**3.4. Consequences in terms of electron-hole pair generation and single events**

This last paragraph examines the consequences of neutron interactions in the different targets in terms of electron-hole pair generation and fundamental mechanism at the origin of single events in electronics. From the computed databases, we calculated in **Figure 11** the total energy deposited by all the secondary products in the different target materials. Although it is a purely theoretical value, this total amount of deposited energy by ionization process is in the range of 10<sup>11</sup> eV for 100 million incident neutrons, which gives an average value in the range of keV per incident neutron, more precisely 1.7 keV for Si, 2.85 keV for Ge, 3.07 keV for C, 2.33 keV for SiC, 2.6 keV for GaAs, and 3.74 keV for GaN. This quantity is found to be minimum for the silicon target and maximum for GaN (**Figure 11**).

Dividing this total energy deposited by all the secondary products by the average energy for creation of an electron-hole pair (given in **Table 1**) gives, for each target material, the upper theoretical limit of the total amount of electron–hole pairs induced by neutrons (via the secondary products). This quantity is shown in **Figure 12** for the different target materials. Also, normalized per incident neutron, this corresponds to 472 e–h pairs for Si, 983 for

lowest total number of interaction events and, except the particular case of carbon-based materials (diamond and SiC), GaN shows the highest event rate with more than 50% of the supplementary events with respect to Si. Diamond shows a very different behavior than the other materials (our simulation results show a particularly elevated number of elastic events for diamond as compared to other materials) since it is an excellent neutron moderator. For silicon carbide, which can be viewed as a "mixture" of Si and C at the atomic level, it shows an intermediate behavior between Si and C with a number of elastic events quasi ×2 with respect to Si due to the presence of C. Concerning the fraction of elastic and inelastic events, three different behaviors can be highlighted: low (< 30%, Ge and GaAs), intermediate (40–60%, Si and GaN), and high (> 60%, C and SiC) elastic event rates; the presence of low-Z elements such as C and N, respectively, in SiC and GaN leads to increase elastic interactions in these last materials with respect to the elastic rates observed for Si and GaAs. For Si, Ge, and GaAs, the total number of generated secondary products is in the same order of magnitude (with Si < Ge < GaAs). For GaN and SiC, the presence of low-Z elements increases the number of elastic events and indirectly increases the total number of secondary products. Carbon-diamond shows the highest number of events/products due to its high power of neutron moderation. Concerning the nature of the secondary products, our simulations show that, for the six materials, the most frequent produced secondary particles are the recoil products due to neutron elastic interactions with the nuclei of the semiconductor lattice, followed by protons in the second position and alpha particles in the third one. All the other products are systematically less produced than these three categories of products. A detailed analysis of the secondary ions produced during neutron interactions in the different target materials in terms of initial energy (when products are released), linear energy transfer (LET), and range in the target material has been also conducted. Recoil nuclei and heavy fragments have been shown to be susceptible to induce single events in a very short range from their emission point and with a relative high efficiency, due to their initial high LET values. On the contrary, protons and alpha particles, characterized by lower LET values but longer ranges in the different semiconductor materials, are susceptible to induce single events farther from their emission point than heavy fragments up to distances of hundred microns for alpha particles and several millimeters for protons. Finally, the consequences of neutron interactions in the different targets in terms of electron–hole pair generation, a fundamental mechanism at the origin of single events in electronics, have been examined. Our results show that germanium corresponds to the worst case and diamond (also SiC) to the best case with regard to e–h pair production, Si, GaAs, and GaN being relatively equivalent and of intermediate behavior

Susceptibility of Group-IV and III-V Semiconductor-Based Electronics to Atmospheric Neutrons…

http://dx.doi.org/10.5772/intechopen.71528

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with respect to this criterion.

Daniela Munteanu and Jean-Luc Autran\*

\*Address all correspondence to: jean-luc.autran@univ-amu.fr

Aix Marseille Université, CNRS, Université de Toulon, Marseille, France

**Author details**

**Figure 11.** Total energy deposited by all the secondary products induced by neutron interactions in the different target semiconductor materials.

**Figure 12.** Number of electron-hole pairs created in the different target semiconductor materials by conversion of the total energy deposited by all the secondary products (**Figure 11**), taking into account the average energy for creation of an electron-hole pair given in **Table 1**.

Ge, 256 for C, 299 for SiC, 542 for GaAs, and 420 for GaN. These data show that germanium corresponds to the worst case and diamond (also SiC) to the best case with regard to production mechanisms of single events, Si, GaAs, and GaN being relatively equivalent with respect to this criterion. This result can be for the most part explained by the values of the average energy for creation of an electron–hole pair which is very low for Ge (2.9 eV) and extremely important for C (12 eV).

### **4. Conclusion**

In this chapter, we presented a detailed study using extensive Geant4 numerical simulation of nuclear events resulting from the interaction of atmospheric neutrons at the terrestrial level with a target layer composed of various group-IV and III-V semiconductor materials including silicon, germanium, silicon carbide, carbon-diamond, gallium arsenide, and gallium nitride materials. The neutron interaction responses of these different semiconductors have been finely compared in terms of nuclear processes, recoil products, secondary ion production, and fragment energy distributions. Our results show that Si exhibits the lowest total number of interaction events and, except the particular case of carbon-based materials (diamond and SiC), GaN shows the highest event rate with more than 50% of the supplementary events with respect to Si. Diamond shows a very different behavior than the other materials (our simulation results show a particularly elevated number of elastic events for diamond as compared to other materials) since it is an excellent neutron moderator. For silicon carbide, which can be viewed as a "mixture" of Si and C at the atomic level, it shows an intermediate behavior between Si and C with a number of elastic events quasi ×2 with respect to Si due to the presence of C. Concerning the fraction of elastic and inelastic events, three different behaviors can be highlighted: low (< 30%, Ge and GaAs), intermediate (40–60%, Si and GaN), and high (> 60%, C and SiC) elastic event rates; the presence of low-Z elements such as C and N, respectively, in SiC and GaN leads to increase elastic interactions in these last materials with respect to the elastic rates observed for Si and GaAs. For Si, Ge, and GaAs, the total number of generated secondary products is in the same order of magnitude (with Si < Ge < GaAs). For GaN and SiC, the presence of low-Z elements increases the number of elastic events and indirectly increases the total number of secondary products. Carbon-diamond shows the highest number of events/products due to its high power of neutron moderation. Concerning the nature of the secondary products, our simulations show that, for the six materials, the most frequent produced secondary particles are the recoil products due to neutron elastic interactions with the nuclei of the semiconductor lattice, followed by protons in the second position and alpha particles in the third one. All the other products are systematically less produced than these three categories of products. A detailed analysis of the secondary ions produced during neutron interactions in the different target materials in terms of initial energy (when products are released), linear energy transfer (LET), and range in the target material has been also conducted. Recoil nuclei and heavy fragments have been shown to be susceptible to induce single events in a very short range from their emission point and with a relative high efficiency, due to their initial high LET values. On the contrary, protons and alpha particles, characterized by lower LET values but longer ranges in the different semiconductor materials, are susceptible to induce single events farther from their emission point than heavy fragments up to distances of hundred microns for alpha particles and several millimeters for protons. Finally, the consequences of neutron interactions in the different targets in terms of electron–hole pair generation, a fundamental mechanism at the origin of single events in electronics, have been examined. Our results show that germanium corresponds to the worst case and diamond (also SiC) to the best case with regard to e–h pair production, Si, GaAs, and GaN being relatively equivalent and of intermediate behavior with respect to this criterion.
