**2. Simulation details**

### **2.1. Semiconductor materials**

For the purpose of this study, we considered different group-IV and III-V semiconductor materials including silicon, germanium, silicon carbide, carbon-diamond, gallium arsenide, and gallium nitride materials. **Table 1** summarizes the main physical and atomic properties of these materials [6] notably in terms of bandgap value, bulk density, average energy for creation of an electron–hole pair and energy threshold to deposit 1.8 fC in the considered material. This last quantity corresponds to a silicon recoil nucleus in silicon material with a kinetic energy of 40 keV, considered in [3] as the lowest deposited charge susceptible to induce a soft error in a bulk 65 nm SRAM memory. For standardization purpose and comparison with results presented in [2], we adopted here the same lowest deposited charge (1.8 fC corresponds to 11,250 electrons) that leads to Eth = 11,250 x Eeh. In other words, all neutron-induced products with energies below Eth will not be considered in the databases (see paragraph 2.3).

## **2.2. Atmospheric source of neutrons**

The different semiconductor materials given in **Table 1** have been irradiated with atmospheric neutrons in Geant4 simulations described below (paragraph 2.3) and schematically represented in the inset of **Figure 1**. For memory, the interaction of primary cosmic rays with the Earth's top Susceptibility of Group-IV and III-V Semiconductor-Based Electronics to Atmospheric Neutrons… http://dx.doi.org/10.5772/intechopen.71528 119


attracting strong interest because of their better electronic transport, optical, or high-frequency properties than Si; they can be envisaged in numerous high-performance applications (e.g., "More than Moore" microelectronics and beyond CMOS, extreme environments, high temperatures, or high-speed electronics) for which the expected device or circuit performances cannot be achieved with silicon. In such a context of growing use of new and specific semiconductors, the question of their susceptibility to natural radiation, primarily to atmospheric neutrons at ground level, is posed for high-reliability-level application domains. A special attention should be particularly paid to low-bandgap materials (Ge and most of III-V materials), envisaged as channel replacement for MOSFETs and steep switching tunnel FETs for low voltage application [2], due to their low ionization energy susceptible to amplify charge generation from sea-level neutron radiation. Following a methodology previously developed for the study of neutron-silicon interactions [3], the present work precisely examines nuclear events resulting from the interaction of atmospheric neutrons at the terrestrial level with a target layer composed of Si, Ge, SiC, C (diamond), GaAs, and GaN materials and representative of the whole sensitive volume of a typical integrated circuit. To perform this task, we constructed using the Geant4 toolkit [4, 5] a specific source of atmospheric neutrons and compiled large databases of neutron-semiconductor interaction events corresponding to tens of thousands of nuclear reactions. Details of these simulations and database compilation are given in Section 2. Section 3 presents a detailed analysis of obtained databases in terms of nuclear processes, recoil products, secondary ion production, and fragment energy distributions. Finally, Section 4 discusses the implications of these results on the rate of

For the purpose of this study, we considered different group-IV and III-V semiconductor materials including silicon, germanium, silicon carbide, carbon-diamond, gallium arsenide, and gallium nitride materials. **Table 1** summarizes the main physical and atomic properties of these materials [6] notably in terms of bandgap value, bulk density, average energy for creation of an electron–hole pair and energy threshold to deposit 1.8 fC in the considered material. This last quantity corresponds to a silicon recoil nucleus in silicon material with a kinetic energy of 40 keV, considered in [3] as the lowest deposited charge susceptible to induce a soft error in a bulk 65 nm SRAM memory. For standardization purpose and comparison with results presented in [2], we adopted here the same lowest deposited charge (1.8 fC corresponds to 11,250 electrons) that leads to Eth = 11,250 x Eeh. In other words, all neutron-induced products with energies below Eth will not be considered in the databases (see paragraph 2.3).

The different semiconductor materials given in **Table 1** have been irradiated with atmospheric neutrons in Geant4 simulations described below (paragraph 2.3) and schematically represented in the inset of **Figure 1**. For memory, the interaction of primary cosmic rays with the Earth's top

single-event transient effects at the device or circuit level.

**2. Simulation details**

**2.1. Semiconductor materials**

118 Numerical Simulations in Engineering and Science

**2.2. Atmospheric source of neutrons**

**Table 1.** Main structural, atomic, and electronic properties of the different group-IV and III-V semiconductor materials considered in the present study. (Data partially from Ref. [6]).

**Figure 1.** Differential flux of cosmic-ray induced high-energy neutrons as measured by Gordon and Goldhagen et al. using a multielement Bonner sphere spectrometer on the roof of the IBM T. J. Watson Research Center in Yorktown Heights, NY [6]. *Inset*: Schematic representation of the neutron irradiation simulated using Geant4 in this work.

atmosphere is at the origin of atmospheric showers that produce secondary particles down to the sea level. After muons, the next most abundant secondary particles at the sea level are neutrons. High-energy neutrons (typically above 1 MeV) represent by far the main threat to electronics at the ground level because these particles being not charged are very invasive and can penetrate deeply in circuit materials where they can interact with atoms to produce charged products (recoil nuclei or secondary ions).

All particles characterized by tiny (i.e., insignificant) ionizing properties and thus negligible impact on electronics in terms of electron-pair generation and single events have been excluded from the simulation. Consequently, the computed databases exclude electrons, positrons, gamma photons, pions, and mesons and only contain protons, alpha particles, and ionizing

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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The target dimensions have been chosen to match the typical dimensions of the sensitive volume of an integrated circuit. In particular, the thickness has been fixed to 20 μm because the electrical charge generated by a reaction product beyond 20 μm would not drift or diffuse to the active area (i.e., the sensitive region of the circuit located close to the semiconductor surface) and, consequently, would not play any role in the occurrence of single events.

An example of the computed databases is given in **Table 3** for a target composed of GaAs material and subjected to atmospheric neutron irradiation. As illustrated in this sample composed of nine events, each neutron-interaction event is described in two or several successive lines: the first line gives the event number, the energy of the incident neutron at the origin of the event, the Cartesian coordinates of the reaction vertex, and the number of secondary products generated; the following lines give for each secondary product the nature of this product, its mass and atomic numbers, its initial energy just after emission/production, and the Cartesian coordinates of its momentum. In the first line of the database sample shown in **Table 3**, the event #11369 corresponds to a neutron elastic interaction with an As nucleus of

**Table 4** summarizes the main size characteristics of the computed databases for the six semiconductor materials listed in **Table 1** and subjected to 100 million of atmospheric neutrons each. Five size parameters (or metrics) are reported in **Table 4** to quantify the different databases in terms of neutron-semiconductor interactions: the number (fraction) of elastic and inelastic events, the total number of events, the total number of generated secondary products with energy above the energy threshold Eth given in **Table 1**, and, finally, the average number of secondary ions produced in the case of inelastic events. **Figures 2** and **3** also graphically represent the fractions of elastic and inelastic events and the total number of interaction events and generated secondary products, respectively. All these results lead to the following remarks:

• Silicon 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

• This result can be explained by the fact that neutron nuclear interaction probability with the elements is even higher than the atomic number Z is. This means that the susceptibility

the semiconductor lattice, giving a recoil As with an energy of 58 keV.

more than 50% of the supplementary events with respect to Si.

of the materials is all the greater as their atomic number is high [11].

products with Z > 2.

**3. Simulation results**

**3.1. Main characteristics of the databases**

To emulate the atmospheric neutron source, the differential flux of cosmic-ray induced highenergy neutrons measured by Gordon and Goldhagen et al. in Yorktown Heights [7] has been considered as the reference input spectrum [8]. This distribution, shown in **Figure 1**, was imported in the Geant4 general particle source (GPS) library [9] to randomly generate incident neutrons mimicking the natural sea-level neutron background.

## **2.3. Geant4 options, models, and simulation runs**

The neutron interaction databases for the different semiconductor materials listed in **Table 1** have been computed in this work using Geant4 version 4.9.4 patch 01. The list of physical processes employed in simulation is based on the standard package of physics lists QGSP\_ BIC\_HP [10]. Concerning the hadronic interactions, in QGSP group of physics lists, the quark gluon string model is applied for high-energy (above ~12 GeV) interactions of protons, neutrons, pions, kaons, and nuclei. The high-energy interaction creates an excited nucleus, which is passed to the precompound model describing the nuclear de-excitation. Nuclear capture of negative particles is simulated within the chiral invariant phase space (CHIPS) model. QGSP\_BIC\_HP list includes binary cascade for primary protons and neutrons with energies below ~10 GeV and also uses binary light ion cascade for inelastic interaction of ions up to few GeV/nucleons with matter. The complete list of the Geant4 classes that we considered for our neutron simulations is summarized in **Table 2**.


For each semiconductor target, a simulation run consists in the generation of 100 millions (10<sup>8</sup> ) of primary incident neutrons on a 20-μm-thick material layer perpendicular to its surface (1 cm<sup>2</sup> ).

**Table 2.** List of the different Geant4 classes considered in the present simulation flow for the description of neutronmatter interactions.

All particles characterized by tiny (i.e., insignificant) ionizing properties and thus negligible impact on electronics in terms of electron-pair generation and single events have been excluded from the simulation. Consequently, the computed databases exclude electrons, positrons, gamma photons, pions, and mesons and only contain protons, alpha particles, and ionizing products with Z > 2.

The target dimensions have been chosen to match the typical dimensions of the sensitive volume of an integrated circuit. In particular, the thickness has been fixed to 20 μm because the electrical charge generated by a reaction product beyond 20 μm would not drift or diffuse to the active area (i.e., the sensitive region of the circuit located close to the semiconductor surface) and, consequently, would not play any role in the occurrence of single events.
