Berlin 2008 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 1: Towards Molecular Spintronics

DS 1.5: Vortrag

Montag, 25. Februar 2008, 11:15–11:30, H 2013

Spin-polarised charge carrier transportin Ni/Alq₃/Co structures — Martin Roggenbuck, •Andreas Opitz, and Wolfgang Brütting — Institute of Physics, University of Augsburg, Germany

The spin state of electrons can be utilised to extend the probabilities of electronic circuits. Organic semiconductors are materiales with high spin diffusion lengths and long spin relaxation times and therefore interesting candidates for spintronics. Recently, spin polarised transport has been reported for diode structures comprising Alq₃ as organic semiconductor sandwiched between two ferromagnetic electrodes [1].

In this work cobalt and nickel are used as electrode materials, which have a high work function and should be hole injecting. At low temperatures a negative magneto-resistance effect of Δ R/R ≈ 4% is observed. However, the measured I-V curves show a higher current in comparison to standard light-emitting devices, like ITO/PEDOT:PSS/Alq₃/LiF/Al. An analysis by secondary ion mass spectrometry confirms that cobalt diffuses into the Alq₃ layer up to a thickness of 70 nm. Furthermore small clusters appear on the Alq₃ film after cobalt deposition, as proven by scanning force and scanning electron microscopy. Nevertheless, the current of the device is still much higher than expected with regard to the reduced film thickness and the lower hole mobility than the electron mobility in Alq₃ [2]. This is an indication for a different origin of the magneto-resistance effect other than transport through the organic semiconductor.

[1] Z. H. Xiong, et al., Nature 427 (2004) 821.

[2] W. Brütting, et al., Org. Electron. 2 (2001) 1.