GeMoW Refractory Ohmic Contact for GaAs / GaAlAs Self‐Aligned Heterojunction Bipolar Transistors

Abstract

We have formed and ohmic contacts to n‐type using different annealing techniques: rapid thermal annealing (RTA) or thermal furnace annealing under a forming gas, and sealed ampul or semi‐open box technique under an As overpressure. A comprehensive study of both contacts is presented using electrical testing, Auger electron spectroscopy, secondary ion‐mass spectrometry, and transmission electron microscopy. This study has led to the optimization of a new refractory ohmic contact, the As‐doped Ge/Mo/W contact. Very low specific contact resistivities (10−7 Ω · cm2), have been obtained, when the contact included an As‐doped Ge layer with a doping level of 1020 atm · cm−3 and was annealed using the semi‐open box technique under an As overpressure. As doped ohmic contacts have also been realized on heterostructures, the specific contact resistivity is , which is a very low value for n‐type refractory ohmic contact realized on heterostructure.