Pinning behavior of gold-related levels in Si usingSi1−xGexalloy layers

The question as to whether the gold-donor and acceptor levels are pinned either to the conduction band, the valence band, or to neither of them is addressed in the present investigation. The donor and acceptor levels in gold-doped $n^{+}p$ and $p^{+}n$ diodes of relaxed, epitaxial ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ of $0<~x<~0.25$ are characterized with deep-level transient spectroscopy (DLTS) and minority-carrier transient spectroscopy (MCTS) and the results are discussed within a thermodynamical model which considers the point defect as a thermodynamic subsystem immersed in the surrounding semiconductor thermostat. It is unambiguously concluded that both levels are pinned to the conduction band. A new effect related to the impact of the statistical distribution of Ge atoms into the lattice on the full width at half maximum of the DLTS or MCTS peaks is clearly observed. Based on these results the so-called entropy-related paradox, i.e., the observation that the entropy change involved in the creation of an electron-hole pair via the gold-acceptor level is significantly larger than that via a direct band-to-band transition, is critically reexamined. It is concluded, however, that the entropy paradox is still unsolved.