A sounder understanding of the structural and electronic properties of ZnO-based diluted magnetic semiconductors (DMS) is required in order to achieve a global picture including all the physical processes involved in the origin of ferromagnetism in these materials¹.

The goal of this work is to gain insight into the electronic and structural properties of (Zn,Mn)O obtained by thermal diffusion of a thin (≅1nm) Mn film grown on ZnO polar faces. The sample is characterazed in-situ by high-energy X-ray photoelectron spectroscopy (hν=3500eV, HEXPS) at BW2, Hasylab.

We followed the evolution of the Mn 2p and the valence band photoelectron spectra of the Mn/ZnO(000-1) system respectively at the different stages of the experiment. During Mn deposition, most of the Mn atoms constituting the 0.25 nm thick film are oxidised by the surface oxygen atoms. The complete overlayer becomes metallic in the multilayer regime and, as a result, Mn related states are observed up to the Fermi level. Upon annealing Mn/ZnO to 660 K, Mn is fully oxidised to the 2+ state due to the formation of a thin MnO layer whose valence band edge appears at a binding energy around 2 eV below the Fermi level. Further annealing to 850K restore the valence electronic structure of ZnO. The simultaneous change in the shape of the Mn 2p spectrum is attributed to a better dilution of Mn into the ZnO lattice and to the formation of (Zn,Mn)O. These interpretations are supported by the evolution of the intensity of the Mn 2p, Zn 3s, and O 1s lines revealing that upon annealing to 850 K the substitution of Zn by Mn and diffusion of Mn into ZnO take place.

Reference:

[1] J.M.D. Coey and S.A. Chambers, MRS bulletin 33, 1053 (2008).

We acknowlodge

- C. Moisson (NOVASiC, Savoie Technolac, B.P. 267, Cedex 73375, Le Bourget-du-Lac, France), for the MCP polishing of the ZnO single crystals

- the support of CTB-BTC, CERUNA-University of Namur, the European Commission (contract RII3-CT 2004-506008 (IA-SFS)), and FSR-F.N.R.S.

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