Hi all,

I am struggling a lot to obtain Ohmic contacts in a rather thin film of
medium doped 30nm GaAs / 20nm InGaAs (both 1x10^17). I guess it could be a
processing issue.

I tried many recipes around, mostly the Au88Ge12 / Ni or Au/Ge/Ni alloy or
even evaporated as well as pressed Indium. Finally a RTA step of 3min
420-450°C. In 99% I obtain rather high resistances, 3-6 orders of magnitude
higher then the bulk. I don't believe that this is uniquely due to surface
depletion, because in some regions (100Microns away) I obtain the low R of
the order of the bulk R.

Does anyone have an idea of processing tricks? I tried already a HCl dip
directly prior to evaporation (no influence) and checked recently the
thicknesses of the individual metal layers.

Any suggestions are greatly welcome.

Daniel