Thermal-property optimization dominated by the stoichiometric ratio in W-Si superconducting single-photon detectors

Mid-infrared superconducting-nanowire single-photon detectors require higher detector sensitivity because of the weaker photon energy. Previous experiments demonstrated that the sensitivity of superconducting-nanowire single-photon detectors (SNSPDs) could be improved by optimizing the stoichiometry of superconducting films. However, the physical mechanism has not been completely studied. In this work, we attempt to explain the optimization mechanism from the hotspot dynamics point of view of thin films and detectors. We obtained the film's electron-transport parameters using magnetoconductance and Hall coefficient measurements and characterized the dynamic process of the hotspot based on the hotspot-relaxation time. Based on our experimental results, it is proposed that the stoichiometry of the $\mathrm{W}$-$\mathrm{Si}$ film plays a role in the specific heat and boundary thermal conductivity, and therefore, affects the thermal relaxation process and the detector's sensitivity. The research results may lay the foundation for the development of highly efficient mid-infrared SNSPD.