Regensburg 2025 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 52: Oxide Semiconductors II

HL 52.2: Vortrag

Donnerstag, 20. März 2025, 15:15–15:30, H14

Blue shift of the absorption onset and bandgap bowing in rutile Ge_xSn_1−xO₂ — •Elias Kluth¹, Yo Nagashima², Shohei Osawa³, Yasushi Hirose³, Jürgen Bläsing¹, André Strittmatter¹, Rüdiger Goldhahn¹, and Martin Feneberg¹ — ¹Institut für Physik, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany — ²Department of Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan — ³Department of Chemistry, Tokyo Metropolitan University, 1-1 Minamiosawa Hachioji, Tokyo 192-0397, Japan

Rutile-GeO₂ has recently attracted increasing research interest as an ultra wide bandgap oxide similar to Ga₂O₃ with the unique advantage that theoretical calculations predict the possibility of ambipolar doping. In contrast rutile-SnO₂ is a well-established transparent conductive oxide (TCO) widely used in solar cells and displays. Alloying SnO₂ with Ge offers a promising pathway to developing deep ultraviolet (DUV) TCOs. However, investigations into the optical properties of the Ge_xSn_1−xO₂ system remain limited.

In this study, we employed spectroscopic ellipsometry in the visible and ultraviolet region to determine the ordinary dielectric functions of Ge_xSn_1−xO₂ thin films grown by pulsed laser deposition (PLD) on rutile-TiO₂ substrates. Our analysis reveals a systematic blue shift of the onset of absorption with increasing Ge content. By evaluating the dielectric functions, we extracted the characteristic transition energies at the absorption onset and determined the bowing parameter of the dipole-allowed direct bandgap to be b=0.70 eV.

Keywords: ellipsometry; oxide semiconductors; optical properties; dielectric function; SnO2