Si PM Photon counting device consisting in APD

Si. PM Photon counting device consisting in APD pixels operating in Geiger mode. Each pixel outputs a signal when it detects one photon. The signal output is the total sum of the outputs from all the pixels. Pixel dimensions can range from 15 x 15 m 2 to 100 x 100 m 2 ore more Applied voltage higher than breakdown voltage p on n n on p Geiger mode overvoltage= supplied voltage breakdown voltage High gain (105 -10 7), good time resolution, insensitive to magnetic field, small size, small operating voltage (below 100 V), high integration level Critical issues : dynamic range, noise (dark current), optical cross-talk , response stability vs. voltage and vs. temperature

The assembly can be monolithic (a single silicon die with several Si. PMs) or hybrid ( several silicon dies on a common package) Hamamatsu monolithic array. S 11828 -3344 M 4 x 4 channels. Each channel has a photosensitive area of 3 x 3 mm 2, made of 3600 pixels with a 50 m pitch Distance from photosensitive area to edge of mount package surface: 500 m

Single photons produce a signal of several millivolts (on a 50 ohm load) Output: A= Ai (as long as the number of photons in a pulse in much smaller than the number of cells) Two ore more photons in the same cell at the same time give the same signal as one photon When Nph > 50% of cells, the deviation from linearity is more than 20%

Gain variation vs. voltage and temperature Hamamatsu Advan. Si. D For stable operation, if the Advan. Si. D temperature is recently quoted: 25 m. V/0 C breakdown not fixed, one has to correct voltage variation the voltage to compensate (feed-back needed)

PDE (photon detection efficiency ) PDE=QE · · Ptrigger geometric fill factor decreases with the number of cells Dynamic range increases with the number of cells is improving with progress of technology. from Advan. Si. D: 70% for 30 m cells p on n (Hamamatsu) n on p (Photonique)

Dark current Dark counts can be triggered by free carriers generated even in the absence of an incoming photon. Dark current increases with overvoltage and temperature. At 25 0 C it can reach a rate from 100 k. Hz to several MHz per mm 2 It can be reduced by puttinga threshold on the number of photons (almost one order of magnitude per 1 photoelectron amplitude of threshold) Advan. Si. D 1 x 1 mm 2, 50 m cells Optical crosstalk It happens when a photon of an avalanche travels to a neighboring cell. More critical in the range 850 -1100 nm. Can be of the order of 5 -7% (gain dependent) Greatly improved using“groove” technique for cell separation(less than 1%)

Pulse shape Rise time determined by silicon and neutral region resitance, space charge, capacitance of the whole device (dominated by the parasitic capacitance of the line connecting the cells to the bias voltage) C: about 10 p. F; trise : some nanoseconds Timing

from FBK (commercial branch: Advan. Si. D) 1 x 8 Si. PM Array - monolithic 1. 5 x 1. 5 mm 2 Si. PM Backside: pads for the 8 independent channels • Monolithic – Silicon die with 8 1. 5 x 1. 5 mm 2 Si. PMs – 1. 7 mm Si. PM pitch – 200 um gap between Si. PMs

1 x 8 Si. PM Array - Hybrid • Hybrid array – – 8 Silicon dies on common package 1. 2 mm circular Si. PMs 1. 7 mm Si. PM pitch Lower fill factor w. r. t. monolithic array • CSP SMD package – 8 channels – 260 um epoxy resin coating (etched in between Si. PMs) 9/16/2020 Company Confidential

Another hybrid