Growth and Structural Properties of Rare Earth Nitride Thin Films
In this thesis aspects of the growth of rare earth nitride thin films and characterisation of the resulting structural, electronic and magnetic properties of the film are investigated. The rare earth nitrides are a class of materials which combine interesting electronic and magnetic properties with potential applications in novel spintronic device structures. We study the formation of a preferential orientation in polycrystalline thin films of GdN deposited by electron-beam physical vapour deposition. X-ray diffraction is used to characterise the crystalline structure of films of varying thickness to identify a preference to grow along the [111] crystal direction, understood in terms of an evolutionary selection process. Variations in the film microstructure as a result of growth parameter variation are also correlated to electronic and magnetic properties. Investigation of the epitaxial growth of SmN on AlN surfaces revealed a novel growth orientation transition, controllable only via the growth temperature. Epitaxial integration of rare earth nitrides with III-nitride surfaces has previously only resulted in (111)-oriented growth on the (0001) surface as is expected from matching of the close-packed planes in the different crystal structures. High growth temperatures (≥800 ℃) induce (001)-oriented growth of SmN on the same (0001) AlN surface. This unexpected cube-on-hexagon geometry is confirmed through ex situ x-ray and in situ electron diffraction, the latter for which a computational simulation tool was developed to model and understand. The viability of using Sm as a temporary capping layer for rare earth nitride thin film samples is investigated. Capping layers are required to passivate samples due to their high reactivity, limiting the range of ex situ characterisation techniques that can be performed on them. Elemental Sm is relatively volatile raising the possibility of removing a Sm cap in situ using moderate annealing temperatures (400 °C to 600 ℃). The ability to remove the capping layer would allow in situ characterisation techniques to be performed in ultra high vacuum systems not directly connected to the growth system. In situ electron diffraction is used to characterise the growth and thermal annealing of Sm grown on top of epitaxial GdN layers, and the effects of the thermal removal process on the structural, electronic and magnetic properties of the GdN layer are investigated.