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Photoemission study of Eu 2+/3+ ions in ferromagnetic (Eu,Gd)Te semiconductor layers

Dziawa P., Orłowski B. A., Osinniy V., Pietrzyk M., Taliashvili B., Story T., Johnson R. L.

Materials Science Poland

2007

Vol. 25, No. 2

377--382

(Eu,Gd)Te ferromagnetic semiconductor layers grown by molecular beam epitaxy technique on BaF2 (111) monocrystalline substrates were investigated by resonant photoemission spectroscopy using synchrotron radiation. In n-(Eu,Gd)Te layers, a ferromagnetic transition induced by electron concentration is observed. Magnetic as well as electrical properties of this material depend strongly on the charge state (2+ vs. 3+) of Eu and Gd ions known to be sensitive to crystal stoichiometry and formation of oxide complexes. The relative concentration of Eu2+ and Eu3+ ions was determined from the analysis of the resonant photoemission energy distribution curves (EDC), measured at photon energies close to 4d-4f resonance. After various in-situ annealing and Ar sputtering procedures, a clear improvement of crystal stoichiometry of (Eu,Gd)Te layers was observed as manifested by the increase of Eu2+ intensity in the spectra. Contribution of Eu 4f shell to the total density of states was also analyzed and found at the valence band edge for Eu2+ ions and about 6 eV lower for Eu3+ ions.

Azotek galu : nowy rozdział w badaniach powierzchniowej struktury elektronowej półprzewodników

Kowalski B. J., Iwanowski R. J., Kopalko K., Orłowski B. A., Sadowski J., Kanski J., Pluciński Ł., Johnson R. L., Grzegory I., Porowski S.

Elektronika : konstrukcje, technologie, zastosowania

2001

Vol. 42, nr 8-9

23-25

The results of investigations of the (0001) (N-polar) surface of GaN bulk crystals are presented together with a brief review of the knowledge about GaN surface electronic structure accumulated up to the present. The band structure of GaN(0001) - (1 x 1) in the directions G-A and G-K has been analysed on the grounds of the data obtained by means of angle-resolved photoemission spectroscopy. The proposed interpretation of the results is shown to be consistent with the available results of calculations based on the model of the GaN(0001) - (1 x 1):Ga surface.