Geometric and compositional modulations are the principal parameters of control to tailor the band profile in germanium/silicon (Ge/Si) heteronanowires (NWs). This has been achieved mainly by alternating the feeding precursors during a uniaxial growth of Ge/Si NWs. In this work, a self-automated growth of Ge/Si hetero island-chain nanowires (hiNWs), consisting of wider c-Ge islands connected by thinner c-Si chains, has been accomplished via an indium (In) droplet-mediated transformation of uniform amorphous a-Si/a-Ge bilayer thin films. The surface-running In droplet enforces a circulative hydrodynamics in the nanoscale droplet, which can modulate the absorption depth into the amorphous bilayer and enable a single-run growth of a superlattice-like hiNWs without the need for any external manipulation. Meanwhile, the separation and accumulation of electrons and holes in the phase-modulated Ge/Si superlattice leads to a modulated surface potential profile that can be directly resolved by Kelvin probe force microscopy. This simple self-assembly growth and modulation dynamics can help to establish a powerful new concept or strategy to tailor and program the geometric and compositional profiles of more complex hetero nanowire structures, as promising building blocks to develop advanced nanoelectronics or optoelectronics.
Keywords: Ge/Si hetero nanowires; nanodroplet hydrodynamics; self-assembly growth.