CMOS-Compatible Ti/TiN/Al Refractory Ohmic Contact for GaAs Heterojunction Bipolar Transistors Grown on Ge/Si Substrate

In this article, we demonstrate the Ti/TiN/Al (15/50/50 nm) ohmic contact on InGaP/GaAs heterojunction bipolar transistors (HBTs) epitaxially grown on 200-mm Si substrate. We study the rapid thermal annealing (RTA) effect of the metal stack on both n-type InGaAs and p-type GaAs. The dc characteristics of the HBT devices fabricated using the Ti/TiN/Al metal contacts have been analyzed. Contact resistances
${(}{R}_{c}{)} < 0.1~\Omega \cdot $
mm for n-InGaAs and
$0.8~\Omega \cdot $
mm for p-GaAs can be achieved. A dc current gain of 45 with a collector–base breakdown voltage (BV
_cbo
) of 15.65 V is achieved. The ideality factor of the emitter–base current (
${n}_{b}$
) and base–collector current (
${n}_{c}$
) is 1.03 and 1.44, respectively, after RTA at 450 °C. The dc characteristics remain stable upon prolonged annealing at 450 °C for 45 min. This high thermal budget non-gold ohmic contact is suitable for Si-CMOS integration and enables the potential for hybrid III-V CMOS technology for 5G and mm-wave applications.