  A common solution for precise magnetic field sensing is to employ spin-active
defects in semiconductors, with the NV center in diamond as prominent example.
However, the three-dimensional nature of diamond limits the obtainable
proximity of the defect to the sample. Two-dimensional boron nitride, which can
host spin-active defects, can be used to overcome those limitations. In this
work, we study spin properties of sp2-bonded boron nitride layers grown using
Metal Organic Chemical Vapor Deposition at temperatures ranging from 700
$^\circ$C to 1200 $^\circ$C. With Electron Spin Resonance (ESR) we show that
our layers exhibit spin properties, which we ascribe to carbon related defects.
Supported by photoluminescence and Fourier-transform infrared spectroscopy, we
distinguish three different regimes: (i) growth at low temperatures with no ESR
signal, (ii) growth at intermediate temperatures with a strong ESR signal and a
large number of spin defects, (iii) growth at high temperatures with a weaker
ESR signal and a lower number of spin defects. The observed effects can be
further enhanced by an additional annealing step. Our studies demonstrate
wafer-scale boron nitride that intrinsically hosts spin defects without any ion
or neutron irradiation, which may be employed in spin memories or magnetic
field detectors.
