Effect of impurities on morphology, growth mode, and thermoelectric properties of (1 1 1) and (0 0 1) epitaxial-like ScN films

ScN is an emerging semiconductor with an indirect bandgap. It has attracted attention for its thermoelectric properties, use as seed layers, and for alloys for piezoelectric application. ScN and other transition metal nitride semiconductors used for their interesting electrical properties are sensitive to contaminants, such as oxygen or fluorine. In this present article, the influence of depositions conditions on the amount of oxygen contaminants incorporated in ScN films were investigated and their effects on the electrical properties (electrical resistivity and Seebeck coefficient) were studied. Epitaxial-like films of thickness 125  ±  5 nm to 155  ±  5 nm were deposited by DC-magnetron sputtering on c-plane Al₂O₃, MgO(1 1 1) and r-plane Al₂O₃ at substrate temperatures ranging from 700 °C to 950 °C. The amount of oxygen contaminants in the film, dissolved into ScN or as an oxide, was related to the adatom mobility during growth, which is affected by the deposition temperature and the presence of twin domain growth. The lowest values of electrical resistivity of 50 µΩ cm were obtained on ScN(1 1 1)/MgO(1 1 1) and on ScN(0 0 1)/r-plane Al₂O₃ grown at 950 °C with no twin domains and the lowest amount of oxygen contaminant. At the best, the films exhibited an electrical resistivity of 50 µΩ cm with Seebeck coefficient values maintained at  −40 µV K⁻¹, thus a power factor estimated at 3.2  ×  10⁻³ W m⁻¹ K⁻² (at room temperature). (paper)