Double epitaxy improves single-photon avalanche diode performance

Photon-Timing Detector Module for Single-Molecule Spectroscopy With 60-ps Resolution

“…High electric fields reduce these fluctuations and FWHM values better than 30 ps have been obtained [14]. The tail is due to the minority carriers photogenerated in the neutral region beneath the junction that succeed in reaching the depletion region by diffusion and trigger the avalanche [13], [14], [21].…”

“…Fig. 1 outlines the basic epitaxial structure introduced in 1988 [13] and developed in various technologies [17], [18]. The breakdown voltage is typically 20 V and the depletion layer is typically 1 m thick.…”

“…The time resolution function of the planar epitaxial SPAD (i.e., the statistical distribution of the delays from the arrival time of the photon to the onset of the current pulse) has a fast peak followed by a slow tail [13], [14]. The peak is due to photons absorbed in the depletion layer and its width is related to the statistical fluctuations in the avalanche build-up and in the propagation from the location of arrival of the photon to the whole active area [14], [20].…”

“…In fact, the typical FWHM value of the SPCM-AQR is 350 ps and the intrinsic limit of SLIK devices, which can be attained operating the detector with different circuits, lies between 220 and 150 ps [11], [12]. However, a different avalanche device structure fabricated in planar silicon technology [13] offered a good prospect for the development of a single-photon timing module (SPTM) capable of fulfilling all the requirements. This goal has been attained: it has made accessible new information about angstrom-scale structural changes in single protein molecules, previously not obtained with other methods, and has made possible a correlation analysis of the fluorescence lifetime that revealed conformational fluctuation at multiple time scales spanning from hundreds of microseconds to seconds [3].…”

Single photon avalanche detectors: prospects of new quenching and gain mechanisms

“…The diffusion tail issue is also improved by the epi-substrate p-n junction, which can be reverse biased to further reduce the p-neutral region thickness. A FWHM of 55 ps [44] was achieved in the original double-epitaxial device, and a photon detection efficiency of roughly 9% for nearly 20 V overbias at 830 nm wavelength was reported [10]. The dual-junction SPAD [42] was an attempt to achieve smaller diffusion tail and superior photon-timing resolution by using two depletion regions.…”