In this paper we present a new technology for the fabrication of Single Photon Avalanche Diodes (SPADs) aimed at combining the advantages of thin and thick SPADs. The new detector is manufactured in a thick epitaxial layer designed to improve the Photon Detection Efficiency (PDE) in the red and near-infrared range while maintaining a good timing resolution. Experimental characterization of the new red-enhanced SPAD (RE-SPAD) confirmed a significant improvement of the PDE compared with thin SPADs; for example the PDE at a wavelength of 800 nm has increased from 15% to about 40%. Nevertheless the temporal resolution is still good, with a timing jitter of about 90 ps FWHM. In the same operating conditions the dark count rate is comparable with the one attainable with a thin SPAD (e.g. less than 25 cps for a 50 µm diameter device cooled down to −5°C). Moreover, being planar, the new technology is compatible with the fabrication of arrays of detectors.

It is demonstrated that remarkable timing performance is achievable with large area single photon avalanche diodes (SPADs), provided that the avalanche current is sensed at very low level, when the multiplication process is still confined within a small area around the photon absorption point. By employing a suitable current pick-up circuit, an unprecedented time resolution of 35 ps was obtained with a 100 µm active area diameter SPAD.

Solution-based single-molecule fluorescence spectroscopy is a powerful experimental tool with applications in cell biology, biochemistry, and biophysics. The basic feature of this technique is to excite and collect light from a very small volume and work in a low concentration regime resulting in rare burst-like events corresponding to the transit of a single molecule. Detecting photon bursts is a challenging task: the small number of emitted photons in each burst calls for high detector sensitivity. Bursts are very brief, requiring detectors with fast response time and capable of sustaining high count rates. Finally, many bursts need to be accumulated to achieve proper statistical accuracy, resulting in long measurement time unless parallelization strategies are implemented to speed up data acquisition. In this paper, we will show that silicon single-photon avalanche diodes (SPADs) best meet the needs of single-molecule detection. We will review the key SPAD parameters and highlight the issues to be addressed in their design, fabrication, and operation. After surveying the state-of-the-art SPAD technologies, we will describe our recent progress toward increasing the throughput of single-molecule fluorescence spectroscopy in solution using parallel arrays of SPADs. The potential of this approach is illustrated with single-molecule Förster resonance energy transfer measurements.