4. Charge induced in SiC diodes by Ion irradiation

The on-state characteristics were measured under *V*G at +2.5 V for the SiC SITs and at +15 V for the Si transistors (IGBTs and MOSFETs). Then, the on-voltage was defined as the value of *V*D at *I*D of 10 A. Figure 9 shows the shift of the on-voltage for the SiC SITs (squares), the Si MOSFETs (triangles) and the Si IGBT (upside-down triangles) as a function of absorbed +/!^z\$!z/\$%"0z+"z+\*w2+(0#!z"+.z0\$!z%z /z\* z0\$!z%z
/z 1!z0+z#))w.5z%.. %¥

ported [29] that the displacement damage effect induced by Compton electrons degrades the gain for Si bipolar transistors. So, the result obtained from the Si IGBT is interpreted in terms +"z 0\$!z)&+.%05z..%!.z.!)+2(z%\*z 0\$!z .%"0z.!#%+\*z c(+3z +,%\*#z.!#%+\*dz 1!z 0+z 0\$!z %/,(!¥ ment damage effect. For the SiC SITs and the Si MOSFETs, since the doping concentration in the drift region is not low, the displacement damage effect might not be observed and as a

age behavior is obtained for the SiC MOSFETs, the large fluctuation of *V*<sup>T</sup> was reported due to the TID effect. Considering gamma-ray irradiation effects on the breakdown voltage, the on-voltage, and *V*T, the characteristics of only the SiC SITs show the stable behaviors up to

 MGy. Thus, we can conclude that the SiC SITs have extremely high radiation resistance, they have an enough potential for electronic devices used in harsh radiation environments

Figure 9. Shift of the on-voltage from the initial value for SiC SITs (squares), Si MOSFETs (triangles) and Si IGBT (upside-

Gy, whereas the on-voltage for the Si IGBTs

z5z c".+)z E^Fz 0+z)+.!z 0\$\*z ECzd^z 0z3/z .!¥

z5^z(0\$+1#\$z 0\$!z/0(!z+\*w2+(0¥

ation shows a very stable behavior up to 107

390 Physics and Technology of Silicon Carbide Devices

remarkably increases after irradiation at 8×105

such as nuclear power plants, space, and so on.

down triangles) as a function of absorbed dose.

107

result, on-voltage shows almost constant values up to 107

%\*!z !/0.10%2!z+.u\* z\*+\*w !/0.10%2!z)("1\*0%+\*/z((! z/z+1./z%\*z!(!0.+\*%z !2%¥ ces by charge (electron-hole pairs) generated by charged particle incidence, especially heavy %+\*/^z\$!z/z+\*z/!)%+\* 10+.z !2%!/z.!z+\*!z+"z0\$!z)+/0z)&+.z%//1!/z"+.z/,!z,,(%¥ tions. On the other hand, for high energy physics using accelerators with high luminosity, such as J-PARC and Super-LHC, Rad-hard particle detectors are expected to be developed. For the development of Rad-hard particle detectors as well as Rad-hard devices for space ,,(%0%+\*/\_z%0z%/z%),+.0\*0z0+z(.%"5z0\$!z!\$2%+.z+"z\$.#!z#!\*!.0! z%\*z !2%!/z5z\$.#¥ ed particle incidence. In a previous study [30f\_z2z!0z(^z.!,+.0! z0\$0z0\$!z\$.#!z+((!¥ tion Efficiency (CCE) obtained from 4H-SiC Schottky diodes by alpha particle incidence was estimated to be 100 %. It was also reported that 4H-SiC Schottky diodes could detect X-rays from radio isotopes [31,32]. Besides, the neutron detection by SiC diodes was investigated previously [33, 34]. As for light ions and X-rays irradiation into SiC, relatively large number of studies has been already reported. On the other hand, from the point of view of SEEs, study of ion irradiation on electronic devices using heavy ions is important. In this section, \$.#!z%\* 1! z%\*z%z %+ !/z5z\$!25z%+\*z%\*% !\*!z%/z.!2%!3! z+\*z0\$!z/%/z+"z+1.z,.!2%¥ ous studies [35-40].

Figure 10. Schematic set-up of the TIBIC system installed at JAEA Takasaki and photo of the TIBIC system.

 \*z +. !.z 0+z +0%\*z 0\$!z %\*"+.)0%+\*z +\*z \$.#!z %\* 1! z %\*z !(!0.+\*%z !2%!/\_z +\*z -!)z \*¥ duced Charge (IBIC) measurements is thought to be one of the useful methods. However, 0\$!z !.!/!z%\*z+((!0! z\$.#!z 1.%\*#z z)!/1.!)!\*0/z/\$+1( z!z+\*/% !.! z"+.z0\$!z¥ 1.0!z !2(10%+\*z +"z \$.#!z%\* 1! z 5z%+\*z !)/\_z /%\*!z 0\$!z !2%!z \$.0!.%/0%/z .!z !¥ graded by radiation damage created in samples by ion incidence [41]. Therefore, single-ion hit Transient Ion Beam Induced Current (TIBIC) was developed at JAERI Takasaki in order to realize the evaluation of ion-induced current with minimizing the influence of damage [42]. Figure 10 shows the schematic set-up of the TIBIC system installed at JAEA Takasaki and the photo of the TIBIC system. The TIBIC collection system connects with a heavy ion microbeam line from the 3MV Tandem accelerator, and consists of a single event triggering system and a fast switch beam shutter system. The transient current signals induced by ions can be detected using a digital sampling oscilloscope (Tektronix 3 GHz TDS694C or 15 GHz TDS6154C). The details of the single ion hit TIBIC collection system are described in Ref. [43f^z%\*!z0\$!z z/5/0!)z+\*\*!0/z3%0\$zz!)z/\*\*%\*#z/5/0!)\_z/,0%(z%)#!/z+"z0.\*/%¥ ent current signals can be obtained.

By the integration of a TIBIC signal, charge collected by a diode can be estimated. Charge

study, Si ions with different energies were applied as probe beams, and the value of energy +"z%z%+\*/z.!z !/.%! z%\*z0\$!z"%#1.!^z\$.#!z+((!0! z5z0\$!z %+ !/z%\*.!/!/z3%0\$z%\*.!/¥ %\*#z,,(%! z%/\_z\* z0\$!z2(1!z+"z+((!0! z\$.#!z/01.0!/z%\*zz\$%#\$!.z%/z.!#%+\*^z+.z!4¥ ample, the saturation is observed above 40 and 60 V for 15 and 18 MeV, respectively. Charge #!\*!.0! z%\*z0\$!z !,(!0%+\*z.!#%+\*z+"zz %+ !z\*z!z+((!0! z5z%0/z!(!0.%z"%!( zc.%"0z+)¥ ponent). On the other hand, charge generated in deeper than the depletion region diffuses, \* z+\*(5z\$.#!z.!\$%\*#z0\$!z.!,(!0%+\*z.!#%+\*z\*z!z+((!0! z5zz %+ !zc%""1/%+\*z+),+¥ \*!\*0dz3\$!.!/z/+)!z#!\*!.0! z..%!./z.!+)%\*!z 1.%\*#z %""1/%+\*^z\$1/\_z%"z0\$!z !,(!0%+\*z.!¥ gion is shorter than the projection range of ions, the decrease in collected charge is observed 1!z0+z0\$!z.!+)%\*0%+\*z+"z#!\*!.0! z..%!./z 1.%\*#z %""1/%+\*^z%\*!z%+\*/z3%0\$z\$%#\$!.z!\*!.¥ #5z\$2!zz(+\*#!.z,.+&!0%+\*z.\*#!\_z0\$!z.!/1(0/z+0%\*! z%\*z%#^zDEz\*z!z-1(%00%2!(5z%\*0!.¥ preted in terms of the drift and the diffusion components. However, in reality, since an extended drift region is temporarily created in a deeper region than the depletion region, the saturation of collected charge occurs even in the case that the depletion region is shorter

At a bias of 150V, the depletion region is estimated to be 7 µm, and this is longer than the ion projection range of Si ions at 18 MeV which is estimated to be 4.8 µm by a Monte Carlo simulation code, SRIM [45f^z\$1/\_z0zz%/z+"zDHCz\_z((z\$.#!z#!\*!.0! z%\*z0\$!zIw%z %¥ odes by Si ion incidence can be collected by the electric field in the depletion layer. The CCE for the 6H-SiC diodes is estimated from the value of charge collected at a bias of 150 V.

where Qexp and Qideal are the value of charge experimentally obtained at 150 V and the ideal value of charge generated in SiC, respectively. The value of Qideal is obtained by the equation

where *E*ion, *E*e-h and *e* are the energy of incident ions, the generation energy of an electronhole (*e*-*h*) pair and electron charge, respectively. In this study, the value of *E*e-h in 6H-SiC is assumed to be 7.8 eV (= 2.8Eg) on the analogy of *E*e-h in Si because the value of the energy for 6H-SiC has not been determined yet. It should be mentioned that the energy loss in the top

measurement system are not considered in this estimation, and the reduction of the CCE due to those effects is estimated to be between 8 and 14 %. The value of the CCE for the SiC

p diodes probed by Si ions at energies of 6, 12, 15 and 18 MeV is estimated to be 74, 83, 86

p diodes as a function of applied bias is shown in Fig. 12. In this

Radiation Response of Silicon Carbide Diodes and Transistors

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393

(Q / Q x 100 exp ideal) (7)

Q / x ideal ion e h = (*EE e* ) (8)

region and by non-ionizing collisions and also the decay of signal in the

collected by the 6H-SiC n+

than the ion projection range [44].

Here, the value of CCE is defined as

Al electrode, the n+

n+

Figure 11 shows TIBIC signals obtained from 6H-SiC n+ p diodes with applied bias of 30, 90 or 150 V. Si ions with 12 MeV were used as probe beams. In this study, the 6H-SiC n+ ,z %¥ odes with 100 - 300 µm diameters were fabricated on p-type substrates with p-type epitaxial layers (Al doping concentration between 8x1014 and 3.5x1015 /cm3 ). The n+ region was formed by three-fold implantation (60, 90, 140 keV) of phosphorus (P) ions at 800°C and subsequent \*\*!(%\*#z0zDIHC[z "+.zFz)%\*z%\*z.#+\*z c.dz0)+/,\$!.!^z\$!z 0\$%'\*!//z\* zz)!\*zz+\*¥ centration of the implanted layer are ~100 nm and 5x1019 /cm3 \_z.!/,!0%2!(5^z1.%\*#z0\$!z\*¥ nealing, the sample surface was covered with a carbon film to avoid the degradation of the surface morphology [24f^z \$!z !0%(/z +"z 0\$!z %+ !z ".%0%+\*z ,.+!//z .!z !/.%! z !(/!¥ where [40]. The peak height of the TIBIC signals increases with increasing applied bias, and the value becomes to 0.50 from 0.19 mA when applied bias increases to 150 from 30 V. The fall-time, which is defined as the time from 90 % to 10 % of the current transient, shorten 3%0\$z%\*.!/%\*#z,,(%! z.!2!./!z%/\_z\* z0\$!z2(1!z !.!/!/z0+zC^GKz".+)zC^LKz\*/z3\$!\*z,¥ plied bias increases to 150 from 30 V. These results can be interpreted in terms of an increase of the electric field in the depletion layer due to increasing applied bias. It is also mentioned the leakage currents of the diodes were in order of 10-11 A at an applied reverse bias of 150 V, and no significant differences in *I* -*V*z\$.0!.%/0%/z!03!!\*z!"+.!z\* z"0!.z z)!/1.!¥ ments were observed.

Figure 11. TIBIC signals obtained from 6H-SiC n+p diodes with applied bias of 30, 90 or 150 V. Si ions with 12 MeV were used as probe beams.

By the integration of a TIBIC signal, charge collected by a diode can be estimated. Charge collected by the 6H-SiC n+ p diodes as a function of applied bias is shown in Fig. 12. In this study, Si ions with different energies were applied as probe beams, and the value of energy +"z%z%+\*/z.!z !/.%! z%\*z0\$!z"%#1.!^z\$.#!z+((!0! z5z0\$!z %+ !/z%\*.!/!/z3%0\$z%\*.!/¥ %\*#z,,(%! z%/\_z\* z0\$!z2(1!z+"z+((!0! z\$.#!z/01.0!/z%\*zz\$%#\$!.z%/z.!#%+\*^z+.z!4¥ ample, the saturation is observed above 40 and 60 V for 15 and 18 MeV, respectively. Charge #!\*!.0! z%\*z0\$!z !,(!0%+\*z.!#%+\*z+"zz %+ !z\*z!z+((!0! z5z%0/z!(!0.%z"%!( zc.%"0z+)¥ ponent). On the other hand, charge generated in deeper than the depletion region diffuses, \* z+\*(5z\$.#!z.!\$%\*#z0\$!z.!,(!0%+\*z.!#%+\*z\*z!z+((!0! z5zz %+ !zc%""1/%+\*z+),+¥ \*!\*0dz3\$!.!/z/+)!z#!\*!.0! z..%!./z.!+)%\*!z 1.%\*#z %""1/%+\*^z\$1/\_z%"z0\$!z !,(!0%+\*z.!¥ gion is shorter than the projection range of ions, the decrease in collected charge is observed 1!z0+z0\$!z.!+)%\*0%+\*z+"z#!\*!.0! z..%!./z 1.%\*#z %""1/%+\*^z%\*!z%+\*/z3%0\$z\$%#\$!.z!\*!.¥ #5z\$2!zz(+\*#!.z,.+&!0%+\*z.\*#!\_z0\$!z.!/1(0/z+0%\*! z%\*z%#^zDEz\*z!z-1(%00%2!(5z%\*0!.¥ preted in terms of the drift and the diffusion components. However, in reality, since an extended drift region is temporarily created in a deeper region than the depletion region, the saturation of collected charge occurs even in the case that the depletion region is shorter than the ion projection range [44].

[42]. Figure 10 shows the schematic set-up of the TIBIC system installed at JAEA Takasaki and the photo of the TIBIC system. The TIBIC collection system connects with a heavy ion microbeam line from the 3MV Tandem accelerator, and consists of a single event triggering system and a fast switch beam shutter system. The transient current signals induced by ions can be detected using a digital sampling oscilloscope (Tektronix 3 GHz TDS694C or 15 GHz TDS6154C). The details of the single ion hit TIBIC collection system are described in Ref.

or 150 V. Si ions with 12 MeV were used as probe beams. In this study, the 6H-SiC n+

odes with 100 - 300 µm diameters were fabricated on p-type substrates with p-type epitaxial

by three-fold implantation (60, 90, 140 keV) of phosphorus (P) ions at 800°C and subsequent \*\*!(%\*#z0zDIHC[z "+.zFz)%\*z%\*z.#+\*z c.dz0)+/,\$!.!^z\$!z 0\$%'\*!//z\* zz)!\*zz+\*¥

nealing, the sample surface was covered with a carbon film to avoid the degradation of the surface morphology [24f^z \$!z !0%(/z +"z 0\$!z %+ !z ".%0%+\*z ,.+!//z .!z !/.%! z !(/!¥ where [40]. The peak height of the TIBIC signals increases with increasing applied bias, and the value becomes to 0.50 from 0.19 mA when applied bias increases to 150 from 30 V. The fall-time, which is defined as the time from 90 % to 10 % of the current transient, shorten 3%0\$z%\*.!/%\*#z,,(%! z.!2!./!z%/\_z\* z0\$!z2(1!z !.!/!/z0+zC^GKz".+)zC^LKz\*/z3\$!\*z,¥ plied bias increases to 150 from 30 V. These results can be interpreted in terms of an increase of the electric field in the depletion layer due to increasing applied bias. It is also mentioned the leakage currents of the diodes were in order of 10-11 A at an applied reverse bias of 150 V,

Figure 11. TIBIC signals obtained from 6H-SiC n+p diodes with applied bias of 30, 90 or 150 V. Si ions with 12 MeV

and no significant differences in *I* -*V*z\$.0!.%/0%/z!03!!\*z!"+.!z\* z"0!.z -

 z/5/0!)z+\*\*!0/z3%0\$zz!)z/\*\*%\*#z/5/0!)\_z/,0%(z%)#!/z+"z0.\*/%¥

p diodes with applied bias of 30, 90

). The n+

,z %¥

region was formed

 z)!/1.!¥

\_z.!/,!0%2!(5^z1.%\*#z0\$!z\*¥

[43f^z%\*!z0\$!z -

ments were observed.

were used as probe beams.

ent current signals can be obtained.

392 Physics and Technology of Silicon Carbide Devices

Figure 11 shows TIBIC signals obtained from 6H-SiC n+

layers (Al doping concentration between 8x1014 and 3.5x1015 /cm3

centration of the implanted layer are ~100 nm and 5x1019 /cm3

At a bias of 150V, the depletion region is estimated to be 7 µm, and this is longer than the ion projection range of Si ions at 18 MeV which is estimated to be 4.8 µm by a Monte Carlo simulation code, SRIM [45f^z\$1/\_z0zz%/z+"zDHCz\_z((z\$.#!z#!\*!.0! z%\*z0\$!zIw%z %¥ odes by Si ion incidence can be collected by the electric field in the depletion layer. The CCE for the 6H-SiC diodes is estimated from the value of charge collected at a bias of 150 V. Here, the value of CCE is defined as

$$\left(\mathbf{Q}\_{\text{exp}} \mid \mathbf{Q}\_{\text{ideal}}\right) \ge 100\tag{7}$$

where Qexp and Qideal are the value of charge experimentally obtained at 150 V and the ideal value of charge generated in SiC, respectively. The value of Qideal is obtained by the equation

$$\mathbf{Q}\_{\text{ideal}} = \left( E\_{\text{ion}} / E\_{\text{c-h}} \right) \,\text{x}\mathbf{e} \tag{8}$$

where *E*ion, *E*e-h and *e* are the energy of incident ions, the generation energy of an electronhole (*e*-*h*) pair and electron charge, respectively. In this study, the value of *E*e-h in 6H-SiC is assumed to be 7.8 eV (= 2.8Eg) on the analogy of *E*e-h in Si because the value of the energy for 6H-SiC has not been determined yet. It should be mentioned that the energy loss in the top Al electrode, the n+ region and by non-ionizing collisions and also the decay of signal in the measurement system are not considered in this estimation, and the reduction of the CCE due to those effects is estimated to be between 8 and 14 %. The value of the CCE for the SiC n+ p diodes probed by Si ions at energies of 6, 12, 15 and 18 MeV is estimated to be 74, 83, 86 and 88 %, respectively. Since the effect of the energy loss in the Al electrode and the n+ .!¥ #%+\*z +\*z 0\$!z .! 10%+\*z +"z 0\$!z z 2(1!z !.!/!/z 3%0\$z%\*.!/%\*#z%+\*z !\*!.#5\_z 0\$!z !4,!.%¥ mental result that higher CCE value is observed by higher energy ion incidence is reasonable. However, even after considering energy loss in those regions, the value of the CCE for 6MeV is not comparable to that for 12, 15 and 18 MeV. This suggests that the CCE is degraded by another effect in the case of 6 MeV-Si.

Figure 13. Relationship between ions species with the same energy (12 MeV) and the value of CCE. The value of CCE is

Radiation Response of Silicon Carbide Diodes and Transistors

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395

The carrier density generated in SiC, and the distributions of e-h pairs are calculated on the basis of Kobetich and Katz (KK) theorem [47]. In this calculation, the KK model improved using empirical equations reported by Fageeha et al. [48] was applied since the KK model overestimates the density of e-h pairs at the core of the ion track. The calculated results of the density of e-h pairs generated in SiC by (Left) 12 MeV-O and (Right) -Au ion irradiation are shown in Fig. 14. In the case of 12 MeV-O ion incidence, the radius of the ion track at the sample surface and projection range of ions are estimated to be S 40 nm and 5.2 )\_z.!/,!¥ tively. On the other hand, the ion track radius at the surface and the ion range for 12 MeV-Au ions are estimated to be S 2 nm and 1.9 µm, respectively. Since the energy (12 MeV) is the same for both O and Au ions, the total number of e-h pairs generated in the ion track region is the same between O and Au ions. Thus, the density of e-h pairs in SiC irradiated with Au ions is much higher than that irradiated with O ions, and the estimated density of e-h pairs in SiC irradiated with 12 MeV-Au ions is a several orders of magnitude higher than that in SiC irradiated with 12 MeV-O ions. In such a high density of e-h pairs, the ambipolar effect occurs easily and the electric field temporarily weakens. As a result, the amount of the recombination between electrons and holes increases. For the dynamics of carriers generated in SiC by heavy ion incidence, please see Ref. [44]. The result obtained in this study indicates that it is important to consider the decrease in the CCE for SiC particle detectors when heavy ions are detected. From the point of view of SEEs in SiC, the decrease in collected charge is thought to be one of the advantages for the development of Rad-Hard devices. The

obtained from the integration of TIBIC signals for 6H-SiC n+p diodes at a bias of 150 V.

similar charge collection behaviours have been also obtained for SiC p+

p diodes were introduced in this article [39].

only results obtained from SiC n+

n diodes, although

Figure 12. Charge collected by 6H-SiC n+p diodes as a function of applied bias. Si ions with different energies were applied as probe beams, and the value of energy of Si ions are described in the figure.

In order to understand the degradation of the CCE due to not energy loss near the surface regions, the effect of ion species on the CCE was investigated. Figure 13z/\$+3/z0\$!z.!(0%+\*¥ /\$%,z!03!!\*z%+\*/z/,!%!/z3%0\$z0\$!z/)!z!\*!.#5zcDEz
!dz\* z0\$!z2(1!z+"z0\$!z^z\$!z2(¥ ue of the CCE is obtained from the integration of TIBIC signals for the 6H-SiC n+ p diodes at a bias of 150 V. The CCE for the diodes probed by O ions is estimated to be 90 %, and this value is the highest of all ion species in Fig. 13. With increasing atomic number, the value of the CCE decreases. The CCE of 42 % is observed by Au ion incidence. The degradation of the CCE for SiC diodes by Au ion incidence was also reported [36]. Zajic et al. suggested that high density of e-h pairs is generated by heavy ions, and generated e-h pairs are easy to recombine in such dense plasma [46].

and 88 %, respectively. Since the effect of the energy loss in the Al electrode and the n+ .!¥ #%+\*z +\*z 0\$!z .! 10%+\*z +"z 0\$!z z 2(1!z !.!/!/z 3%0\$z%\*.!/%\*#z%+\*z !\*!.#5\_z 0\$!z !4,!.%¥ mental result that higher CCE value is observed by higher energy ion incidence is reasonable. However, even after considering energy loss in those regions, the value of the CCE for 6MeV is not comparable to that for 12, 15 and 18 MeV. This suggests that the CCE is

Figure 12. Charge collected by 6H-SiC n+p diodes as a function of applied bias. Si ions with different energies were

In order to understand the degradation of the CCE due to not energy loss near the surface regions, the effect of ion species on the CCE was investigated. Figure 13z/\$+3/z0\$!z.!(0%+\*¥ /\$%,z!03!!\*z%+\*/z/,!%!/z3%0\$z0\$!z/)!z!\*!.#5zcDEz
!dz\* z0\$!z2(1!z+"z0\$!z^z\$!z2(¥

a bias of 150 V. The CCE for the diodes probed by O ions is estimated to be 90 %, and this value is the highest of all ion species in Fig. 13. With increasing atomic number, the value of the CCE decreases. The CCE of 42 % is observed by Au ion incidence. The degradation of the CCE for SiC diodes by Au ion incidence was also reported [36]. Zajic et al. suggested that high density of e-h pairs is generated by heavy ions, and generated e-h pairs are easy to

p diodes at

ue of the CCE is obtained from the integration of TIBIC signals for the 6H-SiC n+

applied as probe beams, and the value of energy of Si ions are described in the figure.

recombine in such dense plasma [46].

degraded by another effect in the case of 6 MeV-Si.

394 Physics and Technology of Silicon Carbide Devices

Figure 13. Relationship between ions species with the same energy (12 MeV) and the value of CCE. The value of CCE is obtained from the integration of TIBIC signals for 6H-SiC n+p diodes at a bias of 150 V.

The carrier density generated in SiC, and the distributions of e-h pairs are calculated on the basis of Kobetich and Katz (KK) theorem [47]. In this calculation, the KK model improved using empirical equations reported by Fageeha et al. [48] was applied since the KK model overestimates the density of e-h pairs at the core of the ion track. The calculated results of the density of e-h pairs generated in SiC by (Left) 12 MeV-O and (Right) -Au ion irradiation are shown in Fig. 14. In the case of 12 MeV-O ion incidence, the radius of the ion track at the sample surface and projection range of ions are estimated to be S 40 nm and 5.2 )\_z.!/,!¥ tively. On the other hand, the ion track radius at the surface and the ion range for 12 MeV-Au ions are estimated to be S 2 nm and 1.9 µm, respectively. Since the energy (12 MeV) is the same for both O and Au ions, the total number of e-h pairs generated in the ion track region is the same between O and Au ions. Thus, the density of e-h pairs in SiC irradiated with Au ions is much higher than that irradiated with O ions, and the estimated density of e-h pairs in SiC irradiated with 12 MeV-Au ions is a several orders of magnitude higher than that in SiC irradiated with 12 MeV-O ions. In such a high density of e-h pairs, the ambipolar effect occurs easily and the electric field temporarily weakens. As a result, the amount of the recombination between electrons and holes increases. For the dynamics of carriers generated in SiC by heavy ion incidence, please see Ref. [44]. The result obtained in this study indicates that it is important to consider the decrease in the CCE for SiC particle detectors when heavy ions are detected. From the point of view of SEEs in SiC, the decrease in collected charge is thought to be one of the advantages for the development of Rad-Hard devices. The similar charge collection behaviours have been also obtained for SiC p+ n diodes, although only results obtained from SiC n+ p diodes were introduced in this article [39].

Figure 14. Calculated results of the e-h density generated in SiC by (Left) 12 MeV-O and (Right) -Au ion irradiation.

For the effects of ion incidence on MOS capacitors fabricated on SiC, it was reported that the peak amplitude of TIBIC signals decreased and the fall time increased with increasing number of incident ions [49-51]. Furthermore, the peak of TIBIC signals can be refreshed to its original value by applying a forward bias of + 1V to the gate electrode. From the measurement of the capacitance of SiC MOS capacitors during O ion irradiation, the value of capacitance was found to increase with increasing number of incident ions. This indicates that the depletion length of the MOS capacitors becomes shorten with increasing number of incident ions. Since large amounts of charge are induced by heavy ion incidence and some of them might flow to the interface between SiO2 and SiC, the degradation of TIBIC signals can be explained by a change in the net bias applied to the gate oxide due to the creation of the inversion region or/and charging up deep traps. The refreshment of TIBIC signals by applying a forward bias can be also interpreted in terms of releasing charge from the interface or/and deep traps. For the effects of heavy ion irradiation on 6H-SiC MOSFETs, Onoda et al. Reported from experimental results and their simulation using the Technology Computer Aided Design (TCAD) [52] that the charge collection behaviours were affected by drift, funnelling, diffusion, and recombination, and especially, the enhancement of transient currents was observed due to the parasitic bipolar action. It was also reported that the enhanced charge collection was observed for 4H-SiC MESFETs by heavy ion incidence [26]. According to device simulations using the TCAD, it was concluded that the enhanced charge collection effect can be interpreted in terms of not only the bipolar action but also the channel modulation effects. For the DDD effect in SiC devices, it was reported that the value of the CCE for SiC n\*p diodes and the majority carrier concentration in them decreased with increasing gamma-rays, electrons or protons and the damage factor of the CCE and the carrier removal rate can be scaled by Non lonizing Energy Loss (NIEL) [53-55].

## 5. Summary

In order to develop Rad-hard devices based on SiC, the radiation response of SiC devices have to be understood. In this chapter, effects of gamma-rays and swift heavy ions on SiC devices were reviewed. Firstly, the gamma-ray irradiation effects on SiC MOSFETs were introduced, and the degradation of their characteristics was discussed on the basis of charge generated in gate oxide and interface traps by irradiation. Then, the radiation resistance of SiC transistors, MOSFETs, MESFETs and SITs was compared to Si transistors. SiC transistors showed higher radiation resistance than Si transistors, and SiC SITs could be operated up to 10 MGy. This indicates that SiC SITs have extremely high radiation tolerance from the point of view of TID effects. Charge generated in 6H-SiC nip diodes by heavy ion incidence was evaluated using TIBIC. The signal peak of the transient current increased, and the fall-time decreased with increasing applied reverse bias. The high CCE values were observed when ions with relatively light mass such as O and Si ions were applied as probe ions. However, the CCE decreased with increasing atomic number, and the value reduced to approximately 40 % when 12 MeV-Au ions were applied as probe ions. From the calculation based on the modified KK model, it was found that the density of e-h pairs in SiC irradiated with heavy ions, such as Ni and Au, is much higher than that in SiC irradiated with O and Si ions. Therefore, the decrease in the CCE by the irradiation of ions with heavy mass was interpreted in terms of the recombination of e-h pairs in plasma.
