Selective area growth of high-quality in-plane InAs nanowires and nanowire networks by molecular-beam epitaxy on Ge substrates

In-plane InAs nanowires and nanowire networks have garnered significant attention in electronics, optoelectronics, and quantum computation due to their small electron effective mass, narrow bandgap, high electron mobility, strong spin-orbit coupling interaction, and large Landé g factor. To date, in-plane InAs nanowires and nanowire networks have been primarily grown on III-V substrates. However, few studies have demonstrated the selective area growth of in-plane InAs nanowires and nanowire networks on CMOS-compatible group-IV Si or Ge substrates. In this work, we first employed conventional selective-area epitaxy to grow in-plane InAs nanostructures on Ge (111) substrates by molecular beam epitaxy. This approach, however, fails to concurrently achieve good selectivity and continuity. To overcome this limitation, we introduced a metal-sown, single-indium-source two-step growth method, which attains both selectivity and continuity but yields nanowires with rough surfaces and limited lengths ( We subsequently proposed an upgraded metal-sown, dual-indium-source two-step growth method, successfully fabricating in-plane InAs nanowires and nanowire networks with smooth surface morphology and lengths exceeding 60 μm. Furthermore, by optimizing the As beam equivalent pressure, overgrowth at network junctions is effectively suppressed, resulting in uniform nanowire networks. High-resolution transmission electron microscopy and Raman spectroscopy confirm the high-quality single-crystalline nature and pure zinc-blende structure of the nanowires and networks. This work establishes a foundation for fabricating high-quality in-plane InAs/superconductor hybrid nanowires and nanowire networks.