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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 (2 at% Si average composition) in preparation for a series of experiments aboard the International Space Station (ISS). The purpose of the microgravity experiments includes differentiating among proposed mechanisms contributing to detachment, and confirming or refining our understanding of the detachment mechanism. Because large contact angle are critical to detachment, sessile drop measurements were used to determine the contact angles as a function of temperature and composition for a large number of substrates made of potential ampoule materials. 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 from 150 deg to an equilibrium value of 117 deg (Ge) or from 129 deg to an equilibrium value of 100 deg (GeSi) over the duration of the experiment. The nature and extent of detachment is determined by using profilometry in conjunction with optical and electron microscopy. The stability of detachment has been analyzed, and an empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed. Results in this presentation will show that we have established the effects on detachment of ampoule material, pressure difference above and below the melt, and silicon concentration; samples that are nearly completely detached can be grown repeatedly in pBN.
Document ID
20020091893
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.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Cobb, S. D.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Motakef, S.
(Cape Simulations, Inc. Newton, MA United States)
Croell, A.
(Freiburg Univ. Germany)
Dold, P.
(Freiburg Univ. Germany)
Curreri, Peter A.
Date Acquired
August 20, 2013
Publication Date
January 1, 2002
Subject Category
Solid-State Physics
Meeting Information
Fourteenth American Conference on Crystal Growth and Epitaxy (ACCGE-14)(Seattle, WA)
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.