Description
Superconducting microstrip single-photon detectors (SMSPDs) consist of a micrometer-wide strip of a strongly disordered superconductor biased with a current close to its critical value. Recently, a single-photon detection efficiency exceeding 90% at a wavelength of 1550 nm was demonstrated [1]. Compared to their more mature counterparts, superconducting nanowire single-photon detectors (SNSPDs), which require electron-beam lithography for nanopatterning, SMSPDs can be fabricated using conventional photolithography. This offers the potential for improved fabrication yield, which is crucial for the realization of large-area detectors and detector arrays with high pixel counts. The performance of SMSPDs is strongly influenced by the properties of the superconducting film, including its superconducting and optical characteristics, as well as its suitability for lithographic processing.
Here, we present the first demonstration and characterization of an SMSPD fabricated from molybdenum carbide (MoC) thin films using maskless laser lithography and plasma etching. The MoC films were deposited by magnetron sputtering. The optical properties of the films were characterized by spectroscopic ellipsometry over a broad spectral range extending from the infrared to the ultraviolet. These properties are important for two reasons: they directly affect the photolithographic process and influence the absorption efficiency of the detector. Furthermore, the optical conductivity of strongly disordered MoC films is significantly modified by quantum corrections [2], providing insight into the electronic properties of the material. The superconducting properties and photon detection efficiency of the fabricated devices were investigated in a 3He/4He dilution refrigerator at temperatures down to 30 mK under flood-illumination conditions.
[1] G. Z. Xu et al., Photonics Research 9, 958 (2021).
[2] P. Neilinger et al., Physical Review B 100, 241106 (2019).