Silicon Clathrate Materials for Advanced Semiconductors

PROJECT NUMBER: 95

AUTHOR: William Schenken, Engineering Physics | MENTOR: Reuben Collins, Physics

MENTOR: Carolyn Koh, Chemical and Biological Engineering | MENTOR: Craig Taylor, Physics

ABSTRACT

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Silicon (Si) clathrates are cage-like, crystalline silicon inclusion compounds. The Si cages are formed around sodium (Na) “guests”. At high concentrations, the Na degenerately dopes the crystal. As the concentration of Na is lowered, the material undergoes a metal-insulator transition. At sufficiently low Na concentrations, the material is a proposed wide bandgap semiconductor. Moreover, in the low Na regime, it is possible to view Na as a shallow donor in Si clathrates, similar to phosphorous in diamond Si. It is thus desirable to understand the properties of the Na guest atoms. Electron paramagnetic resonance (EPR) provides a way of probing the local environment of the paramagnetic Na guests. This project is aimed at synthesizing, characterizing, and modelling Si clathrate samples with low Na concentrations using EPR as a primary tool. We report an analysis of the so-called “hyperfine lines” in the EPR spectrum. We attribute features to interactions of the donor electron with the 29Si isotope, to interactions between multiple Na atoms, and to dangling bond defects surrounding the crystal. These features provide insight to the isolated Na donor wavefunction, to the behavior near the metal-insulator transition, and to the practical development of this material as a useful semiconductor.

VISUAL PRESENTATION

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Sponsored by Phillips 66