Interfacial reactions of palladium thin films on Ge(111) and Ge(001)

Planview and cross-sectional transmission electron microscopy (XTEM), Auger electron spectroscopy and X-ray diffraction (XRD) have been applied to study the interfacial reactions of palladium thin films on Ge(111) and Ge(001) with particular emphasis on the epitaxial growth of Pd 2Ge on Ge(111). Polycrystalline palladium and Pd 2Ge grains as well as epitaxial Pd 2Ge regions were observed in as-deposited (111) samples. Epitaxial Pd 2Ge was found to cover about 60% of the germanium surface area in samples annealed at 160°C. The orientation relationships between epitaxial Pd 2Ge and the germanium substrate were determined to be Pd 2Ge[0001]|Ge[111] and Pd 2Ge( 10 ̄ 10)| Ge ̄ 220). The Pd 2Ge-Ge interface was found to be not very smooth. In samples annealed at 250–500°C, only polycrystalline PdGe was found. Randomly oriented polycrystalline palladium and Pd 2Ge were found in as-deposited (001) samples. In samples annealed at 160°C, Pd 2Ge and PdGe grains were found to coexist. Only polycrystalline PdGe grains were observed in samples annealed at 250–500°C. XTEM observations and XRD data revealed the presence of an epitaxial Pd 2Ge layer, about 20–30 nm in thickness, locally between the palladium metal layer and germanium substrate in as-deposited (111) samples, irrespective of palladium metal layer thickness (30–220 nm) and deposition rate (0.1–0.7 nm s -1). The results for Pd 2Ge and PdGe formation on germanium are compared with those for Pd 2Si and PdSi formation on silicon.