev. B 60, (1999)

Keywords: excitons; Tanguy model; InAs; InSb; ellipsometry