Etching away Ga & Al from GaAs surface

[HopilBae]

I'm sorry to flood your mailbox,
but does anybody have experience of etching away Gallium metal and Aluminium 
metal, without affecting GaAs substrate? The metal layer is deposited inadvertently,
and probably 50~100A thick..
Could anyone let me know what chemicals etch them and how fast?
( BTW, I'm considering HCl:H2O 1:1 as the most promising candidate.. )

Thank you
Hopil