Vibrational lifetimes of light impurities in semiconductors


when experimental data cannot be explained without the help of theory



Dr. Stefan K. Estreicher

Paul Whitfield Horn Professor

Physics Department, Texas Tech University



Light impurities such as hydrogen or oxygen in Si have characteristic local vibrational modes with frequencies far above the highest allowed crystal mode, the optical or Γ phonon, around 530 cm-1. The decay of any Si-H stretch mode above 2000 cm-1 should require at least four crystal phonons. In other words, once excited, any Si-H stretch mode in Si should have a very long lifetime. Yet, recent experiments have shown that these lifetimes vary from 4 to 295 picoseconds. Even worse, fits of the temperature-dependence of these lifetimes to standard theory implies a six phonon process for the mode with a 4ps lifetime and a five phonon process for the one with a 295ps lifetime. This makes no sense at all. In the case of the asymmetric stretch of oxygen in Si, changes in the O or Si isotope affect the frequency by less than 1% but the vibrational lifetime changes by almost an order of magnitude. In this talk I will discuss the calculation of vibrational lifetimes and their temperature dependence from first principles, and show that this is a situation where the experimental data cannot be explained without the help of theory.



Short Bio


Stefan K. Estreicher received a Ph.D. in theoretical physics in 1982 from the University of Zürich, Switzerland. After a few years as a postdoctoral fellow at Rice University in Houston, he joined the Physics Department at Texas Tech University. He is now Paul Whitfield Horn Professor of Physics. He became a Fellow of the American Physical Society in 1997 and won an Alexander von Humboldt Research Award in 2000. He authored or co-authored some 150 papers (two of which in the Annals of Improbable Research). He recently edited a book on the Theory of Defects in Semiconductors (Springer, Heidelberg, Fall 2006) and wrote a book on the History of Wine (Algora, New York, Fall 2006).