Total Tomography of III-V Non-Planar Heterostructures

Northwestern University, Evanston IL

Investigators

Abstract

Nontechnical description: Semiconducting materials, particularly alloys composed of group III and group V elements, are useful for converting electrical energy to light in light-emitting diode devices. Different III-V semiconductors can be combined in heterostructures to make devices smaller and the energy conversion processes more efficient. The project develops fundamental understanding of how semiconducting alloys in nanowire form can be best arranged to control the flow of electrical energy and generate light in the infrared portion of the spectrum. This understanding contributes to the development of on-chip photonic interconnects that overcome the bottleneck in the speed of information transfer between computer chips that process huge volumes of information in cloud computing. The project trains graduate students in cutting-edge three-dimensional characterization methods at Northwestern and in national laboratories. Web-based interactive case studies are used to disseminate advances in these characterization methods, which can accelerate the development of new electronic and photonic technologies. Technical description: The goal of the project is to correlate the composition, strain, and electronic structure of group III-As nanowire core-shell heterostructures in three dimensions to understand how interactions between composition and strain influence nanostructure growth and optoelectronic properties. Atom probe tomography is used to measure three-dimensional composition fields with nanoscale resolution. Based on these composition data, finite element models of relaxed physical structure are created to extract three-dimensional strain information from single nanowire x-ray imaging and diffraction studies. Combined strain and composition data, including dopant distributions accessible only by atom probe tomography, are used to model electronic and optical properties and identify materials factors that limit the performance of III-As core-shell nanowires as infrared light emitting diodes and lasers. Single nanowire Raman, photoluminescence, and electrical measurements are used to spatially map strain, carrier concentrations and lifetimes, and the band offsets that establish confinement potentials.