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.