Charge-state control of ensemble of nitrogen vacancy centers by n–i–n diamond junctions

We fabricated n-type–intrinsic–n-type (n–i–n) diamond junctions to stabilize negatively charged nitrogen vacancy (NV − ) centers. An ensemble of NV centers was generated in a high-purity intrinsic diamond in order to maintain the spin coherence time. The Fermi-energy of the i-layers was controlled by band bending at the two n–i junctions. We confirmed that the NV centers can be modulated toward NV − centers by decreasing the width of the i-layers between adjacent n-layers. The spin coherence time for the NV − centers was maintained even for narrow i-layers.