Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!apple!agate!shelby!brooks@sierra.Stanford.EDU
From: brooks@sierra.Stanford.EDU (Michael B. Brooks)
Newsgroups: sci.electronics
Subject: Re: Ohmic Contacts to n-AlGaAs
Summary: Ref to recipe
Keywords: ohmic contacts  GaAs, AlGaAs
Message-ID: <459@sierra.stanford.edu>
Date: 13 Jan 90 23:06:41 GMT
References: <7940@nigel.udel.EDU> <454@sierra.stanford.edu> <8039@nigel.udel.EDU>
Sender: brooks@sierra.STANFORD.EDU (Michael B. Brooks)
Reply-To: brooks@sierra.UUCP (Michael B. Brooks)
Organization: Stanford University
Lines: 28

In reply to the reference request about the ohmic contacts recipe
(n-type GaAs) there is a body of literature based on M. Murakami`s
group at IBM (Yorktown Heigths).  The recipe is based on  J.Vac.Sci.Technol.
B 4(4), Jul/Aug 1986 pp.903-911, "Microstructure studies of AuNiGe Ohmic
contacts to n-type GaAs", by Murakami, Childs, Baker & Callegari. Thickness
of the Au-Ge layer varies somewhat (our work).  This is not specifically
for contacts to AlGaAs (it`s for GaAs) but it will probably work since
other workers use such recipes.  A similar recipe is from Rai & Ezis et.al.,
J.Appl.Phys. 63 (9), 1 May 1988, p.4723, and is for GaAs-AlGaAs MODFETs:

This is 50A Ni, 170A Ge, 330A Au, 150A Ni, and 2000A Au, which was put 
down via e-beam , followed by "transient annealing" at 525C for a short
time.

What I have cited is  hardly representative of multitudes of contact
schemes available.  These are similar to what I use, and would be considered
"traditional" in some sense, generally known to work.  They all require
horrendous amounts of optimization based on your particular set of equipment.

If I was using a thermal system for metal evap I would be extremely careful
 to limit the heat transported to GaAs.  MEtallization reactions happen
at low temps (<250C) in short times,  and can mess things up if not carefully
controlled.  Beyond this thermal evap ought to be OK.

I haven`t tried the contact scheme you have mentioned John, though I`ll try to
check out the reference.  

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