Infrared dielectric function of p-type Ge0.98Sn0.02 alloys

The dielectric function of heavily doped p-type Ge0.98Sn0.02 alloys was determined using infrared spectroscopic ellipsometry. The free holes contribute a Drude-like term to the dielectric response, from which the resistivity and carrier relaxation time can be determined. The transport parameters extracted from such optical experiments are similar to those found for pure Ge with comparable doping levels. Optical transitions between the split-off, light-hole, and heavy-hole bands contribute a second term to the dielectric function. The overall line shape of the dielectric function corresponding to these transitions shows differences between Ge0.98Sn0.02 and pure Ge. These differences may provide important clues to the valence-band electronic structure of Ge1-ySny alloys.