<sup></sup>The detection and identification of single molecules represent one of the ultimate goals of analytical chemistry. We have
designed, developed and tested a new family of photodetectors with Internal Discrete Amplification (IDA) mechanism.
These photodetectors can operate in linear (analog) detection mode with gain-bandwidth product up to 5.10<sup>14</sup> and one- or
few-photon sensitivity, as well as in the photon counting mode with count rates up to 10<sup>8</sup> cps. Their key performance
characteristics exceed those of photomultiplier tube (PMT) and avalanche photodiode (APD) devices. The measured
parameters of the detectors are: gain > 10<sup>5</sup>, excess noise factor as low as 1.02, maximum count rate > 10<sup>8</sup> counts/s, and rise/fall time < 300 ps. The new family of the photo detectors may become an ideal solution for the problems of
ultrasensitive and single-molecule detection by fluorescence spectroscopy and other optical methods.
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 times 10<sup>14</sup> as well as in photon
counting mode with count rates up to 10<sup>8</sup> counts/sec. The key performance characteristics exceed those of
Photomultiplier Tube (PMT) and Avalanche Photodiode (APD) devices. The detectors have gain > 10<sup>5</sup>, 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.
Recent advances in bio-optical methods for Medical Diagnostics, Optical Biopsy and Non-Invasive Imaging have the
potential to prolong and improve the quality of life while significantly reducing medical costs for the diagnosis and
tracking of diseases. Advances in the Genomics and pharmaceutical discovery using micro-array technology and High
Throughput Screening permit to study thousands of compounds in short periods of time. This paper presents a new Si-based
photonic sensors and sensor arrays with internal discrete amplification that offers the necessary qualities thus
allowing development of a new generation of high gain, ultra low noise, universal analog and counting photodetectors
for bio-optical sensing applications. The new photodetectors can operate in the linear detection mode with a gain-bandwidth
product of up to 10<sup>15</sup>/sec and in the photon counting mode with count rates of up to 10<sup>9</sup> counts/sec. Detectors
based on this amplification mechanism could have performance parameters superior to those of conventional avalanche
photodiodes and photomultiplier tubes. For tested silicon photodetector prototypes, measured excess noise factor is as
low as 1.02 at gains greater than 100,000.