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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 67.3: Poster

Mittwoch, 13. März 2013, 16:00–20:00, Poster A

Structural properties and defect-induced conduction mechanism in spinel-type ferrites — •Kerstin Brachwitz, Michael Lorenz, and Marius Grundmann — Linnéstraße 5, 04103 Leipzig, Germany

Zinc ferrite (ZFO), cobalt ferrite (CoFO), and nickel ferrite (NiFO) are promising candidates for application in magnetic tunnel junctions (MTJs) for both, as conducting electrode and as insulating barrier. In this respect we have investigated such spinel-type ferrite thin films grown by pulsed-laser deposition (PLD). We have varied the growth temperature (T_S) by controlling the heater power in a range from 400^∘ to 690^∘C. The thin films were grown on (100)-oriented strontium titanate (STO) substrates at p(O₂)=5×10⁻⁵ mbar. The out-of-plane orientation of the thin films was found to be (100) and the in-plane epitaxial relation to the substrate was confirmed by φ-scans. 2Θ-ω XRD scans reveal an increasing out-of-plane lattice constant with decreasing substrate temperature for all investigated ferrites. The film thickness of about 200-400 nm and the large lattice mismatch between ferrite film and STO substrate (6-8%) lead to relaxed film growth. The electrical conductivity of the thin films can be tuned btw. 10⁻⁴ and 10² S/m by different substrate temperatures during growth. It increases with decreasing substrate temperature. The conduction mechanism is not only affected by electron hopping between Fe²⁺ and Fe³⁺, but also defects like oxygen vacancies and structural disorder have great influence. The conductivity is thermally activated and a model with two activation energies fits the temperature dependent conductivity.