This investigation involves the comparison of results achieved from three types of crystal growth of germanium and germanium-silicon alloys: (1) Float zone growth (2) Bridgman growth (3) Detached Bridgman growth crystal The fundamental goal of the proposed research is to determine the influence of containment on the processing-induced defects and impurity incorporation in germanium-silicon (GeSi) crystals (silicon concentration in the solid up to 5 at%) for three different growth configurations in order to quantitatively assess the improvements of crystal quality possible by detached growth

Croell, A.

Mazuruk, K.

Volz, M. P.

A series of Ge(1-x)Si(x) crystal growth experiments are planned to be conducted in the Low Gradient Furnace (LGF) onboard the International Space Station. The primary objective of the research is to determine the influence of containment on the processing-induced defects and impurity incorporation in germanium-silicon alloy crystals. A comparison will be made between crystals grown by the normal and "detached" Bridgman methods and the ground-based float zone technique. Crystals grown without being in contact with a container have superior quality to otherwise similar crystals grown in direct contact with a container, especially with respect to impurity incorporation, formation of dislocations, and residual stress in crystals. "Detached" or "dewetted" Bridgman growth is similar to regular Bridgman growth in that most of the melt is in contact with the crucible wall, but the crystal is separated from the wall by a small gap, typically of the order of 10-100 microns. Long duration reduced gravity is essential to test the proposed theory of detached growth. Detached growth requires the establishment of a meniscus between the crystal and the ampoule wall. The existence of this meniscus depends on the ratio of the strength of gravity to capillary forces. On Earth, this ratio is large and stable detached growth can only be obtained over limited conditions. Crystals grown detached on the ground exhibited superior structural quality as evidenced by measurements of etch pit density, synchrotron white beam X-ray topography and double axis X-ray diffraction. The plans for the flight experiments will be described

NASA Technical Reports Server

American Society for Gravitational and Space Research (ASGSR) 
Meeting Abstract 
 
Influence of Containment on the Growth of Silicon-Germanium:  
A Materials Science Flight Project 
 
M. P. Volz 
NASA, Marshall Space Flight Center, EM31, Huntsville, AL 35812, USA 
 
K. Mazuruk 
University of Alabama in Huntsville, Huntsville, AL 35762, USA 
 
A. Cröll 
Kristallographisches Institut, University of Freiburg, Freiburg, Germany 
 
 
 A series of Ge1-xSix crystal growth experiments are planned to be conducted in the 
Low Gradient Furnace (LGF) onboard the International Space Station. The primary 
objective of the research is to determine the influence of containment on the processing-
induced defects and impurity incorporation in germanium-silicon alloy crystals. A 
comparison will be made between crystals grown by the normal and “detached” 
Bridgman methods and the ground-based float zone technique. Crystals grown without 
being in contact with a container have superior quality to otherwise similar crystals 
grown in direct contact with a container, especially with respect to impurity 
incorporation, formation of dislocations, and residual stress in crystals. “Detached” or 
“dewetted” Bridgman growth is similar to regular Bridgman growth in that most of the 
melt is in contact with the crucible wall, but the crystal is separated from the wall by a 
small gap, typically of the order of 10-100 microns. Long duration reduced gravity is 
essential to test the proposed theory of detached growth. Detached growth requires the 
establishment of a meniscus between the crystal and the ampoule wall. The existence of 
this meniscus depends on the ratio of the strength of gravity to capillary forces. On Earth, 
this ratio is large and stable detached growth can only be obtained over limited 
conditions. Crystals grown detached on the ground exhibited superior structural quality as 
evidenced by measurements of etch pit density, synchrotron white beam X-ray 
topography and double axis X-ray diffraction. The plans for the flight experiments will be 
described. 
https://ntrs.nasa.gov/search.jsp?R=20130001845 2019-08-30T23:41:30+00:00Z


Influence of Containment on the Growth of Silicon-Germanium: A Materials Science Flight Project

28th Annual Meeting of the American Society for Gravitational and Space Research
New Orleans, Louisiana
November 28 – December 2, 2012
Influence of Containment on the Growth of       
Silicon-Germanium: A Materials Science Flight Project
M. P. Volz1, K. Mazuruk2, A. Cröll3
1NASA, Marshall Space Flight Center, EM31, Huntsville, Alabama, USA
2University of Alabama in Huntsville Huntsville Alabama USA    , , , 
3University of Freiburg, Freiburg, Germany
https://ntrs.nasa.gov/search.jsp?R=20130001774 2019-08-30T23:40:13+00:00Z
ICESAGE Flight Investigation
• “Influence of Containment on the Growth of Silicon-Germanium” (ICESAGE) is a 
NASA Materials Science Flight Investigation 
• ICESAGE is a collaborative investigation between NASA and the European 
Space Agency (ESA)
• The ICESAGE experiments will be conducted in the Low Gradient Furnace (LGF) 
in the Materials Science Laboratory on the International Space Station (ISS)          
MSL Low Gradient Furnace
Materials Science Laboratory
Overview of the Investigation
This investigation involves the 
comparison of results achieved from
feed
rod     
three types of crystal growth of 
germanium and germanium-silicon 
alloys:
melt
zone
melt melt
•Float zone growth
•Bridgman growth
•Detached Bridgman growth crystal crystal crystal
The fundamental goal of the proposed research is to determine the 
influence of containment on the processing-induced defects and impurity 
incorporation in germanium-silicon (GeSi) crystals (silicon concentration 
in the solid up to 5 at%) for three different growth configurations in order 
to quantitatively assess the improvements of crystal quality possible by 
detached gro th w . 
Why Study Germanium-Silicon Alloys?
• Technological applications
 X ray and neutron optics (gradient crystals)-      
 High-efficiency solar cell material
 Thermoelectric converters 
 Increased carrier mobility compared to silicon, but can still be 
integrated into Si technology
• Characterization methods for silicon and germanium are 
well-established and are applicable to the alloy crystals.
• Relatively well known material properties and material 
tparame ers 
• The vapor pressure of silicon and germanium melts can be 
neglected; they are non-toxic materials.
Technological Challenges of Ge1-xSix
• Large separation of solidus and 
liquidus curves leads to strong
Phase diagram Ge-Si
     
segregation
• Lattice mismatch (4%) leads to 
increased stress, cracks, high
T 
[°
C
]
    
dislocation densities, 
polycrystalline growth
• The reactivity of liquid silicon
Si concentration [at%]
     
leads to a reaction with crucible 
materials (sticking) as well as 
contamination of the melt and the 
crystals
Principles of Detached Bridgman Growth
Pressures in Detached Bridgman Growth
1 2
1 1 Young-Laplace EquationP
R R
      
where
: surface tension
: radii of curvature of the meniscusR R

1 2,       
: pressure differential across the meniscusP
2
where
external
tm
P P gh
r
    
:  external gas pressure differential
 : weight of melt (pressure head)
externalP
gh

2  : capillary pressure from top meniscus
tmr

Calculation of Meniscus Shapes
2
2
3 1
22 22
( )
d z dz
dr dr P Bz r
dd
   
     
Young‐Laplace Equation
11 zz r
drdr
               
2m H CP P P gh r
    0 ,mP rP   P : Dimensionless pressure differential 
2
0 0g rB  
H across the meniscus
B = 3.248; Ge, r0 = 6 mm
B = 4.651; InSb, r0 = 5.5 mm
B Bond number; ratio of gravity force to 
surface tension force
cos ,r
s
  sin ,
z
s
 
sin P Bz
s r
      
Set of 3 coupled differential 
equations
z(0) = 0;  (0) = 90° ‐ 
(1)  90° (1) 1
Boundary Conditions
: growth angle
: contact or wetting angle
 =  – ;  r  = 
Gap Width vs. Pressure Differential (Ge at 1g)
 + > 180°
+ < 180°
0.95
1.00
0.90 = 14.3°
B = 3 248
0.80
0.85  
  = 140°
 = 152°
r
  .
0 70
0.75
 
  = 164°
  = 172°
-5 -4 -3 -2 -1 0 1 2 3 4 5
.
P
Gap Width vs. Pressure Differential (Ge at g = 10-6 g0)
1.0
+ > 180°
+ < 180°
0.8
= 14.3°
0.6
r
B = 3.248 x 10‐6
0.4
r
  = 140°
  = 152°
  = 164°
 = 172°
0 0
0.2
 
-4 -2 0 2 4
.
P
“Attached” Germanium
Partially Attached GeSi
M. P. Volz, M. Schweizer, N. Kaiser, S. D. Cobb, L. Vujisic, S. 
Motakef, F. R. Szofran, JCG 237-239 (2002) 1844-1848
Detached Ge in pBN Ampoule
Etch Pit Densities in Detached/Attached Crystals
M. Schweizer, S. D. Cobb, M. P. Volz, J. Szoke, F. R. Szofran, 
JCG 235 (2002) 161‐166
Etch Pit Density Variation With Attachment
M. Schweizer, S. D. Cobb, M. P. Volz, J. Szoke, F. R. Szofran, JCG 235 (2002) 161‐166
Microgravity Effects
• Microgravity reduces the pressure head (gh) resulting from the 
weight of the melt.
 D t h d th i th t ill f d i te ac e  grow  requ res a  cap ary orces om na e over 
gravitational forces. 
 On Earth, gravity complicates a comparison of detached growth theory 
d i t th h d ti l d than  exper men : e pressure ea  con nuous y ecreases as e 
melt solidifies and the pressure varies along the height of the 
meniscus.
f• Microgravity allows a larger value o  the gap width.
 On Earth, when the gap width becomes too large, gravity overcomes 
surface tension, a stable meniscus cannot be maintained, and the melt 
will flow down between the crystal and ampoule wall.
 A large initial gap width will allow measurement of anisotropy in the 
growth angle.
• Microgravity enables a study of the dynamic stability of 
crystallization independent of thermal effects.
Flight Investigation Objectives
Ten flight experiments have been selected to address the flight objectives 
of the Bridgman component of the ICESAGE investigation. 
1) Test the following detached growth hypotheses:
a. For a given set of growth and contact angles, there exists a 
range of pressure differential between the upper surface of 
the melt and the meniscus at the detachment gap such that 
detachment occurs.
b. Larger gap widths are possible in microgravity than in unit 
gravity.
c. Dynamic stability of detached growth in microgravity does 
not depend on thermal effects.
d Measurement of the growth angle anisotropy can be made in.           
detached growth in microgravity.
2) Quantitatively compare the defect structure and impurity levels of         
microgravity-grown normal and detached Bridgman and float-zone 
crystals to determine the optimum growth process.
Ampoule and Cartridge Layout
• A Ge1-xSix ingot  is placed inside a pyrolitic boron nitride 
(pBN) tube and sealed in a SiO2 ampoule.
• The ampoule is placed inside a cartridge which is         
inserted into the furnace.
• Thermocouples in the cartridge provide for real-time 
monitoring of the thermal profile
pBN tube
SiO2 spacer
ampoule
alumina
sample
cap
alumina
coupler
alumina
coupler thermocouples
Contributing Personnel
Dr. Frank R. Szofran (original U.S. PI), NASA MSFC, Huntsville, AL USA
Dr. Peter Dold (original German PI), Kristallographisches Institut, Freiburg, 
Germany
Prof. Dr. Klaus Werner Benz, Kristallographisches Institut, Freiburg, 
Germany
Dr. Sharon D. Cobb, MSFC, Huntsville, AL USA
Dr Natalie Kaiser Kristallographisches Institut Freiburg Germany.  ,  , , 
Mr. Uwe Kerat, Kristallographisches Institut, Freiburg, Germany
Ms. Alina Mitric, Kristallographisches Institut, Freiburg, Germany
Dr. Shariar Motakef, CAPE Simulations, Inc., Newton, MA USA
Dr. Witold Palosz, USRA/MSFC, Huntsville, AL USA
Ms. Penny Pettigrew, Morgan Research/MSFC
Dr. Markus Schweizer, USRA/MSFC, Huntsville, AL USA
D Lj b i V ji i C Si l ti I N t MA USAr. u om r u s c, ape mu a ons, nc., ew on,  
Prof. John S. Walker, University of Illinois at Urbana-Champaign, Urbana, 
IL USA
Technical Support
C. Bahr/D. Lovell/J. Quick, Morgan Research/MSFC
P. Carpenter/C. Cochrane, USRA/MSFC
S. Gallop, Tec-Masters/MSFC


Influence of Containment on the Growth of Silicon-Germanium: A Materials Science Flight Project

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