Ultrahigh concentration of NV⁻ centers embedded in the CVD epi-diamond layer near the interface with an HPHT diamond substrate

Abstract The negatively charged nitrogen vacancy (NV − ) center ensemble in as-grown chemical vapor deposition (CVD) diamond is a promising candidate for quantum sensing due to its long coherence time and excellent optical properties. However, achieving a high concentration of NV − centers in as-grown CVD diamond remains a critical challenge, which constrains the performance of NV − based sensors. In this study, we observe that NV − center formation efficiency is significantly enhanced during the initial growth phase, with a coherence time <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>*</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> of 1.1 μs. These findings demonstrate that high-concentration NV − centers can be achieved in as-grown diamonds, greatly enhancing their utility in high-performance magnetometers and quantum sensing.