Preparation of the Ge(001) surface towards fabrication of atomic-scale germanium devices

We demonstrate the preparation of a clean Ge(001) surface with minimal roughness (RMS similar to 0.6 angstrom), low defect densities (similar to 0.2% ML) and wide mono-atomic terraces (similar to 80-100 nm). We use an ex situ wet chemical process combined with an in situ anneal treatment followed by a homoepitaxial buffer layer grown by molecular beam epitaxy and a subsequent final thermal anneal. Using scanning tunneling microscopy, we investigate the effect on the surface morphology of using different chemical reagents, concentrations as well as substrate temperature during growth. Such a high quality Ge(001) surface enables the formation of defect-free H-terminated Ge surfaces for subsequent patterning of atomic-scale devices by scanning tunneling lithography. We have achieved atomic-scale dangling bond wire structures 1.6 nm wide and 40 nm long as well as large, micron-size patterns with clear contrast of lithography in STM images.