Formation, microstructure et résistances des contacts AuGe/n-GaAs, AuGe/n-InP, AuZn/p-InP et AuBe/p-InP

We have studied the metallurgy of the contacts AuGe/n-GaAs (12 wt.% Ge), AuGe/n-InP, AuZn/p-InP (12 wt.% Zn) and AuBe/p-InP (0.9 wt.% Be) between 320 and 450 °C by using a set of complementary methods of characterization: scanning electron microscopy, X-ray spectroscopy, glancing angle X-ray diffraction, transmission electron microscopy, Rutherford backscattering, secondary ion mass spectrometry and contact resistance measurements. In all the cases studied, the achievement of ohmic behaviour corresponded to the formation of compounds between the constituents of the thin film and those of the substrate. In the AuGe/GaAs contacts we observed the formation of the ternary compound AuGeAs at temperatures lower than 360 °C and of the AuGeAs and α'-AuGa (13 at.% Ga) alloys at higher temperatures. In the case of contacts on InP, the compounds Au3In, Au9In4, Au2P3 and GeP were detected after various annealings. We discuss the mechanisms of interaction and the effects of the alloy formation on the reproducibility of fabrication and on the reliability of the contacts. The relationship between the microstructure and the resistivity of the contacts is investigated by using Braslau's model of conduction by islets.