A complete fabrication route for atomic-scale, donor-based devices in single-crystal germanium.

Despite the rapidly growing interest in Ge for ultrascaled classical transistors and innovative quantum devices, the field of Ge nanoelectronics is still in its infancy. One major hurdle has been electron confinement since fast dopant diffusion occurs when traditional Si CMOS fabrication processes are applied to Ge. We demonstrate a complete fabrication route for atomic-scale, donor-based devices in single-crystal Ge using a combination of scanning tunneling microscope lithography and high-quality crystal growth. The cornerstone of this fabrication process is an innovative lithographic procedure based on direct laser patterning of the semiconductor surface, allowing the gap between atomic-scale STM-patterned structures and the outside world to be bridged. Using this fabrication process, we show electron confinement in a 5 nm wide phosphorus-doped nanowire in single-crystal Ge. At cryogenic temperatures, Ohmic behavior is observed and a low planar resistivity of 8.3 kΩ/□ is measured.