In this work we present our latest results and analysis of a 10 MeV proton irradiation experiment performed on III-V solar cells. A set of representative devices were irradiated for different fluences, including latticematched GaInP/GaInAs/Ge triple junction, GaInP/Ge double junction, and GaAs and Ge single junction solar cells. The methodology applied included the irradiation of two devices of each type; for a better control of the measurements, non-irradiated devices with the same characteristics of those irradiated were used as reference. The devices were monitored before and after each exposure by in-situ characterization of the electrical response under dark and under illumination using a solar simulator connected to the irradiation chamber through a borosilicate glass window. Ex-situ characterization techniques included dark and 1 sun AM0 illumination I-V curve and external quantum efficiency measurements. Furthermore, results of the numerical simulation of devices with D-AMPS-1D code are presented in order to give a physical interpretation of the results. DLTS spectroscopy preliminary results for single junction GaAs cells are also presented

Algora del Valle, Carlos

Alurralde, M.

Barrera, Marcelo

Barrigón Montañés, Enrique

Espinet González, Pilar

García, J.

Godfrin, E. M.

Ibarra, M. L.

Ochoa Gómez, Mario

Plá, J.

Rey Llorente, Ignacio del

Rodríguez, S.

Rubinelli, F.

Yaccuzzi, E.

Archivo Digital UPM

Effects of 10 MeV proton irradiation on III-V solar cells

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

EFFECTS OF 10 MEV PROTON IRRADIATION OF III-V SOLAR CELLS 
 
 
E. Yaccuzzi1,2, M. Ochoa3, M. Barrera1,2, E. Barrigón3, S. Rodriguez1, P. Espinet3, M.L. Ibarra1,2, J. Garcia1,2,  
E.M. Godfrin1, M. Alurralde1, F. Rubinelli4, C. Algora3, I. Rey-Stolle3, J. Plá1,2 
1 Departamento Energía Solar - Gerencia Investigación y Aplicaciones - CNEA 
2 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) 
Av. General Paz 1499 - (1650) San Martín – Argentina 
Tel. (+54-11) 6772-7128, Fax (+54-11) 6772-7121, jpla@tandar.cnea.gov.ar 
3Instituto de Energía Solar – Universidad Politécnica de Madrid 
Av. Complutense 30; 28040 Madrid -Spain 
4INTEC-CONICET, Universidad Nacional del Litoral 
Güemes 3450, 3000 Santa Fe - Argentina 
 
ABSTRACT: In this work we present our latest results and analysis of a 10 MeV proton irradiation experiment 
performed on III-V solar cells. A set of representative devices were irradiated for different fluences, including lattice-
matched GaInP/GaInAs/Ge triple junction, GaInP/Ge double junction, and GaAs and Ge single junction solar cells. 
The methodology applied included the irradiation of two devices of each type; for a better control of the measurements, 
non-irradiated devices with the same characteristics of those irradiated were used as reference. The devices were 
monitored before and after each exposure by in-situ characterization of the electrical response under dark and under 
illumination using a solar simulator connected to the irradiation chamber through a borosilicate glass window. Ex-situ 
characterization techniques included dark and 1 sun AM0 illumination I-V curve and external quantum efficiency 
measurements. Furthermore, results of the numerical simulation of devices with D-AMPS-1D code are presented in 
order to give a physical interpretation of the results. DLTS spectroscopy preliminary results for single junction GaAs 
cells are also presented. 
Keywords: Radiation Damage, III-V Semiconductors, Space Cells, Concentrator Cells 
 
 
1 INTRODUCTION 
 
Solar cells are the primary source of electrical power 
for spacecraft, satellites and other space vehicles. The 
devices in orbit suffer the irradiation of energetic charged 
particles, leading to degradation in their electrical and 
electronic properties.  
The Solar Energy Department (DES) of the Argentine 
Atomic Energy Commission (CNEA) and the Institute of 
Solar Energy (IES) of the Technical University of Madrid 
(UPM), Spain, collaborate in a scientific project devoted 
to the study of III-V semiconductor-based solar cells. Both 
groups take advantage of their complementary expertise to 
study radiation damage on concentrating photovoltaic 
solar cells optimized for terrestrial applications. This work 
was carried out taking into consideration the results of a 
former work [1] to design a new experiment. The set of 
irradiated samples include GaAs and Ge homojunctions, 
GaInP/Ge double junctions and GaInP/GaAs/Ge triple 
junctions (TJ) solar cells. The experiment included in-situ 
dark and illuminated I-V curve measurements and 
modeling; ex-situ measurements were also performed, 
including external quantum efficiency and DLTS 
spectroscopy. In this paper, the preliminary studies of III-
V solar cell damage using 10MeV proton irradiation are 
presented, so as some insight in the interpretation of 
results. Different characterization techniques and 
numerical simulation were applied to this objective. 
 
2 EXPERIMENTAL SETUP 
 
All experiments have been performed under high 
vacuum using a specially developed chamber installed in 
one of the experimental lines of the CNEA tandem 
accelerator (for further details see also Refs. [2],[3]). In 
order to spread the beam, a 10 μm-thick aluminium foil 
was installed in the beam path about 6 m before the 
chamber (Fig. 1). The resulting beam intensity uniformity 
at the target position was determined before the 
experiment by using an array of 9-Faraday cups (FC) 
positioned a few centimeters behind the sample holder. 
The beam current in each FC was measured using a 
Keithley 6514 electrometer. 
 
 
 
Figure 1: Top view of the irradiation chamber. The holder 
with the samples is on the upper side of the picture. All 
solar cells were wired to allow in situ measurement of I-V 
curves. The array of Faraday cups is seen at the right 
border of the picture. 
 
The results of these measurements were recorded in a 
local computer and this information was replicated in a 
second computer sitting in the accelerator control room. 
The overall beam uniformity was better than 5% over the 
whole target area. To observe the evolution of the 
degradation of the devices during irradiation, the beam 
was interrupted at different fluence values, allowing the 
measurement of I-V curves at each step. The solar cells 
used in this study were fabricated employing the 
metalorganic vapor phase epitaxy (MOVPE) technique. 
The devices, with active areas of 1mm2, were encapsulated 
on copper plates. The irradiated cells set included GaAs, 
31st European Photovoltaic Solar Energy Conference and Exhibition
1439
GaInP and Ge homojunctions, one GaInP/Ge double-
junction and two GaInP/GaAs/Ge triple-junctions (TJ). 
The cells were measured ex situ before and after 
irradiation using a TS-Space AM0 close match solar 
simulator at T = 28ºC with 1.367 kW/m2 (equivalent to 
AM0 spectrum) calibrated with isotype and triple junction 
reference cells. In addition, the solar cells were measured 
in situ before and after each irradiation by a Sciencetech 
solar simulator with AM0 filter coupled to the irradiation 
chamber through a borosilicate window and a source 
measure unit (SMU) Keithley 2602A using the four wire 
configuration. All I-V curves are presented under standard 
conditions (1 sun AM0, 28ºC) after temperature and 
irradiance corrections using as reference the 
measurements performed with the TS-Space simulator.  
 
3 EXPERIMENTAL RESULTS 
 
As example of the evolution of the cells electrical 
parameters versus fluence, Figure 2 shows the normalized 
Jsc degradation curves obtained for GaAs and Ge 
homojunctions, GaInP/Ge double-junction and 
GaInP/GaAs/Ge triple-junction. 
 
 
 
(a) 
 
 
 
(b) 
 
 
 
(c) 
 
 
 
(d) 
 
Figure 2: Normalized Jsc vs. fluence for: a) GaAs solar 
cells, b) Ge solar cells, c) GaInP/Ge double junction solar 
cells and d) GaInP/GaAs/Ge triple junction solar cells. 
 
The degradation of the Jsc is the expected for this type 
of cells and these particular experimental conditions. 
GaInP cells showed the lower sensitivity to irradiation, 
while GaAs showed the higher. A minor trend to 
degradation, close to the experimental error, is also 
observed for the Ge cells. In the case of the TJ cells, the 
GaAs subcell (middle) degradation limits the overall 
current. In this context, current degradation was found 
quantitatively consistent when the spectral response of the 
middle cell (Fig. 3) was used to get the subcell current after 
irradiation. 
The external quantum efficiency (EQE) was measured 
at IES-UPM before and after irradiation. Changes of EQE 
of the GaAs and the TJ solar cells are shown in Fig. 3. The 
curve of the GaAs cell drops in the wavelength range 
between 700 - 900 nm, consistently with the degradation 
of the diffusion length in the base of the device due to 
irradiation. Similar results are presented, for example, in 
references [4] for 10 MeV proton irradiation on a GaAs/Ge 
solar cell and [5] for a GaInP/GaAs/Ge TJ using 2.8 MeV 
protons. 
 
0 1E9 1E10 1E11 1E12
0.91
0.92
0.93
0.94
0.95
0.96
0.97
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0.99
1.00
1.01
 1607D11C
 1607D08A
n
o
rm
a
liz
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d
 J
s
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fluence (p/cm
2
)
GaAs
0 1E9 1E10 1E11 1E12
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0.92
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1.00
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Ge
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fluence (p/cm
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)
0 1E9 1E10 1E11 1E12
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 1888D08H
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n
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fluence (p/cm
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)
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0 1E9 1E10 1E11 1E12
0.91
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1.00
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 1611H2
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n
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)
GaInP/GaAs/Ge
31st European Photovoltaic Solar Energy Conference and Exhibition
1440
 
(a) 
 
 
 
(b) 
 
Figure 3: External Quantum Efficiency for: a) GaAs solar 
cells and b) GaInP/GaAs/Ge triple junction solar cells. 
 
An interesting effect is observed in the Ge bottom cell, 
whose EQE seems to increase after proton irradiation. This 
effect suggests a quenching of the photon coupling 
between the middle and bottom subcells after irradiation. 
In other words, before irradiation the measured EQE of the 
Ge bottom cell is artificially low (and shows some response 
from 800 nm to 900 nm) as a result of photon coupling from 
the GaAs middle cell. Once irradiated, the radiative 
recombination of the middle cell is greatly decreased and the 
real (higher) EQE of the bottom cell is measured. 
 
4 NUMERICAL SIMULATIONS 
 
The electrical transport and light absorption in GaAs 
solar cells were studied with the computer code D-AMPS-
1D [6]-[7]. D-AMPS is an updated version of the one-
dimensional (1D) software AMPS (Analysis of 
Microelectronic and Photonic Devices) developed at The 
Pennsylvania State University, University Park, USA [8]. In 
AMPS finite differences and the Newton–Raphson 
technique are used to solve the system of the Poisson and 
continuity equations subjected to appropriate boundary 
conditions [9]. The three selected unknowns were the quasi-
Fermi levels EFN and EFP and the electron potential  [9]. 
Structures such as homojunctions, heterojunctions, 
multijunctions, etc, resulting from stacking layers of 
different materials can be studied by appropriately selecting 
characteristic parameters such as the gap energy, carrier 
mobilities, absorption coefficients, and doping 
concentrations among others. The letter D stands for new 
developments like the amphoteric state physics [10], the 
Pool–Frenkel effect [7], the Defect Pool model [11], direct 
and recombination tunnelling [12],[7], gap and doping 
continuous grading, light scattering at rough surfaces, light 
interference, etc. These improvements implemented in D-
AMPS allowed a better interpretation of characterization 
results and design of solar cells containing amorphous, 
microcrystalline, and crystalline semiconductor layers. 
More recently, in order to properly model recombination of 
electron–hole pairs in direct gap materials and in heavily 
doped crystalline semiconductors the mechanisms of band-
to-band (direct) and Auger recombination were also added 
to the already existing Shockley–Read–Hall formalism. 
In order to simplify the modelling and first discussions 
the radiation induced lattice defects are modeled as traps 
with a single energy level. The main parameters used in the 
simulations are listed in Table I. 
 
 
 Window Emitter Base BSF Buffer Sustrate 
material GaInP GaAs GaAs AlGaAs GaAs GaAs 
Eg (eV) 1.85 1.42 1.42 1.85 1.42 1.42 
d (nm) 25 177 4833 150 1000 350000 
ND (cm-3) 1x1018 1x1018 0 0 0 0 
NA (cm-3) 0 0 1x1017 2x1018 1x1018 1x1019 
BR (cm3s-1) 1x10-10 7.2x10-10 7.2x10-10 - 7.2x10-10 7.2x10-10 
n (cm2V-1s-1) 400 2051 2051 400 2051 2051 
p (cm2V-1s-1) 40 95 95 40 95 95 
 
Table I: Typical parameters used in the numerical simulations of GaAs cell. Eg: the band gap, d: layer thickness, ND: donor 
doping density, NA: acceptor doping density, R: radiative recombination rate coefficient, n: electron mobility and P: hole 
mobility. 
 
 
200 300 400 500 600 700 800 900 1000
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
 
 
1607D08A
 after irradiation
 bebore irradiation
E
Q
E
 (nm)
200 400 600 800 1000 1200 1400 1600 1800 2000
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
 
 
E
Q
E
(nm)
thick line: before irradiation
thin line: after irradiation
31st European Photovoltaic Solar Energy Conference and Exhibition
1441
The capture cross section for electrons and holes in the base 
at the discrete donor level were assumed 1x10-13 cm-3 and 
1x10-15 cm-3 respectively, considering capture cross 
sections published in the literature [13]. The Jsc as function 
of the donor-like trap energy and density obtained with the 
simulations are shown in Figure 4.  
 
 
 
Figure 4: Jsc as function of the donor-like trap energy and 
density.  
 
At the maximum defect density explored, 1x1017 cm3, 
the short circuit current decreases to its minimum for trap 
energies near midgap. For a defect density of 1x1015cm3 
Jsc decreases about 3% similarly to it is seen in Figure 2a 
for a fluence about of 1x1012 p/cm3.  
Simulations performed with a discrete acceptor level 
showed no significant degradation considering similar 
capture cross sections as that used for the calculations 
showed in Fig. 4. 
 
5 DLTS APPLICATION 
 
We recently set up at DES-CNEA a DLTS (Deep 
Level Transient Spectroscopy) system based on a fast 
capacimeter Boonton model 7200 with analogic output, a 
digitalizer DAQ National Instrument PCI-6132 S, and a 
pulse generator Agilent model 33220A. Sample 
temperature is controlled by a home made holder that 
includes a serpentine for LN2 circulation and a resistive 
heater, allowing temperatures between 80 K and 450 K 
using an electronic PID (Proportional-Integral-Derivative) 
commercial controller. The DLTS measurment is 
performed using a specially developed Labview code 
running in a PC.  
Preliminary results obtained for a GaAs sample similar 
to those irradiated are shown in Fig. 5. Future 
measurements on irradiated samples will lead us to a better 
understanding of the effects of charged particle irradiation 
on solar cells. 
By the other side, we studied the feasibility to describe 
the junction capacity transient using the analytical 
expressions developed by Z. Li [14], taking into account 
material properties, temperature, and the introduction of 
defect levels. This allowed us to perform numerical 
simulation of DLTS spectra. 
 
 
 
Figure 5: DLTS spectra for a GaAs device. Three rate 
windows were used; the corresponding Arrhenius plot is 
in the inset. The defect energy obtained is 0.42eV (respect 
to the valence band).  
 
6 CONCLUSIONS  
 
A 10 MeV proton irradiation experiment was performed 
on III-V solar cells, and various characterization techniques 
were applied. This work was carried out taking into 
consideration the results of a former work to design a new 
experiment.  
The results obtained show the expected trend of 
electrical parameters to degradation. Preliminary results of 
the numerical simulation of devices with D-AMPS- 1D code 
for single junction GaAs cells showed the feasibility of 
modeling the degradation of these cells introducing donor 
like defects in the gap.  
In the future, experimental measurements of energy 
level and cross section of the defects will allow us to gain a 
better physical insight on the effects induced by the 
irradiation in III-V devices. 
 
7 ACKNOWLEDGEMENTS 
 
This work was funded by CNEA, the grants PIP2009-
2011 Nº 02318 and PIP2012-2014 Nº 01052 (CONICET), 
PICT2007 Nº 01143 and PICT2013 Nº 3077(ANPCyT), 
and the bilateral collaboration MINCyT-MICINN 2012-
2013 (Argentina-Spain) Nº ES/11/04 “Fabrication, 
characterization, simulation and test on solar cells based on 
III-V semiconductors”.  
 
8 REFERENCES 
 
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III-V semiconductor materials and solar cells upon 10 
MeV proton irradiation, Proceedings of the 28th 
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[4] W. Yueyuan et al., Radiation damage effects on double-
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-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
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5
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max
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E=0.42 eV 
31st European Photovoltaic Solar Energy Conference and Exhibition
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Effects of 10 MeV proton irradiation on III-V solar cells

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