Spatial homogeneity of superconducting order parameter in NbN films grown by atomic layer deposition

TL;DR

This study demonstrates that NbN films grown by plasma-enhanced atomic layer deposition exhibit remarkable spatial homogeneity of the superconducting order parameter despite high disorder, making them promising for cryoelectronic applications.

Contribution

It shows that PE-ALD-grown NbN films maintain uniform superconducting properties even near the superconductor-insulator transition, unlike typical disordered films.

Findings

Order parameter varies only by 2-3% across the surface.

Films have high sheet resistance up to 1400 Ohm.

High sheet kinetic inductance up to 200 pH.

Abstract

Due to their high kinetic inductance, highly disordered superconducting thin films are a potential hardware for the realization of compact, low-noise elements in cryoelectronic applications. However, high disorder typically results in structural defects that cause spatial inhomogeneity of the superconducting order parameter, thereby impairing the film's properties. Here, we employ scanning tunneling microscopy to demonstrate that NbN thin films fabricated by plasma-enhanced atomic layer deposition (PE-ALD) exhibit unusual spatial homogeneity, even at thicknesses approaching the superconductor-insulator transition. Tunneling spectra acquired across the sample surface show only small variations of the order parameter with a standard deviation of 2-3%, on length scales that significantly exceed the film's grain size. At the same time, the films achieve a relatively high sheet resistance (up to 1400 Ohm) and, consequently, a high sheet kinetic inductance (up to approximately 200 pH), making them well-suited for applications.