THz-VUV Ellipsometry and THz Electron Paramagnetic Resonance Ellipsometry Characterization of SiC and Other Wideband Gap and Ultrawideband Gap Materials
- Informal Seminar
- Date: Sep 30, 2022
- Time: 01:30 PM (Local Time Germany)
- Speaker: Mathias Schubert
- University of Nebraska-Lincoln, Lincoln, USA
- Location: Building G
- Room: G 2.07
- Host: Alexander Paarmann
Here, we introduce frequency-domain Terahertz Electron Paramagnetic
Resonance (EPR) ellipsometry as a new tool to study defects in gallium
oxide and related materials at very high magnetic fields and very high
frequencies. Traditional EPR methods exist in multiple variants and
establish perhaps one of the most ubiquitous measurement techniques in
science . In our new concept, we determine the full polarization
response of intricate defect spins as a continuous function of both
field and frequency. For first investigations, we use our previously
developed optical Hall effect setup . We recently demonstrated this
new approach analyzing the polarized spin response for the nitrogen
defect in SiC . Here, we investigate Fe-doped gallium oxide single
crystals, and detect a large range of spin signatures which strongly
vary with crystal orientation, frequency, and field. Iron is commonly
used to obtain semi-insulating material where Fe2+ acts as compensating
acceptor. The neutral defect Fe3+ is a high-spin system with s=5/2 and
large zero-field splitting. Iron can incorporate at either Ga site but
appears preferentially in octahedral configuration. Different claims
exist about the nature of the spin Hamiltonian and approximate values
for simplified orthorhombic models have been reported. We obtain the
anisotropic g-factor as well as the zero-field Hamiltonian up to fourth
order which allows to discuss the relevance of the monoclinic character
of the local site symmetry. We compare our results with present
knowledge from theory computation approaches. We further discuss the
influence of phonons, strain, and local crystal symmetry, and we predict
THz EPR ellipsometry as a new tool with potential for characterization
of defects in heteroepitaxial systems.
 A. J. Greene et al., APL Materials 10, 029201 (2022).
 E. Zavoisky, Spin-magnetic resonance in paramagnetics, Fizicheskiĭ Zhurnal 9, 211 (1945).
 P. Kühne et al., IEEE Trans. Terahertz Sci. Technol. 8(3), 257 (2018).
 M. Schubert et al., Appl. Phys Lett. 120, 102101 (2022).