Hi Daniel,

That doping level is too low to obtain ohmic contacts on GaAs. All the
contacts that you make will be in Schottky type.

Alinti Brent Garber 

> 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