Electron Spin Effects in Semiconductor Nanostructures

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NON-TECHNICAL ABSTRACTThere is currently an intense worldwide movement to explore the role of the electron spin (a quantum-mechanical magnetic property of the electron) in addition to the electron's charge in contemporary electronics, with an eye on increasing the functionality of electronic microchip devices, particularly in the realm of computation. This award supports a project aimed at addressing this issue by employing state-of-the-art techniques to fabricate and characterize a series of novel semiconductor nanometer scale structures in which the role of the electron spin is enhanced by incorporating magnetic ions. By training graduate and undergraduate students in cutting-edge semiconductor fabrication techniques as well as in designing multi-functional materials, the project is expected to have broad impact far beyond its immediate purely scientific goals. Skills in these areas of materials science are in wide demand in U.S. Industry, National Laboratories, and Academia. Additionally, the Notre Dame team collaborates with many scientists (currently with more than thirty-five other institutions) either by providing research samples or by carrying out joint experiments. This activity of dissemination and sharing of results and know-how (which has the added benefit of exposing students to inter-institutional and inter-disciplinary team collaborations) is expected to further expand as new spin-based electronic materials are developed in the course of the present project. TECHNICAL ABSTRACTThis grant supports a project that focuses on two new but complementary areas involving spin phenomena in low-dimensional magnetic semiconductor systems. (a) The study of changes in the properties of ferromagnetic (FM) semiconductors as their size approaches nanometer dimensions; and (b) exploratory research on growth and properties of phosphide-based FM semiconductors, such as GaMnP and InMnP. Area (a) is motivated by the expectation that, as the physical size of a magnetic semiconductor such as GaMnAs approaches the nanometer scale and becomes comparable to, e.g., the width of ferromagnetic domain walls or the free carrier depletion length, its magnetic properties will significantly change. This becomes especially important as one considers applications of FM semiconductor devices in nanotechnology. Using molecular beam epitaxy (MBE) followed by lithographic techniques, the Notre Dame team proposes to explore the consequences of such reduced size by magnetization measurements, magneto-transport, magneto-optical studies, and ferromagnetic resonance. Area (b) is focused on developing comprehensive research on MBE growth of phosphide-based ferromagnetic semiconductors, followed by a systematic investigation of their spin-based properties. Although the spin properties of alloys such as GaMnP, InMnP and GaMnAsP are expected to be highly promising, and offer a range of important new opportunities, surprisingly little work has been done on this family of materials as compared to the effort given to, e.g., the GaMnAs or InMnAs alloys. Extending the proposed studies to this new family of FM semiconductors is expected to significantly advance the understanding of ferromagnetic semiconductors generally.