Self-Aligned Technology Using Refractory Ohmic Contacts for GaAs/GaAlAs Heterojunction Bipolar Transistors

In this paper, we present a new self-aligned technology using refractory metals to contact the emitter layer, in order to afford the annealing process subsequent to the p type implantation, as the contact also acts as a mask for the p type implantation. GeMoW has been chosen for this purpose, GeMo to form the ohmic contact and W the implantation mask. The influence of the annealing conditions on the specific contact resistivity has been investigated. An As overpressure proved to be necessary for the formation of an ohmic contact.