EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Networks of interconnected semiconductor nanowires (NWs) are essential elements to study fundamental quantum phenomena such as Majorana-mode braiding, quantum interference, multi-terminal Josephson junctions, and the superconductor-insulator transition [1]. Selective-area growth (SAG) is a promising technique to realize such networks on-demand allowing ultimate scalability. Narrow-bandgap InAs and InSb NWs have been successfully grown by SAG directly on wider-gap semiconductor substrates. However, the prospect of high-mobility SAG NWs has not yet been achieved because of 1) a network of misfit dislocations at the NW/substrate interface, and 2) nonuniform composition profiles due to material intermixing between the NW and the substrate.
Herein, we optimize InAs SAG NWs grown by means of molecular beam epitaxy on undoped GaAs(100) substrates covered by a SiOx mask. We demonstrate that an introduction of an InxGa1-xAs buffer layer between the InAs transport channel and the GaAs substrate is an essential step in improving the crystal quality of the channel. Using scanning transmission electron microscopy, we show that all misfit dislocations are effectively trapped at the InGaAs/GaAs interface away from the active layer. We then address the issue of Ga-In material intermixing with fine-tuning of the growth temperature of either InxGa1-xAs or InAs layers. Composition analysis performed by two independent measurements, i.e. electron energy loss spectroscopy and x-ray diffraction, reveals that the Ga fraction in the InGaAs and InAs is progressively decreased with reduced growth temperatures. By reducing the InAs growth temperature from 524 °C to 460 °C, we achieve pure InAs channels. Our optimizations result in a more than twofold increase in electron mobility accessed at 1.7 K.

[1] Alicea, J., et al., Nat. Phys., vol. 7, 2011, pp. 412-7.