Evaluation of a-NbGe films as a candidate material for superconducting nanowire single-photon detector (SNSPD) applications

Abstract We report on the superconducting properties of amorphous NbGe thin films of thickness in the range from 50 to 10 nm, to assess and compare their characteristics for single-photon detector capabilities with respect to established materials for single-photon detector (SPD). Resistance as a function of temperature and magnetic field was measured for the calculation of the microscopic parameters relevant for single-photon detector. HRXRD along with TEM analysis confirmed that the films are of an amorphous nature. Conductance fluctuation mechanisms such as Aslamazov–Larkin and Maki–Thompson were evoked to analyze the zero field ( B = 0 T) resistance data and the results are in compliance with the experimental data. Similarly, the signature of 2D superconductivity in terms of Berezinskii–Kosterlitz–Thouless transition due to the binding and unbinding of vortex and antivortex pairs was also verified for a film thickness upto 25 nm. Longitudinal resistance ( R xx ) together with Hall resistance ( R xy ) was used to evaluate the superconducting and microscopic parameters of the samples both in the superconducting and in the normal state. The evaluation of single-photon detector capability is done majorly through transport measurements and the analysis of magneto-conductance above the transition temperature, through which different scattering mechanisms of the excited quasiparticles upon the incidence of the photon and its thermalization process were analyzed. Current–voltage characteristics performed at small magnetic fields enabled us to determine the vortex dynamics and the associated quasi particle relaxation time scale. Finally, the evaluated characteristics were compared with respect to the established superconducting systems for SPDs such as NbN, MoSi, WSi, NbRe etc. The characteristic time scales such as electron–electron scattering rate ( τ e–e ), electron–fluctuation rate ( τ e–fl ), and electron–phonon scattering rate evaluated from the transport measurements are within the same range as reported for other systems. From the analysis, we establish that a-NbGe could be a potential candidate for superconducting nanowire single-photon detectors (SNSPDs) and also a potential candidate for the wavelength tunability of SNSPDs. Changing the crystallinity of the film can alter the T c , as well as the superconducting energy gap.