1. Dr. Scott R. Messenger SFA, Inc. (messenger@nrl.navy.mil) SPENVIS & GEANT4 workshop Faculty Club Leuven, Belgium 3 - 7 October 2005 Displacement Damage Dose Approach For Determining Solar Cell Degradation In Space With Spenvis Implementation

2. Introduction Space Solar Cell Degradation Calculations –NASA JPL Equivalent Fluence Method –NRL Displacement Damage Dose (D d ) Method Nonionizing Energy Loss (NIEL) –Comparisons SPENVIS Implementation –MULASSIS is the key Notes Future Work Outline S. Messenger, SPENVIS Workshop 2005

3. Omnidirectional, isotropic, energy spectrum in space Unidirectional, normally incident, monoenergetic irradiation of bare solar cells on the ground protons electrons The Problem S. Messenger, SPENVIS Workshop 2005 *Planar, slab geometry

4. P max Degradation Curves for GaAs/Ge Solar Cells (JPL, 1991) S. Messenger, SPENVIS Workshop 2005

5. Equivalent Fluence Method – created by NASA Jet Propulsion Laboratory (JPL) –Can be implemented through available FORTAN programs –Is included in the SPENVIS web-suite (and others) –Has widespread application and over 30 years of heritage Displacement Damage Dose Method (D d ) – created by the US Naval Research Laboratory (NRL) –Does not have widespread application due to lack of distributed computational tool Solar Array Verification and Analysis Tool (SAVANT) is available but only in beta-version (unfunded at present) This paper shows how the SPENVIS web-suite can be used to implement the D d method The Solution S. Messenger, SPENVIS Workshop 2005

6. JPL and NRL Methods NASA Jet Propulsion Laboratory (Pasadena, CA) –Reduces mission space radiation effects to an equivalent 1 MeV electron fluence –Read EOL power from measured 1 MeV electron curve US Naval Research Laboratory (Washington, DC) –Calculate displacement damage dose, D d, for mission –Read EOL power from measured characteristic curve S. Messenger, SPENVIS Workshop 2005

7. JPL Method (Equivalent Fluence Method) Summarized in two publications (developed in 1980’s) –Solar Cell Radiation Handbook, JPL Publication 82-69 (1982) –GaAs Solar Cell Radiation Handbook, JPL Publication 96-9 (1996) Utilizes the concept of relative damage coefficients (RDC’s) Reduces all damage to a 1 MeV electron equivalent fluence and uses 1 MeV electron data to get the EOL result Several computer programs (FORTRAN) are available: –EQFLUX (Si), EQGAFLUX (GaAs), and multijunction (MJ) cell –Other programs (e.g. SPENVIS and Space Radiation) implement JPL method S. Messenger, SPENVIS Workshop 2005

8. Measure PV Degradation Curves (~4 electron and ~8 proton energies) Determine Damage Coefficients for Uncovered Cells Calculate Damage Coefficients for Isotropic Particles w/ Coverglasses of Varied Thickness Read Off EOL Values Determine Incident Particle Spectrum (e.g. AP8) JPL Equivalent Fluence Method 1 MeV Electron Degradation Curve Calculate Equivalent 1 MeV Electron Fluence for Orbit (EQGAFLUX) S. Messenger, SPENVIS Workshop 2005

9. Electron Damage Coefficients Proton Damage Coefficients Electron and Proton Fluence Data (GaAs/Ge, 1991) JPL Equivalent Fluence Method S. Messenger, SPENVIS Workshop 2005

10. Equivalent 1 MeV Electron Fluence where the energy loss is determined from R(E) is the range (for electrons*) where the RDCs for a coverglass thickness t is: *for protons, another term is included to account for end-of-track effects S. Messenger, SPENVIS Workshop 2005

11. Initial Omnidirectional Spectrum Equivalent 1 MeV Electron Fluence Proton Damage Coefficients 1 MeV Electron P max Degradation JPL Equivalent Fluence Method

12. JPL Model Pros/Cons Pros: –Heritage (developed in the 1980s) –Widely available and already incorporated into many space radiation suites (SPENVIS, Space Radiation TM, etc.) Cons: –Much ground test data needed ($$) –Requires 1 MeV electron AND 10 MeV proton data –Currently available for Si (1982), GaAs/Ge (1996), MJ (1999) –Program not particularly user friendly (FORTRAN) –Several flags need to be set –Entire calculation is technology specific (every design change needs requalification, $$) S. Messenger, SPENVIS Workshop 2005

13. NRL Method (Displacement Damage Dose, D d ) Summarized in: –Progress in PV: Research and Applications 9, 103-121 (2001) –Appl. Phys. Lett. 71, 832 (1997) –IEEE Trans. Nucl. Sci. 44, 2169 (1997) RDCs calculated from the nonionizing energy loss (NIEL) Determines degradation curve as a function of D d and uses this curve to get the EOL result Particle transport through the coverglass calculated independently from RDC calculation Computer program (SAVANT) developed by NRL, NASA GRC, and OAI (unfunded at present) – SPENVIS? S. Messenger, SPENVIS Workshop 2005

14. Choose Nonionizing Energy Loss (NIEL) Data (Energy Dependence of Damage Coefficients) Measure Characteristic Degradation Curve vs. D d (D d =NIELxFluence) (2 e - and 1 p + energy) Read Off EOL Value Determine Incident Particle Spectrum (e.g. AP8, AE8) Calculate Slowed-Down Spectrum (SDS) (Shielding) Calculate D d for Mission (Integrate SDS with NIEL) NRL Displacement Damage Dose Method S. Messenger, SPENVIS Workshop 2005

15. NonIonizing Energy Loss NIEL=Rate at which energy is lost to nonionizing events; (UNITS=MeV/cm or MeVcm 2 /g) Differential scattering cross section for displacements Recoil energy Lindhard partition factor S. Messenger, SPENVIS Workshop 2005

16. Several calculations exist, all yielding similar results Notable NIEL calculations (p +, e -, , n o, ions) :  NRL group (NSREC, 1986-2003)  Van Ginneken, 1989  NASA/JPL group (2000-2005, WINNIEL)  CERN group (Huhtinen et al., 2000-2005)  Akkerman and Barak, 2001  Inguimbert & Gigante (NEMO, 2005)  Fischer and Thiel, U. Koln Especially good agreement over practical proton energies for solar cells in space (0.1-10 MeV) NonIonizing Energy Loss S. Messenger, SPENVIS Workshop 2005

17. NIEL for Si (w/Neutron) S. Messenger, SPENVIS Workshop 2005

18. Choose Nonionizing Energy Loss (NIEL) Data (Energy Dependence of Damage Coefficients) Measure Characteristic Degradation Curve vs. D d (D d = NIEL x Fluence) (1 p + and 2 e - energies) Read Off EOL Value Determine Incident Particle Spectrum (e.g. AP8, AE8) Calculate Slowed-Down Spectrum (SDS) (Shielding) Calculate D d for Mission (Integrate SDS with NIEL) NRL Displacement Damage Dose Method S. Messenger, SPENVIS Workshop 2005

19. Displacement Damage Dose (D d ) Unit is MeV/g is analogous to ionizing dose Rad(Si) Protons: n=1 Electrons: 1<n<2 Or, for a spectrum of particles, as that found in space, Slowed-down differential spectra S. Messenger, SPENVIS Workshop 2005

20. Characteristic curve is independent of particle Calculated NIEL gives energy dependence of damage coefficients 4 empirically determined parameters (C,D x,R ep,n) Characteristic Curve With NIEL Measured Data NRL Displacement Damage Dose Method S. Messenger, SPENVIS Workshop 2005

21. Choose Nonionizing Energy Loss (NIEL) Data (Energy Dependence of Damage Coefficients) Measure Characteristic Degradation Curve vs. D d (D d =NIELxFluence) (2 e - and 1 p + energy) Read Off EOL Value Determine Incident Particle Spectrum (e.g. AP8, AE8) Calculate Slowed-Down Spectrum (SDS) (Shielding) Calculate D d for Mission (Integrate SDS with NIEL) NRL Displacement Damage Dose Method S. Messenger, SPENVIS Workshop 2005

22. Based on the Continuous Slowing Down Approximation (CSDA) The rate of energy loss equals that due to the total stopping power (i.e. no energy loss fluctuations, straggling) Particle transport governed by range data CSDA not expected to hold for electrons of low energy An Analytical Calculation Implementing the D d Approach S. Messenger, SPENVIS Workshop 2005

23. Analytical Proton Transport Model S. Messenger, SPENVIS Workshop 2005

24. Choose Nonionizing Energy Loss (NIEL) Data (Energy Dependence of Damage Coefficients) Measure Characteristic Degradation Curve vs. D d (D d =NIELxFluence) (2 e - and 1 p + energy) Read Off EOL Value Determine Incident Particle Spectrum (e.g. AP8, AE8) Calculate Slowed-Down Spectrum (SDS) (Shielding) Calculate D d for Mission (Integrate SDS with NIEL) NRL Displacement Damage Dose Method S. Messenger, SPENVIS Workshop 2005

25. Incident and SDS (Isotropic)NonIonizing Energy Loss Total Mission Dose P max Degradation NRL Displacement Damage Dose Method S. Messenger, SPENVIS Workshop 2005

26. Cumulative Fraction of D d S. Messenger, SPENVIS Workshop 2005

27. SAVANT D d Analysis Code S. Messenger, SPENVIS Workshop 2005 SAVANT: Solar Array Verification and Analysis Tool (NASA, NRL, OAI)

28. Comparison of Results S. Messenger, SPENVIS Workshop 2005

29. NRL D d Model Pros/Cons Pros: –Few ground test measurements needed (3) –Ground test particle energies can be conveniently chosen –Uniform damage deposition required over active region –Shielding algorithm is independent –Allows for rapid analysis of emerging cell technologies –Allows for easy trade studies –Can combine data from different experiments –Allows for alternate radiation particles (neutrons, alphas, etc.) Cons: –Lack of heritage (developed in the mid-1990s) –More suited for sufficiently thin devices (~few  m) –Program currently not available to general public S. Messenger, SPENVIS Workshop 2005

30. Why does the D d Method work so well? S. Messenger, SPENVIS Workshop 2005 The energy dependence of the NIEL closely follows the RDCs over practical energies considered for space applications

31. Proton NIEL Comparison vs. RDCs S. Messenger, SPENVIS Workshop 2005

32. Electron NIEL Comparison vs. RDCs S. Messenger, SPENVIS Workshop 2005

33. Effect of Low Energy Protons on Multijunction (MJ) Solar Cells S. Messenger, SPENVIS Workshop 2005

34. Monoenergetic, Unidirectional Irradiations *T. Sumita, M. Imaizumi, S. Matsuda, T. Ohshima, A. Ohi, and T. Kamiya, Proc. 19 th EPVSEC, Paris, 2004. 3J InGaP 2 /GaAs/Ge S. Messenger, SPENVIS Workshop 2005

35. Proton-Induced QE Degradation in MJ Cells 50 keV protons 100 keV protons 400 keV protons 1 MeV protons S. Messenger, SPENVIS Workshop 2005

36. Monoenergetic, Unidirectional Irradiations Typical ground test conditions (not space conditions) Nonuniform vacancy distribution – Bragg Peak at end of track Different energies can preferentially degrade one sub-junction This effect is not seen in 1 MeV Electron irradiation Top cell degradation Middle cell degradation *T. Sumita, M. Imaizumi, S. Matsuda, T. Ohshima, A. Ohi, and T. Kamiya, Proc. 19th EPVSEC, Paris, 2004. *Results from SRIM 2003 v.26 (www.srim.org) S. Messenger, SPENVIS Workshop 2005

37. Spectrum, Omnidirectional Irradiation Representative of exposure in the space radiation environment The vacancy distribution profile is nearly uniform over active region *Results from SRIM 2003 v.26 using special input file (TRIM.DAT) which specifies random incident angle and energy to simulate L2 spectrum (3 mil SiO 2 ) No special effects due to low energy protons apparent! S. Messenger, SPENVIS Workshop 2005

38. MJ Radiation Response Analysis Methodology Space radiation environment produces virtually uniform vacancy distribution throughout cell –To reproduce this with a monoenergetic, unidirectionally incident particle, we need a fully penetrating proton (>1 MeV) –NO LOW ENERGY PROTON IRRADIATION NECESSARY Total damage induced in cell (i.e. total number of vacancies) in space can be quantified in terms of Displacement Damage Dose (D d ) –Value of D d is calculated by integrating the product of the slowed- down spectrum and the NIEL over energy –Validation exists for several MJ technologies –Enables quick and inexpensive qualification of new technologies –SPENVIS Implementation Soon!!!

39. 1)Incident differential radiation spectra (SPENVIS) 2)Calculation of the “slowed-down” spectra after having passed through shielding (analytical, MULASSIS) 3)Calculation of the total D d for the mission (MULASSIS) 4)Determination of the expected cell degradation (to be added, need characteristic curve info, i.e. C, D x, n, R ep ) SPENVIS Implementation There are four basic components involved in this calculation: MULASSIS is the enabling tool! S. Messenger, SPENVIS Workshop 2005

40. Walk Through SPENVIS – Orbit Generation S. Messenger, SPENVIS Workshop 2005

41. Walk Through SPENVIS – Incident Particle Spectra S. Messenger, SPENVIS Workshop 2005

42. Walk Through SPENVIS – Shielding (Slowed Down Spectra) and Equiv. D d x x x x Run Fluence – gives slowed down spectra NIEL option – performs integration with NIEL to give mission Dd (not fully operational) S. Messenger, SPENVIS Workshop 2005

43. 5093 km, circular, 57 degree, 1 year, 12 mils SiO 2 /Si Calculations Made External to SPENVIS – Equivalent Value of Dd Slowed-down spectra exported as TXT file from MULASSIS Read into MS Excel and integrated with NIEL to give Dd Also calculated by in-house NRL program for comparison Proton D d (MeV/g)Electron D d (MeV/g) MULASSIS3.8E+105.4E+08 In-House Calc3.3E+106.0E+08 protons electrons S. Messenger, SPENVIS Workshop 2005

44. *5093 km, circular, 57 degree, 1 year, 1000 mils Al/Si Thick Shielding Example S. Messenger, SPENVIS Workshop 2005

45. Calculations Made External to SPENVIS – Solar Cell End-of-Life Power Output (c, D x, n, R ep ) Independent Variables S. Messenger, SPENVIS Workshop 2005

46. Mulassis agrees very well with the analytical slab geometry model for protons Mulassis allows for multiple interfaces and layers Effect of electrons usually minimal (However, MULASSIS is probably better since analytical model assumes CSDA) Could be extended for use with heavy ions and neutrons (NIEL is available for most cases) Could be used for other devices where displacement damage is an important damage mechanism (e.g. LED light output, CCD degradation, transistor gain, etc.) Notes S. Messenger, SPENVIS Workshop 2005

47. Continue to work with ESTEC, BIRA, and QINETIQ to further implement the method and perform benchmark tests Develop characteristic radiation degradation curves for current state-of-the-art solar cell technologies Develop capabilities for other devices and irradiation particles Future Work S. Messenger, SPENVIS Workshop 2005