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physica status solidi (a)

Passive charge state control of nitrogen‐vacancy centres in diamond using phosphorous and boron doping

Karin Groot-Berning, Nicole Raatz, Inga A. Dobrinets, Margarita Lesik, Piernicola Spinicelli, Alexandre Tallaire, Jocelyn Achard, V. Jacques, Jean-François Roch, Alexander M. Zaitsev, Jan Meijer, Sébastien Pezzagna

Published Sep 1, 2014• 55 citations
Publisher

Abstract

The control and stabilisation of the charge state of nitrogen‐vacancy centres in diamond is an important issue for the achievement of reliable processing of spin‐based quantum information. The effect of phosphorous and boron doping of diamond on the charge state of nitrogen‐vacancy (NV) centres is shown here. Ensembles of NV centres are produced at a depth of 60 nm in ultrapure diamond by implantation of nitrogen ions. Overlapping with the NV ensembles, donor and acceptor doped regions of different doping levels are prepared by ion implantation of phosphorus and boron followed by annealing in vacuum at 1500 °C. We show how the charge state of NV centres is controlled by the presence of phosphorous or boron atoms in their neighbourhood. For the lowest doping level, spectral measurements on the ensemble of NV centres reveal a higher amount of NV0 in the case of boron and a higher amount of NV− in the case of phosphorus, as compared with undoped regions. This behaviour is strengthened when the doping level is increased. Interestingly, the charge state control of native silicon‐vacancy centres is also evidenced. Finally, we discuss the role of the surface termination of diamond on the average charge state of the NV ensemble (still dominant even at a depth of 60 nm) and confirm that the surface 2D‐hole‐gas (H‐termination) can be compensated by nitrogen itself.

DOI
10.1002/pssa.201431308

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The control and stabilisation of the charge state of nitrogen‐vacancy centres in diamond is an important issue for the achievement of reliable processing of spin‐based quantum information. The effect of phosphorous and boron doping of diamond on the charge state of nitrogen‐vacancy (NV) centres is shown here. Ensembles of NV centres are produced at a depth of 60 nm in ultrapure diamond by implantation of nitrogen ions. Overlapping with the NV ensembles, donor and acceptor doped regions of different doping levels are prepared by ion implantation of phosphorus and boron followed by annealing in vacuum at 1500 °C. We show how the charge state of NV centres is controlled by the presence of phosphorous or boron atoms in their neighbourhood. For the lowest doping level, spectral measurements on the ensemble of NV centres reveal a higher amount of NV0 in the case of boron and a higher amount of NV− in the case of phosphorus, as compared with undoped regions. This behaviour is strengthened when the doping level is increased. Interestingly, the charge state control of native silicon‐vacancy centres is also evidenced. Finally, we discuss the role of the surface termination of diamond on the average charge state of the NV ensemble (still dominant even at a depth of 60 nm) and confirm that the surface 2D‐hole‐gas (H‐termination) can be compensated by nitrogen itself.
The nanometer‐scale engineering of single nitrogen‐vacancy (NV) centres in diamond can be obtained by low‐energy (keV) nitrogen implantation with limited straggling. However, shallow NV centres (a few nanometres deep) generally have inferior overall properties than deeply implanted or deep native NV centres, due to the surface proximity. It has already been shown that the spin coherence time of shallow NVs is improved by overgrowth of a thin diamond layer. However the influence of the overgrowth on the survival, the optical properties and the charge state of the centres has not been studied in detail. In this article, we have overgrown three diamond samples (containing NV centres implanted at different depths) using different procedures. We show the successful overgrowth of a pattern of very shallow (2 nm) implanted NV centres using an optimised overgrowth process. Furthermore, the charge state of ensembles and single NV centres was found to be shifted from NV0 to NV− and stabilised in the negative charge state after overgrowth. The combination of low‐energy high‐resolution ion implantation and high‐purity chemical vapour deposition (CVD) overgrowth procedures opens the way towards the fabrication of scalable and efficient quantum devices based on single defects in diamond. Left: implanted pattern of very shallow NV centres (depth ∼2 nm) using a pierced AFM tip. Right: same pattern after CVD overgrowth of a 4 μm‐thick diamond layer.
Since nitrogen-vacancy (NV) centers in diamond have emerged as crucial quantum sensors in physics and biology, the massive preparation of high-quality and high-concentration shallow NV center samples has become urgent and demanding. As NV centers approach the surface and their concentration increases, charge state instability can degrade coherence and introduce additional noise. This problem is further complicated in high-pressure and high-temperature (HPHT) diamonds due to the presence of unclear impurities and inhomogeneous strain. Through optically detected magnetic resonance testing on various implanted samples, we analyzed the spin and charge state properties of shallow NV center ensembles. Our results reveal that the doping dose significantly influences the quantity of NV−, charge, and charge stability. Our findings indicate that over-implanting nitrogen as electron donors before starting graphitization helps stabilize the charge environment of the shallow NV center ensembles. By controlling the nitrogen ion implantation dose, we optimized charge state stability under photoionization and prepared high-quality NV center ensemble samples in HPHT diamonds at the optimal implantation dose range of 2×1013–8×1013 ions/cm2. This method, which relies solely on nitrogen ion implantation and annealing on HPHT diamond, significantly reduces the cost of sensor samples, greatly benefiting the promotion of quantum sensing.
The negatively-charged nitrogen-vacancy (NV) center is the most studied optical center in diamond and is very important for applications in quantum information science. Many proposals for integrating NV centers in quantum and sensing applications rely on their tailored fabrication in ultra pure host material. In this study, we use ion implantation to controllably introduce nitrogen into high purity, low nitrogen chemical vapor deposition diamond samples. The properties of the resulting NV centers are studied as a function of implantation temperature, annealing temperature, and implantation fluence. We compare the implanted NV centers with native NV centers present deep in the bulk of the as-grown samples. The results for implanted NV centers are promising but indicate, at this stage, that the deep native NV centers possess overall superior optical properties. In particular, the implanted NV centers obtained after annealing at 2000 °C under a stabilizing pressure of 8 GPa showed an ensemble linewidth of 0.17 nm compared to 0.61 nm after annealing at 1000 °C. Over the same temperature range, the ensemble NV−/NV0 ratio increased by a factor of ∼5, although this was accompanied by an overall decrease in the NV count.
ABSTRACT Dense, ultra‐shallow (<10 nm from the surface) ensembles of nitrogen‐vacancy (NV) centers in diamond are sought‐after for realising practical quantum sensing at the nanoscale. However, these ensembles typically suffer from reduced NV creation efficiency and spin coherence compared to their deeper and bulk counterparts. Consequently, most demonstrations in the literature to date have been restricted to using single NV centers with atypical coherence and charge stability properties not achievable across entire ensembles. In this work, we demonstrate that controlled annealing in a high purity forming gas atmosphere improves near‐surface NV formation efficiency to over 20%. This environment preserves a high quality hydrogen termination throughout the anneal, avoiding material etching over many hours at temperatures up to 1100°C and possibly helping to suppress vacancy out‐diffusion. We show that high temperature annealing is especially vital for improving spin properties in high density, ultra‐shallow implanted samples due to the localised damage profiles produced. By allowing the formation of high yield NV ensembles with improved spin properties, the optimised forming gas anneal can facilitate the reliable production of more sensitive diamond sensors than have previously been accessible.
Abstract The negatively charged nitrogen-vacancy centre (so-called NV-centre) in diamond is one of the most promising systems for applications in quantum technologies because of the possibility to optically manipulate and read out the spin state of this defect, even at room temperature. Nevertheless, obtaining high NV densities (>500 ppb) close to the surface (5–20 nm) while maintaining good spin properties remain challenging. In this work we rely on a versatile ion implantation system allowing both implanting nitrogen using N 2 + and creating vacancies with He + ion bombardment at variable energies and fluence to create shallow NV ensembles. By optimizing the ion irradiation conditions as well as the surface preparation prior to treatment we successfully increase the amount of created colour centres while demonstrating narrow magnetic resonance linewidths.
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.