Disorder Engineering of NbTiN SNSPDs via He Ion Implantation

Recent studies have shown that disordered superconducting nanowires act as better photon detectors. We characterize NbTiN superconducting nanowire single-photon detectors (SNSPDs) after local helium-ion implantation using Scanning Tunneling Microscopy and device transport. Surface probing reveals redeposition of NbTiN grains and enables cleaner superconducting gap spectroscopy, in contrary to the conventional expectation that ion implantation degrades superconductivity. Two-terminal transport measurements on locally disordered SNSPDs reveal reduced hysteresis behavior which indicates less latch-prone behavior and improved performance at a given temperature. Transport analysis reveals minor reduction in interfacial cooling strength of the hotspots but near ~50% increase in residual resistivity, indicating enhanced bulk disorder. This is further supported by microwave response shift with disorder, consistent with higher kinetic inductance and longer reset times. Dark-count rate versus bias exhibits a reduced exponential slope, widening the practical operating window of temperature and field. Collectively, these results establish local He⁺ implantation as a reproducible, post-fabrication knob for disorder engineering and performance optimization in NbTiN SNSPDs.