Electron, Neutron, and Proton Irradiation Effects on SiC Radiation Detectors

Abstract

Owing to their low dark current, high transparency, high thermal conductivity, and potential radiation hardness, there is a special interest in silicon carbide (SiC) devices for radiation monitoring in radiation harsh environments and with elevated temperatures and, especially, for the plasma diagnostic systems in future nuclear fusion reactors. In this work, four-quadrant p-n junction diodes produced on epitaxial 4H-SiC substrates are studied. The impact of electron, neutron, and proton irradiations (up to fluences of 1 × 10 16 electrons (e)/cm 2 , 2 × 10 15 neutrons (n)/cm 2 , and 2.5 × 10 15 protons (p)/cm 2 , respectively) on the electrical characteristics is studied by means of current-voltage (I-V) and capacitance-voltage (C-V) techniques. Regardless of the particle type and applied fluences, the results show similar low reverse currents for irradiated SiC devices, which are at least about four orders of magnitude lower than comparable Si devices. The effects of irradiation on interquadrant resistance and charge build-up in the interquadrant isolation are assessed. Furthermore, device performance as a radiation detector is investigated upon exposure to a collimated 239 Pu-241 Am-244 Cm trialpha source. The performance at room temperature is preserved even for the highest irradiation fluences, despite the fact that the rectification character in electrical characteristics is lost. From the results, advantages of using SiC devices in alpha particle detection in harsh environments can be envisaged.

SiC p+n Junction Diodes Toward Beam Monitor Applications

“…The primary radiation defects produced by single particles (protons and pions) or γ-rays were not evaluated in this measurement, however, the number of primary defects are reported as low as that of diamond [22]. Thus, we conclude that the bulk defects introduced by irradiation at the 10 13 neutron equivalent fluence is ignorable, in agreement with the previous studies on neutron-irradiated pn devices [9], [11], [23].…”

“…We note that the area requirement can be fulfilled even with the current 5 mm×5 mm dies by arraying in a 32×32 matrix, singulated from four 4-inch wafers. The influence of radiation on the charge trapping due to the induced bulk defects is not clear yet, however, only a slight decrease on the charge collection is inferred from the irradiation on pn-diode at a comparable neutron equivalent fluence in the previous studies [9], [11], [23]. Even in the case of unexpected I-V degradation during the experiment, there is still an option of device screening with sufficiently low leakage current characteristics under the preirradiation condition.…”

“…Irradiation tests at higher fluences are severe with the current device structure due to the radioactivation of the metals. We note that the 1 MeV neutrons have the same efficiency in the detector degradation as 24 GeV protons at a comparable neutron equivalent fluence [2], [11]. The theoretical nonionizing energy loss (NIEL) calculation performed on SiC can be found in [21].…”

“…Owing to the wide band gap of 3.26 eV and displacement threshold energy of 22-35 eV, SiC holds a stable charge collection efficiency (CCE) even after a 1 MeV neutron equivalent fluent of 10 13 n/cm 2 . Under the same conditions, current n-type silicon detectors show significant degradation in CCE or leakage current characteristic due to the substrate typeinversion [9], [10], [11]. On the other hand, SiC has suffered from the relatively low value of the detection thickness and the excessive net doping concentration of the epitaxial layer in commercially available wafers.…”

“…Surface barrier detectors are easily accessible because the fabrication process is a relatively straightforward technique, and experimental results demonstrated their excellent performance [15], [16]. On the other hand, pn junctions, or p-i-n structures, had not been much focused as radiation sensors due to the process difficulties, especially, unusual high temperature annealing for dopant activation [11], [17]. Nevertheless, the pn or p-i-n structures of SiC are expected to provide radiation sensors with low leakage current as the wide band gap semiconductor in general.…”