Differential Optical Absorption Spectroscopy in Ge-Si Direct and Indirect Bandgap Superlattices

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The proposal is to use differential optical absorption spectroscopy to study and determine the nature of the fundamental bandgap in Ge-Si strained superlattice nanostructures. First principle theoretical studies show that both direct and indirect superlattices exist, and previous experimental studies have given some credible support to these calculations. The experimental demonstration of direct bandgap behavior in Ge-Si nanostructures will open up a whole new vista for Si as a photonic material. A principal goal of the proposed research is to forge a new fundamental understanding of the relationship between superlattice structures and symmetry on one hand, and optical properties on the other. A direct result of this work will be demonstration of how crystalline symmetry, artificially- imposed during growth, can be used to control the optical propertied of semiconductors and other materials.