Michael THEWALT
Simon Fraser University

Redefining the Limits of Semiconductor Spectroscopy

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I will describe recent advances in the ultrahigh resolution spectroscopy of isotopically enriched 28Si, including results for the near-gap bound exciton transitions and the mid-infrared donor and acceptor absorption transitions. While it has long been known that the average isotopic mass of a semiconductor can have a small effect on the low-temperature band gap energy, it is only the recent results for Si which reveal the effects of the isotopic randomness present in samples having the natural isotopic composition. The common assumption that many of these spectroscopies had reached their ultimate limits in high quality natural Si samples is shown to be quite incorrect - these older results were all limited by inhomogeneous isotope broadening. The elimination of this inhomogeneous broadening in 28Si reveals many new features, and new physics, and allows for the determination of previously inaccessible quantities, such as the temperature dependence of the Si band gap below 4.2 K.