Metallurgical study of Ni/GaAs contacts. II. Interfacial reactions of Ni thin films on (111) and (001) GaAs

Abstract

The solid-state interactions at the Ni/(111) and (001) GaAs interfaces were investigated in the temperature range 25–600 °C by Rutherford backscattering spectrometry and channeling experiments, x-ray diffractometry, and four-point probe. The samples were prepared by depositing nickel films, 70 nm thick, onto clean (111) and (001) GaAs single-crystal substrates under 5×10−10 Torr vacuum. Then they were annealed for 1 h at increasing temperatures under a flow of forming gas (90% N2-10% H2). The sequence of phase formation was the following: first, a ternary phase at 200 °C, then a mixture of two ternary phases at 250 and 350 °C, and finally from 400 to 580 °C a mixture of a ternary phase and NiAs. This last structure was stable up to 600 °C on (111) GaAs, but at this temperature a further consumption of GaAs led to a mixture of (NiGa+NiAs) onto (001) GaAs. Small differences were observed versus the orientation of the GaAs samples but all the ternary and binary phases exhibited epitaxial arrangements with both the (111) and (001) GaAs substrates. The ternary-phase diagram for the bulk Ni-Ga-As system provides the basis for understanding the sequence of the above results and much of the information in the literature about Ni/GaAs interfacial reactions.