Ultrathin NbN Films for Superconducting Single-Photon Detectors

Abstract

We present our research on fabrication and structural and transport characterization of ultrathin superconducting NbN layers deposited on both single-crystal Al2O3 and Si wafers, and SiO2 and Si3N4 buffer layers grown directly on Si wafers. The thicknesses of our films varied from 6 nm to 50 nm and they were grown using reactive RF magnetron sputtering on substrates maintained at the temperature 850• C. We have performed extensive morphology characterization of our films using the X-ray diffraction method and atomic force microscopy, and related the results to the type of the substrate used for the film deposition. Our transport measurements showed that even the thinnest, 6 nm thick NbN films had the superconducting critical temperature of 10-12 K, which was increased to 14 K for thicker films.

Technology of Ultrathin NbN and NbTiN Films for Superconducting Photodetectors

“…Some dierences in the contrast levels of atomic-plane lines may suggest existence of oval grains at the upper part of the lm. These were also observed in our previous AFM surface studies [8], as convex bows and can explain as the surface roughness after the RTA annealing. However, annealing at 1000…”

“…Figure 4 shows the RT characteristics before and after the RTA process, indicating the increase of T C from 9.5 K up to 13 K after annealing at 1000 • C in Ar, the eect similar to that earlier observed in NbN lms [8].…”

“…In our previous work [8], we presented our investiga- Fig. 2a we show the IV curves thus below T C and at the lowest studied temperature (inset), which was limited by DC current bias unit.…”

“…We have also performed extensive structural characterization studies of our NbTiN lms and compared them directly to those earlier done for the NbN lms [8]. X-ray A-78 M. Guziewicz et al Fig.…”

Impact of Gd Doping on Morphology and Superconductivity of NbN Sputtered Thin Films

“…The NbN superconductor with relatively lower (in comparison to HTSc) T c (~16 K) is being already used for various superconducting applications [2,3]. Particularly for superconducting devices (tunnel junctions etc.…”