I would like to ask your opinion about a problem we are having with the
following heterostructure
GaAs/ AlSb/ 3000AlGaSb/ 150InAs/ 125AlGaSb/ 50InAlAs/ 30InAs.
We are fabricating hall devices by ion milling through the top four layers
and about 700A into the AlGaSb layer.  The wafer has a resistance between
devices of about 50-100kohm.  Devices we have fabricated with a previous
(slightly different) wafer had a resistance between devices of at least 10x
greater.
   We think that the ion mill may be causing damage or implanting ions into
the AlGaSb layer to cause conductivity.  Or maybe the AlGaSb layer is
reacting with air is some way.  If the problem is the former, we can
possibly do a chemical etch after ion etching.  If the problem is the
latter we can passivate the chip with SiN.  Both of those tests may cause
problems with the devices so I would like to get more information before I
start trying these out.  Any thoughts or alternate opinions would be
appreciated.
Glen

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Glen A. Landry, Ph.D.
Naval Research Laboratory
Materials Physics Branch
Code 6340
4555 Overlook Ave. SW
Washington, DC 20375
USA
Tel.: 202-767-4474 Fax: 202-767-1697
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