The vacancy-donor pair in unstrained silicon, germanium and SiGe alloys

The thermal stability and electronic properties of the vacancy-donor complexes, often referred to as the E centres, have been studied in silicon, unstrained silicon-germanium and pure germanium. The E centres have been introduced by electron irradiation or gamma rays. In silicon, Laplace deep level transient spectroscopy has been used to separate the E centre emission from the di-vacancy, thus enabling very reliable data to be obtained for the vacancy complexes with P, As and Sb. In pure Ge only the E centres associated with P and Sb are reported and in Ge rich SiGe only V-P. In all the samples measured the thermal stability of V-Sb has been found to be significantly higher than V-P. With regard to the energy levels, the activation energy of electron emission from the single-acceptor level of the E centre in silicon are for V-Sb 0.40 eV and for V-P 0.46 eV. For the pure Ge case, the single acceptor is a hole trap with emission to the valence band having energies for V-P of 0. 35 eV and V-Sb of 0.31 eV. Similar values are found for Ge rich SiGe. The double-acceptor state is not seen in silicon but in germanium produces a state with an activation energy for electron emission of 0.30 eV for V-P and 0.38 eV for V-Sb. This is also reflected in the Ge rich alloys of SiGe:P that have been measured in this work.