  Semiconductor nanowires have been playing a crucial role in the development
of nanoscale devices for the realization of spin qubits, Majorana fermions,
single photon emitters, nanoprocessors, etc. The monolithic growth of
site-controlled nanowires is a prerequisite towards the next generation of
devices that will require addressability and scalability. Here, combining
top-down nanofabrication and bottom-up self-assembly, we report on the growth
of Ge wires on pre-patterned Si (001) substrates with controllable position,
distance, length and structure. This is achieved by a novel growth process
which uses a SiGe strain-relaxation template and can be generalized to other
material combinations. Transport measurements show an electrically tunable
spin-orbit coupling, with a spin-orbit length similar to that of III-V
materials. Also, capacitive coupling between closely spaced wires is observed,
which underlines their potential as a host for implementing two qubit gates.
The reported results open a path towards scalable qubit devices with Si
compatibility.
