Abstract
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).
Highlights
Transition metal nitride thin film are widely investigated for their mechanical [1,2,3,4], plasmonic [5], piezoelectric properties [6,7,8], or used as diffusion barriers [9, 10] and more recently for their thermoelectric properties [11]
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 a temperatures of deposition (TD) of 950 °C, only one diffraction peak was detected from the thin film: films deposited on c-plane Al2O3 and MgO(1 1 1) substrates were (1 1 1) oriented and the film on r-plane Al2O3 substrate was (0 0 1) oriented
Summary
Transition metal nitride thin film are widely investigated for their mechanical [1,2,3,4], plasmonic [5], piezoelectric properties [6,7,8], or used as diffusion barriers [9, 10] and more recently for their thermoelectric properties [11]. Vapor deposition (PVD) such as sputtering or arc deposition, it is important to control the purity of the final film. With such techniques, high vacuum or ultra-high vacuum chambers with base pressure of 10−6 to 10−8 Pa are used to minimize the contaminations during the deposition process. Different aspects of the deposition process can be controlled in order to minimize contamination, such as the cleaning processes of chamber and substrates, bake-out, base pressure and purity of target/gas. Even at the best conditions of cleanliness, some transition metals which are more sensitive than others to contamination (oxygen, carbon) will lead to incorporation of impurities in the film during deposition
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