Sorry if this is of no interest of you.

Hello,

I need to selective etch partially(undercut) AlGaAs v.s. GaAs of
p-GaAs/p-AlGaAs/i-GaAs/n-AlGaAs epi from the side of the mesa. And we need to
have same undercut of p-AlGaAs and n-AlGaAs with gold on top of p-GaAs.  Now the
problem is: Without gold or platinum on top of p-GaAs(only tried this two
metals), I can get P-AlGaAs and n-AlGaAs undercut the same. But with gold or
platinum deposited first on p-GaAs, there's huge difference: p-AlGaAs being
etched(undercut) while n-AlGaAs staying intact.  I will really appreciate if
anyone has some solutions to etch evenly with gold in present?  We do need metal
deposition first.

Note:
.. p-AlGaAs denotes p type AlGaAs
.. n-AlGaAs denotes n type AlGaAs
.. the wet etch chemistry I use: buffered HF

Many thanks!
Z.Z.