Silicon Photomultipliers, A New Device For Low Light Level Photon Detection

Silicon Photomultipliers (SiPM) are novel detectors for low level light detection based on arrays of avalanche photodiodes operating in Geiger mode. Offering good characteristics (fast response, high gain, photon counting capability, insensitivity to magnetic fields, low voltage operation) they have the potential to replace classical photomultipliers (PMT) in many applications. Drawbacks are dark rate and optical cross talk. Though their quantum efficiency is already comparable or better than that of bialkali PMT it is still limited by the structures on the light sensitive front surface. A new concept, presently developed at the Max‐Planck semiconductor laboratory, allows boosting the efficiency to almost 100%. Using a fully depleted substrate the light enters through the unstructured backside. A drift diode structure collects the electrons on a small “point like” avalanche structure for multiplication. Engineering the thin entrance window at the backside using antireflective layers a high efficiency can be achieved in a wide wavelength range (300–1000nm). The paper will summarize the status of front illuminated SiPMs and report on the development of the backside illuminated devices.