Characterization of alloyed AuGe/Ni/Au ohmic contacts to n-doped GaAs by measurement of transfer length and under the contact sheet resistance

The results of systematic measurements of transfer length L _T and sheet resistance under the contact R_sk for alloyed AuGe/Ni/Au ohmic contacts to GaAs active layers prepared both by VPE (vapor-phase epitaxy) and by direct selective ion implantation are given. The end resistance measurement technique was used. Also reported are the more commonly measured specific interfacial resistance ρ_c and unit-width resistance r_c. L_T was relatively constant at 1.35 μm. A wide range for R_sk was observed, including values both higher and lower than the pre-alloyed value. It correlates with ρ_c and r_c and demonstrates that variation in the GaAs/contact interface is the source of the commonly observed wide scatter in these parameters