Nitrogen-vacancy centers created by N+ ion implantation through screening SiO2 layers on diamond

Abstract

We report on an ion implantation technique utilizing a screening mask made of SiO 2 to control both the depth profile and the dose. By appropriately selecting the thickness of the screening layer, this method fully suppresses the ion channeling, brings the location of the highest NV density to the surface, and effectively reduces the dose by more than three orders of magnitude. With a standard ion implantation system operating at the energy of 10 keV and the dose of 10 11 cm 2 and without an additional etching process, we create single NV centers close to the surface with coherence times of a few tens of µs.Impurity doping of semiconductors is a fabrication process indispensable for the modern electronic devices, and continues to be so for quantum devices such as siliconbased single-donor spin qubits 1-3 , in which the positions of the individual donors must be controlled precisely. 4Being optically addressable and coherently controllable by microwaves, the single electronic spins associated with the negatively charged nitrogen-vacancy (NV − ) centers in diamond are playing important roles in emergent quantum technology, e.g., as a matter qubit interfacing with a flying qubit 5-8 and as a nanoscale magnetic sensor. 9-11Both applications demand that the NV centers be located close to the diamond surface. 12 For quantum network, shallow NV spins can be efficiently coupled to photons in a nanophotonic cavity.13 For magnetometry, the proximity of the NV sensor to a magnetic specimen is crucial, because their dipolar coupling strength decays as the inverse cube of the separation.So far, shallow NV centers (< 5 nm from the surface) have been created primarily by (i) nitrogen-doping during CVD growth 14-17 and (ii) N + ion implantation. 18-27The CVD approach allows the accurate control of the impurity distribution in the depth direction, whereas the doping is random in the lateral dimensions. Ironically, high-quality CVD diamond films tend to lack vacancies to pair up with nitrogen atoms; an additional process to introduce vacancies, such as electron irradiation 14 , C + ion implantation 16 , or He + ion implantation 17 , is often required, although the creation of shallow NV centers in as-grown films has also been reported. 15Ion implantation introduces both nitrogen atoms and vacancies into diamond. The lateral distributions are controllable by the use of focused ion beam 18 or an array of small apertures. 20-23The main concern is that a) Electronic mail: kitoh@appi.keio.ac.jp b) Electronic mail: e-abe@keio.jp the depth profile intrinsically has broadening approximated by a Gaussian distribution. Importantly, the ions can penetrate deep inside of the crystal lattice due to the ion channeling effect. 28 The prevailing approach is to keep the implantation energy low (< 5 keV).24-27 It is also preferred to set the implantation dose (fluence) low (∼10 8 cm −2 ), so that single NV centers can be resolved optically. On the other hand, standard, multi-purpose ion implantation systems operate at 10 keV or higher with the dos...

Spin coherence and depths of single nitrogen-vacancy centers created by ion implantation into diamond via screening masks

“…It is given by the ratio of the areal density divided by the implanted N + density deduced from Monte Carlo simulations. The low yield of 0.1-0.4% is consistent with our previous observation, 27 and similar to the values obtained in low energy ion implantation (≈ 3 keV). 14 The cause of the latter case is attributed to the lack of vacancies to pair up with nitrogen atoms to form NV centers, but it has been shown that the yield can be improved by carefully adjusting annealing, chemical or plasma etching conditions.…”

“…In Ref. 27, some of the present authors reported that near-surface NV centers can also be created by comparatively high energy (10 keV) N + ion implantation, when combined with a SiO 2 screening mask deposited on the diamond surface. The defining feature of this method is that the region of the highest N + density is located at the surface.…”

“…The basic procedures for sample preparation are as described in Ref. 27, except for two points. The first is the growth of isotopically pure 12 C diamond layer, and the second is the use of 14 N as an implantation species, instead of 15 N. We began with a natural abundant (1.1% of 13 C), type-IIa (001) diamond substrate from Element Six.…”

Construction and operation of a tabletop system for nanoscale magnetometry with single nitrogen-vacancy centers in diamond

“…The simplest approach is to replace the air objective lens with oil immersion one (Table II of The top surface of Sample #3 has a few-micron-thick CVD-grown, undoped 12 C layer, in which single NV centers generated by 14 N + ion implantation exist. 80 The triangle points (△) in Fig. 10(a) are the Hahn echo decay curve.…”

Effect of ultraprecision polishing techniques on coherence times of shallow nitrogen-vacancy centers in diamond

“…Complementary approaches aim to influence the coherence properties during or before NV center creation: Shallow NVs created in a delta-doping process can have coherence times T2 > 100 µs 25 , although this result is not easily repeatable 15,26 . Growing a thin layer of SiO2 before implanting the nitrogen ions does not increase the coherence time 27 . However, growing a thin layer of boron-doped diamond before vacuum annealing and removing it afterwards has been reported to improve T2 up to 180 µs for shallow NV centers 28 .…”