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The structure of a silicon avalanche photodiode (APD) has a significant impact on the probability of light creating charge carriers and on the generated noise due to the multiplication process or excess noise factor (ENF). In this paper, we will review front-illuminated and back-illuminated APD structures and their impact on ENF as a function of wavelength from 400 nm to 1000 nm for recently commercially produced silicon APDs targeting LIDAR and other applications. The experimental setup developed for characterization will be described and highlight the differences between the studied structures. APDs with different junction profiles were produced and measurement of ENF was found to match McIntyre’s theory for experimental k-factors (ratio of the hole impact ionization rate to that of electrons) ranging from approximately 0.05 to 0.008. The generated illuminated noise as a function of responsivity can be used as a guideline to select the APD achieving the best signal-to-noise ratio (SNR) for a given application. To help meeting this condition, optimizing the electrical field profile of an APD and making certain the electrons are the primary carriers initiating the avalanche is critical.

Underflow baffles have gained in popularity over the years as a viable mean to intercept floatables in Combined Sewer Overflows (CSOs). This choice was mainly justified by the extremely low capital cost (CAPEX) and operational cost (OPEX) of this solution, although the efficiency of underflow baffles has never been clearly proven. The only similar application to underflow baffles are scum boards in grit chambers and clarifier. However, the flow conditions at CSOs vary considerably from those in grit chambers and clarifier. For this reason, review of the behavior of floatables in a rapid flow is paramount. Only then can comprehensive design criteria for underflow baffles and overflow chambers be suggested. Pilot scale tests, performed in a 17 metres long basin at various flowrates, had already shown that a critical horizontal velocity for floatables (Vcr) may develop in the overflow chambers. In this follow up study, the fate of intercepted floatables was investigated. It appears from this latest data that permanent capture of floatables decreases rapidly with an increase in the horizontal velocity of the flow, no matter what the baffle depth. Baffle depth increases capture at lower velocities (0.17 m/s) but become irrelevant at higher velocities (0.61 m/s). This data suggests that capture efficiency of existing underflow baffles in overflow chambers can be, at best, very low whenever the horizontal velocity increases above 0.30 m/s or 1 ft/s.

Silicon photomultipliers with high photon detection efficiency in the 350 to 800 nm range and low dark count rate are currently being developed in a variety of geometry, microcell size and area in order to address the needs of the analytical, life science, medical imaging community as well as for various scientific and technological applications. This SiPM development platform is based on previous knowledge of low dark count avalanche photodiode operated in Geiger-mode found in the Excelitas single photon counting module. Low dark counts and low temperature sensitivity are especially important when tiling up SiPMs to form larger area detectors such as block detectors typically used in positron emission tomography. The latest developments include; 1. Optical trenches to suppress crosstalk which allowed to increase the operating voltage range from 5 to 10 V above breakdown, 2. Tailored parasitic capacitance to obtain single photon timing resolution close to 200 ps FWHM and 3. Improved PDE at shorter wavelengths by optimizing the entrance window. A corrected energy resolution of 12.0 % was typically obtained at 511 keV which, alongside the good timing resolution, makes this SiPM a perfect candidate for time-of-flight PET and other application requiring a timing resolution better than 200 ps.

Solid state detectors operating in Geiger mode such as the silicon photomultiplier (SiPM) are poised to replace currently used photomultiplier tubes in many applications due to their robustness, dimension and magnetic insensibility. A next generation SiPM well suited for near UV photons with low dark count rate has been developed. 1 mm, 3 mm and 5 mm devices with 25, 50 and 100 µm micro-cells and geometrical efficiencies ranging from 29% to 74% have been produced. A probability of detection of 58% in photon counting mode at 440 nm has been reached. The photon detection efficiency (PDE) thus ranges from 42% to 17% depending on the geometrical efficiency of the chip. The dark count rate varied between the different designs (25 µm to 100 µm micro-cells, 1 mm to 5 mm chips) and was in the region of 300 kcps per mm2 at room temperature and at an operating voltage maximizing the PDE. Characteristics from this novel low dark count SiPM design will be presented and compared, further developments and improvements will also be discussed.

New fast, ultra low-noise UV-enhanced avalanche photodiodes (APD) were recently developed by Excelitas Technologies (formerly PerkinElmer Optoelectronics, Vaudreuil, QC, Canada). for use with scintillation crystals. The novel epitaxial type “buried junction” APD structure was designed for detecting photons with wavelengths shorter than ∼600 nm at high gain with very low dark current. It typically exhibits extremely low noise level (

Underflow baffles have gained in popularity over the years as a viable mean to intercept floatables in Combined Sewer Overflows (CSOs). This choice was mainly justified by the extremely low capital cost (CAPEX) and operational cost (OPEX) of this solution, although the efficiency of underflow baffles has never been clearly proven. The only similar application to underflow baffles are scum boards in grit chambers and clarifier. However, the flow conditions at CSOs vary considerably from those in grit chambers and clarifier. For this reason, review of the behavior of floatables in a rapid flow is paramount. Only then can comprehensive design criteria for underflow baffles and overflow chambers be suggested. Pilot scale tests, performed in a 17 metres long basin at various flowrates, had already shown that a critical horizontal velocity for floatables (Vcr) may develop in the overflow chambers. In this follow up study, the fate of intercepted floatables was investigated. It appears from this latest data that permanent capture of floatables decreases rapidly with an increase in the horizontal velocity of the flow, no matter what the baffle depth. Baffle depth increases capture at lower velocities (0.17 m/s) but become irrelevant at higher velocities (0.61 m/s). This data suggests that capture efficiency of existing underflow baffles in overflow chambers can be, at best, very low whenever the horizontal velocity increases above 0.30 m/s or 1 ft/s.

Underflow baffles have gained in popularity over the last few year as a viable means to intercept floatables in Combined Sewer Overflows (CSOs). This has happened although the efficiency of underflow baffles has never been clearly proven. Furthermore, there are no guidelines helping planners in the correct and efficient design of underflow baffles. This article proposes design criteria deduced from pilot scale essays performed in a 17 meters basin at various flowrates. These new informations can be used in two different ways. First, these criteria can be used to correctly design a new overflow chamber. Secondly, these criteria can be used to evaluate the efficiency of existing overflow chambers. Preliminary analysis of existing chambers show that interception efficiency of floatables can be very low.