Daniel,

The 12%Ge/Au with a Ni layer, followed by Au sounds right (without
breaking vacuum in between).
Your RTA cycle seems VERY long.  I go 20 seconds @ 420c

Brent



D.Grimm@ifw-dresden.de wrote:
> 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