  In this article we have used stochastic gravitational wave background as a
unique probe to gain insight regarding the creation mechanism of primordial
black holes. We have considered the cumulative gravitational wave background
which consists of the primary part coming from the creation mechanism of the
primordial black holes and the secondary part coming from the different
mechanisms the primordial black holes go through. We have shown that in the
presence of light or ultra light scalar bosons, superradiant instability
generates the secondary part of the gravitational wave background which is the
most detectable. In order to show the unique features of the cumulative
background, we have considered the delayed vacuum decay during a first order
phase transition as the origin of primordial black holes. We have shown the
dependence of the features of the cumulative background, such as the mass of
the relevant light scalars, peak frequencies, etc. on the transition
parameters. We have also generated the cumulative background for a few
benchmark cases to further illustrate our claim.
