High-resolution deep-level transient spectroscopy studies of gold and platinum acceptor states in diluted SiGe alloys

High-resolution Laplace deep-level transient spectroscopy spectra for gold- or platinum-diffused SiGe samples show an alloy splitting that is associated with the alloy fluctuations in the proximity of the defect. For the case of the platinum acceptor state, the effect of the level splitting caused by alloying in the first and also in the second shell of surrounding atoms can be distinguished. For the case of the gold acceptor, only the effect from the first shell of atoms is observable but the manifestation of alloying in the second-nearest shell can be seen as line broadening. We have found that the electronic energy level is affected by alloying in the first-nearest neighborhood by a factor of 2--3 more than by alloying in the second-nearest shell. The absolute values of the energy differences obtained from the Arrhenius plots for different defect configurations agree with those inferred from the peak separations observed in the spectra. A clear preference for gold and platinum to enter substitutional Si sites adjacent to Ge has been revealed. This may be interpreted in terms of an enthalpy lowering as a result of the fact that both metals are able to replace the host silicon atom more easily than the germanium atom in the substitutional position.