Electrical Properties of planar Metal-GdN-Metal junctions for Spintronic Applications

Abstract: In this thesis the properties of planar metal-gadolinium nitride-metal junctions have been studied with the aim of establishing ohmic and Schottky contacts to thin polycrystalline films of n-type gadolinium nitride (GdN). GdN is an intrinsic ferromagnetic semiconductor of the rare earth nitride series. Samples and planar junction devices were grown on sapphire substrates, and the metal contacts were pre-deposited and not annealed. GdN films have been grown at room temperature in a ultra high vacuum system using the physical vapour deposition technique, using solid Gd targets and pure molecular nitrogen as a nitrogen precursor. Nitrogen partial pressures were kept around 10^-5 mbar and deposition growth rates around 2 Å/s. The planar junction devices were tested at temperatures between 5 K and 300 K and the GdN films have resistivities between 3.7·10^4 Ohm'cm and 1 Ohm'cm. Devices were made with contacts out of Au, Ag, Gd, Ti, and Ti/Al bilayer. The manufactured devices display ohmic and rectifying current-voltage characteristics depending on the metal used in making the device. The temperature dependent resistance of the devices show characteristic GdN behaviour. As a metal-GdN-metal junction would be the building block of any REN-based spintronic device, the understanding of their electrical properties is of major importance. Therefore the electrical characterisation of this system is the main goal of this thesis.