Credit: © 2008 AIP

Recently, attention has shifted from traditional solid-state semiconductor-based photon detectors to superconducting, niobium-based, single-photon devices. The energy gap of superconductors is about two to three orders of magnitude smaller than that of semiconductors, thus enabling the creation of much greater densities of excited electrons at the same incident photon energy, and therefore offering higher sensitivities and operating speeds than semiconductors. However, niobium superconducting devices are grown on sapphire substrates, and integrating superconducting single-photon devices with conventional silicon circuitry remains a challenge. Now, Sander Dorenbos and colleagues1 from the Technical University of Delft, The Netherlands, report ultra-high sensitivity superconducting single-photon detectors fabricated by depositing niobium titanium nitride (NbTiN) nanowires on silicon substrates.

NbTiN films were deposited on oxidized silicon substrates by reactive-ion sputtering, and electron-beam lithography was used to fabricate 100-nm-wide and 6-nm-thick nanowire structures over micrometre-sized areas. The detectors were irradiated with laser light in the 650–950 nm wavelength range.

The noise equivalent power — a device figure-of-merit — was 10-19 W Hz-1/2 at 4.2 K. Moreover, despite the deposition on silicon substrates, the background noise (dark counts) of NbTiN was one order of magnitude less than the widely used NbN devices grown on sapphire substrates.