A thermoelectric material can be used to convert heat to electricity, and vice versa, all without moving parts. Thermoelectric devices can be used for a multitude of applications, such as thermoelectric generators (TEGs) and Peltier heaters/coolers. TEGs can be used to generate electricity from e.g. waste heat, and small and efficient Peltier coolers could have a use in microelectronics. The lack of moving parts means that thermoelectric devices generally are robust.

Transition metal nitrides are versatile, durable, and have found use in many different applications. CrN, for instance, is known for its hardness, corrosion resistance, near room-temperature magnetic phase transition as well as its thermoelectric properties. Especially crystalline CrN has interesting thermoelectric properties, including a high power-factor and low thermal conductivity. These properties are essential for the constituent materials of thermoelectric devices. For durability, the stability and mechanical properties of CrN would be a bonus. The thermoelectric properties of CrN have a strong correlation to the stoichiometry, which then becomes crucial to control.

The focus of this thesis is on the thermoelectric properties of CrN, with and without alloying transition metals V and Mo. Doping and alloying can help change properties, both electrical and thermal. I have grown thin films of CrN with and without alloying elements, using reactive magnetron sputtering. Film growth using this technique happens far from thermodynamic equilibrium and thus, not all aspects are easy to control, stoichiometry being one. The films were grown on c-plane sapphire (Al₂O₃ (0001)) substrates.

I investigated thin, epitaxial films of CrMoVN, i.e. CrN thin films co-doped with Mo and V. They were grown on c-plane sapphire substrates, which allows the rock-salt cubic structured CrN to be grown epitaxially, albeit with a non-negligible strain. I investigated the effect of co-doping on phase composition and thermoelectric properties. While the effects of singly doped films (CrVN and CrMoN) were similar to other reports, co-doping with V and Mo resulted in the retention of the rock-salt cubic phase at much higher Mo-content than what has previously been reported. Furthermore, I tackled the issue with stoichiometry, motivated by discrepancies in literature correlating thermoelectric properties and stoichiometry of CrN. After growing sets of thin films of CrN, some epitaxial and some mix-phased, the samples were annealed in ammonia environment to approach the thermodynamic equilibrium of Cr:N = 1:1. The films that were closest to stoichiometry before annealing turned insulator – in line with theory and some articles. The films with larger under-stoichiometry got significantly improved thermoelectric properties, one by as much as 900%.