NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Detached Bridgman Growth of Germanium and Germanium-Silicon Alloy CrystalsEarth based experiments on the science of detached crystal growth are being conducted on germanium and germanium-silicon alloys (2at% Si average composition) in preparation for a series of experiments aboard the International Space Station (ISS) to differentiate among proposed mechanisms contributing to detachment. Sessile drop measurements were first carried out for a large number of substrates made of potential ampoule materials to determine the contact angles and the surface tension as a function of temperature and composition. The process atmosphere and duration of the experiment (for some cases) were also found to have significant influence on the wetting angle. Growth experiments have used pyrolytic boron nitride (pBN) and fused silica ampoules with the majority of the detached results occurring predictably in the pBN. The contact angles were 173 deg (Ge) and 165 deg (GeSi) for pBN. For fused silica, the contact angle decreases to an equilibrium value with duration of measurement ranging from 150 to 117 deg (Ge), 129 to 100 deg (GeSi). Forming gas (Ar + 2% H2) and vacuum have been used in the growth ampoules. With gas in the ampoule, a variation of the temperature profile during growth has been used to control the pressure difference between the top of the melt and the volume below the melt caused by detachment of the growing crystal. The stability of detachment has been modeled and substantial insight has been gained into the reasons that detachment has most often been observed in reduced gravity but nonetheless has occurred randomly even there. An empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed and will be presented. Methods for determining the nature and extent of detachment include profilometry and optical and electron microscopy. This surface study is the subject of another presentation at this Congress. Results in this presentation will show that we have established the effects of different ampoule materials, temperature profiles, pressure differences, and silicon concentrations and that samples that are nearly completely detached can be grown repeatedly.
Document ID
20010019994
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Szofran, F. R.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Volz, M. P.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Schweizer, M.
(Universities Space Research Association Huntsville, AL United States)
Kaiser, N.
(Freiburg Univ. Germany)
Cobb, S. D.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Motakef, S.
(Cape Simulations, Inc. Newton, MA United States)
Vujisic, L. J.
(Cape Simulations, Inc. Newton, MA United States)
Croell, A.
(Freiburg Univ. Germany)
Dold, P.
(Freiburg Univ. Germany)
Rose, M. Franklin
Date Acquired
August 20, 2013
Publication Date
January 1, 2001
Subject Category
Solid-State Physics
Meeting Information
Meeting: International Astronautical Congress
Location: Toulouse
Country: France
Start Date: October 1, 2001
End Date: October 5, 2001
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

Available Downloads

There are no available downloads for this record.
No Preview Available