The different behaviour of CiOi and CiCs defects in SiGe

The behaviour of CiOi and CiCs defects in SixGe1−x with the change of alloy composition were investigated. In photoluminescence (PL) spectra, the photon energy for CiOi is very sensitive to Ge content, shifting to higher energy with the increase of Ge content. In contrast, the CiCs is almost not affected with the Ge content in the studied composition range. The broadening of the zero-phonon lines for these carbon-related defects in dilute SixGe1−x is induced primarily by the atomic mismatch of Ge atoms in Si environment. By comparing the numerically calculated results with the measured data, it is shown that the CiOi have site preference for Ge atoms, but CiCs do not display such a trend. With the effective-mass model for the defects in excited states, and reference to the deep-level transient spectroscopy (DLTS) data, the different PL characteristics between CiOi and CiCs can be explained.