Regensburg 2013 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 67: Focus Session (Posters): Crystalline n-type semiconducting oxides - SnO2, Ga2O3, and In2O3 for novel devices
HL 67.5: Poster
Wednesday, March 13, 2013, 16:00–20:00, Poster A
ZnFe2O4 dielectric function — •Tammo Böntgen, Kerstin Brachwitz, Rüdiger Schmidt-Grund, Michael Lorenz, and Marius Grundmann — Universtät Leipzig, Institut für Experimentelle Physik II, Linnéstr. 5, Germany
We present a detailed investigation of the dielectric function (DF) of spinel ZnFe2O4 (ZFO) thin films on a-plane sapphire. The films were grown by pulsed laser deposition at various temperatures and oxygen partial pressures. The optical measurements were carried out using spectroscopic ellipsometry in the spectral range from 0.5 eV to 9.5 eV. For the ZFO DF model dielectric functions (Gauss and critical-point-functions) were used to allow the derivation of transition energies and unravel the effect of the different growth conditions (i.e. temperature, substrate, oxygen pressure). The observed transitions are related to transitions allowed by ligand field theory. The dominant transitions were observed at ≈3.5 eV and ≈6 eV and identified as Fe3d and Fe4s transitions. ZFO has a special position within the spinel ferrites because Zn and its ions have a filled 3d shell. Thus no on site d-d transitions and no transitions from the O2p to the Zn3d band are possible. This results in a high transparency (compared to other ferrites) and reduces the number of observed transitions. While the oxygen partial pressure has a neglectable effect on the optical properties, the growth temperature induces a distinct shift in the transition energies was found. Also a notable shift of the absorption edge is observed. This change can be correlated to a change in the lattice constant as observed using wide-angle X-ray diffraction.