Planar Silicon SPADs with 200 µm diameter and 35 ps photon timing

Time-correlated single photon counting (TCSPC) is exploited in emerging scientific applications in life sciences, such as single molecule spectroscopy, DNA sequencing, fluorescent lifetime imaging. Detectors with wide active area (diameter > 100 μm) are desirable for attaining good photon collection efficiency without requiring complex and time-consuming optical alignment and focusing procedures. Fiber pigtailing of the detector, often employed for having a more flexible optical system, is also obtained more simply and with greater coupling efficiency for wide-area detectors. TCSPC, however, demands to detectors also high photon-timing resolution besides low noise and high quantum efficiency. Particularly tight requirements are set for single-molecule fluorescence analysis, where components with lifetimes of tens of picoseconds are often met. Small photon timing jitter and wide area are considered conflicting requirements for the detector. We developed an improved planar silicon technology for overcoming the problem and providing a solid-state alternative to MCP-PMTs in demanding TCSPC applications. We fabricated Single Photon Avalanche Diodes (SPADs) with 200 μm active area diameter and fairly low dark counting rate (DCR). At moderately low temperature (-25 °C with Peltier cooler) the typical DCR is 1500 c/s and it is not difficult to select devices with less than 1000 c/s. The photon detection efficiency peaks at 48% around 530 nm and stays above 30% over all the visible range. A photon timing resolution of 35 ps FWHM (full width at half maximum) is obtained by using our patented pulse pick-up for processing the avalanche current.