InSb Heterostructures for Spin and Quantum Electronic Experiments

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TECHNICAL EXPLANATION This project explores spin properties and quantum effects in InSb heterostructures, and aims to optimize such structures for applications that rely on these phenomena. The number of experiments that focus on spin properties of electrons in semiconductors has increased substantially in recent years. Much of this effort is motivated by a vision of new types of devices that exploit spin-polarized currents. Many challenges remain, including finding the most efficient materials and configurations for spin injection and spin manipulation, and developing a range of techniques for characterizing spin properties. The requirement of ballistic transport for some devices provides an additional challenge. Narrow band gap materials are a promising solution since large spin effects caused by the Rashba, Dresselhaus, and Zeeman energy terms are correlated with narrow gaps. Because InSb has the smallest band gap of any III-V semiconductor, spin effects are expected to be among the largest. The PIs have demonstrated success in the growth of InSb quantum wells, as evidenced by ballistic transport over distances of 0.5um at temperatures as high as 185K. The approach has four components: 1)Energy splittings will be probed using an electron spin resonance technique. By varying quantum well structural parameters, factors that influence the Rashba effect will be identified. This is expected to contribute to a more complete understanding of the Rashba and Dresselhaus splittings with the goal of optimizing structures for large zero-field splitting. 2)The large Rashba and Dresselhaus mechanisms are predicted to have interesting consequences in electron focusing experiments. The separate trajectories for electrons with different spin projections will be studied via spin filters based on magnetic focusing. 3)Point-contact techniques for studying spin splitting will be studied. In these one-dimensional channels spin-orbit effects are predicted to lead to much richer conductance spectra. InSb is well suited to this study due to both the large Rashba term and the small effective mass that leads to large confinement energies. 4)Magneto-optical experiments on anti-crossings between Landau levels with opposite spin and on bilayer systems will provide further insight into spin interactions and novel electronic states. These studies are made possible by advances in the materials science of InSb-based heterostructures. Proposed improvements to the heterostructure design will be guided by transmission electron microscopy studies of crystalline defects, which are an important factor limiting the electron mobility and mean free path. Defect densities will be reduced through modification of the buffer layers used on GaAs substrates and through the use of InSb substrates. With the proposed improvements, ballistic transport will persist to longer lengths and higher temperatures. NON-TECHNICAL EXPLANATIONThe project addresses fundamental materials research with strong technological relevance to electronics and photonics, and effectively integrates research and education. The research goes beyond its relevance to developing technologies that exploit spin properties. Research will be integrated with education at various levels. Outreach efforts include the development and implementation of a module on magnetism for use with K-5 students. The curriculum for engineering and physics majors will be improved by the introduction of spintronics as a special topic in two courses. Finally, this research effort will enlist the participation of numerous undergraduates and graduate students. Members of underrepresented groups, particularly women, will continue to be integral to the research.