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Dr. Scott R. Messenger SFA, Inc. (messenger@nrl.navy.mil)

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

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Dr. Scott R. Messenger SFA, Inc. (messenger@nrl.navy.mil)

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

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

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

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

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

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

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

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

  12. JPL Model Pros/Cons • Pros: • Heritage (developed in the 1980s) • Widely available and already incorporated into many space radiation suites (SPENVIS, Space RadiationTM, 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, Dd) • 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 Dd 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. NRL Displacement Damage Dose Method Determine Incident Particle Spectrum (e.g. AP8, AE8) Choose Nonionizing Energy Loss (NIEL) Data (Energy Dependence of Damage Coefficients) Calculate Slowed-Down Spectrum (SDS) (Shielding) Measure Characteristic Degradation Curve vs. Dd (Dd=NIELxFluence) (2 e- and 1 p+ energy) Calculate Dd for Mission (Integrate SDS with NIEL) Read Off EOL Value S. Messenger, SPENVIS Workshop 2005

  15. NonIonizing Energy Loss NIEL= Rate at which energy is lost to nonionizing events; (UNITS=MeV/cm or MeVcm2/g) Lindhard partition factor Differential scattering cross section for displacements Recoil energy S. Messenger, SPENVIS Workshop 2005

  16. NonIonizing Energy Loss • Several calculations exist, all yielding similar results • Notable NIEL calculations (p+, e-, a, no, 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) S. Messenger, SPENVIS Workshop 2005

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

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

  19. Displacement Damage Dose (Dd) Unit is MeV/gis analogous to ionizing doseRad(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. NRL Displacement Damage Dose Method Measured Data Characteristic Curve With NIEL • Characteristic curve is independent of particle • Calculated NIEL gives energy dependence of damage coefficients • 4 empirically determined parameters (C,Dx,Rep,n) S. Messenger, SPENVIS Workshop 2005

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

  22. An Analytical Calculation Implementing the Dd Approach • 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 S. Messenger, SPENVIS Workshop 2005

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

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

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

  26. Cumulative Fraction of Dd S. Messenger, SPENVIS Workshop 2005

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

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

  29. NRL Dd 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 mm) • Program currently not available to general public S. Messenger, SPENVIS Workshop 2005

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

  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 3J InGaP2/GaAs/Ge *T. Sumita, M. Imaizumi, S. Matsuda, T. Ohshima, A. Ohi, and T. Kamiya, Proc. 19th EPVSEC, Paris, 2004. S. Messenger, SPENVIS Workshop 2005

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

  36. 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 Monoenergetic, Unidirectional Irradiations Top cell degradation Middle cell degradation *Results from SRIM 2003 v.26 (www.srim.org) *T. Sumita, M. Imaizumi, S. Matsuda, T. Ohshima, A. Ohi, and T. Kamiya, Proc. 19th EPVSEC, Paris, 2004. S. Messenger, SPENVIS Workshop 2005

  37. Representative of exposure in the space radiation environment The vacancy distribution profile is nearly uniform over active region Spectrum, Omnidirectional Irradiation *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 SiO2) 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 (Dd) • Value of Dd 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. SPENVIS Implementation There are four basic components involved in this calculation: • Incident differential radiation spectra (SPENVIS) • Calculation of the “slowed-down” spectra after having passed through shielding (analytical, MULASSIS) • Calculation of the total Dd for the mission (MULASSIS) • Determination of the expected cell degradation (to be added, need characteristic curve info, i.e. C, Dx, n, Rep) 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. Dd • Fluence – gives slowed down spectra • NIEL option – performs integration with NIEL to give mission Dd (not fully operational) x x x Run x S. Messenger, SPENVIS Workshop 2005

  43. 5093 km, circular, 57 degree, 1 year, 12 mils SiO2/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 electrons protons S. Messenger, SPENVIS Workshop 2005

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

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

  46. Notes • 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.) S. Messenger, SPENVIS Workshop 2005

  47. Future Work • 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 S. Messenger, SPENVIS Workshop 2005

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