nasty arsenic compounds from GaAs etching?

Hi

I hope you can help me with following question:

I had to clean a fume hood that was heavily contaminated from etching
gallium arsenide with a bromine in methanol solution. It was not cleaned for
years.

During the dissolution reaction of GaAs, a volatile compound is apparently
formed that deposits everywhere in the fume hood forming a white layer.
These residues are only poorly soluble in methanol but easily in water. I
was thinking about a possible formation of compounds like
trihydroxymethylarsine or some brominated organic arsenic compounds. I don't
know the dissolution reaction of GaAs in this mixture, but I read that
hydroxymethyl radicals are formed when Br2 is added to MeOH. Initially the
product is volatile, then probably hydrolyzes/oxidizes to something else
that sticks to the walls and glassware.

Does someone have an idea what this could be? When cleaning up, I was very
careful and assumed the substance to be highly toxic and treated the waste
as As-contaminated. Now I'm primarily worried about the potential danger to
lab users that are not aware of such contamination if they come in contact
with this material if there will be such contamination again in future.

I posted the same question also in the forum: forum.chemikalien.de under
Allgemeine Chemie.

Thanks for your help
Andreas Rutz


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