New trends on photodetectors

The working horse for the detection of photons is the photomultiplier tube (PMT) which has been a commercial product since 1936. It is an elaborated device but still, after 70 years, impressive improvements have recently been achieved. PMTs however have two severe draw backs: they are sensitive to magnetic fields and they are expensive because the complicated mechanical structure inside the vacuum container is mostly handmade. This initiated the search for alternative devices. Photon sensitive semiconductor devices (PIN-photodiodes, avalanche photodiodes and recently Geiger-mode avalanche photodiodes) have been developed and have already replaced PMTs in many fields of research and will gain more ground in the near future. Geiger-mode avalanche photodiodes have an especially high potential because they have high gain and need no or only a simple amplifier and they can be produced with a standard and cost effective CMOS technique. However, when very large areas have to be covered the cheapest device is still probably a gaseous photomultiplier. Detectors based on the so-called Gas Electron Multiplier (GEM) foils, which minimize the harmful ion feedback, have high gain and even so a very long lifetime.