Control of thin NbN film superconducting properties by ScN buffer layer

Abstract This work investigates the effect of a scandium nitride (ScN) buffer layer on the superconducting properties of niobium nitride (NbN) thin films. The use of a ScN buffer layer significantly improves the characteristics of 29 nm-thick NbN films: the critical temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> increases from 9 K to 12.5 K, while the resistivity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> </mml:math> at 20 K decreases from 330 µ Ω·cm to 210 µ Ω·cm compared to films without a buffer layer. These enhancements are attributed to the better lattice matching between NbN and ScN, which results in а higher quality crystal lattice of the NbN film, as confirmed by transmission electron microscopy and x-ray diffraction data.