Kristen A. Sunter

Fabrication Process Yielding Saturated Nanowire Single-Photon Detectors With 24-ps Jitter

We present an optimized fabrication process for superconducting nanowire single-photon detectors that allowed us to obtain a yield of ~70% for detectors based on 80-nm-wide niobium nitride nanowires. We fabricated detectors that showed 24-ps timing jitter and saturated detection efficiency without the need for cryogenic amplifiers, allowing for operation in a low-bias low-dark-count-rate regime while operating at maximum detection efficiency.

Eight-fold signal amplification of a superconducting nanowire single-photon detector using a multiple-avalanche architecture

Superconducting nanowire avalanche single-photon detectors (SNAPs) with n parallel nanowires are advantageous over single-nanowire detectors because their output signal amplitude scales linearly with n. However, the SNAP architecture has not been viably demonstrated for n > 4. To increase n for larger signal amplification, we designed a multi-stage, successive-avalanche architecture which used nanowires, connected via choke inductors in a binary-tree layout. We demonstrated an avalanche detector with n = 8 parallel nanowires and achieved eight-fold signal amplification, with a timing jitter of 54 ps.

Infrared transmissometer to measure the thickness of NbN thin films

We present an optical setup that can be used to characterize the thicknesses of thin NbN films to screen samples for fabrication and to better model the performance of the resulting superconducting nanowire single photon detectors. The infrared transmissometer reported here is easy to use, gives results within minutes, and is nondestructive. Thus, the thickness measurement can be easily integrated into the workflow of deposition and characterization. Comparison to a similar visible-wavelength transmissometer is provided.

Optical modeling of superconducting nanowire single photon detectors using the transfer matrix method

We present optical modeling of superconducting nanowire single photon detector devices using an analytical approach based on the transfer matrix method. We find that the optimal dielectric layer thicknesses vary slightly with the thickness and fill factor of the NbN layer and explore novel device geometries that can be described as a stack of thin films, such as devices on multilayered substrates, free-standing membranes, and optical fiber facets. In addition, the analytical results here show the importance of accounting for coherence correctly when an integrated cavity is included in the device structure and the relative insignificance of an anti-reflection coating in most cases.

Effect of temperature on superconducting nanowire single-photon detector noise

Today Superconducting Nanowire Single-Photon Detectors (SNSPDs) are commonly used in different photon-starved applications, including testing and diagnostics of VLSI circuits. Detecting very faint signals in the near-infrared wavelength range requires not only good detection efficiency, but also very low Dark Count Rate (DCR) and jitter. For example, low noise is crucial to enable ultra-low voltage optical testing of integrated circuits. The effect of detector temperature and background thermal radiation on the noise of superconducting single-photon detectors made of NbN meanders is studied in this paper. It is shown that two different regimes can be identified in the DCR vs. bias current characteristics. At high bias, the dark count rate is dominated by the intrinsic noise of the detector, while at low bias current it is dominated by the detection of stray photons that get onto the SNSPD. Changing the detector temperature changes its switching current and only affects the high bias branch of the characteristics: a reduction of the DCR can be achieved by lowering the SNSPD base temperature. On the other hand, changing the temperature of the single-photon light source (e.g. the VLSI circuit under test) only affects the low bias regime: a lower target temperature leads to a smaller DCR.