Charge transport in strained Si1−yCy and Si1−x−yGexCy alloys on Si(001)

We have investigated the temperature dependencies of charge carrier densities and Hall mobilities in tensile strained Si1−yCy and in compressively strained Si1−x−yGexCy layers. In both cases, the measured charge carrier densities at room temperature are not affected substantially by the addition of a small concentration of carbon (<1%) under identical growth conditions and dopant fluxes. The measured Hall mobilities monotonically decrease with increasing carbon content for electrons in Si1−yCy, and for holes in Si1−x−yGexCy, respectively. Our results indicate that electrically active defects are formed with the addition of carbon. These defects are presumably connected with carbon/Si interstitials or other C-related complexes. It seems to be difficult to attribute the formation of those electrically active defects solely to contaminations originating from the used carbon evaporation source. We observed that donor- and acceptor-like defects are formed in Si1−yCy as well as in Si1−x−yGexCy layers with roughly a constant ratio, independent of source temperature.