This document discusses materials science research related to testing and manufacturing in space, with a focus on growing indium iodide (InI) crystals. It includes: 1) Details on previous experiments growing tellurium and zinc-doped indium antimonide crystals on the International Space Station in 2002 using SUBSA hardware. 2) An overview of why InI is a promising room temperature radiation detector material due to its properties such as bandgap and atomic number. 3) Details of experiments growing InI crystals in microgravity using SUBSA and the challenges of high vapor pressure detector materials.

1. Materials Science Research:
CARL KIRKCONNELL, PRESIDENT, WEST COAST SOLUTIONS
JUD READY, DEPUTY DIRECTOR, GEORGIA TECH INSTITUTE FOR MATERIALS
ALEKSANDER OSTROGORSKY, PROFESSOR, ILLINOIS INSTITUTE OF TECHNOLOGY
ALEXEI CHURILOV, SENIOR SCIENTIST, RADIATION MONITORING DEVICES, INC.
Testing and Manufacturing in Space

2. W. Jud Ready
DEPUTY DIRECTOR, INNOVATION INITIATIVES

3. LIGHT TRAPPING 3D PHOTOVOLTAICS
Solves “thick-thin” conundrum
Light Trapping = more absorbance
Thinner layers = less recombination
Traditional planar photovoltaics allow for
only a single impingement of the photon,
limiting absorption. Anti‐reflection (AR)
coatings can improve upon this deficiency,
but only to a limited extent due to
wave‐length dependency of the AR
coating.
The CNT‐based textured device permits
multiple impingements of a single photon
significantly increasing absorption
probability.

4. When choosing a photovoltaic material, several idealities are understood:
1. Robust p-type or n-type conductivity
2. Strong optical absorption coefficient
3. Direct bandgap of ~1.5 eV
4. Low-cost, abundant, non-toxic chemical elements
5. Low-cost material fabrication and growth
6. Compatible with a variety of technologies, structures, and
applications
Cu2ZnSnS4 (CZTS) posses all of these qualities!
A quaternary semiconductor compound belonging to a class of
materials known as chalcogenides
CZTS is fundamentally similar to CuInxGa1-xSe2 (CIGS)
THIN FILMS - CZTS

5. Copper-zinc-tin-sulfide (CZTS) thin-films are next-generation solar cells
comprised of cheap, Earth-abundant materials
- High absorption coefficient (>104 cm-1)—ideal for thin film purposes
- Direct energy band-gap implies resistance to radiation
- 1.5 eV band-gap—highest solar conversion efficiency based on Shockley-
Queisser Limit
CZTS PHOTOVOLTAICS

6. 1 in.
3-D CZTS CELL STRUCTURE

7. FLIGHT HARDWARE
20 PV cells in both 3D and planar
configurations will be launched via SpaceX
September 9, 2015 to be tested outside the
International Space Station (ISS).
The samples will be returned to Earth to be
investigated for radiation and physical
damage after 6 month external exposure.
4U cubesat
With 20 PV cells

8. Cubesat is passed outside ISS via JEM air lock
CZTS TESTING IN SPACE ENVIRONMENT

9. 1. J. Flicker and W. J. Ready, “Derivation of Power Gain for Three Types of Three
Dimensional Photovoltaics Cells Based on Tower Arrays with Flat Tops and Smooth,
Vertical Sidewalls.” Progress in Photovoltaics: Research and Applications. Vol. 19,
pp. 667-675 (2011).
2. X.J. Wang, J.D. Flicker, B.J. Lee, W.J. Ready and Z.M. Zhang, “Visible and Near-
infrared Radiative Properties of Vertically Aligned Multi-walled Carbon Nanotubes.”
Nanotechnology, Vol. 20 pp. 215704-215713, (2009).
3. Jack Flicker and Jud Ready, “Simulations of Absorbance Efficiency and Power
Production of Three Dimensional Tower Arrays for Use in Photovoltaics.” Journal of
Applied Physics, Vol. 103, pp. 113110 (2008).
4. S.P. Turano, J.D. Flicker; W.J. Ready, “Nanoscale Coaxial Cables Produced From
Vertically Aligned Carbon Nanotube Arrays Grown via Chemical Vapor Deposition
and Coated with Indium Tin Oxide via Ion Assisted Deposition.” Carbon, Vol. 46, No.
5, pp. 723-728, (2008).
5. US Patent #8,350,146 -- Three Dimensional Multi-junction Photovoltaic Device
(January 2013).
REFERENCES

10. ACKNOWLEDGEMENTS

11. GTRI_B-‹#›
Questions?
W. Jud Ready
jud.ready@gatech.edu
404-407-6036

12. DETACHED MELT AND VAPOR GROWTH OF
InI IN SUBSA HARDWARE
Prof. Aleksandar Ostrogorsky, PI, IIT
Dr. Alexei V. Churilov, RMD
Watertown, MA
Dr. Martin P. Volz
NASA MSFC, Huntsville, AL
Dr. Lodewijk van den Berg,
Constellation Technology Largo F
Prof. Dr. Arne Cröll
University of Freiburg, Germany.
SUBSA
“1” (1995-2004) Te and Zn doped InSb
“2” (2015->2017) InI

13. SAMPLE HEADER
• SCR 1998
• Design review 2000
• Endeavour, Expedition 5, 2002.
• Seven Te- and Zn-doped InSb (MP 512 C)
semiconductor crystals were grown.
SUBSA 2002 in MSG
W. Bonner

14. SAMPLE AMPOULE ASSEMBLY (SAA)

15. SUBSA AMPOULE ASSEMBLY
Length = 30 cm
The Piston-Spring
Support
Quartz plug InSb Graphite
Baffle
Spring
16
mm
O.D.
I.D. = 12.0 mm
•InSb seed
•50g InSb, doped with Te or Zn (MP 512 C)
•Sealed under vacuum.
Bill Bonner

16. SUBSA HARDWARE AT AT GLANCE
1 Process Control
Module
1 DaqPad
Video
Camera
LabVIEW 6i processes data
on MSG Laptop Computer
Cartridge head and 4 TCs

17. SUBSA DESIGN REWIEW 6/8/2000

18. SUBSA STATUS ON SUNDAY 2/3/2002
FedEx Custom Critical “White Gloves” service
departing MSFC’s Microgravity Development Lab at
approximately 3:30 PM CST on Sunday 2-3-2002.
The SUBSA-PFMI flight hardware & software arrived at
KSC on Monday morning, February 4, 2002, in good
condition.
Photo by Tec-Masters / Reggie Spivey
February 3, 2002

19. CREW OF THE EXPEDITION FIVE
June 5, 2002. Shuttle Endeavour, Flight UF-2 -STS-111
Valery Korzun
Expedition commander
Sergei Treschev
flight engineer

20. REAL TIME VIDEO –
CONTROL OF SEEDING AND GROWTH RATE
Solid/Liquid
Interface
Seed Interface
Solid/Liquid
Interface
Precise seeding
Monitoring room at RPI
Dr. Whitson
July 11, 2002
f = 0.5 cm/hr

21. Results SUBSA #10: Zn-doped
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30 35
x [mm]
SIMS_1
SIMS_2
Smith_Co=3.5e18
18
3
10Zn
cm

  
D-shaped section with attached seed
de-wettingSeed
D =1.2 x 10-4 cm2/s
SUBSA 10: Zn-doped; with baffle
Zn-doped => k0=2.9
k0 >1 is proffered for
growth in microgravity.

22. SUBSA RESULTS:
1. Demonstrated reproducible diffusion-controlled “segregation”
2. Diffusion coefficients for Te and Zn in InSb
3. Segregation theory:
BPS (1953)
Ostrogorsky and Muller (1992)
Ostrogorsky (2012): CZ, Bridgman, ZM..
keff
=
CS
CL
= F k0
,D, fdSF( )
k0 is equilibrium segregation coefficient
f [cm/s] is freezing rate
D[cm2/s] diffusion coefficient.
“stagnant film” thickness
dFC
=1.61D1/3
n1/6
w-1/2
keff
= F k0
,Pe,Re,Gr,Pr,Sc,( )
ω =crystal rotation rate
Steady laminar flow !
g =?
GrL
=
gb DT L3
n2
Witt et al.
J.Electrochem
Soc.125 (1978)
Chapter 25, Handbook of Crystal Growth, 2nd ed.

23. SUBSA RESULTS: SEGREGATION THEORY
FOR ZONE REFINING
Pfann’s book:
Zone Refining”, 1966.
Ostrogorsky and Glicksman,
“Handbook of Crystal Growth”, 2014.
d = ?
fd
D
= ?
keff
= F k0
,Pe,Re,Gr,Pr,Sc,( )

24. Why semiconductor ? Why InI ?
• High spectroscopic resolution:
to identify special nuclear materials
• Hand-held, RT battery operation
0 2%
7 %
4% 6%
3LaBr
NaI
CZTGe
Limit of
semiconductors
0.2 %
Limit of
scintilators
2 %
2HgI
1%
• 1.5<Eg< 2.5 eV, to minimize the leakage current
• High density
• One of the elements should have Z>50
• Acceptable mechanical properties, for device fabrication and
use.
InI
Eg=2 eV
ρ=5.6 g/cm3
Z=53

25. REQUIREMENTS FOR RT DETECTORS
Room Temperature (RT) operation requirements
energy gap: 1.5 eV< Eg <2.5 eV
Z>50
II III IV V VI
Best
Z [eV]
Si 14 1.12
Ge 32 0.7
GaAs 33 1.43
InP 49 1.35
AlSb 51 1.6
CdTe 52 1.49
ZnTe 52 2.25
HgI2 80 2.13
HgBr
2 80 3.6
PbI2 82 2.55
BiI3 83 1.75
TIBr 81 2.8
TlI 81 2.15
Cd0.8Zn0.2Te
“CZT”
III-V
compounds

26. Structure, hardness, Z, Eg, mobility
Structure
Knoop
kg/mm2
Ρ
[g/cm3]
Z Eg μe μh Comments
III-V
AlSb 460 4.22 31/51 1200 700 good/difficult
GaAs Zincblende 450 5.34 31/33 1.42 8000 400 low Z and Eg
InP Zincblende 400 4.79 49/15 1.35 4600 150 low Z and Eg
II-VI
CdTe Zincblende 45 - 60 6.2 48/52 1.52 1000 80 good/difficult
ZnTe Zincblende 92 6.0 30/52 2.25 good/difficult
GaSe Se-Ga-Ga-Se 4.55 31/34 2.02 215 van der Waals
CdSe Wurtzite 90-130 5.8 48/34 1.73 720 75
CdS Wurtzite-cubic 18 4.82 48/16 2.42 75 75
Layered
HgI2 α-tetragonal 10 6.36 80/53 2.13 100 4 van der Waals
PbI2 rombohedral 10 6.16 82/53 2.35 8 2
van der Waals
BiI3 rombohedral 10 5.78 83/53 1.73 van der Waals
iodides InI orthorhombic 27 5.39 49/53 2.0 22 NOT TOXIC
TlI Orthorhombic 18 7.29 81/53 2.15 transformation
bromides TlBr cubic 12 7.56 81/35 2.68 7 2 toxic
TlBrI orthorhombic 27 81/53/35

27. WHY INDIUM IODIDE?
2727
15 mm diameter
• Promising semiconductor RT detector material + not toxic; MP= 360 C
(perfect for SUBSA furnace)
• Developed procedures for synthesis, ZR, melt growth, vapor growth
• RPI (2006-2009); IIT (2009-present), RMD (2015).
• DoE, NNSA

28. CZOCHRALSKI GROWTH OF InI
• Detector materials have high
vapor pressure; growth in sealed
ampoules.
• CZ growth of a detector crystal
demonstrated for the first time

29. DISTRIBUTION OF PRECIPITATES
CZOCHRALSKI BRIDGMAN
0 3 6 9 12 15 18 21 24 27
104
105
106
Density of precipitates in InI CZ01
Volume: 800x800x100 m3
Black - last to freeze
Red - first to freeze
Density(cm-3
)
diameter (m)
0 3 6 9 12 15 18 21 24
104
105
106
Density of precipitates in InI Bridgman
Volume: 800x800x100 m3
Black - last to freeze
Red - first to freeze
diameter (m)
Density(cm-3
)

30. PURIFICATION BY ZONE REFINING (ZR)
100 g ingot, after 70 ZR passes IIT 2012
350 g ingot, was ZR and grown in an open boat, under dynamic gas flow
5% H2 +95 %Argon, RMD 2015.
RMD 2015
IR-light
No inclusions (?)

31. Inclusions in InI and CdTe
RMD 2015
IR-light
No inclusions (?)
IR-TRANSMISSION IMAGES
• InI sample originating from InI-ZR-05
experiment has no inclusions • CdTe sample with inclusions

32. Crystal Growth of Cs2LiYCl6:Ce in
Microgravity
ALEXEI CHURILOV, SENIOR SCIENTIST, RADIATION MONITORING DEVICES, INC.
ALEKSANDAR OSTROGORSKY, PROFESSOR, ILLINOIS INSTITUTE OF TECHNOLOGY
JOSHUA TOWER, SENIOR SCIENTIST, RADIATION MONITORING DEVICES, INC.
MARTIN VOLZ, MATERIALS SCIENTIST, NASA MARSHALL SPACE FLIGHT CENTER

33. CLYC (Cs2LiYCl6:Ce)
CLYC is the first commercial dual-mode scintillator:
gamma-ray spectroscopy AND neutron detection
Fast, accurate isotope identification
CLYC crystals
CLYC instruments
RadEye RIIDEye
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
0
1
2
3
AmBe spectrum
137
Cs spectrum
662 keV
3.4 MeV
intensity,arb.units
energy, MeV
~ 3.8% FWHM
Gamma rays
~ 2.5% FWHM
neutrons

34. CLYC FEATURES
• Bright response and high efficiency for neutrons
• 1 cm of 95% 6Li enriched CLYC  ~80% efficiency for thermal neutron detection
• Pulse shape discrimination (PSD) for gamma-
rays and neutrons
• Rise & decay times different for n and γ (PSD)
• Good proportionality  gamma-ray energy
resolution
• 25-30% better than NaI(Tl), FWHM ~ 4% @ 662 keV
• Fast neutron detection due to presence of 35Cl

35. CLYC PULSE SHAPE DISCRIMINATION
Ability to differentiate between gamma rays
and neutrons based on pulse shapes
0 200 400 600
0.0
0.2
0.4
0.6
0.8
1.0
1.2
gamma
neutron
window 2window 1
neutron
gamma
windows
counts,arb.units
time, ns
Neutrons
Gamma Rays
Neutrons
Gamma Rays
Thermal neutrons

36. FAST NEUTRON DETECTION WITH CLYC
0 1 2 3 4 5 6
En
=thermal
CLYC:Ce
1.1 MeV
1.6 MeV
2.3 MeV
intensity,arb.units
CP energy, MeV
3.9
2.9
2.1
35Cl + 1n  1p + 35S + energy
0.5 1.0 1.5 2.0 2.5 3.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
35
Cl
CPenergy,MeV
neutron energy, MeV
Proportional to 1n energy

37. DEFECTS IN CLYC
Grain Boundaries Inclusions Cracks
Growth in microgravity to address defect formation mechanisms

38. • Absence of density-driven segregation of
components
 Eliminated effect of density differences between CLYC
components (CsCl, LiCl, YCl3) → more uniform initial melt
composition
• Absence of thermal buoyancy-driven
convection in the melt
 More axially homogeneous composition of CLYC components in
crystals
• Weightlessness of the melt volume
 Melt confined by surface tension → Reduced cracking
Key advantages of microgravity for crystal
growth research:

39. TECHNICAL APPROACH
• Utilize existing SUBSA hardware: furnace, ampoules, glovebox
• Conduct a series of tests in identical ground-based hardware
• Optimize SUBSA growth ampoules for CLYC
• Grow 4 CLYC crystals on ISS with varied parameters:
 Ampoule geometry
 Temperature setpoint
 Nucleation method (seeded and self-nucleated)
 Detached and confined melt
• Do a set of reference ground-based experiments under the same thermal
conditions as in space.
• Characterize and compare crystals grown in space and on the ground.
SUBSA ampoule. Cs2LiYCl6:Ce will be used in place of InSb charge and
seed. Four external thermocouples will be attached to the ampoule for
temperature monitoring.
Length = 300 mm
OD = 16 mm
Internal atmosphere: vacuum 10-6 Torr.

40. SUBSA HARDWARE
Image from camera

41. SUMMARY
• RMD, Inc. developed and commercialized Cs2LYCl6:Ce –
the first scintillator crystal used for detection of both gamma-
rays and neutrons.
• Four CLYC crystals to be grown on ISS.
• Goals:
 Understand mechanisms of defects formation in CLYC crystal growth without
interference of gravity.
 Focus on optimization of parameters with the largest impact on quality and yield,
for improved production on Earth.
Integrated on PMT
Packaged ø2”x2” CLYC crystal 0 200 400 600 800
0.0
0.5
1.0
E = 24eV or 3.6%
662 keV
intensity,counts/sec
energy, keV