Due to its high free carrier mobility and low dopant activation temperature, germanium is considered as an important future material to replace Si in semiconducting applications. The functional properties of doped germanium are highly influenced by the occupied lattice sites of the dopants in the single-crystalline Ge lattice. Despite its fundamental and technological importance, it is very challenging to obtain detailed and direct experimental information on the lattice location of dopants. One of the very few suitable techniques to perform such experiments, is electron emission channeling (EC).

We present a lattice location study of several impurities in Ge from EC experiments, complemented with ab initio calculations. More specifically, we determined the occupied lattice sites of transition metals (Fe, Cu and Ag), electrical (In), magnetic (Mn) and isovalent (Sn) dopants in germanium. As expected, a fraction of these impurities was found to substitute Ge host atoms, but in contrast to common expectation, a significant fraction was observed on the bond-centered (BC) site as well, i.e. in the center of two nearest neighbor substitutional sites. From ab initio calculations, we have assigned the BC impurities to impurity-vacancy complexes in the so-called split-vacancy configuration. Moreover, the calculations indicate that vacancies - which are abundantly available during ion implantation - are trapped by the substitutional dopants, resulting in an unstable complex, which spontaneously relaxes towards the split-vacancy configuration. These results indicate that the introduction of vacancies might induce lattice site changes of the substitutional impurities towards the BC site, hence opening up a possible way to externally manipulate the lattice location of dopants.    

 

Stefan Decoster*, Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
Stefaan Cottenier, Center for Molecular Modeling, Ghent University, Technologiepark 903, 9052 Zwijnaarde, Belgium
Ulrich Wahl, Instituto Tecnológico e Nuclear, Unidade de Física e Aceleradores, Estrada Nacional 10, Apt. 21, 2686-953 Sacavém, Portugal
Joao Guilherme Correia, Instituto Tecnológico e Nuclear, Unidade de Física e Aceleradores, Estrada Nacional 10, Apt. 21, 2686-953 Sacavém, Portugal
André Vantomme, Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium

*presenting author