  A 2D model of an InGaAs/InAlAs single photon avalanche photodiode has been
developed. The influence of the active area structure in the multiplication
region on the diode's operating parameters has been studied. It was found that
changing the diameter of the structure's active region leads to a change in the
dark current in the linear part of the current-voltage curve and a change in
the breakdown voltage. Reducing the diameter of the active region from 25
$\mu$m to 10 $\mu$m allowed decreasing the dark current in the linear mode by
about $10$ dB. It has been shown that the quality of the SPAD device can be
assessed by knowing the avalanche breakdown voltage and the overall
current-voltage curve plot if we consider structures with the same
multiplication region thickness and different remaining layers. The higher the
breakdown voltage, the better the structure's quality due to smaller local
increases in the field strength. Following this statement, we conclude that for
further use in single-photon detectors, it is reasonable to pick specific SPADs
from a batch on the sole basis of their current-voltage curves.
