Epitaxial Ge/Si(100) Quantum Dots and Mn-Based Ferromagnetic Group IV Semiconductors

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This project aims to investigate fundamental materials issues related to lithographically templating ensembles of heteroepitaxial Ge/Si(100)quantum dots. Ideal ensembles consist of periodically arranged, identical, coherent (defect free) Ge islands. Epitaxial overgrowth of electron beam lithography patterned substrates will be employed to periodically position the dots. This technique is expected to have advantages over other methods for ordering heteroepitaxial quantum dots. The lithographic template is planarized during strained-layer SiGe overgrowth, effectively translating topographic periodicity at the patterned substrate into elastic periodicity at the planar growth front. Quantum dot placement at elastic energy minima on a planar substrate allows them to be easily integrated into functional architectures. Additionally, any etch-induced damage is buried during overgrowth. Dot spacing and periodicity may be varied through changes in the pat-tern pitch, providing flexibility for producing periodic single or multi-dot arrays. Planarization during strained SiGe layer overgrowth relies on the interplay between surface morphology, com-position and misfit strains. The project will employ atomic force microscopy to characterize sur-face topography and state-of-the-art high spatial resolution electron microscopy to characterize composition to achieve greater understanding. A new class of Mn-based, ferromagnetic, group IV semiconductors, lattice-matched Si:Mn and strained SiGe:Mn, will also be grown on Si(100) in order to assess their utility for 'spintronics' applications in Si-based materials. These magnetic semiconductors will be integrated into heterostructures incorporating heteroepitaxial Ge quantum dots so that the efficiency for injection of spin-polarized carriers may be assessed. %%% The project addresses fundamental research issues associated with electronic/photonic materials having technological relevance and emphasizes the integration of research and education. The project will involve graduate students from underrepresented groups and undergraduate students. The dissertation research of a female graduate student will be supported and a Hispanic graduate student will be involved in a closely related project supported by an ASU/National Labs fellowship. Undergraduate students will be supported by REU supplements and the ASU Physics REU site award. The PI will be involved in activities which broaden its scope and impact, including participation in development of a Nanoscience and Technology graduate program at ASU. This will be an interdisciplinary program spanning the Colleges of Liberal Arts and Sciences and En-gineering and Applied Sciences.***