Synchrotron radiation photoemission spectroscopy was used to investigate thermal reactions on the Cl-terminated SiGe(1 0 0)-2 × 1 surface. Populations of GeCl and SiCl surface species during thermal annealing are monitored by measuring the intensities of their corresponding Ge 3d, Si 2p and Cl 2p core level components. Experimental results indicate that the initially clean SiGe alloy surface is dominated by Ge-Ge and Ge-Si dimers, and that, after Cl2 adsorption, thermodynamic forces drive Si in the subsurface region to replace Ge in the GeCl species. Consequently, chlorine desorbs in the form of SiCl2 above ∼700 K, leading to etching of Si.
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