Traditionally, differences in lattice constant and thermal expansion coefficient have prevented the growth of III-V semiconductors on group IV materials. For example, the crystal lattice mismatch between indium phosphide and germanium is 3.7%. But, it appears that growing the materials in nanowire form prevents these factors becoming an issue.
To deposit the wires on germanium, the scientists coated the substrate surface with a thin layer of gold. Once it was heated, the gold film broke up into small particles. These acted as catalysts for the growth of indium phosphide nanowires by a vapour-liquid-solid (VLS) process.
In this way, the team grew indium phosphide nanowires onto Ge(111) and Ge(100) surfaces. Researchers said they initially chose germanium rather than silicon because to remove the surface oxide from it is less troublesome.
"Although this process [VLS] is not new, our team at Philips and the Kavli Institute of Nanoscience was the first to apply it to successfully grow III-V materials on silicon and germanium substrates," said Erik Bakkers of Philips Research.
The team also made electrical contacts connect to doped indium phosphide nanowires grown on n-type Ge(111). The wires typically had a contact resistivity of less than about 10-8 ω cm2.
Since publishing their work in Nature Materials, the scientists say they have also grown indium phosphide nanowires on silicon substrates, overcoming a lattice parameter mismatch of 8.7%.