Investigation of Thin Film Supercurrent and Photodetection in Wide Niobium Nitride Wires

Abstract

Over the past two decades, superconducting nanowire single photon detectors have become the dominant platform for detection at telecommunication wavelengths. Despite their practical success, the theoretical framework that describes the detection mechanism within the nanowire is continually evolving. Early phenomenological models suggested that a hot region forms across the superconducting strip after the arrival of a photon, producing a measurable voltage only if the diameter of the hot region extends across the width of the strip. However, predictions based on the kinetic-equation approach showed that within a certain operating regime detection no longer depends on the strip’s width. This prediction was later supported by the experimental demonstration of single photon detection in strips 1-3 𝜇m wide. The ability to fabricate detectors with larger widths would allow for higher signal to noise ratios as well as higher fabrication yield compared to narrow wires. These advantages could potentially unlock some long sought after applications of single photon detectors such as large area detectors or >kilopixel arrays of detectors. In order to produce wide wire detectors the design and material properties must be well optimized. This thesis will cover the development of wide single photon detectors using nitrogen rich niobium nitride.