NbN nanowire superconducting single photon detectors fabricated on MgO substrates

摘要

High sensitivity ultrafast nanowire superconducting single photon detectors (SSPD) in the near infrared wavelength range have been fabricated with ultrathin (3.5nm) NbN films grown on R-plane sapphire substrates by dc reactive magnetron sputtering in Ar+N{sub}2 mixture [1]. The main drawback of this approach is that in order to obtain the superconducting δ cubic fcc phase of NbN the substrate must be heated up to 900°C during deposition, which makes it difficult to integrate the detector with waveguides and microcavities, typically realized on other substrates (such as GaAs and Si) and not compatible with these temperatures. In an effort to develop an exportable technology, NbN films ranging from 3.5 to 150nm in thickness have been deposited by current controlled dc magnetron sputtering in a mixture of Ar and N{sub}2 on single crystal MgO and GaAs substrates. Substrate temperature T{sub}S during deposition was as low as 500°C. In order to maximize the critical temperature T{sub}C, effects of the reactive gas total pressure P{sub}(tot) and composition on film crystal structure and electrical properties have been studied. For 150nm thick films, T{sub}C reaches a maximum of 16.1K on MgO and 14.8K on GaAs, which are state of the art values. In 5nm thick films, T{sub}Cs as high as 10K and 11K have been obtained on GaAs and MgO, respectively (Fig. 1).