In this work, nitrogen vacancy (NV) centers of high nitrogen diamond implanted with arsenic ions were investigated by photoluminescence spectroscopy. The transition of the NV center charge state was discussed by the regularly changing laser excitation power and measurement temperature following high-temperature annealing. After high-temperature annealing, the amorphous layer generated by arsenic ion implantation is transformed into a graphitization layer, resulting in a decrease in the NV yield. The electric neutral NV (NV0) center and negatively charged NV (NV) center are affected by both radiation recombination and Auger recombination with increasing laser power. Accompanied by the increasing measurement temperature, the intensities of NV centers gradually decreased and eventually quenched. In addition, the charge states of NV and NV0 centers were undergoing a transition. The zero phonon line positions of NV centers were also red shift, it was attributed to the dominant role of electron–phonon interaction in the temperature-dependent displacement of diamond energy gaps. The full width at half maxima of NV center were broadened significantly at higher temperatures.

As a potential carrier for quantum computing and communication qubits, the nitrogen vacancy (NV) centers of diamond exhibit special properties for the implementation of novel quantum devices.1,2 It has development potential in numerous applications of quantum state engineering and magnetic sensors3,4 due to its long-lived spin quantum state and evident atomic like characteristics like optical transitions in solid-state devices.5 The NV centers can be created through ion implantation or annealing after irradiation.6,7 Low energy ion implantation is the most frequently method that creating NV centers close to a surface.8,9 Moreover, the NV centers in the shallow surface have more outstanding sensitivity and resolution; therefore, the shallow surface NV centers produced by ion implantation are clearly more valuable for investigation.10,11

Santori et al. investigated the effect of gallium ion implantation and annealing on the vertical distribution of NV centers and found that NV centers must be created in close proximity to the surface for coupling to optical structures.12 Van Dam et al. created NV centers using nitrogen ion implantation followed by high-temperature annealing and found that the optical coherence of NV centers is not determined by the intrinsic effects of diamonds but is related to the creation position and lattice damage.13 Naydenov reported a method to improve the yield of NV, which used 15 N (isotope) to distinguish NV centers created from residual nitrogen (14 N) in diamonds.14 Pezzagna discovered that for the full investigated range of less than 1% to almost 50%, the yield for NV center generation increased with the ion energy.15 

According to Ref. 16, the donor energy level of substituted As in diamond is located below the minimum conduction band value of 0.4 eV, which is much shallower than that of substituted P. Therefore, it is considered a shallow donor through calculation. As as the shallow level n-type dopant in diamond was reported by the previous studies.16,17 In addition, the research studies about the As dopant and the existence form in diamond were significant to the n-type diamond. Sun18 used density functional theory to calculate and discuss the substitution defect structure of arsenic doped diamond and ultimately proved that arsenic impurity is a competitive candidate material for n-type doped diamond. However, due to extremely low solubility and large ion radius, arsenic atoms are difficult to enter the lattice as substitutes.19 Creating and observing changes in the charge states of NV centers after large radius ion implantation is a challenge. Therefore, the ion implantation was employed to achieve the As dopant in diamond, and the effect on the charge state of NV centers in diamond was investigated.

This work focuses on a 3 × 3 × 0.5 mm3 diamond, which was synthesized by high-temperature high pressure (HTHP) at Xi'an Jiaotong University, China. The nitrogen impurity content is higher than 20 ppm. Subsequently, the French IBS ICM-200 ion implantation machine was used to inject the (100) surface on the right angle side of the sample at room temperature at an incidence angle of 7°, with an energy of 130 keV and a dose of 5 × 1015 cm−2 arsenic ions. Due to the large covalent radius of arsenic ions, the implanted arsenic ions were deposited on the surface of diamond, resulting in the formation of a black colored layer in the As ion implantation area of diamond. Subsequently, the ion-implanted diamond was annealed for 60 min at 1350 °C in a circulating argon environment, and the severe amorphous layer transformed into a graphitization layer after annealing, which was related to the threshold of recoverable vacancy concentration.20,21

Next, the material was examined using a confocal Raman microscope (Renishaw) that has a Linkam THMS600 low-temperature cooling stage. By controlling the flow rate of liquid nitrogen and accurately adjusting the measurement temperature, the measurement from 80 K to room temperature can be achieved. With a 532 nm excitation wavelength on an Nd-YAG semiconductor laser, the selected laser power can be adjusted to 50, 25, 5, 2.5, 0.5, 0.25, 0.05, and 0.025 mW, respectively. Detecting the ion implantation surface of the sample that using PL spectroscopy.

The PL spectrum of high nitrogen diamond before arsenic ion implantation is shown in Fig. 1, which was obtained by excitation with 532 nm laser at 80 K and 0.5 mW (1% power level). Before ion implantation, high concentrations of nitrogen impurities led to a much higher intensity of NV centers in the spectrum than the characteristic Raman peak of diamond. In addition to the very high NV centers, a zero phonon line (ZPL) with an intensity about twice that of NV0 centers appeared at 563.2 nm. According to the work of Kiflawi,22 the line at 563.2 nm is most likely associated with nitrogen interstitials, which may have been produced by the rapid crystal development.23 

FIG. 1.

PL spectra of high nitrogen diamond before arsenic ion implantation recorded at 80 K with a laser excitation wavelength of 532 nm.

FIG. 1.

PL spectra of high nitrogen diamond before arsenic ion implantation recorded at 80 K with a laser excitation wavelength of 532 nm.

Close modal

As shown in Fig. 2, after ion implantation, due to the overlap between the damaged black layer near the surface and the As implanted layer, the optical signal in the PL spectrum is incredibly feeble, with a sharp drop in intensity at 563.2 nm and the NV centers. In addition, the comparison of the charge states of NV centers before and after ion implantation shows that little has changed. The characteristic peaks of diamond cannot be distinguished in the spectrum, indicating that arsenic ions have been successfully implanted into the crystal surface.

FIG. 2.

PL spectra of high nitrogen diamond after arsenic ion implantation recorded at 80 K with a laser excitation wavelength of 532 nm.

FIG. 2.

PL spectra of high nitrogen diamond after arsenic ion implantation recorded at 80 K with a laser excitation wavelength of 532 nm.

Close modal

The longitudinal expected range of implantation depth was calculated by means of simulations with the Stopping and Range of Ions in Matter (SRIM) program. For each ion, we forecast damage profiles after implantation at a beam energy of 130 keV using detailed calculations with full damage cascades. Among them, the diamond substrate has a density of 3.515 g/cm3. The lattice binding energy is 7.5 eV, surface binding energy is 3.69 eV, and the average displacement energy is 37.5 eV.24 The outputs of ion distribution and damage event calculation at an ion implantation dose of 5 × 1015 ion cm−3 are shown in Fig. 3, simulated the angle of As ion implantation into diamond in this experiment (7°), and the displacements per atom (dpa) are computed using the vacancy output of the damage event computations.

FIG. 3.

The effect of SRIM software on predicted ion concentration and dpa with depth at an injection angle of 7°.

FIG. 3.

The effect of SRIM software on predicted ion concentration and dpa with depth at an injection angle of 7°.

Close modal

As shown in Fig. 3, the projection range of arsenic ions in diamond is quite small. Similar to Pinault's research,25 when the incident angle is 7°, and the implantation range of arsenic ions is restricted to 30–130 nm (black curve). This means that arsenic ions cannot enter the lattice substitution position or pass through the lattice gap, which means that the injected arsenic ions will only collect on the surface to form the corresponding implantation layer. The associated vacancy density is displayed as a function of injection depth as shown as the red curve; when the injection angle is 7°, the calculated vacancy density exceeds the damage critical threshold by a significant amount (1 × 1022 cm−3).21 The sample exhibits severe graphitization after high-temperature annealing.

After high-temperature annealing, the PL spectra of diamond with arsenic ion implantation are shown in Fig. 4 at liquid nitrogen temperature. The line at 563.2 nm disappears with the diffusion of nitrogen interstitials after high-temperature annealing.23 Due to the limitation of measurement intensity, four power levels are measured in the 0.025–0.5 mW range under 532 nm laser excitation. The results indicate that the annealed NV centers exhibit a significant laser power dependence, as shown in Fig. 4(a). The PL intensity of the NV centers is directly proportional to the laser power, and its relationship can be expressed by26,
I P L = a P k ,
(1)
where P is the laser excitation power, and a and k are constants; the PL intensity of the NV centers rises to varied degrees under various excitation circumstances. According to previous research and conclusions, the following equation expresses the directly proportional between the excitation power P and the total of radiation recombination rate (RL), Auger recombination rate (RAug), and trap mediated Shockley read hall recombination rate (RSRH):26,27
P R L + R Aug + R SRH .
(2)
FIG. 4.

PL spectra of diamond after arsenic implantation and high-temperature annealing at 80 K using a 532 nm laser at various excitation intensities. (a) PL intensities of NV centers under various excitation powers; (b) the ratio of NV/NV0 at various excitation powers.

FIG. 4.

PL spectra of diamond after arsenic implantation and high-temperature annealing at 80 K using a 532 nm laser at various excitation intensities. (a) PL intensities of NV centers under various excitation powers; (b) the ratio of NV/NV0 at various excitation powers.

Close modal
In actuality, the intensity of PL is influenced by radiation recombination and can be understood as a proportional relationship. Therefore, Eq. (1) can be changed to the following equation:
R L I P L = a P k .
(3)

According to previous studies,31 when the k value is 1, the radiation recombination rate (RL) dominates in Eq. (2), which is very close to the fitting of the NV0 centers in our experimental data. The Auger recombination rate (RAug) has a significant impact on the PL intensity when the k value is 2/3. When the value of k is 2, the recombination rate (RSRH) will be determined by Eq. (2). After non-linear fitting of the data, the k values of NV0 center and NV center were maintained at 0.90 and 0.81, respectively. Therefore, the combined effect of radiation recombination and Auger recombination is the main factor affecting the power dependence of the NV center laser after high-temperature annealing of arsenic ion-implanted diamond. In addition, Auger recombination affects the NV center more than the NV0 center.31 Due to the presence of a graphite layer, after laser excitation, more energy is released through nonradiative recombination rather than radiation recombination. Thus, we think that a significant factor contributing to the low k value is strong graphitization on the crystal surface.

The effect of excitation power on the central charge state of NV at low temperature under 532 nm laser excitation is shown in Fig. 4(b). As shown in the figure, the concentration ratio of the NV center to NV0 center usually decreases with increasing excitation power. Laser excites electrons from the NV center to the conduction band region and then recombines with vacancies in the valence band region. The presence of bound electrons causes the k value to tend toward Auger recombination, resulting in the conversion of NV centers to NV0 centers.31 Simultaneously, when laser excitation strength increases, the concentration of NV0 centers gradually rises. This is consistent with the results by Siyushev et al.28 

Figure 5 shows the PL spectra of diamond annealed at 1350 °C with an excitation power of 0.5 mW from low temperature (80 K) to room temperature (280 K) under 532 nm laser excitation. From Fig. 5, it can be seen that the strength of the NV centers increases with the increase in the measurement temperature. Due to the excitability of defects, the NV center manifests as a movement in the location, and the NV centers are quenched. The PL intensity data of the NV centers at various measurement temperatures are displayed in Fig. 5(a). The following illustrates the relationship between the test temperature and the PL intensity of the NV centers:29,
1 / I P L = A 0 + B 0 exp ( E a / k b T ) ,
(4)
where the constants are A0 and B0, Ea is the thermal quenching activation energy during the transformation of diamond NV center, kb is the Boltzmann constant, and the thermal quenching activation energies of diamond NV0 and NV centers are 63 and 96 meV, respectively. Under the influence of temperature, nonradiative transitions dominate the transition process of emitting electrons, and the ZPL intensity at the NV centers progressively decreases as the measurement temperature rises, which manifested by the occurrence of the intensity quenching phenomenon. The difference between the ground state and excited state intersection point and the excited state minimum value yields the thermal quenching activation energy of the NV center.30 
FIG. 5.

PL spectra (1% power level) of high nitrogen diamond at various measurement temperatures (80–280 K) after annealing at 1350 °C. (a) The variation in the NV center strength with measurement temperature; (b) NV/NV0 ratio at various measurement temperatures.

FIG. 5.

PL spectra (1% power level) of high nitrogen diamond at various measurement temperatures (80–280 K) after annealing at 1350 °C. (a) The variation in the NV center strength with measurement temperature; (b) NV/NV0 ratio at various measurement temperatures.

Close modal

The intensity ratio of NV charge states (NV/NV0) at various measurement temperatures is displayed in Fig. 5(b). It is evident from Fig. 5(b) that as the measured temperature rises, the intensity ratio shows an upward trend, but the overall upward trend is relatively small. This phenomenon is significantly different from the research of Guo et al. In their report, there was no significant change in the NV/NV0 ratio as the measurement temperature increased.31 The main reason for this discrepancy is that the alternative nitrogen atom content was likewise extremely low in the diamond sample used in Guo's experiment due to its extremely low nitrogen content. There is much nitrogen in the diamond sample that was used in this experiment. Thus, a high number of substituted nitrogen atoms influence the charge state between NV centers as the measurement temperature rises. In spite of the possibility that some of the substitution nitrogen atoms (nitrogen substituting the position of carbon atom) absorb nitrogen vacancy center and create NV defects, electrons gradually break away from the frozen state and migrate, while still combining with nearby NV defects to form NV centers. Meanwhile, Groot-Berning reported on the donor behavior of phosphorus and the acceptor behavior of boron.32 Similar to phosphorus ion implantation, As ion implantation is beneficial for stabilizing and increasing the yield of NV centers. In addition, because of the amorphization brought caused by arsenic ion implantation, the sample could recover fewer vacancies after annealing, and the yield of NV centers is relatively low, leading to a low overall intensity of NV charge states, ranging from 0.1 to 0.2.

Figure 6 shows the trend of FWHM and ZPL centers changing with temperature. The FWHM increases as the measuring temperature rises, and there is a significant red shift phenomenon in the ZPL centers. The temperature dependence of the FWHM for the NV0 and NV centers is depicted in Fig. 6(a). The changes in these values can be explained by the formula: ω = m0 + n0T3, in which m0 and n0 are constants. From Fig. 6(b), it is noticeable that when the temperature rises, the ZPL centers of NV and NV0 both exhibit peak redshift, with the maximum displacement of NV and NV0 centers being 1.16 and 0.75 nm, respectively. A linear shift (δE) is produced in the PL spectrum by the collective action of secondary electron–phonon coupling and lattice expansion.33 The trend of linear displacement with temperature T can follow the formula: δE = a0T4 + b0T2 + c0, where the constants are a0, b0, and c0, δE = δE (80 K) − δE (T). T4 and T2 are attributed to the combined effect of lattice vibration and electron–phonon coupling and the thermal softening effect of the chemical bond,34,35 respectively. Guo et al. believed that the enhanced “hardness”31 of diamond atomic structures with fault structures can be attributed to a smaller ZPL displacement. Therefore, we also believe that the NV0 centers in this experiment have a higher “hardness” than the NV centers.

FIG. 6.

Temperature-dependent PL spectra of high nitrogen diamond following annealing at 1350 °C. (a) The variation in the ZPL position with temperature; (b) the variation in the FWHM with temperature.

FIG. 6.

Temperature-dependent PL spectra of high nitrogen diamond following annealing at 1350 °C. (a) The variation in the ZPL position with temperature; (b) the variation in the FWHM with temperature.

Close modal

In summary, we used photoluminescence to investigate the temperature dependence of the relevant NV centers after high-temperature annealing of high nitrogen diamond implanted with arsenic ions. After high-temperature annealing, the degree of graphitization of diamond implanted with arsenic ions is significant. The results indicate that as the laser excitation power increases, the sublinear growth in NV centers is caused by bound electrons and diamond graphitization, while radiation recombination and Auger recombination operate simultaneously on the NV0 and NV centers. However, compared to low nitrogen diamond, the degree of ionization conversion of the NV centers is not high. In addition, as the measurement temperature increases, the concentration of NV centers is higher than that of NV0 centers. This is attributed to the high concentration of NS0 in high nitrogen diamonds, which provides electrons for nearby NV defects to form NV centers. However, the variation in the NV/NV0 ratio is not significant, and the temperature has a strong dependence on the displacement of ZPLs and the increase in the FWHM. The broadening FWHM of ZPL provides the best fitting with the curve of ω = m0 + n0T3. The red shift of ZPLs under the interplay of lattice expansion and higher electron–phonon coupling strength may be characterized as δE = a0T4 + b0T2 + c0 as the temperature increases.

This work was supported by the National Natural Science Foundation of China (NNSFC) (Grant No. U21A2073) and Shanxi Province Natural Science Foundation (Grant Nos. 202303021211210 and 202203021222207).

The authors have no conflicts to disclose

Chenyang Huangfu: Formal analysis (equal); Investigation (equal); Methodology (equal); Writing – original draft (equal). Yufei Zhang: Conceptualization (equal); Supervision (equal); Visualization (equal); Writing – review & editing (equal). Jinchen Hao: Project administration (equal); Supervision (equal). Gangyuan Jia: Project administration (equal); Supervision (equal). Haitao Wu: Writing – review & editing (equal). Xujie Wang: Writing – review & editing (equal). Wei Wang: Conceptualization (equal); Supervision (equal); Visualization (equal); Writing – review & editing (equal). Kaiyue Wang: Conceptualization (equal); Supervision (equal); Visualization (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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