In this paper we present a physically-based model aimed at calculating the Photon Detection Efficiency (PDE) and the\ud temporal response of a Single-Photon Avalanche Diode (SPAD) with a given structure. In order to calculate these quantities, it is necessary to evaluate both the probability and the delay with which a photon impinging on the detector area triggers an avalanche. Three tasks are sequentially performed: as a first step, the electron-hole generation profile along the device is calculated according to the silicon absorption coefficient at the considered wavelength; successively, temporal evolution of the carriers distribution along the device is calculated by solving drift diffusion equations; finally, the avalanche triggering probability is calculated as a function of the photon absorption point.\ud Validation of the model has been carried out by comparing simulation and experimental results of a few generations of detectors previously realized in our laboratory. Photon detection efficiency has been measured and calculated for wavelengths ranging from 400nm to 1000nm and for excess bias voltages ranging from 2 to 8V. Similarly, temporal response has been investigated at two different wavelengths (520 and 820nm). A remarkable agreement between experimental and simulation results has been obtained in the entire characterization domain simply starting from the measured doping profile and without the need of any fitting parameter. Consequently, we think that this model will be a valuable tool for the development of new detectors with improved performances

After a brief review of the physics of photon detection in single photon avalanche diode (SPAD) devices, in this paper we will outline the principle of operation of a model we developed with the aim of calculating both photon detection efficiency (PDE) and temporal response (TR) of these detectors. Then we will apply the model to the devices currently available in order to critically analyze some experimental results. We will show in particular how the use of the model allows us to gain a better understanding of the influence of each device parameter in determining both the PDE and the TR. Finally we will discuss some modifications that can be applied to the device structure in order to overcome such limitations. Their effectiveness in improving both the PDE and the TR will be investigated by means of the aforementioned model. The aim is to provide the reader with an insight of which performances can be expected in the next few years if a strong development of the SPAD structure is pursued

Improving SPAD performances, such as dark count rate and quantum efficiency, without degrading the photontiming jitter is a challenging task that requires a clear understanding of the physical mechanisms involved. In this paper we investigate the contribution of the avalanche buildup statistics and the lateral avalanche propagation to the photon-timing jitter in silicon SPAD devices. Recent works on the buildup statistics focused on the uniform electric field case, however these results can not be applied to Si SPAD devices in which field profile is far from constant. We developed a 1-D Monte Carlo (MC) simulator using the real non-uniform field profiles derived from Secondary Ion Mass Spectroscopy (SIMS) measurements. Local and non-local models for impact ionization phenomena were considered. The obtained results, in particular the mean multiplication rate and jitter of the buildup filament, allowed us to simulate the statistical spread of the avalanche current on the device active area. We included space charge effects and a detailed lumped model for the external electronics and parasitics. We found that, in agreement with some experimental evidences, the avalanche buildup contribution to the total timing jitter is non-negligible in our devices. Moreover the lateral propagation gives an additional contribution that can explain the increasing trend of the photon-timing jitter with the comparator threshold

In recent years, a growing number of applications demand better timing resolution from single-photon avalanche diodes (SPADs). The challenge is pursuing improved timing resolution without impairing other device characteristics such as quantum efficiency and dark count rate. This task requires a clear understanding of the statistical phenomena involved in the avalanche current growth in order to drive the device engineering process. Past studies state that in Si SPADs the avalanche injection position statistics is the main contribution to the photon-timing jitter. However, in recent re-engineered devices, this assumption has been questioned. To address this issue, we developed an experimental setup capable of characterizing the photon-timing jitter as a function of the injection position by means of a laser focused on the device active area. The results not only confirmed that the injection position statistics is not the main contribution to photon-timing jitter, but also evidenced interesting dependences of the timing performances on the injection position. Furthermore, we found a relationship between the photon-timing jitter and the specific resistance of the devices, which has been investigated by means of photoluminescence measurements

In recent years a growing number of applications demands always better timing resolution for Single Photon Avalanche Diodes. The challenge is pursuing the improved timing resolution without impairing the other device characteristics such as quantum efficiency and dark counts. This task requires a clear understanding of the physical mechanisms necessary to drive the device engineering process. Past studies state that in Si-SPADs the avalanche injection position statistics is the main contribution to the photon-timing jitter. However, in recent re-engineered devices, this assumption is questioned. For the purpose of assessing for good this contribution we developed an experimental setup in order to characterize the photontiming jitter as a function of the injection position by means of TCSPC measurements with a laser focused on the device active area. Results confirmed not only that the injection position is not the main contribution to the photon-timing jitter but also evidenced a radial dependence never observed before. Furthermore we found a relation between the photon-timing jitter and the specific resistance of the devices. To characterize the resistances we studied the avalanche current density distribution in the device active area by imaging the photo-luminescence due to hot-carrier emission