MICROSTRUCTURAL ANALYSIS OF AU PT/TI CONTACTS TO P-TYPE INGAAS/

A detailed study on the microstructural changes that occur on annealin g of Au/Pt/Ti ohmic contacts to n-type InGaAs has been carried out. Th e metal layers were deposited sequentially by electron beam evaporatio n, onto, InGaAs, doped with Zn to a level of 7 x 10(18) cm(-3), that w as epitaxially grown on [100] InP substrates. The deposition sequence and metal layer thicknesses were: Ti (25 or 30 nm), Pt (25 or 30 nm) a nd Au (250 or 300 nm). Samples were annealed at temperatures ranging f rom 250-425 degrees C in a nitrogen atmosphere. As-deposited contacts were Schottky barriers, while a minimum contact resistance of 2 x 10(- 5) Omega cm(2) was obtained by annealing in the 375-425 degrees C rang e. Annealing resulted in the inward diffusion of Ti and outward diffus ion of In and As, leading to the formation of TiAs, metallic In and Ga -rich InGaAs at the Ti/lnGaAs interface. The Pt diffusion barrier was effective in preventing In diffusion into the outer Au layer and minim izing Au diffusion to the semiconductor.