Ge/Si(100) Island and Wetting Layer Composition

Etching water soluble Ge-oxides was used to investigate Si interdiffusion into epitaxial Ge/Si(100) samples. The Ge coverage, θ _Ge, was measured using Rutherford backscattering spectrometry (RBS) before and after water etching of samples grown at substrate temperatures between 400°C and 650°C. θ _Ge was correlated with sample morphology determined using atomic force microscopy (AFM). The local Ge concentration was qualitatively assessed using energy dispersive x-ray (EDX) analysis. For samples grown at T=400°C, water completely dissolves the islands and no Ge is detected by RBS. For samples grown at T=600 and 650°C, AFM detects no change in the surface morphology and RBS indicates that 650°C decreases by about 3 monolayers (ML). These results suggest that for growth at T=400°C, both the islands and wetting layer are relatively pure Ge while for growth at T≥600°C, the wetting layer is Ge rich compare to the SiGe alloy islands, EDX confirms this conclusion detecting no Ge signal between islands for etched samples grown at T≥600°C. Our results suggest that for growth at T≥600°C, Si interdiffusion into islands is through the region underneath the islands instead of from the wetting layer.