Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uwm.edu!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!lll-winken!decwrl!shelby!brooks@sierra.Stanford.EDU
From: brooks@sierra.Stanford.EDU (Michael B. Brooks)
Newsgroups: sci.electronics
Subject: Re: Ohmic Contacts to n-AlGaAs
Summary: try Ni first
Keywords: ohmic contacts  GaAs, AlGaAs
Message-ID: <454@sierra.stanford.edu>
Date: 11 Jan 90 23:55:32 GMT
References: <7940@nigel.udel.EDU>
Sender: brooks@sierra.STANFORD.EDU (Michael B. Brooks)
Reply-To: brooks@sierra.UUCP (Michael B. Brooks)
Organization: Stanford University
Lines: 23

I never expected to find this on the net John! I`m happy to reply,
since this is my thesis research project here at SU.  Try the Ni
first, in this recipe, as a starter.  If possible, give Rapid
Thermal Annealing a whirl:

E beam evaporate:
50-100A Ni
~750A Au/Ge Eutectic
250A Ni
1000A Au (for reduced resistivity, the overlayer of Au is essential)

RTA times 30-45 sec or so, 450C or less
furnace anneal, 450C, under 5 min., forming gas
Note that the amount of Au/Ge is variable, and can be evaporated as
separate layers of the same overall composition. One must have
a thin layer of Ni first to prevent the balling effects that you
noticed (it`s more complicated than this, a black art really)

See Gallium Arsenide, by MJ Howes and Dv.Morgan (John Wiley & Sons, 1985),
or Gallium Arsenide Processing Techniques by RE Williams, (Artech House,
1984) for starters.

Mike Brooks/Stanford Electronics Labs (solid state)/SU