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What are As precipitates and As antisites in a GaAs sample?

by armandowww
Tags: antisites, gaas, precipitates, sample
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armandowww
#1
Dec19-05, 12:47 PM
P: 78
What are As precipitates and As antisites in a GaAs sample? Being more specific, my material is low temperature grown with an annealing process.
Thanks anyway
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Astronuc
#2
Dec28-05, 09:56 PM
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You might wish to look into buying this article.

Dislocations and precipitates in gallium arsenide
http://scitation.aip.org/getabs/serv...cvips&gifs=yes

Gallium arsenide single crystal solar cell structure and method of making - United States Patent 4370510 - maybe some useful background. One can download or view tiff files of the patent, or browse html online.

Search by patent number - http://patft.uspto.gov/netahtml/srchnum.htm

As precipitates will also depend on dopants and other impurities. I have seen reference to arsenates, which seems to imply oxygen, which I presume is an impurity.
luckycharms
#3
Mar27-06, 12:22 AM
P: 26
I know I'm bumping an older thread, but here goes.

Simply put, a GaAs crystal consists of alternating Ga and As atoms (actually two interpenetrating fcc sublattices called a zincblende, ZnS, or sphalerite structure) such that there is a 1:1 ratio of Ga to As atoms. For a variety of reasons that we can get into, when you grow GaAs at low temperature you tend to end up with slightly more arsenic atoms than gallium atoms in the crystal. The question is where do the arsenic atoms go?

Three places. They go 1) where they're supposed to go 2) where gallium is supposed to go 3) in between the other atoms (interstitials)

An As antisite is when an arsenic atom shows up where a gallium atom is supposed to be. An As precipitate is when the excess As atoms cluster together, usually around an existing defect (dislocation) in the crystal. This precipitation can occur when the As atoms diffuse during the annealing process.

The reasons for this can be quite specific to the particular method used for growing the crystal. The result is generally the same: the appearance of As atoms in positions they aren't "expected" to be in changes the electronic behavior, usually by introducing energy levels within the bandgap.


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