Can Highly Enriched Si-28 Reveal New Things About Old Defects?

Recent studies have demonstrated remarkable improvements in the spectroscopy of shallow impurities by using highly enriched Si-28 to eliminate the inhomogeneous isotope broadening inherent in natural Si. Here, we show that similar dramatic improvements in the linewidths of electronic transitions of two well-known deep levels can be achieved in highly enriched 28 Si. New fine structure is revealed in the absorption spectrum of the Se double donor, and one of the transitions of Se+ becomes so sharp that a splitting due to a hyperfine coupling with the I = 1/2 nuclear spin is revealed for 77 Se+. Under an applied magnetic field, the electronic and nuclear spins can be individually determined leading to the possibility of applications in quantum computing. The photoluminescence transitions of the well-known 1014meV Cu-related luminescence center also sharpen dramatically in 28Si, allowing fine structure due to Cu isotope shifts to be resolved. Current models disagree as to whether this center contains one or two Cu atoms, but our results clearly demonstrate the involvement of four Cu atoms. (c) 2007 Elsevier B.V. All rights reserved.