Hi Moshe,

I dont know how much it would help you, but if I understand it right,
you should be looking into the binary system of Au-Si. You should have
the temperature close to or lower than eutectic point of the Au-Si
system.So that underneath Si layer (few nanometers) diffuses into Au.
I would suggest N2 environment should be fine for this. Shortest time
to start trying would be 10 minutes.

Hope this helps.

Regards,
Suraj Patil