Andrew A. Woodworth

Glenn Research Center, Cleveland, Ohio

Ali Sayir and Philip G. Neudeck

Glenn Research Center, Cleveland, Ohio

Balaji Raghothamachar and Michael Dudley

Stony Brook University, Stony Brook, New York

Characterization of 4H 000-1> Silicon Carbide 

Films Grown by Solvent-Laser Heated

Floating Zone

NASA/TM—2012-217708

September 2012
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Andrew A. Woodworth

Glenn Research Center, Cleveland, Ohio

Ali Sayir and Philip G. Neudeck

Glenn Research Center, Cleveland, Ohio

Balaji Raghothamachar and Michael Dudley

Stony Brook University, Stony Brook, New York

Characterization of 4H 000-1> Silicon Carbide 

Films Grown by Solvent-Laser Heated

Floating Zone

NASA/TM—2012-217708

September 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

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Acknowledgments

The NASA Postdoctoral Program, NASA Vehicle Systems Safety Technologies Project in the Aviation Safety Program, and 

the US Department of Energy Vehicle Technology Program via Space Act Agreement (NASA GRC SAA3-1048, DOE IA #

DE-EE0001093/001) monitored by Susan Rogers provided funding for this work. Technical help from J. Anthony Powell, David 

Spry, Fredric Dynys, Thomas Sabo, Mark Dieringer, Michelle Mrdonovich-Hill, Francisco Solá-López, Beth Osborn and Charles 

Blaha is greatly appreciated. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by 

the U.S. Department of Energy, Offi ce of Science, Offi ce of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

Available from

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Available electronically at http://www.sti.nasa.gov

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217708 1 

Characterization of 4H 000-1 Silicon Carbide Films Grown by 

Solvent-Laser Heated Floating Zone

Andrew A. Woodworth1

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Ali Sayir and Philip G. Neudeck 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Balaji Raghothamachar and Michael Dudley 

Stony Brook University 

Stony Brook, New York 11794 

Abstract 

Commercially available bulk silicon carbide (SiC) has a high number (2000/cm2) of screw 

dislocations (SD) that have been linked to degradation of high-field power device electrical performance 

properties. Researchers at the NASA Glenn Research Center have proposed a method to mass-produce 

significantly higher quality bulk SiC. In order for this bulk growth method to become reality, growth of 

long single crystal SiC fibers must first be achieved. Therefore, a new growth method, Solvent-Laser 

Heated Floating Zone (Solvent-LHFZ), has been implemented. While some of the initial Solvent-LHFZ 

results have recently been reported, this paper focuses on further characterization of grown crystals and 

their growth fronts. To this end, secondary ion mass spectroscopy (SIMS) depth profiles, cross section 

analysis by focused ion beam (FIB) milling and mechanical polishing, and orientation and structural 

characterization by x-ray transmission Laue diffraction patterns and x-ray topography were used. Results 

paint a picture of a chaotic growth front, with Fe incorporation dependant on C concentration. 

Introduction 

The use of silicon carbide (SiC) power electronics are widely accepted to be capable of enabling 

systems that are significantly lighter, smaller, and electrically more efficient than systems comprised of 

conventional silicon (Si) based electronics. Although some SiC devices (e.g., Schottky diodes and fieldeffect transistors (FETs)) have been developed, the performance of most SiC power devices are 

significantly degraded/limited because of a high density of crystal defects in all commercially-available 

SiC semiconductor wafers. Among the more serious defects in these SiC wafers is a defect known as a 

“closed-core” screw dislocation (SD), with densities typically greater than 2000 per cm2

 (Refs. 1 to 3). 

Eliminating these dislocation defects (i.e., reducing them to densities 1 per cm2

) would unlock more of 

SiC’s enormous (as yet unfulfilled) promise to revolutionize nearly all high-power electronic systems. 

Recently, SiC growth perpendicular to the c-axis has been shown to grow higher quality (lower defect 

density) bulk SiC (Ref. 4). Researchers at the NASA Glenn Research Center have proposed a method to 

mass-produce high quality bulk SiC (Ref. 5). This technique starts by growing a long continuous single 

 

 

1

NASA Glenn Research Center, NASA Postdoctoral Program Fellow. 
NASA/TM—2012-217708 2 

crystal SiC fiber in the crystallographic c-direction, and then laterally (perpendicular to the c-direction) 

enlarging the fiber into a high quality boule via chemical vapor deposition growth. In order for this bulk 

SiC growth method to become a reality, growth of both long single crystal SiC fibers and lateral growth 

of the fiber by CVD must be achieved. Therefore, two parallel development tracks have been formed: SiC 

fiber growth and lateral CVD. 

In order to create long single crystal SiC fibers, growth has been implemented that combines the 

advantages of two well known growth methods: Laser Heated Floating Zone (proven for oxide-based 

crystals) (Ref. 6) and Traveling Solvent Method (demonstrated for SiC) (Ref. 7). Solvent-Laser Heated 

Floating Zone (Solvent-LHFZ) (Ref. 8) couples the potential to grow long fibers with a solvent system 

capable of growing SiC. 

Experiment 

Characterization of the grown crystals and their growth fronts were carried out by depth profile, cross 

sectional analysis and x-ray techniques. Secondary ion mass spectroscopy (SIMS) was performed on the 

C-face (000-1) face of several samples with an analysis area of ~175×175 m in order to create depth 

profiles of the metal solvents incorporated into the grown crystals. Focused ion beam (FIB) milling and 

mechanical polishing were used to make cross sections of the crystals, which were then examined by 

scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and orientation and 

structural characterization studies were carried out by x-ray transmission Laue diffraction and white beam 

x-ray topography at the Stony Brook Synchrotron Topography Station, Beamline X19C at the National 

Synchrotron Light Source, Brookhaven National Laboratory. 

Experiments were carried out in a custom vacuum system under 15 slm flow of argon at 115 torr, 

using a CO2 laser as the heat source. A more detailed description of the system can be found elsewhere 

(Ref. 8). At the heart of the system, a 0.5 by 0.5 by 15 mm 4H-SiC crystal (long axis parallel to the 

0001 direction) is mounted so that the carbon face (000-1) of the crystal is facing down. The growth 

surface varied from on axis to roughly 10° from the (000-1). Directly below the crystal, a ~2 mm diameter 

feed rod (composed of the source material for crystal growth) is mounted vertically. The laser heats and 

melts the top end of the feed rod creating a melt (liquid) composed of the crystal growth materials. The 

seed crystal is then brought into contact with the melt allowing the liquid to wet the seed crystal. The 

melting and wetting processes are critical to the success of the experiments; if the feed rod fails to melt 

into a stable liquid, or wet the seed crystal, then no crystal growth can occur. 

For these experiments Fe was chosen as the metal solvent based upon its well known ability to 

dissolve both C and Si. Exact compositions were derived from examining the Fe-Si-C (1150 °C) ternary 

diagram (Ref. 9), which indicated that there are two ranges of compositions that would produce a liquid + 

SiC phase. With this knowledge, a high Fe composition (Fe/Si ~ 1.9, C = 8 at.%), and a high Si 

composition (Fe/Si ~ 0.35, C = 8 percent) were chosen. While studying the effects of Fe/Si concentration 

is important, the effects of different C concentrations may be even more important. Therefore, a third 

composition was chosen at the high Si (Fe/Si ~ 0.35) composition with double the C (16 at.%). Specific 

seed crystal, feed rod preparation, and post experiment crystal processing information can be found 

elsewhere (Ref. 8). 

Since significant transport of material starts once a melt is formed, growth temperatures are given 

relative to the observed melting point (M.P.) of the source material (e.g., growth temperature = total 

observed temperature – M.P.). Also, due to the possible wide range of emissivity (Fe = 0.3 (Ref. 10) 

tographite = 0.9 (Ref. 11)) and small size (~2 mm2

) heated zone, none of the listed optical pyrometermeasured temperatures are corrected for emissivity. 
NASA/TM—2012-217708 3 

Discussion 

As has been previously reported (Ref. 8) (summarized in Table 1), experimental runs using source 

materials with high Fe content failed to produce a stable melt, and were abandoned. The high Si source 

material easily formed a stable melt and predictably melted at 1170 °C (Table 1). Both the 8 and 

16 at.% (high Si) compositions melted at similar temperatures (M.P. = 25 °C or  2 percent absolute 

temperature). Growth is found to increase with an increase in C present in the source material and also 

with temperature. These results indicate that temperature did have an effect on the amount of C 

transported from the source material to the growing crystal. 

X-ray transmission Laue diffraction pattern (Fig. 1(a)) recorded using the synchrotron white beam on 

selected grown crystals matches exactly with (1-100)-oriented 4H-SiC x-ray transmission Laue 

diffraction pattern (Fig. 1(b)) simulated using the LauePt software (Ref. 12). The grown crystal retained 

both the orientation and polytype of the seed crystal and is therefore considered single crystal and 

epitaxial. The x-ray topographs (not shown) from the grown crystals are highly distorted indicating that it 

is under significant inhomogeneous strain.

TABLE 1.—SUMMARY OF RESULTS. M.P.= TEMPERATURE AT WHICH THE FEED ROD FORMED 

A MELT, (at.% = ATOMIC PERCENT). TEMPERATURES ARE NOT CORRECTED FOR EMISSIVITY 

APPROXIMATE FE CONCENTRATIONS IN THE SiC CRYSTAL LAYERS ARE LISTED 

Figure 1.—X-ray transmission Laue diffraction pattern (a) recorded from the LHFZ layer portion of fiber 

sample matches exactly with a (1-100)-oriented 4H-SiC x-ray transmission Laue diffraction pattern 

(b) simulated using the LauePt software (Ref. 12). 

Fe Concentration (atom/cm3)

Fe/Si (atomic ratio) C (at.%) M.P. (°C) M.P.+90 °C M.P.+190 °C

High-Si (Fe/Si~0.35) 8 1170 ~1017 ~1017

16 1195 ~1018 ~1018

High-Fe (Fe/Si~1.9) 8 N/A No Growth

(a) (b)
NASA/TM—2012-217708 4 

Figure 2.—(a) Interior of a cross-section of a growth front exposed by mechanical polishing (b) FIB of cross 

section of a grown crystal. 

SEM images reveal two different morphologies (shown elsewhere (Ref. 8)), a platelet-like 

morphology (present on ~75 percent growth fronts examined) and a step flow like growth front (present 

on about 25 percent of the grown surfaces examined). One important note is that the occurrence of either 

type of growth front did not correspond to a specific growth condition, and in a couple of cases both 

morphologies were produced in different regions of a single sample surface. Cross-sectional analysis 

reveals many voids (Fig. 2(a)) and Si-Fe rich pockets (confirmed with EDS, Fig. 2(b)) sealed in the 

grown crystal layer. These voids and inclusions are very possibly the source of the stress detected by the 

topography measurements. 

One possible explanation for the formation of the Fe rich inclusions is that each platelet of the 

platelet-like growth front is actually many competing individual growth fronts that eventually collide to 

form new defects as the SiC closes over the trapped solvent. The crystal then continues growing using the 

newly formed defect. A similar process has been reported by Dudley et al. (Ref. 13) in the physical vapor 

transport method of SiC crystal growth. 

SIMS results (Fig. 3) shows that the concentration of Fe in the grown crystals varies in three 

significant ways. First, “bumps” in the SIMS profile are believed to arise from the Fe rich inclusions seen 

by FIB cross sectional analysis, as indicated by the arrows in Figure 3. With an analysis area much larger 

than the inclusions, the “bump” width and magnitude is an average over the entire SIMS analysis area. 

This explains why the “bumps” visible by SIMS are also visible by SEM/EDS. Second, these results also 

indicate that for both high and low C concentration source materials the Fe concentration decreases more 

than an order of magnitude from the surface. This decrease may indicate a change in melt composition as 

a function of growth time. Please note that for crystals grown with low C concentration source material, 

the Fe concentration drops almost two orders of magnitude in the first 

0.25 m. The reason for this large change is unknown, but is possibly either an artifact of the post-growth 

etch, which removes excess source material/solvent, and/or the cooling of the crystal/solvent system at the 

end of a growth or the SIMS process. Third and also indicated in Table 1, the crystals grown with source 

material containing a higher C concentration incorporated an order of magnitude more Fe than did 

crystals grown from melts containing less C at either growth temperature. Further SIMS analysis reveals 

that Fe incorporation into grown crystals exhibits the same correlation to C concentration in the source 

material independent of growth rate. Therefore C concentration in the source material seems to dictate the 

amount of Fe solvent incorporated into the matrix of the grown crystal, and that the Fe concentration is 

considerably less sensitive to growth temperature. 

voids

30 m

Fe‐rich inclusions

2 m

(a) (b) <000

‐1>

<000

‐1>
NASA/TM—2012-217708 5 

Figure 3.—SIMS analysis of a high C (at.% = 16, growth rate = 40 m/hour) and low C 

(at.% = 8, growth rate = 4 m/hour) grown at M.P.+90 C. The arrows indicate Fe rich 

areas in the grown crystals. Note Fe/Si = 0.35 in the feed rod. 

Conclusions 

This paper has reported further characterization of 4H-SiC crystal layers grown by the recently 

implemented Solvent-LHFZ technique. X-ray diffraction and topography confirmed that the grown 

crystals were single crystal in nature (replicating polytypic and crystallographic direction of the seed), but 

under significant amount of inhomogeneous strain. Cross sectional analysis by mechanical polishing and 

FIB, and along with SIMS analysis revealed voids and Fe rich inclusions throughout the grown crystals 

and is most likely the source of the strain. These voids and Fe rich areas are possibly created by growth 

fronts colliding and sealing off pockets and then creating defects which help propagate the growth front. 

SIMS analysis also revealed that Fe inclusion into the grown crystal seems to be a function of the C 

content of the grown crystal and not growth temperature or growth rate. These results lead us to believe 

that in order to grow a long, high-quality 4H-SiC single crystal fiber, the growing crystal must be reduced 

to a single growth font and that the C content of the source material will have to be tuned both with 

consideration to growth rate and also to Fe incorporation into the grown crystal. 

1016

10167

1018

1019

1020
NASA/TM—2012-217708 6 

References 

1. P.G. Neudeck W. Huang and M. Dudley., Solid-State Elec., 42, 1257 (1998). 

2. J. Zhang, G. Chung, E. Sanchez, M.J. Loboda, S. Sundaresan and R. Singh International Conference 

on Silicon Carbide and Related Materials, Cleveland, OH, September 11-16 (2011) (to be 

published). 

3. R. Berechman, S. chung, S. Soloviev and M. Skowronski, International Conference on Silicon 

Carbide and Related Materials, Cleveland, OH, September 11-16 (2011) (to be published). 

4. Y. Urakami, I. Gunjishima, S. Yamaguchi, H. Kondo, F. Hirose, A. Adachi and S. Onda, 

International Conference on Silicon Carbide and Related Materials, Cleveland, OH, September 11-

16, 2011 (to be published). 

5. J.A. Powell, P.G. Neudeck, A.J. Trunek and D.J. Spry, U.S. Patent 7,449,065 issued November 11, 

2008. 

6. C.A. Burrus and J Stone, App. Phys. Lett., 26, 318-320 (1975). 

7. L.B. Griffiths and A.I. Mlavsky, Electrochem. Soc., 111, 805 (1964). 

8. A.A. Woodworth, et al., International Conference on Silicon Carbide and Related Materials, 

Cleveland, OH, September 11-16, 2011 (to be published). 

9. T. Yoshikawa, S. Kawanishi, and T. Tanaka, Int. Conf. on Adv. Structure and Funct. Mater. Des., 

2008, J. Phys.: Conf. Series 165 (2009) 012022. 

10. H.B. Wahlin and H.W. Knop, Phys. Rev., 74 (1948) 687. 

11. M.R. Null and W.W. Lozier, J. Appl. Phys., 29 (1958) 1605. 

12. X.R. Huang, J. Appl. Cryst., 43, 926 (2010). 

13. M. Dudley, X.R. Huang, W. Huang, A. Powell, S. Wang, P.G. Neudeck and M. Skowronski, 

Appl. Phys. Lett., 75, 784, (1999). 

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Characterization of 4H <000-1> Silicon Carbide Films Grown by Solvent-Laser Heated 

Floating Zone 

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Andrew A. Woodworth, NASA Glenn Research Center, NASA Postdoctoral Program Fellow. Alternate report number DOI: 

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14. ABSTRACT

Commercially available bulk silicon carbide (SiC) has a high number (>2000/cm2) of screw dislocations (SD) that have been linked to 

degradation of high-field power device electrical performance properties. Researchers at the NASA Glenn Research Center have proposed a 

method to mass-produce significantly higher quality bulk SiC. In order for this bulk growth method to become reality, growth of long single 

crystal SiC fibers must first be achieved. Therefore, a new growth method, Solvent-Laser Heated Floating Zone (Solvent-LHFZ), has been 

implemented. While some of the initial Solvent-LHFZ results have recently been reported, this paper focuses on further characterization of 

grown crystals and their growth fronts. To this end, secondary ion mass spectroscopy (SIMS) depth profiles, cross section analysis by 

focused ion beam (FIB) milling and mechanical polishing, and orientation and structural characterization by x-ray transmission Laue 

diffraction patterns and x-ray topography were used. Results paint a picture of a chaotic growth front, with Fe incorporation dependant on C 

concentration. 

15. SUBJECT TERMS

Silicon carbides; Crystal growth; Melts; Single crystals 

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