Shallow Ohmic Contacts to p-InGaAs Based on Pd/Ge with Implanted Zn or Cd

Abstract

ABSTRACTThe development of shallow ohmic contacts for the thin p-InGaAs layer (p≤1*1019 cm−5) of InP-based heterojunction bipolar transistors is a severe challenge to contact technology. While standard metallizations reveal several drawbacks, Pd/Ge-based systems emerged as promising candidates. In this work, Zn or Cd was implanted into the inner Pd contact layer for lowering contact resistivity. We present a study of the electrical and metallurgical properties of Pd/Ge contacts to p-InGaAs, and the influence of Zn and Cd implanted into the metallization. The resistivity of implanted and annealed (450-575 °C) contacts is reduced up to one order of magnitude compared to the unimplanted contact. Backside SIMS measurements show that annealing leads to a very limited interdiffusion at the interface. Cd and Zn diffuse into the InGaAs layer to a depth of approx. 30 and 40 nm, respectively. Due to these features, this implanted Pd/Ge contact scheme is a promising candidate for shallow contacts to p-InGaAs.