Hello, I need to learn as much as I can about single photon counting pixel detectors (producing a signal for each photons hitting the detector) e.g. PILATUS. I do not understand how this type of detectors counts single photons as opposed to integrating the energy of multiple photons (CCD, MOS, CMOS...). By which mechanism does one reach the single photon counting mode ? Also, I understand that a CCD detector is basically an array of MOS capacitors. From what I understand of MOS, the gate voltage applied between the metal and the p-type silicon creates a depletion region. The photoelectrons produced in the depletion region will be trapped in it, while the hole will leave the region. My question is: is this depletion region used to trap the photoelectrons ? Is this depletion region considered as the potential well seen in this representation: http://tinyurl.com/lxlhcjq ? If anyone has resources on these subjects I would be glad to read them, thanks!