METALLURGY OF OHMIC CONTACTS TO INP

Metallurgical aspects in the design and formation of ohmic contacts to InP are considered and reviewed in this paper. InP and related ternar y and quaternary semiconductors (e.g. InGaAs and InGaAsP) are utilized primarily in optoelectronic devices found in fibre optic applications , such as lasers and photodetectors. These devices are operated under high current densities (4-10 kA/cm(2)), with dimensions in the range 2 -150 mu m in width. Low resistance (ohmic) contacts are required to li nk the active regions of the semiconductor devices to the external cir cuit. The small dimensions associated with these devices place severe materials processing constraints on the formation of ohmic contacts. S ome of the issues that have to be addressed include contact stability (the metallization/semiconductor system is a multicomponent system in a nonequilibrium state), metallization adhesion to the semiconductor, contact uniformity and extent of reaction with the semiconductor. A ve ry powerful tool for examining contact metallizations in three dimensi ons on a very fine scale is transmission electron microscopy (TEM). Th is technique can provide imaging, structural and compositional informa tion from very small volumes. The capabilities of TEM analysis in char acterizing metallization/semiconductor microstructures are demonstrate d, with emphasis on the above issues.