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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.