The degradation characteristics of silicon-germanium heterojunction bipolar transistors (SiGe HBTs) under different bias modes (forward, cutoff and saturation) during irradiation were reported after multiple pulsed neutron-gamma irradiation at room temperature. The radiation-sensitive parameters of the test samples, including base current IB, collector current IC and DC current gain β, were measured and compared before and after every reactor n-γ pulse irradiation. The test results show that IB increased with increasing fluence, and IC slightly increased in the low base-emitter voltage VBE region (approximately from 0.4 V to 0.5 V) and decreased in the high-VBE region (approximately VBE>0.5 V). Moreover, the degradation degree of the test samples was different under different bias conditions. The performance of the test samples under cutoff bias mode displayed the most serious degradation, while those under forward bias mode suffered minimum damage. Meanwhile, the time-dependent annealing characteristics of the DC current gain for SiGe HBTs at various bias conditions were compared and analyzed.
When detecting fast neutrons, generally select materials with high hydrogen content, such as polyethylene and lithium hydride. It’s known that polyethylene is widely used and has high detect efficiency. Therefore, this paper uses Geant4 software to simulate 4H-SiC-based PiN fast neutron detector with polyethylene converter of varies thickness. With the increase of converter thickness, the conversion efficiency of 1–14MeV monoenergetic fast neutron will first increase and then decrease. By analysing the trend of conversion efficiency, the thickness is determined as 1000um. Then, the 1MeV, 2MeV, 4MeV and 8MeV monoenergetic neutrons and typical fats neutron source: Am-Be neutron source are simulated under the thickness of 1000um convertor, the particle types and energy distribution to the sensitive volume and the energy deposition of particles in the sensitive region are also obtained. Through the analysis of recoil proton energy spectrum, the relationship between incident neutron energy and recoil proton energy are studied. Also, through the analysis of PKA (primary knocked-out atoms) energy spectrum, we found that the main reactions in epi-layer are 28Si(n,n’) 28Si, 12C(n,n’) 12C, 28Si(n,α) 25Mg, 28Si(n,p) 28Al, etc. It is found that heavy ions such as C and Si produced by neutrons in sensitive volume account for a large proportion. The above research finally helps to investigate the deposit energy in the epi-layer.
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