Fund Project:Project supported by the Science Challenge Project (Grant No. TZ2018004) and the National Natural Science Foundation of China (Grant No. 11975179)
Received Date:10 January 2020
Accepted Date:19 June 2020
Available Online:19 June 2020
Published Online:05 October 2020
Abstract:Gallium nitride (GaN), one of the third-generation wide-bandgap semiconductors, offers significant application for advanced electronic devices utilized in neutron irradiation environments, like the defense, space, and aerospace, etc. In these applications, neutron irradiation-induced defects affect the properties of GaN and eventually degrade the performance of devices. In this work, neutron transport process in GaN is simulated by using the Monte Carlo-based code, Geant4 toolkit under four different irradiation conditions, e.g. high flux isotope reactor, high temperature gas-cooled reactor, pressurized water reactor, and atmospheric neutron irradiation. The energy spectra of primary knock-on atoms (PKA) in GaN and the corresponding weighted spectra under those irradiation conditions are analyzed. It is found that there is one unusual “peak” at around 0.58 MeV in the Primary recoil spectrum, regardless of the irradiation conditions. This peak is attributed to the neutron reaction of hydrogen nucleus, i.e., (n, p). Because of the remarkable (n,p) reaction cross-section of low-energy neutron, the intensity of this peak is related to the ratio of low-energy neutron to the total neutron spectrum. By comparing these PKA energy spectra in GaN, we can see that the PKA energy spectrum created under atmospheric neutron irradiation is similar to that in the high flux isotopic reactor. Specifically, the energy distribution of PKA is wide, and the magnitude of energy is lower than those under fission neutron irradiation conditions. In combination with the effects of nuclear reaction products on electrical properties, the high flux isotopic reactor is more suitable for simulating the irradiation of GaN in an atmospheric neutron energy spectrum environment. These above results can provide not only some insights into the evaluation of the degradation of GaN-based electronic devices under neutron irradiation, but also dataset for the study of radiation damage effect of GaN in simulated neutron environment. Keywords:geant4/ gallium nitride/ primary recoils spectrum/ neutron irradiation effect
本文模拟的中子能谱范围主要在10–3—107 eV之间, 图2给出了不同能量的中子在氮化镓材料中的平均自由程, 为了确保统计的大多数中子与靶材料只发生一次相互作用, 靶材料厚度设为0.5 cm, 本文中Geant4建模的几何结构如图3所示, 大小为1 cm × 1 cm × 0.5 cm. 图 2 中子在GaN中的平均自由程 Figure2. The mean free path of neutrons in GaN.
图 3 Geant4中模拟的几何模型 Figure3. Simulated geometric model in Geant4.
图9给出了不同中子能谱在GaN中选取Ga、N、B、C四种初级反冲原子分别做初级反冲原子能谱. 由图9可知, 不同的初级反冲原子的初级反冲原子能谱也显示出大气中子能谱范围较宽; 几种主要的初级反冲原子能谱存在一定的差异, 其中压水堆能谱和高温气冷堆能谱下, GaN中的初级反冲能谱比较接近: 图9(d)中显示, 核反应产物C元素的初级反冲能谱中, 大气中子能谱和同位素堆能谱下比较接近. 图 9 不同中子能谱在氮化镓中对应的初级反冲原子的能谱分布 (a)Ga初级反冲原子能谱; (b)N初级反冲原子的能谱; (c)B初级反冲原子的能谱; (d) C初级反冲原子的能谱 Figure9. Primary recoils spectrum distribution for different neutron spectra for the primary recoil particle type of (a) Ga, (b) N, (c) B, (d) C.