Physics Division Seminars bring us speakers on a variety of physics related subjects. Usually these are held in the Building 6008 large Conference Room, at 3:00 pm on the chosen day, but times and locations may vary. For more information, contact our seminar chairman,
Tel (Office): (865) 574-6124 (FAX): (865) 574-1268
Silicon is not only the most technologically important semiconductor, it is also the material in which much of semiconductor physics, and semiconductor spectroscopy, has been learned and perfected. 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, mixed isotopic composition. The common assumption that many 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. I will report on progress in determining the actual linewidths of the bound exciton transitions in high quality 28Si, which have E/DE (FWHM) > 4 x 106! The elimination of this inhomogeneous isotopic 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.