Superconducting Nanowire Single-Photon Detectors (SNSPDs) offer several advantages over traditional photodetectors. However, they have limitations related to their latching dead time and dark count rate. This research explores the integration of graphene as an on-chip thermal and electrical shunt in NbTiN superconducting detectors, marking the first application of a 2D material in this capacity. We investigate the impact of graphene on the performance of NbTiN detectors within the multiphoton regime. The NbTiN nanowires are produced via DC reactive magnetron sputtering with a thickness of 25 nm and optical or electron beam lithography onto SiOx/Si substrate. The monolayer graphene is grown by Chemical Vapor Deposition (CVD) and transferred on top of the nanowires. The characterization of the samples has been performed in a close-circuit cryostat setup (3.8 K). The experimental of nominally identical devices with and without graphene, reveal a shift in critical temperature (Tc), a broader superconducting transition, and a significantly reduced electrical hysteresis in the hybrid system. Preliminary results show a non-latching behavior of NbTiN meanders with graphene under pulsed laser illumination of 640 nm photons with a repetition rate up to 1 MHz, emphasizing its efficacy as a shunt resistor speeding up the detector and increasing the detection efficiency. The increased FWHM also highlights the role of graphene in the electrothermal feedback and dissipation. In conclusion, this pioneering work contributes valuable insights into the intricate interplay between 2D materials and superconducting detectors, paving the way for future advancements in this field.
Ramón Bernardo Gavito, Fernando Jiménez Urbanos, Jonathan Roberts, James Sexton, Benjamin Astbury, Hamzah Shokeir, Thomas McGrath, Yasir Noori, Christopher Woodhead, Mohamed Missous, Utz Roedig, Robert Young
In this work, we show how the hysteretic behaviour of resonant tunnelling diodes (RTDs) can be exploited for new functionalities. In particular, the RTDs exhibit a stochastic 2-state switching mechanism that could be useful for random number generation and cryptographic applications. This behaviour can be scaled to N-bit switching, by connecting various RTDs in series. The InGaAs/AlAs RTDs used in our experiments display very sharp negative differential resistance (NDR) peaks at room temperature which show hysteresis cycles that, rather than having a fixed switching threshold, show a probability distribution about a central value. We propose to use this intrinsic uncertainty emerging from the quantum nature of the RTDs as a source of randomness. We show that a combination of two RTDs in series results in devices with three-state outputs and discuss the possibility of scaling to N-state devices by subsequent series connections of RTDs, which we demonstrate for the up to the 4-state case.
In this work, we suggest using that the intrinsic uncertainty in the conduction paths of resonant tunnelling diodes can behave as a source of randomness that can be integrated into current electronics to produce on-chip true random number generators. The N-shaped I-V characteristic of RTDs results in a two-level random voltage output when driven with current pulse trains. Electrical characterisation and randomness testing of the devices was conducted in order to determine the validity of the true randomness assumption. Based on the results obtained for the single RTD case, we suggest the possibility of using multi-well devices to generate N-state random switching devices for their use in random number generation or multi-valued logic devices.
When mechanically exfoliated two-dimensional (2D) materials are used for device applications, their properties strongly depend on the geometry and number of layers present in the flake. In general, these properties cannot be modified once a device has been fabricated out of an exfoliated flake. In this work we present a novel nano-patterning method for 2D material based devices, Pulsed eBeam Gas Assisted Patterning (PEBGAP), that allows us to fine tune their geometry once the device fabrication steps have been completed.
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