Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 23: Oxide Semiconductors I

HL 23.11: Vortrag

Dienstag, 8. März 2016, 12:30–12:45, H13

Electronic band structure and infrared lattice dynamics of single-crystal nickel oxide (NiO) — •Stefan Zollner, Cayla M. Nelson, Travis I. Willett-Gies, Ayana Ghosh, and Lina S. Abdallah — New Mexico State University, Las Cruces, NM, USA

Using spectroscopic ellipsometry, we determined the dielectric function of bulk NiO from 25 meV to 6 eV to study its lattice dynamics and electronic structure. In the visible and UV, NiO looks remarkably similar to Si: Both materials are transparent in the near-infrared. A slow rise of the absorption throughout the visible is followed by a sharp peak at 3.4 eV (Si) and 3.8 eV (NiO). In Si, this peak is caused by transitions from the highest valence band to the lowest conduction band along the (111) direction of the BZ. In NiO, it is associated with the charge-transfer (Hubbard) gap. In both materials, the peaks broaden and redshift with increasing temperature, due to electron phonon interactions. Many recent band structure calculations for NiO focus on the charge-transfer absorption peak (3.8 eV) and ignore the absorption below the main peak. Our data show a direct band gap of NiO at 0.85 eV, which we attribute to interband transitions from the Ni+O valence band to the Ni(4s) conduction band at the zone center. We also find strong TO phonon absorption in infrared ellipsometry spectra, which is modified by two-phonon absorption.