In-plane selective area InSb–Al nanowire quantum networks

Abstract

Strong spin-orbit semiconductor nanowires coupled to a superconductor are predicted to host Majorana zero modes. Exchange (braiding) operations of Majorana modes form the logical gates of a topological quantum computer and require a network of nanowires. Here, we utilize an in-plane selective area growth technique for InSb-Al semiconductor-superconductor nanowire networks. Transport channels, free from extended defects, in InSb nanowire networks are realized on insulating, but heavily mismatched InP (111)B substrates by full relaxation of the lattice mismatch at the nanowire/substrate interface and nucleation of a complete network from a single nucleation site by optimizing the surface diffusion length of the adatoms. Essential quantum transport phenomena for topological quantum computing are demonstrated in these structures including phase-coherence lengths exceeding several micrometers with Aharonov-Bohm oscillations up to five harmonics and a hard superconducting gap accompanied by 2e-periodic Coulomb oscillations with an Al-based Cooper pair island integrated in the nanowire network.

Multiterminal Josephson Effect

“…On the experimental side, although nanowire network systems proximitized by superconductors have been investigated as a promising platform for topological quantum computation, the experiments are still limited to measuring two-terminal properties [38][39][40][41][42][43]. Multiterminal supercurrents were reported in graphene-based junctions [44], where a heating effect of coexisting disspative currents on supercurrent transport was mainly discussed.…”

Universal Platform for Scalable Semiconductor‐Superconductor Nanowire Networks

“…A second Si x N y mask is deposited, and the same method is used to first etch the mask opening and then selectively grow the InSb nanowire network using MOVPE. [ 22,23 ] The initially grown InP walls act as shadowing objects during the subsequent superconductor deposition and allow for selective growth on the InSb network.…”

“…The growth behavior shows many parallels to InP (111)B with the 10.4% lattice mismatch between substrate and nanowire compensated by misfit dislocations directly at the interface. [ 22 ] These dislocations can be revealed through an inverse fast Fourier transformation (IFFT) of the TEM image, as depicted in Figure 2e.…”

“…The right growth conditions confine the subsequent nanowire synthesis to the mask openings, allowing for scalable and highly flexible growth of complex in‐plane selective area networks. [ 22–24 ] But the difficulty of creating semiconductor‐superconductor segments remains. Until now, aluminium (Al) was subsequently evaporated and selectively wet etched, a method frequently used on out‐of‐plane nanowires.…”

“…Until now, aluminium (Al) was subsequently evaporated and selectively wet etched, a method frequently used on out‐of‐plane nanowires. [ 22,25 ] Experiments show however, that even highly selective etchants inflict damage on the semiconductor surface, lowering the device performance. [ 18,19 ]…”