Abstract
The Pd-GaAs(001) interfacial reactions after annealing treatments in vacuo have been investigated using cross-sectional transmission electron microscopy, X-ray energy-dispersive spectroscopy, X-ray diffraction and scanning electron microscopy. Our observations show that the reactions occur as the following processes:
(1) from room temperature to 250°C, Pd + GaAs→Pd2Ga + Pd2(GaxAs1−x) (x = 0·D52–0·62, Pd2As-type structure);
(2) from 250 to 350°C, Pd + GaAs→Pd2Ga + PdAs2 + Pd12(GaxAs1−x)y (x = 0·5–0·D07, y = 8·5–17·D0, Th7S12-type structure) and
(3) from 350 to 500°C, Pd12(GaxAs1−x)y + GaAs→lPdGa + As↑.
It is demonstrated that Ga and As atoms as well as Pd atoms are the diffusion species in the reactions. In the specimen annealed at 300[ddot]C, it is found for the first time that a separation is present at the interface between compounds and Pd, which might be related to Kirkendall voids or to the remainder of the native oxide on the GaAs substrate. The phase Pd12(GaxAs1−x)y is found to have poor adhesion to the GaAs substrate and to the PdGa phase. The compound morphologies are discussed on the basis of the experimental results.