Zn-implanted Pd-based ohmic contacts to p-In0.53Ga0.47As for the base layer of InP/In0.53Ga0.47As heterojunction bipolar transistors

InP/In_0.53Ga_0.47As heterojunction bipolar transistors for high-frequency applications impose stringent requirements on the ohmic contact to the thin p-In_0.53Ga_0.47As base layer. If high current gain is required it is favorable to limit the base layer doping and the contact resistivity. Usually, nonalloyed metallizations do not yield sufficiently low contact resistivity in the relevant doping range, whereas alloyed systems suffer from inherent problems with nonplanar interfaces and comparably deep penetration of contact components. Alternatively, low-ohmic contacts on p-In_0.53Ga_0.47As can be fabricated by implantation of p-dopant into nonalloyed metallizations. We have recently demonstrated the feasibility of this concept in the case of Zn or Cd implanted Pd/Ge contacts on p-In_0.53Ga_0.47As and show now that Pd/Au-based contacts are even more suitable for this purpose. A comparative study of both systems, e.g. Pd/Ge and Pd/Au/LaB ₆/Au, is presented