I. Milostnaya, A. Korneev, M. Tarkhov, A. Divochiy, O. Minaeva, V. Seleznev, N. Kaurova, B. Voronov, O. Okunev, G. Chulkova, K. Smirnov, and G. Gol’tsman

Moscow State Pedagogical University, Moscow 119992, Russia

OverviewSingle Photon Superconducting Detectors (SSPDs)

● Developed in collaboration of the MSPU (Prof. Gregory Gol’tsman group) and University of Rochester (Prof. Roman Sobolewski group)1-4, fabricated at MSPU

● Based on superconducting nanowires made from ultra-thin superconducting films.

● Operation is based on photon-induced resistive hotspot formation in the current-carrying superconducting nanowire2.

● Operated at temperatures 2 - 4.2 K well below Tc at a bias current Ib close to Ic.

● Capable of single photon counting in the VIS and IR waveranges.

● Further improvement of the SSPD performance in the IR and THz ranges is expected by implementation of superconducting materials with a lower Tc having a narrow energy gap.

● First MoRe SSPDs were fabricated and tested.

Superconducting Single Photon Nanowire Detectors Development for IR and THz applications

State-of-the-art NbN SSPDs

L08

At operational temperature 4 K 2 KQuantum Efficiency, % at VIS >10 >30 at NIR (1.3–1.55 μm) >6 > 20 at MIR (6 μm) ~0.5Dark Counts, s-1 <1 <10- 4

NEP, W/Hz1/2

at VIS and NIR ~10-17 ~10-21

at MIR (5 μm) ~10-18

Wavelength range, μm 0.5 - 6

Device performances

0.4 0.6 0.8 1 2 4

10-5

10-4

10-3

10-2

10-1

100

101

102

T=5K

QE %

T=3K

QE3K/QE5K=200

SSPDs Fabrication at MSPU

The mature technology is developed for NbN SSPDs. Deposition of 4-nm-thick NbN film on Sapphire substrate by DC magnetron sputtering of Nb target in in Ar+N2 mixture Patterning of stripe windows by direct e-beam lithography Formation of Au contacts by optical lithography Formation of meander-shaped structure with reactive ion etching

NbN films properties:• Thickness 4 nm• Critical temperature Tc=10-11K• Transition width Δ Tc=0.3K• Critical current density jc=7x106 A/cm2

’Standard’ Device Design• SSPDs are designed as meander-shaped nanowires connected to Au contact pads intended for connection to a coplanar waveguide.

• Drawback: response time is significantly affected by a nanowire kinetic inductance.

Response of a single 500-µm-long nanowire

SEM image of the 10 m x 10 m SSPD

Advanced SSPD Design• Multisection SSPDs with lower kinetic inductance are designed as several meander nanowires connected in parallel• Subnanosecond photoresponse time achieved

Oscillograms of the response for 2-section (a) and 5-section (b) SSPDs

• Meander size 10x10μm2

• Nanowire width 80 - 100 nm• Line pitch 200 nm• Nanowire length up to 500 μm

MoRe SSPD

The use of a material with the narrow energy gap and low quasiparticles diffusivity should shift the detectors sensitivity towards longer wavelengths.

• Motivation.

• ‘Standard’ SSPD nanowire meander structures of good quality were fabricated and tested.

Ultrathin (4-10 nm thick) MoRe films were deposited by DC magnetron sputtering of a Mo60/Re40 target.

Oscillogram of the single-photon response of a 200-nm-wide MoRe nanowire

Dependence of a counting rate on a bias current

• First single-photon response was obtained for 1.26m photons at operational temperature of 4.2K.

• Technology of ultra-thin MoRe films suitable for SSPD was developed.

Best MoRe films properties: Thickness 4 nm 10 nm

Critical temperature Tc=7.7 K 9.7K

Transition width Δ Tc=0.1K 0.2K

Critical current density at 4.2K jc=1.1x106 A/cm2

Sheet resistance Rs=65-75 /□

5 6 7 8 90.0

0.2

0.4

0.6

0.8

1.0

R, a

.u.

T, K

4-nm thick MoRe film MoRe SSPD

References

[1] G. Gol'tsman at al., Appl. Phys. Lett. 79 (2001), 705.

[2] A. Semenov at al., Physica C, 352 (2001), 349.

[3] G. Gol’tsman et al., IEEE Trans. on Appl. Supercond. 13(2) (2003), 192.

[4] A. Korneev et al., Appl. Phys. Lett. 84 (2004), 5338.

[5] A. Korneev et al., SPIE Europe Int. Congress on Optics and Optoelectronics, Prague,  Czech Republic, 16 - 19 April 2007.