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