Charge dynamics at nitrogen impurities and nitrogen-vacancy centers in diamond

Abstract

The nitrogen-vacancy (NV) center in diamond is the prototype quantum defect that enables a variety of diamond-based quantum technologies. However, charge-state instability and spectral diffusion, often induced by substitutional nitrogen impurities (N${}_{\mathrm{C}}$), remain key challenges for device performance. Here, we employ first-principles density functional theory calculations to quantitatively investigate nonradiative carrier capture processes mediated by multiphonon emission at both the NV center and the N${}_{\mathrm{C}}$ impurity. For relevant cases, we also compute the rates of radiative and thermal emission processes. For N${}_{\mathrm{C}}^0$ $\to$ N${}_{\mathrm{C}}^{-}$, we obtain an electron capture coefficient of $2.2\times 10^{-8}$ cm${}^3$s${}^{-1}$ at 300 K. Both the magnitude and temperature dependence are in excellent agreement with experimentally measured capture cross sections. Electron capture at N${}_{\mathrm{C}}^{+}$ is even faster, with a capture coefficient of $1.0\times 10^{-4}$ cm${}^3$s${}^{-1}$ at 300 K. For the NV center, we find that carrier capture rates involving only the ground states of NV${}^0$ and NV${}^{-}$ are negligibly slow. However, capture into the excited states (NV${}^{0\ast }$ and NV${}^{-\ast }$) is significantly faster. In particular, the capture coefficient for the hole capture process NV${}^{-}$ $\to$ NV${}^{0\ast }$ is as large as $1.8\times 10^{-7}$ cm${}^3$s${}^{-1}$ and largely temperature-independent. Hole capture at NV${}^{-}$ will thus occur via nonradiative capture into an excited state of NV${}^0$ followed by fast radiative decay to the NV${}^0$ ground state. Similarly, electron capture at NV${}^0$ will occur via the NV${}^0$ $\to$ NV${}^{-\ast }$ $\to$ NV${}^{-}$ pathway, but with a lower nonradiative capture coefficient ($2.1\times 10^{-9}$ cm${}^3$s${}^{-1}$ at 300 K). Our calculated capture coefficients and rates provide essential information for analyzing charge-state dynamics.

Submitted to Physical Review B