SPAD (Single Photon Avalanche Detector) works beyond Breakdown Voltage which is mentioned as Geiger Mode. But how this actually working. When bias voltage aceede breakdown voltage, generally high current flow started.But case of SPAD , this is not the case. Why ? Should not we found a high current without any photon impact as bias voltage crossed breakdown voltage?
I'm bit of confused here. I searched to understand how this is operating over breakdown voltage but found nothing helpful . They just mention that it operate beyond breakdown voltage and when any photon impact , it gives high current . But Though it's beyond the breakdown voltage, when no photon impact occur, why don't we found anything? Why no significant amount of current flow without photon impact ? My knowledge in this topic is not that much , so detail explanation will be appreciated. Thanks in advance .