Si-implantation for low ohmic contact resistances in RF GaN HEMTs

In this work, Si implantation and activation for lowering the ohmic contact resistance (R_c) of mm-wave GaN HEMTs has been investigated. Various combinations of annealing temperature/duration and implantation doses were tested. Dopant activation was performed using a modified procedure in an MOCVD tool, involving fast temperature ramping and annealing the samples for 8 min at 1150 °C. Thereby, ∼0.02 ± 0.01 Ω mm contact resistance was achieved on a fully doped region and ∼0.1 ± 0.02 Ω mm when only the source and drain contact region was n-type doped. For comparison, a well-established alloyed Ti/Al/Ni/Au ohmic contact scheme without implantation, was used as reference resulting in an average R_c ∼ 0.34 ± 0.12 Ω mm on the same wafer. Besides the three times lowered contact resistance the implanted contacts also showed a significantly improved on-wafer homogeneity.