Microstructure and contact-resistance temperature dependence of Pt/Ti/Ge/Pd ohmic contacts to GaAs

Abstract

The development of GaAs device technology has demonstrated the need for fabrication of low resistance thermally stable ohmic contacts. Gold based contacts have been the overwhelming choice for ohmic contacts in device applications. In particular, Au/Ge/Ni and Zn/Au alloyed contacts have been used for n and p-GaAs respectively. Numerous investigations have shown that Au-based contacts to GaAs have avery complex morphology after annealing. Specifically, structural interface inhomogeneities, such as protrusions and newly formed lateral interface phases lead to non-planar metalsemiconductor interfaces which in turn cause nonuniform current flow and consumption of the GaAs substrate. This type of interface morphology is not acceptable for device applications where a large electrical field or a shallow contact is required. In particular, devices such as heterojunction bipolar transistors (HBT's) cannot tolerate contacts with lateral and vertical interface inhomogeneities.This study employed crosssectional transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and electrical measurements (transmission line mode), to systematically investigate the structural, chemical and electrical properties of the Pt/Ti/Ge/Pd contacts to both n and p+ GaAs as a function of annealing temperatures.