Charge-state stability of single NV centers in HPHT-type IIa diamond

TL;DR

This study explores how electric fields and optical excitation influence the charge stability of NV centers in HPHT diamond, revealing that electrical bias can stabilize the negatively charged state crucial for quantum applications.

Contribution

It demonstrates the role of electrical bias and residual boron in stabilizing NV- charge state in weakly doped HPHT diamond, with detailed charge conversion dynamics analysis.

Findings

Electric fields increase NV- population and improve spin readout.

Charge conversion occurs on minute to nanosecond timescales, influenced by bias.

Residual boron acceptors are key to charge stability.

Abstract

This is a preliminary version. Improvements and additional analysis will be included in a revised manuscript. We investigate the charge-state stability of individual nitrogen-vacancy (NV) centers in weakly doped HPHT IIa diamond containing sub-ppm concentrations of boron and nitrogen. Using Ti/Al coplanar electrodes on an oxygen-terminated surface, we study how applied electric fields and optical excitation jointly govern NV charge conversion. By combining voltage-dependent photoluminescence, real-time charge-state monitoring, laser-power saturation with spectral decomposition, and time-resolved measurements, we reveal that electric fields several micrometers from the contacts significantly increase the NV- population and enhance spin readout. At low excitation powers, the NV- population evolves on minute timescales following compressed-exponential kinetics, consistent with slow space-charge rearrangement in ultra-insulating diamond. Under pulsed excitation, we observe hundreds-of-nanoseconds NV-/NV0 conversion driven by hole capture, which is strongly suppressed by applied bias. Our results demonstrate that residual boron acceptors play a key role in determining charge-state stability and show how electrical bias can reliably stabilize NV- in weakly doped bulk diamond.