Characterization of AuGe / Ni / Au Contacts on GaAs / AlGaAs Heterostructures for Low‐Temperature Applications

Abstract

We show that the Ge‐to‐Ni ratio in the three‐level contact metallization is an important parameter which determines the value of the contact resistance. An optimum atomic ratio around 0.8–1.0 is found to reproducibly yield contact resistivities in the range of 101–102 Ω‐mm. The role of the Ge/Ni ratio was observed for contacts to heavily doped surface layers and for contacts to heterostructures used for two‐dimensional electron gas (2DEG) transistors and quantum Hall resistance standards. The contacts obtained on 2DEG heterostructure samples maintain their characteristics down to the lowest temperatures tested (0.3 K), showing that this system is suitable for contacts to critical structures such as quantum Hall resistance standards used for metrological purposes.