Title: Manipulating carbon related spin defects in boron nitride by changing the MOCVD growth temperature

Abstract: 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.