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We have designed and developed a new family of photodetectors with Internal Discrete Amplification (IDA) mechanism They operate as solid state photomultiplier devices at room temperature and may be used in numerous applications where high bandwidth of the detector is necessary in combination with maximum sensitivity and low excess noise. The photodetectors can operate in linear detection mode with gain-bandwidth product up to 5·10 14 as well as in photon counting mode with count rates up to 10 8 counts/sec. The key performance characteristics exceed those of Photomultiplier Tube (PMT) and Avalanche Photodiode (APD) devices. The detectors have gain > 10 5 , excess noise factor as low as 1.03, photoresponse rise/fall time < 300 ps, and timing resolution (jitter) < 200 ps. The combination of low excess noise at high gain and wide bandwidth, as well as scalability to large active areas, presents the main advantages of this technology over conventional photodetector solutions. Ultra low excess noise is one of the main features of the internal Discrete Amplification Detector (DAD), and in this paper its nature has been investigated more comprehensively. We investigated the behavior of the noise-factor and afterpulsing, and conclude that both have the same physical nature. Optical cross-talk between channels is shown to be responsible for the afterpulsing phenomenon, and, in turn, is the main source of excess noise. Thus, the noise characteristics of an DAD device and its timing resolution may be significantly improved as they are limited not by the discrete amplifier channel properties itself, but by the cross-talk, which strongly depends on the device design.

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