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arXiv:2501.00177

Theoretical Investigation of Yield-Enhancing Equilibrium Negatively Ionized Tin-Vacancy Center Preparation Pathways in N-Doped Diamond

Aditya Bahulikar, Steven L. Richardson, Rodrick Kuate Defo

Published Dec 30, 2024• 0 citations
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Abstract

The elucidation of the mechanism of Sn$V^-$ formation in diamond is especially important as the Sn$V^-$ color center has the potential to be a superior single-photon emitter when compared to the N$V$ and to other Group IV color centers. The typical formation of the Sn$V$ involves placing Sn in diamond by ion implantation, but the formation of a charged Sn$V$ species requires an additional complication. This complication is related to the energy cost associated with electronic transitions within the host diamond. Effectively, producing the Sn$V^-$ charge state using an electron obtained from a band edge of the host diamond is less energetically favorable than having the Sn$V^-$ receive an electron from a neighboring donor dopant. Among donor dopants, substitutional N (N$_\text{C}$) is always present in even the purest synthetic or natural diamond sample. The mechanism of electron donation by N$_\text{C}$ has been proposed by Collins for charging the N$V$ in diamond and it has been used to interpret many experimental results. Therefore, in this paper we use DFT to explore the pathways for the formation of the Sn$V^-$ charge state due to electron donation arising from the presence of N$_\text{C}$ in the host diamond. Explicitly, defect concentrations are calculated in equilibrium in each of the explored pathways to determine the yield of the Sn$V^-$ throughout each of the pathways. The importance of our work is to suggest experimental ways of enhancing the yield of charged states like the Sn$V^-$ in diamond for transformative applications in optoelectronics and quantum information.

DOI
10.48550/arxiv.2501.00177

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The elucidation of the mechanism of SnV−V^-V− formation in diamond is especially important as the SnV−V^-V− color center has the potential to be a superior single-photon emitter when compared to the NVVV and to other Group IV color centers. The typical formation of the SnVVV involves placing Sn in diamond by ion implantation, but the formation of a charged SnVVV species requires an additional complication. This complication is related to the energy cost associated with electronic transitions within the host diamond. Effectively, producing the SnV−V^-V− charge state using an electron obtained from a band edge of the host diamond is less energetically favorable than having the SnV−V^-V− receive an electron from a neighboring donor dopant. Among donor dopants, substitutional N (NC_\text{C}C​) is always present in even the purest synthetic or natural diamond sample. The mechanism of electron donation by NC_\text{C}C​ has been proposed by Collins for charging the NVVV in diamond and it has been used to interpret many experimental results. Therefore, in this paper we use DFT to explore the pathways for the formation of the SnV−V^-V− charge state due to electron donation arising from the presence of NC_\text{C}C​ in the host diamond. Explicitly, defect concentrations are calculated in equilibrium in each of the explored pathways to determine the yield of the SnV−V^-V− throughout each of the pathways. The importance of our work is to suggest experimental ways of enhancing the yield of charged states like the SnV−V^-V− in diamond for transformative applications in optoelectronics and quantum information.
The elucidation of the mechanism of SnV− formation in diamond is especially important as the SnV− color center has the potential to be a superior single-photon emitter when compared to the NV and to other Group IV impurity-vacancy color centers in diamond. The typical formation of SnV involves placing Sn in diamond by ion implantation, but the formation of a charged SnV species requires an additional complication. This complication is related to the energy cost associated with electronic transitions within the host diamond. Effectively, producing the SnV− charge state using an electron obtained from a band edge of the host diamond is less energetically favorable than having the SnV− receive an electron from a neighboring donor dopant. Among donor dopants, substitutional N (NC) is always present in even the purest synthetic or natural diamond sample. The mechanism of electron donation by NC has been proposed by Collins for charging the NV in diamond and it has been used to interpret many experimental results. Therefore, in this paper, we use density functional theory (DFT) to explore the pathways for the formation of the SnV− charge state due to electron donation arising from the presence of NC in the host diamond. Explicitly, defect concentrations are calculated in equilibrium in each of the explored pathways to determine the yield of the SnV− throughout each of the pathways. The importance of our work is to suggest experimental ways of enhancing the yield of charged states like the SnV− in diamond for transformative applications in optoelectronics and quantum information.
Experiments with the negatively charged nitrogen vacancy (NV−V^-V−) in diamond highlight this defect's promise for coherent storage of quantum information. They have also spurred investigations of other color centers in diamond formed by defects that consist of Group IV element (Si, Ge, Sn, Pb) and vacancies which have different atomic structure than the NV−V^-V− center. To date, these other color centers have not exhibited coherence quite as impressive as that of the NV−V^-V− center. Spectral diffusion and the low Debye-Waller factor are important limitations of the NV−V^-V− center that make investigation of the other color centers necessary to advance the field. In this work we use density-functional theory (DFT) to study the thermodynamics and kinetics associated with the NVVV, SiVVV, GeVVV, SnVVV and PbVVV color centers in diamond. We find agreement between our theoretical calculations and the charge state of various color centers as observed in intrinsic diamond. We determine the Fermi level values that enhance the production of isolated color centers, which may lead to longer coherence times than their present values.
The nitrogen-vacancy (NV) lattice defect in diamond, consisting of an N substitutional atom and an adjacent C vacancy, is commonly observed in two charge states, negative (NV−) and neutral (NV0). The NV− defect exhibits spin state-dependent fluorescence and is, therefore, amenable to optical methods for spin-state readout, while the NV0 is not. Hence, the NV− defect is much more useful for quantum sensing and quantum information processing. However, only NV0 electroluminescence has been observed, even from centers showing NV− in photoluminescence. In the present work, we use first-principles electronic structure calculations to determine adiabatic charge transition levels for the conversion of NV− to NV0 in the presence of substitutional N or P impurities, which provide the charge of the NV− center. We find that the adiabatic charge transition levels in the presence of such impurities lie at energies close to or lower than the zero-phonon line of the NV− center and that these energies only decrease as the concentration of N donors increases. This work, therefore, elucidates the absence of observed electroluminescence from the NV− and proposes a path toward observation of the phenomenon.
Tin-vacancy (SnV) and other group-IV vacancy centers in diamond (SiV, GeV, and PbV) are intensively studied as promising alternatives to the nitrogen-vacancy (NV) center for quantum-based applications. The knowledge and the control of their charge state are therefore major issues. Here, using p-i-p planar junctions, we explore the charge states of implanted single SnV centers. We find two classes of centers, emitting either at 620 nm (SnV – ) or at 646.8 nm but not both. We demonstrate the active and reversible tuning of individual SnV – centers. However, unlike the NV centers, which we tune reversibly and continuously between NV – (638 nm), NV 0 (575 nm), and NV + (dark) states, the two kinds of SnV centers do not tune from one to the other. These findings indicate that the 646.8 nm line is likely owing to another Sn-related defect rather than to the neutral charge state of the split vacancy SnV defect along the ⟨111⟩ axis. Furthermore, p-i-p structures can be used efficiently to induce a tunable band bending, stabilize SnV – and NV – states, and explore the charge-state transition energies of many defect centers.
Group IV color centers in diamond have garnered great interest for their potential as optically active solid-state spin qubits. The future utilization of such emitters requires the development of precise site-controlled emitter generation techniques that are compatible with high-quality nanophotonic devices. This task is more challenging for color centers with large group IV impurity atoms, which are otherwise promising because of their predicted long spin coherence times without a dilution refrigerator. For example, when applied to the negatively charged tin-vacancy (SnV – ) center, conventional site-controlled color center generation methods either damage the diamond surface or yield bulk spectra with unexplained features. Here we demonstrate a novel method to generate site-controlled SnV – centers with clean bulk spectra. We shallowly implant Sn ions through a thin implantation mask and subsequently grow a layer of diamond via chemical vapor deposition. This method can be extended to other color centers and integrated with quantum nanophotonic device fabrication.
The negatively charged nitrogen-vacancy defect (NV)−^-− in diamond has attracted much attention in recent years in qubit and biological applications. The negative charge is donated from nearby nitrogen donors that could limit or stem the successful application of (NV)−^-−. In this Letter, we unambiguously identify the \emph{neutral} nitrogen-vacancy defect (NV0^00) by \emph{ab initio} supercell calculations. Our analysis shows that i) the spin state can be \emph{selectively} occupied optically, ii) the electron spin state can be manipulated by time-varying magnetic field, and iii) the spin state may be read out optically. Based on this NV0^00 is a new hope for realizing qubit in diamond \emph{without} the need of nitrogen donors.