Method in crystal growth using liquid encapsulation techniques permits GaAs synthesis of materials from constituent elements whose vapor pressures are high at temperature at which they react spontaneously. Techniques may be useful for synthesis of GaP

Haggerty, J. S.

Wenckus, J.

English

NASA Technical Reports Server

May 1972	 CORRECTED COPY
	
B7210172 
NASA TECH BRIEF 
NASA Headquarters
	
-0 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Improved Synthesis of Intermetal Compounds 
The problem: 
At the present, most of the reactive compounds in the 
polycrystalline form are produced using the horizontal 
Bridgman techniques. However, because of this lengthy 
processing, the cost of these compounds is high. 
The solution: 
An improved method in crystal growth has been 
developed by using liquid encapsulation techniques. Three 
GaAs synthesis runs, yielding approximately 140 gm/ 
run, were successfully completed under a molten B203 
encapsulant with ambient gas pressure up to 6.2 x iO' 
dynes/cm 2
 (900 psig). The developed technique permits 
the synthesis of materials from the constituent elements 
whose vapor pressures are high at the temperature at 
which they react spontaneously. 
How it's done: 
The GaAs synthesis is accomplished in the high-
pressure furnace through the following heating cycle: 
(a) By the use of the degas susceptor, arsenic oxide 
is vaporized at 300°C and I CF4
 Torr for 12 hours; 
(b) The B 2 0 3 is then passed over the arsenic oxide 
charge at 425°C and 1.7 x 106 dynes/cm2 (25 psi) for 
2 to 4 hours; 
(c) Under increased temperature and pressure of 
525°C and 5.4 x 107 dynes/cm2 (800 psi), respectively, 
the B 2 0 3 is driven into the voids in the charge for 1 to 
2 hours;
(d) The elements are reacted to form the GaAs 
melt under 1450°C and 5.4 x.10' dynes/cm 2
 for 1 hour;
(e) For an additional 1/2 hour, the melt is homo-
genized by freezing it to 1200°C and then raising the 
temperature to 1450°C again under the constant pressure 
of 5.4 x 10' dynes/cm2; 
(1) The pressure is now lowered to 1.4x 106 dynes/ 
cm  (20 psi) and the compound is cooled at room 
temperature for 1/2 hour. 
During steps (a) and (b), the degas susceptor is posi-
tioned low within the rf heating coil to induce an inverted 
steep axial temperature gradient allowing the B 2 0 3 to 
flow without excessive heating of the unreacted As. 
After step (c), the susceptor is raised within the rf coil 
and retained in this position through the remainder of 
the synthesis. The described technique may also be use-
ful for synthesis of GaP. 
Patent status: 
Title to this invention has been waived under the 
provisions of the National Aeronautics and Space Act 
[42 U.S.C. 2457 (f)], to the Arthur D. Little, Inc., 
Cambridge, Massachusetts, 02140. 
Source: J. S. Haggerty and J. Werickus of

Arthur D. Little, Inc. 
under contract to
NASA Headquarters 
(HQN-1 0690) 
• 
S
Category 04 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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Improved synthesis of intermetal compounds

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