Thank you Brad and Edward!  Ideally, I would like etching rate difference
within 20% for both p-AlGaAs and n-AlGaAs.  I thought about using vapor and
maybe dry etch to cut the current path.  Any good suggestion on that? I
don't even know if anybody has done that before.

Thanks again for your valuable input!

Z.Z

----- Original Message -----
From: "SEBESTA Edward" 
To: "General MEMS discussion" 
Sent: Wednesday, November 12, 2008 7:09 AM
Subject: [mems-talk] selective etch of AlGaAs/GaAs with different doping
andmetal in present


>I agree with Mr. Cantos that it is very likely a galvanic effect.
> Another possibility is diluting your etchant with ethyl glycol. That
> would reduce the effect of the gold to solution current and might block
> the emf. I don't know this for a fact, but it is something I am looking
> into.
>
> Keeping the resist one, as Mr. Cantos suggests, should help some, just
> by reducing the area of the gold in contact with the solution and
> thereby reducing the current.
>
> Perhaps some sacrificial layer can be deposited on the gold or a polymer
> to block contact with the solution. These are highly speculative
> suggestions as is the ethyl glycol.
>
> Ed