Complementary ion beam analysis and photo electron spectroscopy study of oxygen contamination in epitaxial GdN films on YSZ substrates

Gadolinium nitride (GdN) is a ferromagnetic material with a Curie temperature at 75 K and with promising electronic properties. In the present study, the low-energy ion-beam assisted epitaxial growth of thin GdN films on yttria-stabilized zirconia (YSZ) substrates is investigated. For this purpose, Gd was deposited on the substrate and simultaneously irradiated with a hyperthermal nitrogen ion beam at a constant substrate temperature of 750 C. To prevent rapid oxidation of GdN in air, a GaN protective layer was deposited. According to x-ray diffraction (XRD), the formation of epitaxial GdN on YSZ(100) was achieved, but time-of-flight secondary ion mass spectrometry (TOF-SIMS) showed that first a gadolinium oxide layer was formed and during further deposition the GdN phase was dominating over the still coexisting oxide. This was confirmed by quantitative elastic recoil detection analysis (ERDA) exhibiting a high degree of oxygen contamination over the whole film thickness. The chemical nature of the contamination was assessed by photo electron spectroscopy (XPS). It could be excluded that the oxygen contamination originated from residual gases in the ultra-high vacuum recipient. Instead, the oxygen was found to diffuse from the YSZ substrate into the GdN film.