The impact of oxidation temperature on the formation of single photon-emitting defects located at the silicon dioxide (SiO2)/silicon carbide (SiC) interface was investigated. Thermal oxidation was performed in the temperature range between 900 and 1300 °C. After oxidation, two different cooling processes—cooling down in N2 or O2 ambient—were adopted. Single photon emission was confirmed with second-order correlation function measurements. For the samples cooled in an N2 ambient, the density of interface single photon sources (SPSs) increased with decreasing oxidation temperature with a density that could be controlled over the 105 to 108 cm−2 range. For the O2 cooled samples, on the other hand, many interface SPSs were formed irrespective of the oxidation temperature. This is attributed to the low-temperature oxidation during the cooling process after oxidation.

A single photon source (SPS) is recognized as one of the most promising key components to realize quantum sensing and quantum cryptography. Some point defects in wide bandgap semiconductors are known to exhibit single photon emission and are known as “color centers.” They have several advantages compared to fluorescence of a wide range of quantum systems (e.g., trapped ions, single molecules, and carbon nanotubes), such as room temperature operation and integration with semiconductor devices. The negatively charged nitrogen-vacancy in diamonds emits single photons at room temperature and is widely acknowledged as the most investigated and advanced color center.1–3 Silicon carbide (SiC) also harbors color centers, and the negatively charged silicon vacancy (VSi) receives much attention.4–8 Controlling the spin of a single VSi has been reported.9 Although such color centers are promising, one of the disadvantages is their relatively low brightness and low spin contrast. SPSs also exist at the interface of silicon dioxide (SiO2) and SiC, and they exhibit photons at least an order of magnitude brighter than the other color centers in SiC.10–14 However, the defect structure of the interface SPS has not been clarified and its density is not well controlled. Since the interface SPSs can be easily formed by thermal oxidation, the formation process of thermal oxides differs from one laboratory to another, leading to a poor understanding of the interface SPSs.

In this study, the impact of oxidation temperature on the density of the interface SPS was investigated. The density of the interface SPSs can be controlled over a broad range from 105 to 108 cm−2 by simply changing the oxidation temperature. The samples oxidized at low temperatures include high densities of the interface SPS. The similarity in the oxidation temperature dependence of the interface SPS to that of the interface states near the conduction band edge indicates that the origin of the interface SPSs is likely a carbon-related defect. In addition to that, defects at the SiO2/SiC interface play an important role as not only SPSs for quantum technology but scattering centers in a metal–oxide–semiconductor field-effect transistor for power electronics. Since the interface SPSs originate from some kinds of SiO2/SiC interface defects, several research groups have recently proposed that the photoluminescence (PL) mapping for the interface SPSs can be an alternative method to characterize the interface quality.13,15,16 From this point of view, the relationship between the SPS density and interface state density (Dit) obtained in this study is also briefly discussed.

High-purity semi-insulating 4H-SiC(0001) substrates grown by high-temperature chemical vapor deposition were used in this study. The substrates were dipped in H2SO4 + H2O2, HCl, HCl + HNO3, and HF solutions. Then, the substrates were rinsed in de-ionized water and loaded into an oxidation furnace. The furnace temperature was raised to the oxidation temperature at a ramping rate of 20 °C/min with an O2 gas flow. The oxidation temperature was changed from 900 to 1300 °C. The oxidation time varied in the range of 5 min to 20 h. After the thermal oxidation, we adopted two different cooling processes: (i) cooling down in O2 ambient (O2 cooling) and (ii) changing the gas flow from O2 to N2 before cooling (N2 cooling). The cooling rate was 5 °C/min for both cooling processes. The SiO2 thickness was in the range of 2 to 35 nm, which was measured by spectroscopic ellipsometry.

The optical experimental setup consisted of a stage scanning confocal microscope, as shown in Fig. 1.17,18 The excitation laser was a continuous-wave laser (λ = 532 nm), and the laser power was 6–9 mW before an objective lens. Note that the defects characterized and analyzed in this study are limited to those accessible by the 532-nm laser. When a laser with another wavelength is used, different defects can be measured.10 The samples were mounted on a three-axis piezo actuator and scanned at a step size of 200 nm with an objective lens with a numerical aperture of 0.9. The luminescence from the samples was collected with the same objective lens and measured by a single-photon counting module (SPCM) or a spectrometer equipped with a charge coupled device camera. The second-order correlation function g2(τ) was also measured using two SPCMs. In order to cut the excitation light, a 575 or 600-nm long-pass filter was placed in front of the multi-mode fiber with a core diameter of about 10 μm (SMF-28) to propagate the photons to the SPCMs or the spectrometer, respectively. We manually counted the number of bright spots in the PL mapping image. Note that a bright spot may include more than one SPS when SPSs are located within the diffraction-limited volume. All measurements were performed at room temperature.

FIG. 1.

Experimental setup. Laser light is focused using an objective lens. The fluorescence collected with the objective lens is analyzed using the single-photon counting modules or the spectrometer.

FIG. 1.

Experimental setup. Laser light is focused using an objective lens. The fluorescence collected with the objective lens is analyzed using the single-photon counting modules or the spectrometer.

Close modal

We also prepared n-type 4H-SiC (0001) epilayers with a donor density of 1 × 1017 cm−3 on n-type substrates to form metal–oxide–semiconductor capacitors. The n-type epilayers were chemically cleaned and oxidized at 1300 °C at the same time as the semi-insulating substrates were oxidized. After the oxidation, circular Al electrodes were deposited (diameter: 300–500 μm). The quasi-static and 1 MHz capacitance-voltage measurements were performed to extract the Dit.

Figure 2 shows confocal scanning images of the samples oxidized at temperatures of 900, 1100, and 1300 °C. Figures 2(a)2(c) and 2(d)2(f) are acquired from the samples with O2 cooling and N2 cooling, respectively. In the case of O2 cooling, lots of bright spots are confirmed and no significant difference can be seen among the samples oxidized at the different oxidation temperatures. On the other hand, bright spots remarkably decreased with elevating the oxidation temperature for the N2 cooled samples [Figs. 2(d)2(f)]. We did not observe any single bright spots from the sample oxidized at 1300 °C with N2 cooling even when the scanning area was expanded to 50 × 50 μm2.

FIG. 2.

Confocal scanning images (20 × 20 μm2) of the SiC samples oxidized at the temperatures of 900, 1100, and 1300 °C with (a)–(c) O2 cooling and (d)–(f) N2 cooling.

FIG. 2.

Confocal scanning images (20 × 20 μm2) of the SiC samples oxidized at the temperatures of 900, 1100, and 1300 °C with (a)–(c) O2 cooling and (d)–(f) N2 cooling.

Close modal

The second-order correlation function g2(τ) of bright spots in the samples oxidized at 1100 °C with O2 cooling and N2 cooling is depicted in Figs. 3(a) and 3(b), respectively. Note that the experimental data were normalized and corrected in the way described in Ref. 19. A dip at around zero delay is not clearly obtained from the sample with O2 cooling. The bright spot of the sample with O2 cooling may consist of a few SPSs owing to its high density [Fig. 2(b)]. On the other hand, from the sample with N2 cooling, a sharp dip is observed, meaning that well isolated SPSs were formed. The red curve shown in Fig. 3(b) shows the fitting result using a three-level model.20 The g2(0) is estimated to be 0.2, which is less than 0.5. Then, bright spots observed in the scanning images are regarded as interface SPSs. Note that one main reason why g2(0) is not zero even for the fitting result is due to the timing jitter of the phonon detectors.21 The photoluminescence (PL) spectra from bright spots in the samples oxidized at 1100 °C with O2 cooling and N2 cooling are shown in Figs. 3(c) and 3(d), respectively. The spectra exhibit wide variability in the emission peaks. Note that the peaks include zero-phonon lines and phonon sidebands. The peak wavelength is in the range between 600 and 750 nm, which is consistent with previous studies using an excitation laser with a wavelength of 532 nm.12,13 Many peaks in the PL spectra from the O2 cooling sample are detected, whose number is larger than that from the N2 cooling sample, supporting that g2(0) becomes unity in the O2 cooling sample [Fig. 3(a)] due to several SPSs located at bright spots within the excitation volume of the laser.

FIG. 3.

A second-order correlation function g2(τ) of bright spots in the samples oxidized at 1100 °C with (a) O2 cooling and (b) N2 cooling. The red curve shown in (b) represents the fitting result using a three-level model. Examples of photoluminescence spectra from bright spots in the sample oxidized with (c) O2 cooling and (d) N2 cooling.

FIG. 3.

A second-order correlation function g2(τ) of bright spots in the samples oxidized at 1100 °C with (a) O2 cooling and (b) N2 cooling. The red curve shown in (b) represents the fitting result using a three-level model. Examples of photoluminescence spectra from bright spots in the sample oxidized with (c) O2 cooling and (d) N2 cooling.

Close modal

Figure 4 depicts the oxidation time dependence of the bright spot density. The oxidation was performed at a temperature of 1150 °C with N2 cooling, and the oxidation time varied from 5 to 300 min. The bright spot density does not strongly depend on the oxidation time and reaches around 2 × 106 cm−2 except for the sample that was oxidized for 5 min. The relatively low density of the 5-min oxidation sample is attributed to the very short oxidation time (SiO2 thickness: 3 nm). Bright spot density saturates at a certain value soon after oxidation proceeds.

FIG. 4.

Dependence of bright spot density on oxidation time at the oxidation temperature of 1150 °C.

FIG. 4.

Dependence of bright spot density on oxidation time at the oxidation temperature of 1150 °C.

Close modal

The oxidation temperature dependence of the bright spot density is shown in Fig. 5(a). As shown in Figs. 2(a)2(c), the bright spot density of the samples with O2 cooling is high and does not depend on the oxidation temperature. On the other hand, the bright spot density of the samples with N2 cooling dramatically decreases with elevating the temperature and control of the bright spot (interface SPS) density in the range from 105 to 108 cm−2 is achieved by changing the oxidation temperature.

FIG. 5.

(a) Bright spot density vs oxidation temperature in the SiO2/SiC structure. Black squares and red circles represent the samples with O2 cooling and N2 cooling, respectively. (b) Arrhenius plot of the bright spot density (N2 cooling).

FIG. 5.

(a) Bright spot density vs oxidation temperature in the SiO2/SiC structure. Black squares and red circles represent the samples with O2 cooling and N2 cooling, respectively. (b) Arrhenius plot of the bright spot density (N2 cooling).

Close modal

First, we discuss why the bright spot (interface SPS) density does not vary depending on the oxidation temperature for the samples with O2 cooling. During the cooling period after the oxidation with an O2 gas flow, oxidation at the SiO2/SiC interface slightly proceeds. The bright spot density in the samples with O2 cooling was close to that in the sample oxidized at the lowest temperature (900 °C) with N2 cooling. According to previous studies, the SiC(0001) surface is known to be oxidized at 900 °C, whereas oxidation hardly proceeds at 800 °C.22 Considering that all the samples with O2 cooling were slightly oxidized at 900 °C or lower during the cooling process, the present result suggests that the bright spot density is determined by the temperature at which the oxidation takes place at last, regardless of what temperature the sample was previously oxidized at. To examine this hypothesis, we prepared a SiC sample oxidized at a low temperature (900 °C) with O2 cooling and subsequently oxidized the SiC at a high temperature (1300 °C) with N2 cooling. Confocal scanning images of this sample (not shown) revealed that bright spots, whose density was consistent with the density extracted from Fig. 2(a) (900 °C, O2 cooling), were formed at the first oxidation step, and they were removed by the next high-temperature oxidation, which clearly indicates that the bright spot density is determined by the oxidation condition performed at last.

The defect structure of SPSs at a SiO2/SiC interface has not been identified yet, and we briefly discuss the origin of the SPSs. A SiO2/SiC interface works as a channel of a SiC metal–oxide–semiconductor field-effect transistor, which is of importance as a next generation power device to reduce energy loss, and intensive research has been done to investigate defects at the SiO2/SiC interface.23 It has been reported that unintentional oxidation during cooling down after oxidation introduces interface states whose density is higher than that in the sample without oxidation during the cooling process.24 Reference 24 reported that the Dit (and flat band shift) does not depend on the oxidation temperature for the samples oxidized with O2 cooling. The reason for a lower density of interface states in the sample oxidized without unintentional oxidation during cooling down was explained by favorable out-diffusion of COx, whereas excess carbon atoms remained at the SiO2/SiC interface when low-temperature oxidation occurred. High-temperature oxidation effectively reduces such excess carbon-related defects (interface states).25 The energy distributions of the Dit estimated by a high (1 MHz)-low method are given in Fig. 6. The lower Dit was obtained from the sample oxidized with N2 cooling, which is the same trend given in the literature.24 Taking account of the similarity between the temperature dependence of the Dit and the bright spot density, the SPSs observed in this study may originate from carbon-related defects. Figure 7 illustrates excitation and emission polarization measurements of bright spots observed at the SiO2/SiC interface. As previously reported,11,26 we also confirmed that the interface SPSs measured in this study hold emission and absorption dipoles that are aligned with the SiC lattice, indicating that the defects are located on the SiC side (not in the oxide layer). First-principles calculations predict that dicarbon antisites (defects), which are located on the SiC side, are easily introduced by low-temperature oxidation and form multiple energy levels inside the energy bandgap of SiC.27,28 Such a carbon-related defect is a possible origin of the interface SPSs. Note that the Arrhenius plot of the bright spot density [Fig. 5(b)] yields the activation energy of −(3.8 ± 1.0) eV, which is close to the absolute value of the activation energy of the SiO2 growth rate (2.9 eV).24 The removal rate of the SPSs, or the reduction rate of the excess carbon-related defects, may be determined by the oxidation rate.

FIG. 6.

Energy distribution of the interface state density of the sample oxidized at 1300 °C with O2 and N2 cooling extracted by the high (1 MHz)-low method.

FIG. 6.

Energy distribution of the interface state density of the sample oxidized at 1300 °C with O2 and N2 cooling extracted by the high (1 MHz)-low method.

Close modal
FIG. 7.

(a) Excitation and (b) emission polarization measurements of three bright spots observed at the SiO2/SiC interface. The red, blue, and yellow dots show the measurement results for different bright spots.

FIG. 7.

(a) Excitation and (b) emission polarization measurements of three bright spots observed at the SiO2/SiC interface. The red, blue, and yellow dots show the measurement results for different bright spots.

Close modal

The origin of the SPS interface is a controversial issue. Hijikata et al. proposed that oxygen-vacancy defects are the possible origin of the interface SPSs by comparing their experimental results with the ab initio study.14 Although we believe that the results obtained in this study can be explained by considering the origin of the interface SPSs as carbon-related defects, our study does not exclude oxygen-vacancy defects as a candidate for the origin of the interface SPSs. Further studies are required to clarify the specific defect structure of the interface SPS.

As briefly discussed in the Introduction, PL mapping receives attention as a technique to characterize the SiO2/SiC interface quality. Woerle et al. reported that the interface SPS density depends on the Dit, which was electrically measured.15 In this study, the higher Dit was obtained from the sample with the highest SPS density (1300 °C with O2 cooling) compared with the sample with almost no SPSs (1300 °C with N2 cooling), which partly agrees with the results given in the literature.13,15 It is well known that the as-oxidized SiO2/SiC interface includes high Dit and post-oxidation annealing in nitric-oxide (NO) effectively reduces Dit. Even for the sample with low SPS density (1300 °C with N2 cooling) obtained in this study, the Dit is still high compared to that of the NO-annealed SiO2/SiC interface.29 Then, we conclude that a low SPS density indicates that the SiC was oxidized at a high temperature but does not ensure that the Dit is as low as that with NO annealing. Although PL mapping using a confocal microscope could be a noncontact, nondestructive, spatially resolved technique to assess the quality of the SiO2/SiC interface, interface states consist of many types of defects and further studies are required to clarify which type of defects can be characterized by the PL mapping method.

In this study, the oxidation temperature of SiC was systematically varied and its impact on the density of photon-emitting defects was investigated. For the samples cooled in an N2 ambient, the bright spot density monotonically decreased with increasing the oxidation temperature and was controlled in the wide range from 105 to 108 cm−2. The SPSs tended to be formed by oxidation at low temperatures. The similarity between the temperature dependence of the SPS density and that of the SiO2/SiC interface state density indicates that the origin of SPSs is likely a carbon-related defect. Identification of the atomistic structure of the defect is required for understanding and controlling the physical properties of the defect.

We gratefully acknowledge the financial support in the form of Kakenhi Grants-in-Aid (Grant Nos. 21H04444 and 22H01155) from the Japan Society for the Promotion of Science (JSPS) and the MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) (Grant No. JPMXS0118067634). H.T. acknowledges JST, PRESTO Grant No. JPMJPR2257, Japan.

The authors have no conflicts to disclose.

Mitsuaki Kaneko: Conceptualization (lead); Data curation (lead); Formal analysis (lead); Investigation (lead); Project administration (lead); Validation (lead); Visualization (lead); Writing – original draft (lead). Hideaki Takashima: Data curation (supporting); Formal analysis (supporting); Investigation (supporting); Methodology (lead); Software (lead); Writing – review & editing (supporting). Konosuke Shimazaki: Data curation (supporting); Investigation (supporting); Methodology (supporting); Visualization (lead); Writing – review & editing (supporting). Shigeki Takeuchi: Funding acquisition (lead); Resources (lead); Supervision (lead); Writing – review & editing (lead). Tsunenobu Kimoto: Funding acquisition (lead); Resources (lead); Supervision (lead); Writing – review & editing (lead).

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

1.
A.
Gruber
,
A.
Dräbenstedt
,
C.
Tietz
,
L.
Fleury
,
J.
Wrachtrup
, and
C. V.
Borczyskowski
, “
Scanning confocal optical microscopy and magnetic resonance on single defect centers
,”
Science
276
,
2012
2014
(
1997
).
2.
M.
Pompili
,
S. L. N.
Hermans
,
S.
Baier
,
H. K. C.
Beukers
,
P. C.
Humphreys
,
R. N.
Schouten
,
R. F. L.
Vermeulen
,
M. J.
Tiggelman
,
L.
dos Santos Martins
,
B.
Dirkse
,
S.
Wehner
, and
R.
Hanson
, “
Realization of a multinode quantum network of remote solid-state qubits
,”
Science
372
,
259
264
(
2021
).
3.
R.
Schirhagl
,
K.
Chang
,
M.
Loretz
, and
C. L.
Degen
, “
Nitrogen-vacancy centers in diamond: nanoscale sensors for physics and biology
,”
Annu. Rev. Phys. Chem.
65
,
83
105
(
2014
).
4.
H.
Kraus
,
D.
Simin
,
C.
Kasper
,
Y.
Suda
,
S.
Kawabata
,
W.
Kada
,
T.
Honda
,
Y.
Hijikata
,
T.
Ohshima
,
V.
Dyakonov
, and
G. V.
Astakhov
, “
Three-dimensional proton beam writing of optically active coherent vacancy spins in silicon carbide
,”
Nano Lett.
17
,
2865
2870
(
2017
).
5.
M. E.
Bathen
,
A.
Galeckas
,
J.
Müting
,
H. M.
Ayedh
,
U.
Grossner
,
J.
Coutinho
,
Y. K.
Frodason
, and
L.
Vines
, “
Electrical charge state identification and control for the silicon vacancy in 4H-SiC
,”
Npj Quantum Inf.
5
,
111
(
2019
).
6.
M.
Widmann
,
M.
Niethammer
,
D. Y.
Fedyanin
,
I. A.
Khramtsov
,
T.
Rendler
,
I. D.
Booker
,
J.
Ul Hassan
,
N.
Morioka
,
Y.-C.
Chen
,
I. G.
Ivanov
,
N. T.
Son
,
T.
Ohshima
,
M.
Bockstedte
,
A.
Gali
,
C.
Bonato
,
S.-Y.
Lee
, and
J.
Wrachtrup
, “
Electrical charge state manipulation of single silicon vacancies in a silicon carbide quantum optoelectronic device
,”
Nano Lett.
19
,
7173
7180
(
2019
).
7.
M.
Niethammer
,
M.
Widmann
,
T.
Rendler
,
N.
Morioka
,
Y.-C.
Chen
,
R.
Stöhr
,
J. U.
Hassan
,
S.
Onoda
,
T.
Ohshima
,
S.-Y.
Lee
,
A.
Mukherjee
,
J.
Isoya
,
N. T.
Son
, and
J.
Wrachtrup
, “
Coherent electrical readout of defect spins in silicon carbide by photo-ionization at ambient conditions
,”
Nat. Commun.
10
,
5569
(
2019
).
8.
T.
Nishikawa
,
N.
Morioka
,
H.
Abe
,
H.
Morishita
,
T.
Ohshima
, and
N.
Mizuochi
, “
Electrical detection of nuclear spins via silicon vacancies in silicon carbide at room temperature
,”
Appl. Phys. Lett.
121
,
184005
(
2022
).
9.
M.
Widmann
,
S.-Y.
Lee
,
T.
Rendler
,
N. T.
Son
,
H.
Fedder
,
S.
Paik
,
L.-P.
Yang
,
N.
Zhao
,
S.
Yang
,
I.
Booker
,
A.
Denisenko
,
M.
Jamali
,
S. A.
Momenzadeh
,
I.
Gerhardt
,
T.
Ohshima
,
A.
Gali
,
E.
Janzén
, and
J.
Wrachtrup
, “
Coherent control of single spins in silicon carbide at room temperature
,”
Nat. Mater.
14
,
164
168
(
2015
).
10.
A.
Lohrmann
,
N.
Iwamoto
,
Z.
Bodrog
,
S.
Castelletto
,
T.
Ohshima
,
T. J.
Karle
,
A.
Gali
,
S.
Prawer
,
J. C.
McCallum
, and
B. C.
Johnson
, “
Single-photon emitting diode in silicon carbide
,”
Nat. Commun.
6
,
7783
(
2015
).
11.
A.
Lohrmann
,
S.
Castelletto
,
J. R.
Klein
,
T.
Ohshima
,
M.
Bosi
,
M.
Negri
,
D. W. M.
Lau
,
B. C.
Gibson
,
S.
Prawer
,
J. C.
McCallum
, and
B. C.
Johnson
, “
Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation
,”
Appl. Phys. Lett.
108
,
021107
(
2016
).
12.
Y.
Abe
,
T.
Umeda
,
M.
Okamoto
,
R.
Kosugi
,
S.
Harada
,
M.
Haruyama
,
W.
Kada
,
O.
Hanaizumi
,
S.
Onoda
, and
T.
Ohshima
, “
Single photon sources in 4H-SiC metal-oxide-semiconductor field-effect transistors
,”
Appl. Phys. Lett.
112
,
031105
(
2018
).
13.
B. C.
Johnson
,
J.
Woerle
,
D.
Haasmann
,
C. T.-K.
Lew
,
R. A.
Parker
,
H.
Knowles
,
B.
Pingault
,
M.
Atature
,
A.
Gali
,
S.
Dimitrijev
,
M.
Camarda
, and
J. C.
McCallum
, “
Optically active defects at the SiC/SiO2 interface
,”
Phys. Rev. Appl.
12
,
044024
(
2019
).
14.
Y.
Hijikata
,
S.
Komori
,
S.
Otojima
,
Y.-I.
Matsushita
, and
T.
Ohshima
, “
Impact of formation process on the radiation properties of single-photon sources generated on SiC crystal surfaces
,”
Appl. Phys. Lett.
118
,
204005
(
2021
).
15.
J.
Woerle
,
B. C.
Johnson
,
C.
Bongiorno
,
K.
Yamasue
,
G.
Ferro
,
D.
Dutta
,
T. A.
Jung
,
H.
Sigg
,
Y.
Cho
,
U.
Grossner
, and
M.
Camarda
, “
Two-dimensional defect mapping of the SiO2/4H-SiC interface
,”
Phys. Rev. Mater.
3
,
084602
(
2019
).
16.
J.
Woerle
,
B. C.
Johnson
,
R.
Stark
,
M.
Camarda
, and
U.
Grossner
, “
Fast defect mapping at the SiO2/SiC interface using confocal photoluminescence
,”
Mater. Sci. Forum
1062
,
389
394
(
2022
).
17.
K.
Shimazaki
,
H.
Kawaguchi
,
H.
Takashima
,
T. F.
Segawa
,
F. T.-K.
So
,
D.
Terada
,
S.
Onoda
,
T.
Ohshima
,
M.
Shirakawa
, and
S.
Takeuchi
, “
Fabrication of detonation nanodiamonds containing silicon-vacancy color centers by high temperature annealing
,”
Phys. Status Solidi A
218
,
2100144
(
2021
).
18.
K.
Fukushige
,
H.
Kawaguchi
,
K.
Shimazaki
,
T.
Tashima
,
H.
Takashima
, and
S.
Takeuchi
, “
Identification of the orientation of a single NV center in a nanodiamond using a three-dimensionally controlled magnetic field
,”
Appl. Phys. Lett.
116
,
264002
(
2020
).
19.
A.
Beveratos
,
S.
Kühn
,
R.
Brouri
,
T.
Gacoin
,
J.-P.
Poizat
, and
P.
Grangier
, “
Room temperature stable single-photon source
,”
Eur. Phys. J. D
18
,
191
196
(
2002
).
20.
R. N.
Patel
,
T.
Schröder
,
N.
Wan
,
L.
Li
,
S. L.
Mouradian
,
E. H.
Chen
, and
D. R.
Englund
, “
Efficient photon coupling from a diamond nitrogen vacancy center by integration with silica fiber
,”
Light: Sci. Appl.
5
,
e16032
(
2016
).
21.
H.
Takashima
,
A.
Fukuda
,
K.
Shimazaki
,
Y.
Iwabata
,
H.
Kawaguchi
,
A. W.
Schell
,
T.
Tashima
,
H.
Abe
,
S.
Onoda
,
T.
Ohshima
, and
S.
Takeuchi
, “
Creation of silicon vacancy color centers with a narrow emission line in nanodiamonds by ion implantation
,”
Opt. Mater. Express
11
,
1978
(
2021
).
22.
T.
Kobayashi
,
T.
Okuda
,
K.
Tachiki
,
K.
Ito
,
Y.-i.
Matsushita
, and
T.
Kimoto
, “
Design and formation of SiC (0001)/SiO2 interfaces via Si deposition followed by low-temperature oxidation and high-temperature nitridation
,”
Appl. Phys. Express
13
,
091003
(
2020
).
23.
T.
Kimoto
and
H.
Watanabe
, “
Defect engineering in SiC technology for high-voltage power devices
,”
Appl. Phys. Express
13
,
120101
(
2020
).
24.
T.
Hosoi
,
D.
Nagai
,
M.
Sometani
,
Y.
Katsu
,
H.
Takeda
,
T.
Shimura
,
M.
Takei
, and
H.
Watanabe
, “
Ultrahigh-temperature rapid thermal oxidation of 4H-SiC(0001) surfaces and oxidation temperature dependence of SiO2/SiC interface properties
,”
Appl. Phys. Lett.
109
,
182114
(
2016
).
25.
T.
Hosoi
,
Y.
Katsu
,
K.
Moges
,
D.
Nagai
,
M.
Sometani
,
H.
Tsuji
,
T.
Shimura
, and
H.
Watanabe
, “
Passive–active oxidation boundary for thermal oxidation of 4H-SiC(0001) surface in O2/Ar gas mixture and its impact on SiO2/SiC interface quality
,”
Appl. Phys. Express
11
,
091301
(
2018
).
26.
M.
Widmann
,
M.
Niethammer
,
T.
Makino
,
T.
Rendler
,
S.
Lasse
,
T.
Ohshima
,
J.
Ul Hassan
,
N.
Tien Son
,
S.-Y.
Lee
, and
J.
Wrachtrup
, “
Bright single photon sources in lateral silicon carbide light emitting diodes
,”
Appl. Phys. Lett.
112
,
231103
(
2018
).
27.
S.
Wang
,
S.
Dhar
,
S.-r.
Wang
,
A. C.
Ahyi
,
A.
Franceschetti
,
J. R.
Williams
,
L. C.
Feldman
, and
S. T.
Pantelides
, “
Bonding at the SiC–SiO2 interface and the effects of nitrogen and hydrogen
,”
Phys. Rev. Lett.
98
,
026101
(
2007
).
28.
T.
Kobayashi
and
Y.-i.
Matsushita
, “
Structure and energetics of carbon defects in SiC (0001)/SiO2 systems at realistic temperatures: Defects in SiC, SiO2, and at their interface
,”
J. Appl. Phys.
126
,
145302
(
2019
).
29.
K.
Tachiki
,
M.
Kaneko
, and
T.
Kimoto
, “
Mobility improvement of 4H-SiC (0001) MOSFETs by a three-step process of H2 etching, SiO2 deposition, and interface nitridation
,”
Appl. Phys. Express
14
,
031001
(
2021
).