The problem of whether Au donor and acceptor levels were pinned to the conduction band, the valence band, or to neither, was considered. The donor and acceptor levels, in Au-doped n+p and p+n diodes, of relaxed epitaxial Si1-xGex, where x ranged from 0 to 0.25, were characterized by means of deep-level transient spectroscopy and minority-carrier transient spectroscopy. The results were explained in terms of a thermodynamic model which considered the point defect to be a thermodynamic sub-system that was embedded in a surrounding semiconductor thermostat. It was unambiguously concluded that both levels were pinned to the conduction band. A new effect was clearly observed, which was related to the influence of a statistical lattice distribution of Ge atoms upon the full-width at half-maximum of the deep-level transient spectroscopic or minority-carrier transient spectroscopic peaks. On the basis of these results, the so-called entropy-related paradox (that the entropy change involved in the creation of an electron-hole pair via the Au acceptor level was significantly larger than that via a direct transition) could be critically re-examined. However, the entropy paradox remained unsolved.

A.Mesli, P.Kringhøj, A.N.Larsen: Physical Review B, 1997, 56[20], 13202-17