Ⅲ-1. Atomic & Solid State Physics (Ion)
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Evaluation of horizontal irradiation for SiC vertical diodes
M. Iwata,∗1 M. Takahashi,∗1 N. Ohtani,∗1 N. Nemoto,∗1 and H. Shindou∗1
Silicon carbide (SiC) devices are the candidates fornext generation power device for space applications because of their excellent electric property. To clarify thedestruction mechanism of SiC devices caused by heavyions, which is a critical issue for usage in harsh radiation environments, we have conducted experiments under various irradiation conditions.
The test was conducted on the 650 V commercial SiC
vertical diodes with a junction barrier Schottky (JBS)
structure, which is the same as in the previous report.1)
Test devices were decapped and irradiated with 84 Kr
ions at room temperature in air using RIKEN AVF coupled with the RIKEN Ring Cyclotron (RRC). The energy of ion at incident edge of the device was 3040 MeV.
Irradiations were performed from diﬀerent sides: one
was from the upper side, the other was from the left side,horizontal to the device surface, as shown in Fig. 1. A
reverse voltage (VR ) was applied to the device and theleakage current (IR ) was continuously monitored during
irradiation. Further, VR was initialized at 240 V and increased in 40 V steps after the total ﬂuence at each VR
reached 1.0 × 106 ions/cm2 . The maximum VR in thistest was 640 V, which was close to the rated voltage ofthe test device.

Fig. 1. Irradiation direction to the device.

Figure 2(a) shows the transition of IR at the end of irradiation at each VR . The device irradiated from the left
side was broken at VR = 600 V, whereas that irradiatedfrom the upper side was not broken until the maximum
VR . Figure 2(b) shows the transition of IR with increasing ﬂuence at VR = 600 V irradiated from the left side;
IR abruptly increased and reached approximately 6 mA.
The same test was conducted for diﬀerent samples toconﬁrm the eﬀects of crystal direction relative to ion
tracks. The samples were 650 V SiC diodes createdby the same company; however its structure was planartype, which does not have p+ regions at the Schottkycontact. No increase in IR was observed when irradiatedfrom both sides, which implies that interaction between
the p+ regions and charges generated by a heavy ion
aﬀected the device breakdown more than crystal direction.
∗1Research and Development Directorate, Japan Aerospace Exploration Agency

Fig. 2. (a) Transition of IR during irradiation and (b) Transition of IR at VR = 600 V irradiated from left side.

Follwing the test, a surface damage considered evidence of single-event burnout (SEB) was observed on thedevice irradiated from the left side. It was located approximately 320–450 µm from the left edge of the device.
Focusing on linear energy transfer (LET) transition in
the device, the highest LET with a Bragg peak was
43.8 MeV/(mg/cm2 ) at 383 µm, which is approximately
the center of the damage site. Note that incidence position in device thickness direction remained unclear inthis test; however, for triggering SEB, an ion was introduced into the depletion layer because deposited charges
must be accelerated by the electric ﬁeld.
The electric ﬁeld lines within depletion layer are perpendicular to the surface under certain VR ; thus, charges
generated by an ion move vertically in vertical diodes.
These charges are ampliﬁed in the collection process,which can cause device degradation or destruction. Although less ampliﬁcation can be expected for horizontal irradiation because reduction in charge multiplication with increasing tilt angle has been reported,2) a
rapid increase in IR and surface damage were observedin the device irradiated from the left side. The same behavior could not be observed at normal incidence (i.e.,
perpendicular to the device surface) with the same ion
and device; gradual increase of IR at lower VR was observed instead. Focusing on a small vertical region in
the device, charges generated by horizontal irradiation
are considered to exist as a point, and all charges including ampliﬁed charges might be collected in an extremely
short period of time. However, the time for all charges
to be collected at normal incidence might be longer thanhorizontal irradiation because charges are generated in a
vertical line along an ion track. This diﬀerence in collecting time period might aﬀect the diﬀerence in destruction
mode.
References
1) M. Iwata et al., RIKEN Accel. Prog. Rep. 5, 106 (2022).
2) A. Javanainen et al., IEEE Trans. Nucl. Sci. 64, 2031
(2017).

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