Berlin 2012 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 10: High- and low-k-dielectrics (jointly with DS)

DF 10.5: Talk

Wednesday, March 28, 2012, 10:50–11:10, EB 407

P-type conductivity in oxygen deficient HfO_2−x thin films grown by Reactive Molecular Beam Epitaxy — •Erwin Hildebrandt¹, Jose Kurian¹, Mathis Müller¹, Thomas Schroeder², Hans-Joachim Kleebe¹, and Lambert Alff¹ — ¹Institute of Materials Science, Technische Universität Darmstadt, Germany — ²IHP, Frankfurt(Oder), Germany

Highly oxygen deficient thin films of hafnium oxide HfO_2−x were grown using reactive molecular beam epitaxy on c-cut sapphire substrates. The oxygen content and, thus, oxygen vacancy concentration was engineered by controlled oxidation using RF-activated oxygen during growth. Hafnium oxide, a high-k dielectric insulator in its stoichiometric form, turns into a p-type semiconductor above a threshold of oxygen vacancies with up to 6 times 10²¹ charge carriers per cm³. The introduction of oxygen vacancies reduces the optical band gap from 5.7 eV for stoichiometric HfO₂ by more than 1 eV. The absence of crystalline and/or amorphous metallic hafnium phases was proven by X-ray diffraction and a tilting series using High-Resolution Transmission Electron Microscopy. We suggest the formation of an oxygen vacancy induced p-type defect band within the energy gap as the origin of the observed p-type conductivity [1].

[1] E. Hildebrandt, J. Kurian, M. M. Müller, T. Schroeder, H.-J. Kleebe, and L. Alff, Appl. Phys. Lett. 99, 112902 (2011).