Mo-based contacts on silicon carbide

4H-SiC-based devices have reached a high level of technological maturity and are now widely used in many applications, including electric mobility, renewable energy systems, industrial processes and consumer electronics. Despite their excellent performance, further efforts are still required to improve device characteristics. In this context, device processing represents a key opportunity to gain superior control over the electrical properties of the final devices, with the aim of tailoring their behavior to specific application requirements. In Schottky diode technology, the Schottky barrier height (ϕB) is strongly related to the metal used for contact fabrication. Recently, molybdenum (Mo) has attracted significant interest owing to its good thermal stability and its ability to form contacts with relatively low ϕB, a feature that is beneficial for reducing power losses. In addition, Mo can be deposited by sputtering in a reactive atmosphere to form nitride films, providing a route to tailor the electrical properties of the contact in a controlled manner. In this study, the electrical and structural properties of Mo-nitride contacts on 4H-SiC were investigated. Three different Mo-nitride contacts were fabricated by varying the nitrogen content in the sputtering chamber during the deposition from a Mo-target. In particular, nitrogen content of 40%, 50% and 60% of the total gas mixture was considered and the corresponding samples were labelled MoN40%, MoN50% and MoN60%, respectively. A Mo film deposited by sputtering in pure Ar was used as reference. Rapid thermal annealing (RTA) was performed in N2 at 400 °C for 10 min. Electrical characterization, based on current-voltage (I-V) measurements under forward and reverse bias, was combined with X-ray diffraction (XRD) structural analysis, to investigate the film properties and correlate the observed variation in ϕB with the contact structural properties. In the as-deposited contacts, electrical measurements showed only a slight shift of the forward I-V curves towards lower voltage with increasing nitrogen amount, with ϕB decreasing from 1.09 to 1.03eV. An increase in leakage was observed only in the MoN60% sample. After RTA treatment, the forward characteristics showed a slight positive shift for the Mo-contact and a more pronounced negative variation for the Mo-nitride ones. In this case, ϕB varied over a wide range, from 1.13 to 0.82 eV with increasing nitrogen amount. The ideality factor n remained close to 1.05 for all samples, while the leakage current increased after RTA compared with the as-deposited contacts. XRD analysis identified the phases formed in the Mo-nitride films. In particular, the MoN0.5 phase was detected in the MoN40% and MoN50% samples, whereas a nitrogen-richer phase (Mo2N1.5) was formed in the MoN60% sample. The different composition of the MoN60% sample is well correlated to the Schottky barrier height reduction and can explain the electrical behavior of the contacts.