Aluminum nitride as a capping layer for rare-earth nitride thin films

Stefan Cwik, Ruhr University Bochum, Bochum, Germany
Michael Krasnopolski, Ruhr University Bochum, Bochum, Germany
Detlef Rogalla, Ruhr University Bochum, Bochum, Germany
Hans – Werner Becker, Ruhr University Bochum, Bochum, Germany
Anjana Devi, Ruhr University Bochum, Bochum, Germany

Rare earth nitride (REN) materials such as gadolinium nitride (GdN) are promising materials for application in devices for spintronics due to their unique magnetic properties. However, the oxophilic nature of REN makes them difficult to handle. Hence, they have not been thoroughly studied experimentally, especially by means of metal organic chemical vapor deposition (MOCVD). As a consequence, very few reports exist in research literature on the fabrication of REN layers. In order to avoid the oxidation of a REN thin film, a protective capping layer can be deposited on top of the material. This capping layer should be dense and preferentially amorphous to avoid diffusion of oxygen through the grain boundaries of the REN layers.

From our earlier work, the implementation of MOCVD grown copper thin films as a potential oxygen barrier led to encouraging results [1]. The copper capping led to a considerably slower oxidation of the MOCVD grown GdN as oxygen could still diffuse through the grain boundaries. This was because the copper films deposited on the GdN was not dense, but rather consisted of polycrystalline copper grains. As an alternative capping layer, we have investigated aluminum nitride (AlN) which was deposited with via MOCVD.

Due to the small lattice mismatch between AlN and REN, stress and strain at the interface can be avoided. The deposition of AlN films was optimized individually for the fabrication of dense, amorphous AlN thin film with minimum oxygen contamination and controllable thickness. In a subsequent step, this new capping layer concept via MOCVD was evaluated for the GdN thin films. The influence of the capping layer on the composition and morphology of REN materials was investigated in detail. The functional properties of the fabricated stack were evaluated with superconducting quantum interference devices (SQUID) measurements.

[1] Tobias B. Thiede, Michael Krasnopolski, Andrian P. Milanov, Teresa de los Arcos, Andreas Ney, Hans-Werner Becker, Detlef Rogalla, Jörg Winter, Anjana Devi, and Roland A. Fischer, Chem. Mater. 2011, 23, 1430–1440

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