Energy levels of Zn in Si1-xGex alloys: The change-over from highly localized deep states to shallow-level centers

Deep level transient spectroscopy measurements were performed on Zn-doped S i1-xGex with x between 0 and 0.48. Our investigations reveal two deep hole traps which are attributed to the acceptor states Zn0/- and Zn-/2- of subst itutional Zn. Taking into account band-offset data for Si1-xGex, we have fo und that the energy level related to Zn0/- is horizontally aligned across t he composition-dependent bandgap for x up to approximate to 30 at% Ge which gives evidence for a localized defect state in this composition range. For higher Ge concentrations the data suggest a continuous change-over to a sh allow level center. The defect level related to the second hole trap decrea ses with increasing Ge content.