Electronic structure and thermoelectric properties of epitaxial Sc1−xVxNy thin films …

The electronic structure of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi mathvariant="normal">S</a:mi><a:msub><a:mi mathvariant="normal">c</a:mi><a:mrow><a:mn>1</a:mn><a:mo>−</a:mo><a:mi>x</a:mi></a:mrow></a:msub><a:msub><a:mi mathvariant="normal">V</a:mi><a:mi>x</a:mi></a:msub><a:msub><a:mi mathvariant="normal">N</a:mi><a:mi>y</a:mi></a:msub></a:mrow></a:math> epitaxial films with different alloying concentrations of V are investigated with respect to effects on thermoelectric properties. Band structure calculations on <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mi mathvariant="normal">S</f:mi><f:msub><f:mi mathvariant="normal">c</f:mi><f:mrow><f:mn>0.75</f:mn></f:mrow></f:msub><f:msub><f:mi mathvariant="normal">V</f:mi><f:mrow><f:mn>0.25</f:mn></f:mrow></f:msub><f:mi mathvariant="normal">N</f:mi></f:mrow></f:math> indicate that V <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:mrow><k:mn>3</k:mn><k:mi>d</k:mi></k:mrow></k:math> states lie in the band gap of the parent ScN compound in the vicinity of the Fermi level. Thus, theoretically, the presence of light (dispersive) bands at the Γ point with band multiplicity is expected to lead to lower electrical resistivity, while flat (heavy) bands at <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"><l:mrow><l:mi>X</l:mi></l:mrow><l:mo>−</l:mo><l:mrow><l:mi>W</l:mi></l:mrow><l:mo>−</l:mo><l:mrow><l:mi>K</l:mi></l:mrow></l:math> symmetry points are associated with higher Seebeck coefficients than that of ScN. Hence, to probe the thermoelectric properties experimentally, epitaxial <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:mrow><m:mi mathvariant="normal">S</m:mi><m:msub><m:mi mathvariant="normal">c</m:mi><m:mrow><m:mn>1</m:mn><m:mo>−</m:mo><m:mi>x</m:mi></m:mrow></m:msub><m:msub><m:mi mathvariant="normal">V</m:mi><m:mi>x</m:mi></m:msub><m:msub><m:mi mathvariant="normal">N</m:mi><m:mi>y</m:mi></m:msub></m:mrow></m:math> thin film samples were deposited on MgO(001) substrates. All the samples showed N substoichiometry and pseudocubic crystal structure. The N-vacancy-induced states were visible in the Sc <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:mrow><r:mn>2</r:mn><r:mi>p</r:mi></r:mrow></r:math> x-ray absorption spectroscopy spectra. The reference ScN and <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"><s:mrow><s:mi mathvariant="normal">S</s:mi><s:msub><s:mi mathvariant="normal">c</s:mi><s:mrow><s:mn>1</s:mn><s:mo>−</s:mo><s:mi>x</s:mi></s:mrow></s:msub><s:msub><s:mi mathvariant="normal">V</s:mi><s:mi>x</s:mi></s:msub><s:msub><s:mi mathvariant="normal">N</s:mi><s:mi>y</s:mi></s:msub></s:mrow></s:math> samples up to <x:math xmlns:x="http://www.w3.org/1998/Math/MathML"><x:mrow><x:mi>x</x:mi><x:mo>=</x:mo><x:mn>0.12</x:mn></x:mrow></x:math> were <y:math xmlns:y="http://www.w3.org/1998/Math/MathML"><y:mi>n</y:mi></y:math> type, exhibiting carrier concentration of <z:math xmlns:z="http://www.w3.org/1998/Math/MathML"><z:msup><z:mrow><z:mn>10</z:mn></z:mrow><z:mn>21</z:mn></z:msup><z:mo> </z:mo><z:mrow><z:mi mathvariant="normal">c</z:mi><z:msup><z:mrow><z:mi mathvariant="normal">m</z:mi></z:mrow><z:mrow><z:mo>−</z:mo><z:mn>3</z:mn></z:mrow></z:msup></z:mrow></z:math>, typical for degenerate semiconductors. For the highest V alloying of <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML"><cb:mrow><cb:mi>x</cb:mi><cb:mo>=</cb:mo><cb:mn>0.15</cb:mn></cb:mrow></cb:math>, holes became the majority charge carriers, as indicated by the positive Seebeck coefficient. The underlying electronic structure and bonding mechanisms in <db:math xmlns:db="http://www.w3.org/1998/Math/MathML"><db:mrow><db:mi mathvariant="normal">S</db:mi><db:msub><db:mi mathvariant="normal">c</db:mi><db:mrow><db:mn>1</db:mn><db:mo>−</db:mo><db:mi>x</db:mi></db:mrow></db:msub><db:msub><db:mi mathvariant="normal">V</db:mi><db:mi>x</db:mi></db:msub><db:msub><db:mi mathvariant="normal">N</db:mi><db:mi>y</db:mi></db:msub></db:mrow></db:math> influence the electrical resistivity, Seebeck coefficient, and Hall effect. Thus, this paper contributes to the fundamental understanding to correlate defects and thermoelectric properties to the electronic structure in the Sc-N system with V alloying. Published by the American Physical Society 2024