Shallow donors in Ge-rich GeSi bulk crystals

Abstract

We report on the change of shallow donor energy levels with alloy composition in Ge-rich Ge1−xSix bulk crystals. For phosphorus, we find a strong, linear increase of the ionization energy with increasing Si content for 0<x<0.1, whereas, for antimony the ionization energy shifts only slightly to higher energies with increasing Si content up to x=0.11. We observe a rapid increase of the antimony ionization energy in the composition range 0.11<x<0.16, where the change in the conduction band minimum from Ge- to Si-like occurs. The different behavior of phosphorus and antimony in Ge-rich GeSi reflects the different short range impurity potentials of these donors and, thus, different mixing of bands.