Superconducting Nanowire Single Photon Detectors based on NbRe nitride ultrafilms

Abstract

The influence of the reactive DC sputtering parameters on the superconducting properties of NbReN ultrathin films was investigated. A detailed study of the current-voltage characteristics of the plasma was performed to optimize the superconducting critical temperature, Tc. The thickness dependence of Tc for the films deposited under different conditions was analyzed down to the ultrathin limit. Optimized films were used to fabricate superconducting nanowire single photon detectors which, at T=3.5 K, show saturated internal detection efficiency (IDE) up to a wavelength of 1301 nm and 95% IDE at 1548 nm with recovery times and timing jitter of about 8 ns and 28 ps, respectively.

Figures (5)

• Figure 1: (a) Current-Voltage characteristics for $p_{\mathrm{Ar}}=3$$\mu$bar and different N$_{2}^{\%}$ by varying the sputtering power, $P$. The black curve corresponds to the plasma in a pure Ar atmosphere. The dashed lines indicate the isopower curves (see gray labels). Numbers indicate the $T_{\mathrm{c}}$ values of the films 15-nm-thick deposited in the specific conditions. (b) Normalized resistance versus temperature curves for 15-nm-thick films deposited at $p_{\mathrm{Ar}}=3$$\mu$bar, $P=$ 350 W, and varying the N$_{2}^{\%}$ content. Normalized R(T) curves of films at deposited at N$_{2}^{\%}=$ 25 both at 150 and 250 Watt are reported by thin and thick violet line, respectively.
• Figure 2: (a) Current-Voltage characteristics for $p_{\mathrm{Ar}}=3.5$$\mu$bar. The navy (red) curve corresponds to the plasma in a pure Ar (for a nitrogen flow of 0.12 sccm, where the jump as a function of the nitrogen flow appears, see inset). The gray lines indicate the isopower curves (see gray labels). The blue isopower lines define the region of negative slope (see text). Numbers indicate the $T_{\mathrm{c}}$ values of the films deposited in some specific conditions for $d_{\mathrm{NbReN}}=10$ nm. (b) Dependence of low temperature resistivity on $P$ for films of different thickness, from 6 to 20 nm, deposited at a nitrogen flow in the range 0.12-0.24 sccm. (c) Dependence of $T_{\mathrm{c}}$ on the sputtering power for films of different thickness from 6 to 20 nm deposited in the same condition as panel (b).
• Figure 3: $T_{\mathrm{c}}(d_{\mathrm{NbReN}})$ dependence in the low thickness limit for a selection of films representative of the sample sets under study as indicated in the legend. The lines are guide to the eye.
• Figure 4: (a) SEM image of a representative SNSPD device; (b) normalized photon count rate data points (dots) and sigmoidal fittings (lines) for $\lambda$ ranging from 785 nm to 1548 nm (left axis) and DCR (right axis) at $T = 3.5$ K; (c) normalized photon count rate at $\lambda =$ 1548 nm and $T = 3.5$ K in logarithmic scale.
• Figure 5: (a) Single pulse at $T = 3.5$ K (blue), with exponential fit of the decay (red); $t_{\text{rise}}$ and $t_{\text{fall}}$ are shown. (b) Timing jitter at $T = 3.5$ K for a similar detector; data (points) and Gaussian fit (line).