Effect of the substrate on the electrical transport and fluctuation processes in NbRe and NbReN ultrathin films for superconducting electronics applications

C Barone,C Attanasio,V Granata,C Cirillo,D Santoro,G Carapella,S Pagano

doi:10.1038/s41598-022-05511-5

Abstract

NbRe-based superconducting thin films recently received relevant interest in the field of low-temperature electronics. However, for these materials the electrical conduction mechanisms, in particular in the normal state, still need to be investigated in more detail. Here, NbRe and NbReN films of different thicknesses have been deposited on two different substrates, namely monocrystalline Si and text {SiO}_2 buffered Si. The films were characterized by DC electrical transport measurements. Moreover, a connection with the charge carriers fluctuation processes has been made by analyzing the electrical noise generated in the normal state region. Despite the films morphology seems not to be affected by the substrate used, a lower noise level has been found for the ones grown on text {SiO}_2, in particular for NbReN. From this study it emerges that both NbRe and NbReN ultrathin films are of very good quality, as far as the low-temperature electrical noise and conduction are concerned, with noise levels competitive with NbN. These results may further support the proposal of using these materials in a nanowire form in the field of superconducting electronics.

Highlights

NbRe-based superconducting thin films recently received relevant interest in the field of lowtemperature electronics
All the analyzed samples exhibit very small grain sizes, with apparent diameter smaller than 20 nm even in the case of the films 100-nm-thick. This result confirms that the films under study are moderately oriented with small crystallites in agreement with X-ray diffraction measurements reported in Refs.6 and[8]
NbRe and NbReN films 10- and 100-nm-thick have been deposited on Si and SiO2 substrates, whose choice does not seem to strongly influence the morphological and superconducting properties

Summary

Introduction

NbRe-based superconducting thin films recently received relevant interest in the field of lowtemperature electronics. Despite the films morphology seems not to be affected by the substrate used, a lower noise level has been found for the ones grown on SiO2 , in particular for NbReN From this study it emerges that both NbRe and NbReN ultrathin films are of very good quality, as far as the low-temperature electrical noise and conduction are concerned, with noise levels competitive with NbN. While the first single photon detectors made of NbRe were already realized and showed good metrics, especially concerning time performances[12], NbReN still need to be tested in a device form, NbReN-based SNSPDs are expected to extend the operational frequency range of NbRe with comparable time response This is due to the reduced value of the superconducting gap, comparable to that of amorphous superconductors, and to the short quasi-particle relaxation r ates[8]. The interaction between the quasi-particles (qp) and the substrate via phonon escape in the last stage of the detection process, is an example of normal state processes where fluctuations may play an important role[21]

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Results

Conclusion