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Article

Semiconductor Material Damage Mechanisms Due to Non-Ionizing Energy in Space-Based Solar Systems

by
Anthony Peters
1,
Matthias Preindl
1 and
Vasilis Fthenakis
1,2,*
1
School of Engineering and Applied Science, Columbia University, New York, NY 10027, USA
2
Brookhaven National Laboratory, Upton, NY 11973, USA
*
Author to whom correspondence should be addressed.
Energies 2025, 18(3), 509; https://doi.org/10.3390/en18030509
Submission received: 21 December 2024 / Revised: 20 January 2025 / Accepted: 21 January 2025 / Published: 23 January 2025
(This article belongs to the Section A2: Solar Energy and Photovoltaic Systems)

Abstract

:
Radiation impacts on space-based systems operating on various orbits are evaluated in this paper. Specifically, satellite operations in Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geosynchronous Orbit (GEO) are analyzed. Special focus is given on quantifying the effect of high-energy particle space radiation on materials used for critical power components, where component fault can lead to total mission failure. Methods, using multiple computational platforms for the quantification of non-ionizing energy loss (NIEL) and displacement damage dose (DDD), are used to assess semiconductor damage at specific orbital altitudes. Detailed simulations were conducted for Gallium Arsenide Indium Phosphide (GaInP/GaAs/Ge) solar cells with various cover glass thicknesses, and the survivability of GaInP/GaAs/Ge cells was compared with that of Si cells. It was assessed that radiation exposure due to high-energy protons at 10,000 km is more prevalent than 20,000 km orbits and that electron bombardment is a major electronic damage culprit. For MEO at 10,000 km, MEO at 20,000 km, and GEO at 36,000 km, we determined the 1-year maximum power (Pmax) losses due to protons to be 23%, 8%, and 1% and losses due to electrons to be 11%, 14%, and 10%. Total integrated spectra Pmax losses for those altitudes are 25%, 16%, and 10%, respectively.

Graphical Abstract

1. Introduction

This paper investigates photovoltaic (PV) cells and conversion electronic degradations due to radiation damage. PV arrays are the keystone components of a satellite power system, where their efficiencies and damage mechanisms in space-based applications are explored. Furthermore, the specific modalities by which these arrays and devices are designed to operate are discussed and potential system resiliency enhancements (such as recommended cover glass thickness) are identified with space-based solar (SBS) as an example satellite system for analysis [1,2]. SBS harvesting and radiofrequency (RF) microwave power beaming are being explored for its potential to power spacecrafts or satellites in various orbits and transmit power to remote areas on earth. One of the challenges associated with such applications is potential damage to the SBS power conversion electronics by the high-density proton and electron fields in orbits where SBS systems may operate. As the power throughput of an SBS system will increase, the PV array footprint in orbit will also increase, with some SBS projections exceeding 1300 m2. In such cases, extending the service life and protecting the critical PV arrays from radiation at higher orbits is paramount for mission success.

1.1. Study Objective

This paper is the first of its kind study focusing on SBS radiation impacts from primarily proton radiation on Medium Earth Orbit (MEO) at altitudes of 10,000 to 20,000 kilometers (km). This paper quantitatively addresses component degradation, system efficiency, and survivability for a large-scale SBS module configuration with power beaming operation in MEO. It focuses on performance degradation by exploring semiconductor damage mechanisms for semiconductor materials used in the PV and the RF emission power electronics of the SBS systems. In addition, the survivability in various radiation zones of PV modules protected with various cover glass types and thicknesses is quantified. System improvements for satellites in LEO, including thermal concerns, atomic oxygen, and physical damage from space debris, are factors to consider for protection; in MEO/GEO, the biggest concern is radiation. Other future considerations to add might include PV array structural strength and rigidity, while also being thermally efficient to radiate heat away from the satellite and avoid specular reflections, which can lead to isolated hotspots and thus accelerate fatigue, thus reducing satellite efficiency and service life. Other system improvements, such as enhanced optical absorption of Gallium Arsenide (GaAs), Cadmium Telluride (CdTe), and Indium Phosphide (InP) nanowires to improve system performance in high radiation (i.e., MEO) and/or highly fluctuating temperature environments (i.e., LEO), can aid in prolonging the service life of satellites; however, the technology is not currently utilized for satellite design and is therefore not explored in this paper [3,4,5]. Therefore, the study is limited to focusing on degradation to space-qualified PV cells currently employed on satellite power systems.

1.2. SBS Prototype

A sandwich module used for SBS missions is considered for this paper as the primary device used for radiation assessment [1]. This was selected due to the large PV footprint being used to scale up from 20 m2 arrays to ~1300 m2, where an analysis of the power collection degradations is critical for achieving maximum power output while on orbit. Such analyses for PV degradation can help support SBS experiments, such as the Air Force Research Laboratory (AFRL) Space Solar Power Incremental Demonstrations and Research program and other satellites intended to operate in MEO [2]. This element comprises three layers: (1) photovoltaic layer, (2) DC-to-RF conversion (the generation of the microwave signal frequency and transmission amplification), and (3) the antenna element responsible for the microwave energy transmission, which is illustrated in Figure 1.
The advantage of the sandwich module design is that it takes sunlight and converts it to RF in a single pass through a device stack. The photovoltaics used in the sandwich module are commercial GaInP/GaAs/Ge triple-junction cells with efficiencies of 28.3% PV cells available from the Emcore Corporation and Spectrolab shown in Figure 2 below [2].
Record efficiencies of multi-junction GaInP/GaAs/Ge solar cells under concentrated light in the lab exceeds 47%, so the commercialization of much higher, 28% efficiency cells are feasible. The sandwich also includes electronics for DC-to-RF conversion and the subsequent amplification.

2. Semiconductor Damage Mechanism and Assessment

2.1. Assumptions and Limitations

We implemented multi-faceted space radiation modeling using multiple sources of experimental data (e.g., Space Environment Information System (SPENVIS) and International Radiation Environment Near-Earth (IRENE)) and modeling tools available from the NASA Jet Propulsion Laboratory (JPL), Johns Hopkins Applied Physics Laboratory, European Space Agency (ESA), AFRL, and Naval Research Laboratory (NRL) [6,7,8,9,10,11,12,13,14,15,16]. Our modeling platform also includes the use of the IRENE active electron and active proton (AE9/AP9) standard model for quantifying electron and proton energy fluxes and densities and solar particle fluences estimated using the Emission of Solar Protons—Prediction of Solar particle Yields for Characterizing Integrated Circuits from JPL and Solar Accumulated and Peak Proton and Heavy Ion Radiation Environment databases from ESA [17,18,19,20].
For radiation processes resulting in energy losses due to particle collisions within a material, the basic framework for analysis assumes two body scatterings [21], where collision length and the mean free path between successive collisions is considered through Rutherford Coulomb scattering. Two-body scattering refers to the interaction between two particles, where they exchange energy and momentum, typically resulting in deflection or change in their velocities. In this study, it is the relationship between an incoming particle with a specified kinetic energy in electron volts (eV) interacting with a particle within a lattice structure (e.g., source material cross section). For the behavior of particles interacting with semiconductor materials, radiation damage causes the creation of Frenkel pairs (e.g., pairs consisting of a displaced atom from a lattice site and the corresponding vacancy in the previously occupied lattice site) [22,23]. This leads to (1) current leakage; (2) the creation of deep and shallow defects, which can act as carrier trapping centers; and (3) the buildup of space charge, which switches a field effect transistor to an off state [24]. Additionally, there can be surface damage resulting in a further increase of the surface charge leakage. For the assessment presented in this paper, radiation processes are represented through particle–matter interactions under varying intensities and the spectral fluence predicted for a particular orbit as a function of orbital altitude.

2.1.1. Nuclear Stopping Power

Nuclear stopping power is pertinent to the evaluation of a material’s stopping power at relativistic and nonrelativistic energies and directly relates to the slowed-down spectrum analysis discussed later. Nuclear stopping power is a process whereby charged particles, electrons, and protons can lose energy by displacing atoms inside of a medium because of interaction (e.g., traversing) through the lattice structure. For particle velocities of <10 keV, the charge neutralization begins to dominate the collision and accelerate the energy loss process. Additionally, the ion electronic stopping power decreases and the energy loss due to collisions inside the lattice structure with target nuclei are no longer negligible (e.g., reflected as the nuclear stopping power). In this analysis, we omitted the density effect due to the non-participation of inner shells in the collision-loss process [23].
Since there are multiple layers and compound materials inherent in a solar cell design, the treatment of different atomic species needs to be considered. In such a case, a material containing several atomic species can be treated according to Bragg’s additivity rule [25]. This allows us to consider the material as a combination of atoms, which would contribute to the overall stopping power separately. However, at low energy, the application of the additivity rule can introduce errors because the stopping power contributed by each element is influenced by chemical binding effects. These errors can amount to approximately 15% at energies near the stopping power peak [23].
The GaInP/GaAs/Ge solar cell is a semiconductor with different chemical compositions in each layer, there are assumed to be varying atomic differential cross sections. Therefore, the amount of energy transferred in the interaction with each atom in the lattice structure (considering the number of atoms per cm3) needs to be accounted for. As a result, our analysis assumed differential collision probabilities for energy loss while traversing the material accounting for its thickness, where each atom in the lattice has a different chance to interact with something since it has different collision cross sections. This particle behavior with various kinetic energies passing through each layer of the semiconductor material is what is referred to as the slowed-down spectrum analysis. An important portion of the slowed-down spectrum analysis considerations would entail atomic recoil probabilities, measured in cm2/g, which account for a compound or mixture for specific chemical lattice structures [12,23]. The nuclear stopping power (measured in MeV/cm) for energies higher than 10 keV was used in the Monte Carlo Solar Cell Radiation Environment Analysis Model (MC-SCREAM) analysis.
Due to large proton and electron kinetic energies expected on orbit, large energy transfers in the chemical lattice structure for the solar cells (especially thinner devices) are predicted. The resultant scattering would be described by its relativistic extension, and thus, the application of Moller’s differential cross section is used [25]. This differential cross-section assumption is important because it is used to determine the overall stopping power for the material and contributes directly to the slowed-down spectrum analysis utilized in the end-of-life (EOL) modeling described in Section 3.2. For lower electron energies and the resulting smaller energy transfers, the energy loss is related to the atomic oscillator strength and is independent of the incoming particle’s charge [25].

2.1.2. NIEL and DDD

Non-ionizing energy loss (NIEL) is a process where incoming particle energy has interactions that occur inside an atomic lattice structure that results in atomic displacements or, in the case of collisions, where the knock-on atom does not move from its lattice location, and the energy is dissipated in lattice vibrations [24,26]. NIEL was calculated for chemical compound materials such as multijunction solar cells by means of Bragg’s additivity rule; in this instance, the overall NIEL (MeV cm2/g) is obtained as a weighted sum, where each material layer contributes proportionally to the atomic weight fraction [27]. Primary effects include the point defects created in the chemical lattice structure, and secondary defects are created during the diffusion of the primary defects, such as cascading [24]. Primary knock-on atom assumptions for recoiling energy above the displacement energy threshold assume the following: (1) two body hard sphere atomic collisions, (2) a sharp displacement threshold displacement energy, and (3) no inelastic energy losses in secondary collisions; for this analysis, cascading effects were omitted.
The displacement damage dose (DDD) for a given type of particle with specified energy is the product of the fluence and the NIEL of the incident radiation [6,15]. The MC-SCREAM tool developed by NRL assumes the use of the DDD, which depends on the given parameters inherent in a selected PV device and is difficult to define a real intrinsic DDD for protons and electrons, as the amount of damage produced by a given radiation fluence varies [8]. In our study, we assumed a 15% Frenkel pair recombination rate (fsurv = 0.15) to fit the 10 MeV proton classical NIEL profile, in agreement with the commonly accepted values for such kinds of parameters [10,16]. The DDD was calculated under various mission parameters for the SBS satellite platform, with the only radiation shielding for the PV array available through a borosilicate-type Cover Glass Modular-Grade (CMG) bonded to GaInP/GaAs/Ge cells via a silicon-based adhesive [28,29,30]. Terrestrial PV cover glass is used for protection from weather elements, and it is typically made from tempered glass; space-based cover glass uses specialized materials such as fused silica, is much thinner to minimize spacecraft weight, and is designed for protection from space radiation. It is also assumed that the DDD accounts for the electron, proton, and solar proton exposure to the solar cell through the active regions.

2.2. Method of Assessment

Our assessment utilized a multistep process to fully assess the space radiation impact on different semiconductor materials and started by analyzing the nuclear stopping power from a relativistic perspective [6,15,26]. Step 1 was accomplished using the Screened Relativistic Non-Ionizing Energy Loss (SR-NIEL) open-source calculator available from Jun et al., 2004 [12,15]. This was to determine a semblance of the materials’ natural ability to withstand single-particle bombardment under varying intensities and energy levels and was tabulated for input into MC-SCREAM. Use of the SR-NIEL calculator was utilized to calculate the radiation hardening property that is characteristic for a selected PV device configuration [15]. The input parameters for each simulation included the following: incident particle energy type (i.e., proton, heavy ion, and electron), target material, and energy limits. For electrons, the selected nuclear form factor model was exponential (as opposed to Gaussian or Uniform); the form factor accounted for the spatial distribution of charge density probed in the electron-nucleus scattering [11]. For the target material, the atomic number was selected as well as the Stoichiometric index. For the heavy ion consideration, iron (Fe) ions were used for calculations in this study. NIEL profiles were calculated to determine particle–matter behavior for common semiconductor materials and tabulated for use in the MC-SCREAM tool. This was useful specifically when analyzing compound materials and utilizing Bragg’s additivity rule to account for PV devices with multiple layers).
Step 2 was to gather radiation spectra, which were collected using the AE9/AP9 IRENE model [16]. The radiation spectra ranges are critical for analysis, as this is representative of the specific orbit type (i.e., MEO and GEO) used to determine which orbit is best for PV survivability. Forecast radiation data were gathered for circular orbit altitudes of 1000 km to 36,000 km, with an inclination of 55 degrees, for mission durations of 1 to 15 years. Step 3 involved radiation sources and effects modeling using the Space Environment Information System (SPENVIS) [18,31]. Step 3, the orbit generator tool utilized classical orbital elements, such as orbital altitude, and the trapped radiation IRENE AE9/AP9 model was correlated to Monte Carlo simulations. This yielded trapped electron and proton radiation spectra data for use in Step 4, which was conducted using the MC-SCREAM tool to calculate PV performance and EOL correlation.
EOL does not explicitly indicate the time when a component reaches the end of service life but refers to the specified mission duration in which the component is assessed (e.g., a 1- or 15-year EOL is the service window of operation). Within this step, radiation spectra data were loaded, and the PV cell layers were defined. Cell layering includes defining shielding parameters, cover glass type and thickness, cell technology, and any other materials used to build the array (i.e., epoxies and coatings such as magnesium fluoride—MgF2). The radiation spectra combined with the cell layering was input into the slowed-down spectrum analysis, followed by displacement dose, which yielded a final PV cell degradation and EOL correlation. Specifics on each step and the results are provided in detail in subsequent sections. This paper focused primarily on the PV material assessment and specifically calculated the degradations of PV devices in terms of maximum power (Pmax), open circuit voltage (Voc), and short circuit current (Isc), resulting in the EOL % presented.

3. Results

3.1. SR-NIEL and Radiation Spectra Predictions

The proton and electron NIEL profile for various semiconductor materials is shown in Figure 3 below; the GaAs NIEL profile used in our DDD calculations was MC-SCREAM.
In Figure 3a,b, we can observe that the NIEL is nearly four orders of magnitude higher due to protons over that of electrons; however, the energies for protons are much higher, calculated between 1 and 100 MeV for protons and <0.1 MeV for electrons. This is important for the analysis since when the radiation spectra are mapped for each circular orbit altitude, the exposure rate will vary for electrons and protons and will cause different levels of damage. Protons with higher energies will cause more damage but may occur less frequently; conversely, electrons with less energy are more prolific and will cause more sustained damage over time. The screened relativistic modeling approach used for NIEL yielded data in this analysis to compute the overall DDD and EOL determination of specific semiconductor devices, specifically PV cells [27,29]. Single-particle interactions with corresponding energy ranges are calculated to determine the nuclear stopping power for specific materials, with GaN showing a noticeable increase in radiation survivability over GaAs, most likely due to the lowest NIEL for electrons. It was observed that mission time (i.e., duration of exposure) and mission altitude (i.e., satellite operating height) were independent of the total NIEL calculation. However, this stage of the analysis did not yet account for multiple layers of compound materials or junctions, nor did it account for the relative thicknesses of the material to be traversed for an incident particle. This was selected as a starting point to quantify the radiation hardening characteristic for select materials; however, other considerations, such as thermal performance, power conversion efficiency, and form factors, should be considered for future analysis.
For radiation mapping in the circular orbits, radiation spectra for trapped protons and electrons were gathered from SPENVIS. This radiation analysis used the following input parameters (i.e., spacecraft trajectories) for SPENVIS in the “orbit generators” tool: (1) a single-mission segment for various mission durations (run for 1- and 15-year segments), (2) satellite orientation that had one axis pointed to the sun, (3) semimajor axis (1000 km to 36,000 km in 1000 km increments), (4) inclination fixed at 55 degrees, (5) right ascension of the ascending node (RAAN) of 0 degrees, (6) an argument of perigee at 90 degrees, and (7) eccentricity of 0.005. AE9/AP9 model inputs were run using model version 1.50, with Monte Carlo simulations of 999 runs, default AE9/AP9 energies in the 95th percentile. Solar radiation pressure and atmospheric drag for spacecraft trajectories in SPENVIS were not accounted for in this radiation spectra prediction. Radiation spectra were collected for both integral and differential flux based on the orbit generator tool results, where data were logged into Microsoft Excel and separated into energy value tables for later use in PV damage assessments. A visual representation of the 1-year integral flux radiation data for the various orbital altitudes is shown in Figure 4a,b below.
Based on the radiation spectra forecasts for the given 1-year orbital parameters, a satellite operating in the inner Van Allen Belt (1000 km to 12,000 km), 8.5 to 10 MeV protons with spectral fluences ranging from 1.57 × 1010 to 2.67 × 1012 MeV−1 cm−2, is the most common in this orbit. The electron spectral fluence is less, with fluences at 8.5 MeV electron energies ranging from 1.39 × 108 to 9.84 × 109 MeV−1 cm−2. For the 1-year orbital parameters, a satellite operating in the outer Van Allen Belt (13,000 km to 36,000 km) will be exposed to high-energy electrons at 8.5 MeV for spectral fluences ranging from 3.72 × 109 to 1.08 × 1010 MeV−1 cm−2. However, it will encounter higher spectral fluences > 1.58 × 1015 MeV−1 cm−2 for lower electron energies of 0.04 MeV. While proton energies are higher than electrons (>10 MeV), the forecasted integral flux indicates significantly lower (as much as 13 orders of magnitude less) spectral fluences, where 8.5 MeV protons show spectral fluences as low as 1.81 × 102 MeV−1 cm−2. As a result, from the radiation spectra data collected, it appears that high-energy and low-energy electrons could be more damaging than protons for satellites operating at altitudes > 13,000 km due to the high electron spectral fluences.

3.2. PV Device Degradations

Inputs to the MC-SCREAM model for this analysis include radiation spectra calculated for 1- and 15-year mission durations, with orbital altitudes ranging from 1000 km to 36,000 km. PV electrical characteristics calculated for degradation were Pmax, Voc, Isc, and shown as % performance at end of life/beginning of life. To input the PV device, we conducted MC-SCREAM simulations using the Emcore GaInP/GaAs/Ge triple-junction solar cell [29], with corresponding stacking completed in the multilayer shielding developer tool. Once the multilayer interface is established, the next step is to determine the NIEL profile for the modeled GaInP/GaAs/Ge PV cells. Radiation spectra obtained from IRENE AE9/AP9 are loaded into Microsoft excel data tables and imported into MC-SCREAM for the determination of the slowed-down spectrum analysis for each layer with resultant displacement damage dose. The slowed-down spectrum analysis is a calculation of the “slowed down” spectra after having passed through shielding or multiple layers of various materials [8,10]. The next step is to correlate the different layer shielding with PV losses, which yields results for Pmax, Voc, and Isc losses for 1- and 15-year mission durations. Once the electrical performance characteristics have been attained, the study is rerun for varying CMG thicknesses of 50.8, 76.2, 101.6, and 127 µm (2, 3, 4, and 5 mil, respectively). Using the integral flux for trapped electrons and protons, some determinations can be made to optimize the SBS PV array as a function of orbital altitude and mission duration.
Once the NIEL profile and spectra were loaded into MC-SCREAM, the slowed-down spectrum analysis was executed with the total dose calculated, then the DDD, with the final output shown for Pmax degradations. All the results were tabulated, with the spectrally combined trapped proton and trapped electron results for each altitude calculated; an example is shown in Figure 5 below to illustrate a sample PV Pmax degradation for trapped protons and electrons at 10,000 km.
The results shown in Figure 5 are that of a combined spectra analysis (i.e., both proton and electron damage contributing to the total PV damage), which uses the integral flux radiation spectra data collected using SPENVIS shown in Figure 4a,b. This MC-SCREAM tool can determine the Isc, Voc, and Pmax degradations based on the PV damage mechanism of the displacement damage dose (DDD). This analysis was completed for (1) individual Pmax degradations due to electrons, (2) individual Pmax degradations due to protons, and (3) combined spectra. Pmax degradations using the MC-SCREAM tool were repeated for orbit altitudes of 1000 km to 36,000 km in 1000 km increments with the results tabulated in MS Excel for data processing and visualization, sorted by PV Pmax losses due to electrons, protons, and combined spectra. Figure 6 and Figure 7 below show the differences in power degradations for trapped protons and electrons, respectively. Figure 7 shows the average of total combined spectra for protons and electrons (and the average of the damage caused between 50.8 to 127 µm (2 to 5 mil) thickness of CMG thickness). Figure 6, Figure 7 and Figure 8 are representative of 1- and 15-year mission durations with orbital altitudes ranging from 1000 km to 36,000 km.
In Figure 8, for 1-year mission durations we can see region (a) shows where electron flux dominates in orbits 1000 km to 7000 km, thus contributing more to overall PV damage. Region (b) is the area where proton flux becomes more prevalent and impactful to total combined spectra Pmax losses; both behaviors are observed in the 15-year analysis. Point (c) is the point where proton radiation spectra forecast begins to improve rapidly and clearly shows the correlation between electron flux and total combined spectra Pmax losses. This behavior is further observed in the 15-year analysis, with greater proton spectral flux improvement as a function of orbital altitude, as indicated by point (d).
The maximum power degradation is mostly attributed to the trapped electrons despite having lower energy ranges than the protons. Using integral flux, the proton and electron spectral fluence increases between 1000 km to 2000 km, resulting in a higher NIEL dose, while also yielding lower Pmax values for both the 1- and 15-year analysis. This behavior is also observed from 2000 km to 10,000 km for protons. However, as proton and electron radiation spectral fluence decreases as the orbit altitude increases beyond 10,000 km, this yields more favorable Pmax performance at higher altitudes. This Pmax performance trend is also observed when analyzing the calculated proton and electron NIEL dose rates shown in Figure 9; proton and electron doses peak at 13,000 km and 16,000 km, respectively.
Orbit altitudes of 20,000 km and 36,000 km offer similar radiation dose and Pmax characterization for gallium arsenide PV cells; however, GEO 36,000 km has the lowest NIEL dose. In the use-case of SBS, where closer proximity to earth is more favorable for power beaming operations, this analysis concludes that radiation damage in MEO 20,000 km with 15-year mission durations can be supported with minimal cover glass thickness. From the data, it is also concluded that a cover glass thickness of 76.2 µm (3 mil) offers suitable protection, offering near identical radiation protection as higher cover glass thicknesses. An amount of 76.2 µm (3 mil) CMG for satellites operating at 20,000 km yields proton/electron Pmax performance at 92.4%/86.4% and 69.8%/60.4%% for 1- and 15-year mission durations, respectively. The lowest Pmax performance in orbital altitude performance is observed at 13,000 km for protons at 55% and 16,000 km for electrons at 44%, where the combined spectra Pmax losses for both protons and electrons at those altitudes are 66% and 50%, respectively. Using the combined spectra to account for both proton and electron flux and intensities, the total Pmax losses for those MEO 10,000 km are 25%, MEO 20,000 km are 16%, and GEO 36,000 km are 10%.

3.3. Comparison of Results

This analysis covers a wide range of orbital altitudes and calculated Pmax performance for GaInP/GaAs/Ge PV cells under various radiation spectra. As observed in the data, the radiation impacts from protons and electrons for LEO at altitudes of 1500 km to 5000 km have the largest difference in resultant EOL Pmax degradations. Therefore, it was important to corroborate the results with similar orbits (i.e., 55-degree inclination angles with low eccentricity) from the previous literature. Woike (1992) modeled a GaAs PV array with an orbit of 960 km and inclination angle of 60 degrees, which forecasts a 4% power density drop in the first year and a ~16% power density drop after 10 years assuming 3 mil cover glass thicknesses [32]. The author shows power density losses at 1% in the first year at 1000 km and ~9% after 15 years. Additionally, although the spectral fluence and dose rates are similar but not identical to our analysis, Woike (1992) modeled 60-degree inclination at 20,372 km for 3 mil cover glass and showed power density losses at 6% and ~25% for 1- and 10-year mission durations, respectively. Since the radiation spectra for our analysis in this paper is collected at 55-degree inclination, the results are similar with ours at 7% in 1 year and 29% in 15 years; additionally, it forecasts ~25% losses after 10 years at 20,372 km [32]. Assuming the damage tapers off as mission duration increases (i.e., most of the Pmax is lost in shorter mission durations, within the first 100 days), then this is in reasonable agreement with our results.
For altitudes < 1000 km in LEO, which extends from 160 km to 2000 km, the International Space Station (ISS) operating at 460 km is the selected candidate for showing PV degradations and comparing GaAs to Si-based PV technologies. Kerlslake and Gustafson (2003) shows that crystalline silicon solar cells used on the ISS have observed on-orbit short circuit current (Isc) degradation rates for the ISS ranging from 0.15% to 0.45% per year in LEO, with 0.8% in modeling predictions [33]. Our analysis results are shown using Pmax power remaining; however, using MC-SCREAM, we are still able to compare results with other studies, as the electrical performance for open circuit voltage, short circuit current, and maximum power is calculated. Our Isc analysis results for altitudes < 1000 km using 2 mil CMG cover glass shows 0.065% losses for 1-year mission durations, with the majority of the losses attributed to electrons in that orbit. Therefore, comparing results using Isc for Kerslake and Gustafson (2003) to our analysis for altitudes < 1000 km in LEO indicates greater survivability for GaAs PV cells over Si cells. When modeling the Si PV cells on the ISS using MC-SCREAM, forecast Isc degradations forecast 0.76%, which is within 0.03% of predictions in [33]. This also highlights how the analysis in our paper is unique since we are correlating the damage as a function of orbital altitude (specifically MEO) while also quantifying the mission duration variable. As LEO altitudes > 2000 km accelerates annual degradation, using the LeoLabs orbit visualization tool, it was determined that nearly 99% of LEO satellites operate > 1500 km to avoid this radiation-intense zone [34]. To date, out of 21,604 satellites currently in LEO, 21,408 reside in orbit altitudes below 1500 km.
For GEO, 1- and 15-year Pmax losses are shown in the study from Messenger, Jackson, and Warner (2010), where the forecasted radiation spectra values align with intensities for protons and electrons in GEO altitudes. It shows that for protons and electrons at GEO for 15 years, the EOL % Pmax performance for 2, 3, 4, and 5 mil cover glass is 72%, 76%, 78%, and 80%, respectively [7]. Although the inclination of 60 degrees is noted, the orbit altitude for GEO is unspecified but is usually understood at an altitude of 35,786 km. The cover glass used in this analysis was SiO2 instead of CMG, which is used in our analysis, as well as an inclination angle of 55 degrees. Fused silica (SiO2) cover glass (ρ = 2.32 g/cm3) and 2 mils of DC 93-500 silicone adhesive (ρ = 1.06 g/cm3) were used in this study [7]. Using SiO2 as the cover glass material in MC-SCREAM simulations using worst-case orbital proton and electron fluences at 13,000 km and 16,000 km for our study, we found that CMG offered only slightly better Pmax performance of 1% to 1.5% over SiO2. Using the multijunction GaInP/GaAs/Ge PV cell configuration shown in Figure 2, our analysis for 36,000 km at 15 years using 4 mil CMG cover glass shows 4% due to protons (total dose rate = 8.72 × 108 MeV/g) and 31% due to electrons (total dose rate = 3.79 × 1010 MeV/g).
The TacSat-4 satellite experiment provided valuable data for comparison on PV degradations in high radiation zones [13]. A low-eccentricity near circular MEO and GEO is proposed in this study for the SBS mission, whereas TacSat-4 operated in a 4 h highly elliptical earth orbit (HEO) and passed through high-energy proton and electron belts 12 times per day, with a 63.4-degree inclination, perigee (e.g., the closest point of approach to Earth) at 700 km, and apogee (e.g., the farthest point of the orbit from Earth) at 12,050 km [13]. The radiation data collected from SPENVIS used orbit altitudes of 1000 km to 36,000 km using an inclination of 55 degrees for 1- and 15-year mission durations. As the radiation intensity at 10,000 km contains both high- and low-energy protons at high fluence, the TacSat-4 experiment provides valuable on-orbit radiation data for that region specifically. From the TacSat-4 Solar Cell Experiment (TSCE), radiation data were collected by the Compact Environment Anomaly Sensor instrument and initially showed that an Emcore triple-junction GaAs solar cell with 6 mil (0.1524 mm) CMG cover glass and 2 mils (0.0508 mm) of DC 93-500 bonding agent (e.g., no magnesium fluoride–MgF2–coating used) yields a Pmax of 0.74, which was designed to meet power requirements for 1 year of operation [13]. The PV array used 6 mil CMG cover glass and showed that omnidirectionally incident protons having energy from 1 to 10 MeV are the most important in causing damage to the underlying cell [13]. Results also showed that the PV array reached baseline 1-year values in <4 months, which exceeded projections based on the AE9/AP9 95th percentile worst-case environment [13].
Accelerated EOL degradation trends using the TacSat-4 demo helped shape this analysis by indicating a need for assessing PV arrays as a function of orbital altitude (for a near circular orbit to maximize SBS overflight consistency) and mission duration. Additionally, it was completed to consider cover glass thicknesses < 6 mil as well as assume worst-case AE9/AP9 95th percentile forecasts for proton and electron fluence in the Pmax calculations. A satellite traversing in and out of radiation zones based on the HEO profile will have more variability in the spectral fluence as opposed to the MEO and GEO profiles used in this analysis due to the low eccentricity. With 6 mil CMG cover glass on the front of the TSCE and a 12 mil Germanium backside substrate, the maximum power output of the solar cells drops to 84.9% of beginning-of-life values. Messenger (2017) stated that this is in reasonable agreement with the Emcore manufacturer’s datasheet, which indicates a drop in power to 89% after irradiation by 1 × 1014 #/cm2 1-MeV electrons [8].
Lozinski et al. (2019) shows Pmax performance for satellites using multijunction GaAs PV cells with 4 mil (100 μm) cover glass thickness in highly elliptical earth orbit (HEO) [35]. The major difference in this study is that the orbit is HEO (highly elliptic with altitudes ranging from 300 km to 33,000 km) and that the cover glass thicknesses are shown for 4, 6, and 8 mil thicknesses. Most losses occur in the first year (<100 days) and then plateau, with 4 mil cover glass showing damage due to protons at 6% to 15%. There is considerable variability with the radiation spectra in this study and can impact the NIEL dose rate for the PV cell (similar to TacSat-4 data); however, it does show that there is significant damage that can occur from variable changes in orbital altitude shifts and operations in HEO. Figure 10 below shows a color-coded chart to summarize and compare the results for GaAs PV cells.
The items in red show greater than 10% disagreement in the results; however, this is attributed to (1) greater than 10% difference in mission durations (e.g., comparing 10-year Pmax degradations to 15-year Pmax degradations) and (2) the variability in the predicted proton and electron spectral fluence in HEO compared to low eccentricity orbits calculated for MEO and GEO in our analysis.

4. Conclusions

This paper assessed damage due to proton and electron bombardment of GaAs PV cells operating on various orbits around the earth. As MEO is associated with higher proton energy fluxes than both LEO and GEO, it was anticipated that radiation damage would be higher in MEO than in the other orbits. However, this study determined electrons, rather than protons, to be the prime electronic damage culprits; consequently, the total spectrally combined power losses in MEO’s upper range was found to be only slightly higher than the losses expected in GEO. Radiation exposure due to high-energy protons at 20,000 km is much less prevalent than exposure at 10,000 km orbits. For MEO at 10,000 km, MEO at 20,000 km, and GEO at 36,000 km, we determined 1-year Pmax losses due to protons to be 23%, 8%, and 1% and losses due to electrons to be 11%, 14%, and 10%; we determined 15-year Pmax losses due to protons to be 51%, 31%, and 5% and 36%, 40%, and 34% due to electrons.
However, MEO 20,000 km has obvious advantages over GEO regarding launching, maintenance, and transmission losses due to long distances, metrics that must also be considered when selecting orbital altitudes. Overall, satellite operation in MEO 20,000 km may be advisable although radiation damage will be slightly higher than in GEO 36,000 km. We also examined encapsulation systems for radiation shielding and determined that CMG cover glass thickness of 76.2 µm (3 mil) offers a balance between reduced weight and radiation shielding from electrons. As presented, using this analysis method to predict EOL based on the NIEL/TNID degradation mechanisms is critical for the determination of radiation survivability for critical electrical components on spacecraft. In the case of an SBS mission or any spacecraft equipped with PV arrays for primary power, protection from the harsh radiation environment is key for extending the service life and power output for the system. Designing a system that is protected from trapped high-energy particles while simultaneously balancing weight from cover glass is a principal consideration for all satellite operations and design.

Author Contributions

Conceptualization, A.P., M.P. and V.F.; methodology, A.P.; software, A.P.; validation, A.P., M.P. and V.F.; formal analysis, A.P.; investigation, A.P., M.P. and V.F.; resources, A.P., M.P. and V.F.; data curation, A.P.; writing—original draft preparation, A.P.; writing—review and editing, A.P., M.P. and V.F.; visualization, A.P.; supervision, M.P. and V.F.; project administration, M.P. and V.F.; funding acquisition, V.F. All authors have read and agreed to the published version of the manuscript.

Funding

This study received no external funding.

Data Availability Statement

Data supporting the reported results, such as MATLAB code and the computational analysis for orbital modeling, can be found by contacting the lead author.

Acknowledgments

A.P. is grateful to Chris Rodenbeck and Paul Jaffe for their research in SBS and wireless power transmission. Additional thanks for the scientific review of our research are given to Thomas Peng, Chris Morath, Julie Logan, Robert Walters, William Johnston, Ryan Hoffman, and Chad Lindstrom. Also, thanks are due to Scott Messenger for his extensive work in NIEL and DDD for PV materials.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The illustration of the functional layers contained in the SBS sandwich module used in [1].
Figure 1. The illustration of the functional layers contained in the SBS sandwich module used in [1].
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Figure 2. Layering used in the MC-SCREAM modeling tool for the GaAs/InP ATJ PV cell; the back surface field (BSF) is positively doped InGaP.
Figure 2. Layering used in the MC-SCREAM modeling tool for the GaAs/InP ATJ PV cell; the back surface field (BSF) is positively doped InGaP.
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Figure 3. Calculated NIEL profiles for various semiconductor materials using trapped proton (a) and electron energies (b).
Figure 3. Calculated NIEL profiles for various semiconductor materials using trapped proton (a) and electron energies (b).
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Figure 4. One-year proton (a) and one-year electron (b) radiation spectra as a function of orbital altitude.
Figure 4. One-year proton (a) and one-year electron (b) radiation spectra as a function of orbital altitude.
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Figure 5. Spectrally combined trapped protons and trapped electron Pmax degradation for a GaInP/GaAs/Ge PV cell at a 10,000 km, 55-degree inclination orbit assuming a 76.2 µm (3 mil) CMG thickness.
Figure 5. Spectrally combined trapped protons and trapped electron Pmax degradation for a GaInP/GaAs/Ge PV cell at a 10,000 km, 55-degree inclination orbit assuming a 76.2 µm (3 mil) CMG thickness.
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Figure 6. MC-SCREAM trapped proton damage for 1- and 15-year mission durations under varying cover glass thicknesses.
Figure 6. MC-SCREAM trapped proton damage for 1- and 15-year mission durations under varying cover glass thicknesses.
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Figure 7. MC-SCREAM trapped electron damage for 1- and 15-year mission durations under varying cover glass thicknesses.
Figure 7. MC-SCREAM trapped electron damage for 1- and 15-year mission durations under varying cover glass thicknesses.
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Figure 8. MC-SCREAM combined average spectra damage for both protons and electrons for 1- and 15-year mission durations using average maximum power calculations from 50.8 to 127 µm (2 to 5 mil) thicknesses.
Figure 8. MC-SCREAM combined average spectra damage for both protons and electrons for 1- and 15-year mission durations using average maximum power calculations from 50.8 to 127 µm (2 to 5 mil) thicknesses.
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Figure 9. MC-SCREAM calculated displacement damage dose rates for protons and electrons.
Figure 9. MC-SCREAM calculated displacement damage dose rates for protons and electrons.
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Figure 10. The PV cell MC-SCREAM comparison of results from the literature (left) and the author’s analysis (right). Retrieved from [7,14,32,35].
Figure 10. The PV cell MC-SCREAM comparison of results from the literature (left) and the author’s analysis (right). Retrieved from [7,14,32,35].
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Peters, A.; Preindl, M.; Fthenakis, V. Semiconductor Material Damage Mechanisms Due to Non-Ionizing Energy in Space-Based Solar Systems. Energies 2025, 18, 509. https://doi.org/10.3390/en18030509

AMA Style

Peters A, Preindl M, Fthenakis V. Semiconductor Material Damage Mechanisms Due to Non-Ionizing Energy in Space-Based Solar Systems. Energies. 2025; 18(3):509. https://doi.org/10.3390/en18030509

Chicago/Turabian Style

Peters, Anthony, Matthias Preindl, and Vasilis Fthenakis. 2025. "Semiconductor Material Damage Mechanisms Due to Non-Ionizing Energy in Space-Based Solar Systems" Energies 18, no. 3: 509. https://doi.org/10.3390/en18030509

APA Style

Peters, A., Preindl, M., & Fthenakis, V. (2025). Semiconductor Material Damage Mechanisms Due to Non-Ionizing Energy in Space-Based Solar Systems. Energies, 18(3), 509. https://doi.org/10.3390/en18030509

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