Shallow Impurity Absorption Spectroscopy in Isotopically Enriched Silicon

Karaiskaj et al. showed that the isotopic randomness present in natural Si (natSi) causes inhomogeneous broadening of many of the ground state to excited state infrared absorption transitions of the shallow donor phosphorous and acceptor boron. This was surprising since it was thought that the observed linewidths of shallow impurities in silicon are at their fundamental lifetime limit. We report improved high-resolution infrared absorption studies of these impurities in isotopically enriched 28Si, 29Si and 30Si. The new data improves on the linewidths of earlier spectra due to reduced concentration broadening. Some of the transitions in 28Si show the narrowest FWHM ever reported for shallow donor and acceptor absorption transitions.