Thermal donors in silicon-rich SiGe

We have investigated thermal donor formation at 450 °C in oxygen-rich SiGe with more than 1% Ge content by Hall measurements and infrared spectroscopy. These measurements prove the presence of double donors in annealed Si-rich SiGe samples. The ionization energies of the donors correspond to those of the thermal double donors in Si, only the formation rate is reduced. Due to alloy effects, we observe only broadbands in the low-temperature infrared absorption spectra in SiGe instead of individual lines of neutral and singly ionized thermal donors in Si. The shift of these absorption bands to lower energies with longer heat treatment and a corresponding decrease of the ionization energy found from Hall measurements indicates the formation of shallower donor species.