Electrical detection of TV2a-type siliconvacancy spin defect in 4H-SiC MOSFETs
Cite as: Appl. Phys. Lett. 120, 064001 (2022); https://doi.org/10.1063/5.0078189
Submitted: 11 November 2021 • Accepted: 11 January 2022 • Published Online: 08 February 2022
Yuta Abe, Akihumi Chaen,

Mitsuru Sometani, et al.

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Appl. Phys. Lett. 120, 064001 (2022); https://doi.org/10.1063/5.0078189© 2022 Author(s).

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Electrical detection of TV2a-type silicon vacancy
spin defect in 4H-SiC MOSFETs
Cite as: Appl. Phys. Lett. 120, 064001 (2022); doi: 10.1063/5.0078189
Submitted: 11 November 2021 . Accepted: 11 January 2022 .
Published Online: 8 February 2022
Yuta Abe,1,2
Akihumi Chaen,1 Mitsuru Sometani,3Takeshi Ohshima,1,2
and Takahide Umeda1,a)Shinsuke Harada,3 Yuichi Yamazaki,2

AFFILIATIONS
1Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573, Japan

2
3

National Institutes for Quantum Science and Technology (QST), Takasaki 370-1292, Japan
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japana)

Author to whom correspondence should be addressed: umeda.takahide.fm@u.tsukuba.ac.jp

ABSTRACT
Color centers in silicon carbide (4H-SiC) are potentially usable as spin defects for quantum sensing and quantum information technology. In
particular, neutral divacancies (the P6/P7centers, VSiVC0) and a certain type of silicon vacancies (the TV2a center, VSi- at the k site) arepromising for addressing and manipulating single spins. Although the TV2a spin is readable at room temperature, the readout techniques
have been limited to luminescence-based ones (e.g., optically detected magnetic resonance). In this study, we demonstrated electrical detection of TV2a-type silicon vacancies at room temperature by using electrically detected magnetic resonance on 4H-SiC metal–oxide–semiconductor ﬁeld effect transistors (MOSFETs). TV2a spin defects were embedded in the channel region of well-deﬁned 4H-SiC MOSFETs via
controlled proton irradiation. The number of detected TV2a spins was estimated to be 105. We also found that the charge state of the TV2aspin defect can be controlled by varying the gate voltage applied to the MOSFET.
Published under an exclusive license by AIP Publishing. https://doi.org/10.1063/5.0078189

Color centers in wide-bandgap semiconductors are potentiallyusable as spin defects or spin qubits for quantum sensing,1 quantum
communication,2 and quantum computing.3 The negatively charged
nitrogen-vacancy center (the NV center, electron spin S ¼ 1) in diamond is the most widely studied spin qubit, because it shows not only
extremely strong luminescence but also its spin states that can be
manipulated and readout at room temperature.4 Another promising
host platform for spin defects is silicon carbide (4H-SiC).5 4H-SiC
shows great potential for integration of various electronic devices [pndiodes, bipolar transistors, junction- and metal–oxide–semiconductorﬁeld effect transistors (JFETs and MOSFETs) and complementaryMOS (CMOS) circuits.6 In particular, 4H-SiC is regarded as a suitable
integration platform for electronic and quantum devices. So far,single-spin addressing and single-spin manipulation have been alreadydemonstrated using spin defects in 4H-SiC.7–10 4H-SiC has two promising spin defects: a negatively charged silicon vacancy formed at the ksite (the TV2a center, k-site VSi, S ¼ 3/2)7,8 and neutral divacancies(the P6/P7 centers, VSiVC0, S ¼ 1).9,10 The VSi center is the mostwidely studied, because its optically detected magnetic resonance(ODMR) is detectable at room temperature.7,8 Furthermore, creationof VSi by versatile means such as proton beam writing11 makes it

Appl. Phys. Lett. 120, 064001 (2022); doi: 10.1063/5.0078189
Published under an exclusive license by AIP Publishingpossible to design hybrid electronic and quantum devices. However,the VSi center has a much weaker ODMR contrast than that of NV.
To develop other readout techniques as well as all-electrical quantum
devices, electrical detection of the VSi spin is desirable. Actually, electrical detection of NV centers in diamond has recently been demonstrated.12 In 4H-SiC, electrically detected magnetic resonance (EDMR)
was used to detect the VSi signal in the device currents of 4H-SiC pn
diodes13 and 4H-SiC MOSFETs.14 In MOSFETs, VSi centers weregenerated as MOS interfacial defects,14 while in pn diodes, they wereintentionally created by irradiation.13 In the latter case, a strong electrical signal was observed and utilized for high-sensitivity magnetic
sensing.14 Namely, the VSi spin is most probably highly active to electrical currents. However, the detected VSi center is not the TV2a center [VSi(k)], which is realized the single spin manipulation at room
temperature, but rather only another VSi center [negatively charged
silicon vacancy formed at the h site, VSi(h)]. So far, the TV2a-typespin defect has not been detected electrically.
In this Letter, we demonstrate electrical detection of the TV2aspin defect by using the EDMR technique on a proton-irradiated
4H-SiC(0001) MOSFET. The TV2a centers were carefully created in
the channel region of the MOSFET via proton irradiation. The 4H-SiC

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MOSFETs could generate a high channel current as well as had few
EDMR signals from MOS interface defects. These features led to theirhaving higher sensitivity to the spin defect and less interference frominterface signals. In a previous EDMR study, we characterized theinterface defects in the relevant MOSFET and determined their spin
density.15 By using a coexisting EDMR signal from the interface
defects, we could estimate the number of electrically detected TV2a
spins.
In addition, by taking advantage of the MOSFET, we could electrically control the charge state for the TV2a spin defect. Here, it is

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indispensable to tune its charge state properly for detecting its electron
spin. For example, the loss of an electron from the NV center indiamond causes severe degradation in luminescence and the ODMR
signal.16 In the present study, we used the gate bias of the MOSFET totune the charge state of VSi.
Figure 1(a) shows the setup for electrical detection of VSi centersin a 4H-SiC MOSFET. In the experiment, we used n-channel lateral
Si-face 4H-SiC MOSFETs15 that include VSi centers in the vicinity of
the MOS interface. This setup is based on bipolar-ampliﬁcation-effect(BAE) EDMR spectroscopy, which is highly and selectively sensitive to

FIG. 1. (a) Electrical detection of VSi spin defects embedded in 4H-SiC MOSFETs. We used BAE-EDMR detection. (b) Optical image of 4H-SiC MOSFETs used in the
EDMR study. The MOSFET had 5-lm gate length and 150-lm gate width. (c) Simulated depth proﬁles of implanted protons (lower ﬁgure) and silicon-atom monovacancies(upper ﬁgure). Depth “0” is deﬁned at the surface of the top passivation SiO2 layer. TRIM simulations were for a ﬂorescence of 1  1013 Hþ/cm2. (d) Id-Vg characteristic of
4H-SiC MOSFETs before and after proton irradiation. Voltage was swept from –5 to 15 V and back again. (e) Schematic diagram of the formation energy of VSi in 4H-SiC. The
charge state of VSi is determined by the Fermi level (EF) position from the valence band edge (EV). The Fermi level can be controlled by the gate voltage (Vg) of MOSFETs,
and top of diagram shows Vg applied during EDMR measurement. The region highlighted in orange is the range of the Fermi level that VSi is detectable by EDMR.

Appl. Phys. Lett. 120, 064001 (2022); doi: 10.1063/5.0078189
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Applied Physics Lettersinterface defects.17,18 The MOSFETs used in this study had a gate
length of 5 lm [Fig. 1(b)], which is the best for BAE-EDMR measurements. The MOSFETs have 50-nm-thick gate thermal oxide and were
subjected to standard post oxidation annealing in NO gas at 1250  C
for 60 min, which improved their ﬁeld-effect mobility to
30 cm2 V1 s1. The EDMR signal from the interface defects was dramatically reduced by 1/40.15
To create VSi defects inside the channel region, we carried out
proton irradiation with a ﬂuence of 1  1013 cm2 over the whole ofthe MOSFET. It is known that proton irradiation can create VSi defects
around the ion-stop region in SiC crystals.19 Figure 1(c) shows simulated depth proﬁles of protons and silicon-atom monovacancies in agate-stack structure, which were obtained by the Monte Carlo simulation code, TRIM.20 The top SiO2 layer is a protective passivation layer(150 nm). The acceleration energy can be used to control the formation of VSi defects precisely. We chose 80 keV, at which a sharp distribution (peak width 30 nm) of Si monovacancies may be obtained, as
shown in Fig. 1(c). This distribution fully covers the thickness of thechannel layer (7–8 nm) of the present MOSFET.
Before irradiation, the MOSFETs were characterized using
EDMR15 and various other techniques.21 Their drain current (Id)-gate
voltage (Vg) characteristics are shown in Fig. 1(d). The drain current
after irradiation decreased compared with the value before irradiation,
as a result of implantation damage. The ﬁeld-effect mobility fell to
10 cm2 V1 s1, and hysteresis increased slightly. Despite that the proton irradiation degraded the electrical characteristics the MOSFET inthese ways, it was still usable for the BAE-EDMR measurements
reported below. The charge state of VSi is determined by the Fermi
level [Fig. 1(e)]. The range of the Fermi level that the charge state ofVSi is singly negative is 1.3–2.66 eV from the valence band edge.22 In
order to detect VSi by EDMR, the gate voltage of the MOSFET must
be applied so that the Fermi level is within this range. We discuss thislater in Fig. 3.
BAE-EDMR measurements were carried out at room temperature under microwave excitation (9.462 GHz and 200 mW) andmagnetic-ﬁeld modulation at 1.562 kHz and 0.5-mT width. We introduced constant current (Id) from the drain electrode and monitored
the source current (IEDMR). Using a lock-in ampliﬁer synchronizedwith the magnetic-ﬁeld modulation, electron-spin-resonance (ESR)induced current changes in IEDMR were recorded as a function of thestatic magnetic ﬁeld. The magnetic ﬁeld was rotated in the (11 00)
plane. Figure 2(a) shows the angular dependence of the EDMR spectra
for the MOSFETs before and after irradiation. The blue spectra
obtained before irradiation reveal higher signal intensities; their intensities are, thus, normalized to those of the red spectra obtained after
irradiation. In other words, proton irradiation degraded the EDMR
detection. This may have been caused by the drain-current degradation [cf. Fig. 1(d)], although the exact reason is still unclear. A strong
central signal [indicated by the black arrow in Fig. 2(a)] was detectedfrom both the irradiated MOSFET and non-irradiated one: it originates from nitrogen-related interface defects of nitrided 4H-SiC(0001)
MOS interfaces.15 After irradiation, a new doublet signal with zeroﬁeld splitting appeared (the red arrows in the ﬁgure). Figure 2(b) plots
the position of the new signal as a function of the magnetic-ﬁeld angle.
The observed angular dependence is consistent with that of the TV2aspin defect that was calculated from the spin-Hamiltonian of TV2a (gvalue, g ¼ 2.0029, and ﬁne-splitting parameters, D ¼ 35 MHz, E ¼ 0).23

Appl. Phys. Lett. 120, 064001 (2022); doi: 10.1063/5.0078189
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This result indicates we demonstrated to detect the TV2a spin defect[the VSi(k) center] electrically.
To discuss the central spectral region where another type of VSi[the VSi(h) center] exhibits a single-peak signal without zero-ﬁeld
splitting, we performed an analysis by subtracting the EDMR spectrum before irradiation from that after irradiation. Figure 2(c) shows
two typical results where the VSi(k) and VSi(h) signals either overlap
or do not overlap. A single-peak signal seems to appear near the interface signal. Moreover, this signal seems to be isotropic [cf. Fig. 2(b)]and is consistent with the VSi(h) signal. However, its position does
not exactly match the theoretical positions of VSi(h). We deduce that
this inconsistency may be due to distortion from the interface EDMR
signal. This signal consists of two components: a signal from the interfacial K center (SiN3) and one from the incomplete K center(SiC2N).15 Therefore, the proton irradiation may have modiﬁed
these interface defects by knocking out nitrogen atom(s). As a result,the interface EDMR signal may have become distorted after irradiation, resulting in a constant shift of the subtracted signal.
Here, let us estimate the number of detected TV2sa spins by referring to the coexisting interface signal. It was reported that the interface
signal corresponds to a spin density of 2.6  1011 cm2 (the total density of K centers and incomplete K centers estimated for the “NO60”
specimen).15 Since the gate area of the present MOSFET is 1  105cm2 (200  5 lm2), the number of interface “spins” is estimated to be
2.6  106. We assume that the area of the integrated EDMR signal(absorption EDMR signal) is proportional to the number of detected
spins. Comparing the area of the TV2a signal with that of the interface
signal, we deduce the number of observed TV2a centers to be 1  105
spins for our experimental setup.
Next, we measured the EDMR spectra for various gate voltages
and plotted the signal intensities of TV2a (peak-to-peak signal heights)
and the relevant detection currents (IEDMR) as a function of Vg [Fig.
3(a)]. The TV2a signal was only detectable at around Vg ¼ 0 V (2 toþ1 V), implying that the VSi center was singly negatively charged inthis Vg range. In other words, its charge state changed from 1 to 2
above Vg ¼ 2 V and from 1 to zero below Vg ¼ 3 V. To examine
the gate-bias dependence of the charge states of VSi, we carried out
capacitance-voltage (C-V) measurements and determined the Fermi
level (EF) for each Vg. For this purpose, we used a p-type MOS capacitor that imitated the gate-stack structure of the present n-channel
MOSFET. The MOS capacitor and the MOSFETs were from the sametest-element-group SiC chip, meaning that they had been subjected tothe same fabrication process as well as the same irradiation. Figure3(b) shows the C-V curves of the MOS capacitor, where Vg was swept
from 20 to 20 V and then back again. In the ﬁgure, the constantcapacitance region in the downward sweep is caused by the pinningeffect due to interface defects. Using the above C(Vg) data, we estimated EF at the MOS interface by using equation (1) of Ref. 24. In Fig.
3(b), the calculated EF values are shown with respect to the valenceband top (EV). As noted earlier, the EF pinning occurred in the range
between 10 and 0 V. Above 0 V, EF rose rapidly toward the conduction band bottom (EC). This behavior matched that of the detectedcurrent in Fig. 3(a), which rapidly increased through the formation of
the inversion layer.
Figure 3(c) draws the EF position for each Vg together with thetheoretical (0/), (/2) and (2/3) levels of VSi(k) and VSi(h).22,25
The VSi centers can change their charge states from 0 to 3 depending

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FIG. 2. (a) EDMR spectra of proton irradiated 4H-SiC MOSFETs measured at room temperature and with different magnetic ﬁelds. Each spectrum after irradiation (red line)
was measured under IEDMR ¼ 600 nA and Vg ¼ 0 V. Spectra before irradiation (blue lines) were measured under IEDMR ¼ 500 nA and Vg ¼ 5 V. The blue spectra obtained
before irradiation reveal higher signal intensities; their intensities are, thus, normalized to those of the red spectra obtained after irradiation. The black arrow indicates the
EDMR signal from the interface defects.15 Red arrows correspond to a spin defect of VSi(k) (TV2a center) with a zero-ﬁeld splitting of 70 MHz. (b) Angular map of EDMR signals. Solid lines are theoretical values calculated for VSi(k) (TV2a, S ¼ 3/2) and VSi(h) (S ¼ 3/2, without zero-ﬁeld splitting). (c) Difference between EDMR spectra before
and after irradiation, showing the possible presence of a single-peak signal [probably due to VSi(h)] close to the interface signal.

on EF. Looking at this diagram, the TV2a spin defect is only detectableat Vg ¼ 1 V, which is consistent with the experimental result.
However, it is likely that the TV2a signal was still observable undersome negative Vg biases, where VSi0 should be stable, an apparent discrepancy. We suggest that the reason for this discrepancy may be the
distribution of VSi defects, which formed not only at the MOS interface but also at deeper positions. EDMR measures the whole of VSi inthe channel layer. On the contrary, the above EF estimation is valid
just at the MOS interface. Accordingly, the EDMR result is affected bydeeper VSi defects that feel a weaker Vg dependence as compared tothose at the interface. As a result, we can expect there to be a mismatchof the gate-bias dependences.
Although electrical detection of the TV2a spin defect was demonstrated, its sensitivity was extremely low. For instance, the accumulation time for recording an EDMR spectrum such as the one shown in
Fig. 2 was as long as 12 hours. However, we should note that anothertype of VSi spin [VSi(h)] was used to make an electric-circuit-basedmagnetic sensor with ultra-high sensitivity,13 implying that the TV2aAppl. Phys. Lett. 120, 064001 (2022); doi: 10.1063/5.0078189
Published under an exclusive license by AIP Publishingspin [VSi(k)] also acts as a highly electrically-active color center, andthis would enable us to electrically access its spin state with high sensitivity. Thus, in principle, it should be possible for the sensitivity to bedramatically improved by making a number of optimizations. The ﬁrst
would be to further increase the detection current. As mentioned
above, proton irradiation substantially degraded the detection current
as well as the EDMR signals. By optimizing the formation process ofVSi, the EDMR sensitivity could be dramatically increased.
For instance, the proton beam writing (PBW) technique is useful tocreate VSi selectively.11 Proton irradiation in this study degraded
the MOSFETs since irradiation was performed on whole of the
MOSFETs. PBW can create VSi with fewer degradation of the
MOSFETs than this study. After irradiation, some amounts of residual
defects can be removed by relatively-low temperature annealing without VSi disassociation.26 In addition, the device design could be optimized: e.g., a comb-shaped gate pattern would vastly increase thechannel current (i.e., the detection current). Other improvements canbe made by lowering the detection temperature and by illuminating

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FIG. 3. (a) Gate-bias (Vg) dependence of the EDMR signal intensity of TV2a spin defects and detection current (IEDMR) for EDMR. The TV2a spin defect was clearly observed
within a limited Vg range (2 to 1 V). Noise levels of EDMR detection are also shown. (b) Estimation of the Fermi level (EF) vs Vg from MOS C-V measurements. The left axis
indicates C-V curves measured for the p-MOS capacitor, from which we calculated EF at the MOS interface shown in the right axis. (c) Energy-band diagram of 4H-SiC andcharge states of the VSi center determined by ﬁrst-principles calculation.22,25 The region highlighted in orange is the ideal detectable range for the VSi- spin defect. Red triangles
indicate EF positions vs Vg determined from (b).

the light (by causing photo-induced spin polarization), which bothenhance the populational difference between the spin levels as well as
the resultant ESR signal. In fact, the ESR signal of TV2a was strongly
enhanced under such conditions.27 Combining these methods will
make it possible for quantum technologies to detect the TV2a spin
defect electrically.
In summary, we introduced VSi spin defects [the TV2a center orVSi(k), S ¼ 3/2, zero-ﬁeld splitting ¼ 70 MHz] into the channel regionof 4H-SiC MOSFETs by using optimized proton irradiation. By taking
advantage of the BAE-EDMR technique, which is highly sensitive tointerface defects, we demonstrated electrical detection of the TV2aAppl. Phys. Lett. 120, 064001 (2022); doi: 10.1063/5.0078189
Published under an exclusive license by AIP Publishing

EDMR signal at room temperature. This center had already been
established to be an optically detectable spin qubit, and our experimentshows that it is also electrically detectable. We also showed that the
charge state of the TV2a spin defect could be controlled by varying thegate bias of the MOSFET. Furthermore, this MOSFET platform
enabled us to estimate the number of detected TV2a spins, because its
MOS interface provides a reference EDMR signal whose spin density
is known. The number of electrically detected TV2a spins was roughly
estimated to be 1  105. At the present stage, the sensitivity of electricaldetection is extremely low. However, much higher sensitivity is
believed to be possible, and we discussed various ways of improving it.

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This work was partly supported by JSPS KAKENHI via Grant
Nos. 20H00340, 20H00355, and 21H04553.
AUTHOR DECLARATIONSConflict of Interest
The authors declare no conﬂict of interest.
DATA AVAILABILITY
The data that support the ﬁndings of this study are available
from the corresponding author upon reasonable request.
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