Total Tomography of Nonplanar Heterostructures for Quantum Information Processing

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Nontechnical description: Semiconducting materials, particularly alloys composed of group III and group V elements, are extensively used in devices that process information electronically and convert electrical currents to light, enabling fast and efficient communication considered essential in modern society. Different III-V semiconductors can be combined in heterostructures at the nanometer scale to make devices with the potential to process information in entirely new ways by exploiting quantum mechanics. This project is using advanced deposition and characterization methods with the goal to develop fundamental understanding of how semiconducting alloys can be formed into nanoscale wires with superconducting contacts to produce new modes of information storage, computation, and communication. Furthermore, this project aims to maintain the competitiveness of the United States in new information technologies and the future workforce. Towards that end, graduate students are trained in cutting-edge three-dimensional characterization methods at Northwestern University and in national laboratories on materials systems relevant to quantum technologies.Technical description: Substrate-templated nanowire heterostructures grown in network topologies are candidates for quantum computing schemes involving Majorana quasiparticles. Band-offsets in narrow band-gap III-As/Sb semiconductors can produce the required confinement potentials for electrons, but heterostructures must be grown with the appropriate size, geometry, and precision to enable the desired coupling to metal and superconducting contacts. The goal of this project is to correlate the composition, strain, and electronic structure of III-As/Sb heterostructures in three dimensions to understand how composition and strain influence nanostructure growth and electronic properties, particularly the spatial distribution of free carriers in quasi-one-dimensional bands with strong spin-orbit coupling. Optical properties of quantized emitters in these heterostructures are also investigated. Atom probe tomography is used to measure three-dimensional nanoscale composition fields of III-As/Sb nanowire heterostructures. Based on these composition data, finite element models of relaxed physical structure are used to simulate and interpret synchrotron-based single nanowire x-ray diffraction and imaging. The combined strain and composition data, including dopant distributions measured by atom probe tomography, are used to develop models of nanostructure growth and electronic properties. Correlated single nanowire cathodoluminesence provides spatially resolved measurements of band-gap and active carrier concentrations, and correlated transmission electron microscopy measurements constrains atom probe and x-ray reconstructions of composition and strain, respectively.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.