  Superconducting Nanowire Single Photon Detector (SNSPD) emerges as a
potential candidate in the multiple fields requiring sensitive and fast
photodetection. While nanowires of low temperature superconducting detectors
are mature with commercial solutions, other material options with higher
transition temperature and faster responses are currently being explored.
Towards this goal, we develop a generalized numerical model that incorporates
the thermodynamic properties of the superconducting material and identifies the
minimum resolvable photon count for a given bias and device parameters. A phase
diagram of detection and latching phases with the minimum number of photons as
a function of biasing current and biasing temperature for each material system
is presented. We show using the developed model that while low temperature
superconducting (LTS) nanowires are more sensitive to the incident photon at
different wavelengths, the ultimate limit of a single photon can be achieved
using high temperature superconducting (HTS) material such as
YBa2Cu3O7-{\delta}, albeit at stringent biasing conditions. On the contrary,
ultrafast response time with three orders of magnitude smaller response times
can be achieved in select HTS materials making it an appealing for several
practical applications.
