Comparison of AuGe/Ni/Au, AuGe/Pd/Au, Ti/Pt/Au, and WSi/Ti/Pt/Au ohmic contacts to n-type InGaAs

A comprehensive study of AuGe/Ni/Au, AuGe/Pd/Au, Ti/Pt/Au, and WSi/Ti/Pt/Au ohmic contacts to n-type InGaAs for AlGaAs/GaAs HBT fabrication is presented using various measurements in order to investigate the correlation of the microstructures with the specific contact resistance. As the results, AuGe-based ohmic contact systems with Ni or Pd as the barrier metal show the degradation of specific contact resistance at the relatively low alloying temperature. It is believed because the InGaAs layer near the interface is decomposed due to the out-diffusion of indium. On the other hand, Ti/Pt/Au and WSi/Ti/Pt/Au ohmic systems maintain their excellent electrical resistivities even after alloying at high temperature of 400 degrees C because barrier metals prevent indium and other elements from moving out of interface. Especially for Ti/Pt/Au contact, the specific contact resistance of 8.8 x 10(-10) Omega-cm(2), which is one of the best ohmic data reported up to date, is obtained after RTA at 375 degrees C for 10 s.