Adhesion characteristics of Pd/Ge Ohmic contacts on GaAs/AlGaAs multilayer structures

The adhesion characteristics of Pd/Ge Ohmic contact metallization on GaAs/AlGaAs multilayer structure are studied using scratch tests in a Nano-indentor. The effect of annealing on the scratch resistance of the metallization was measured and correlated with contact resistance and surface roughness. The scratch depth and qualitative evaluation of adhesion show best adhesion/wear resistance for films annealed at 300°C. It is found that the minimum contact resistance is also observed after annealing at this temperature. Profiles of scratch cross section at a constant force of 200 μUN indicate that, the scratches do not extend into the substrate for anneals at temperature <400°C. The optimum contact resistance of Pd/Ge contact is ∼(0.75+0.10Ω-mm) which is 15 times larger than those for optimized AuGe/Ni/Au contacts (0.05±0.01Ω-mm). The measured surface roughness is ∼2.0±0.5nm, which is ∼10 times lower than that of AuGe/Ni/Au based contact that gave the lowest contact resistance.