Interacting donor atoms in silicon: Valley-orbit coupling

In the framework of the Burt-Foreman envelope function theory and effective-mass approximation, we develop a theoretical model for an arbitrary number of interacting donor atoms embedded in silicon. The model takes into account the effective mass anisotropy and the valley-orbit coupling. Taking as an example diatomic phosphorus molecular ion, we investigate the impact of the orientation and internuclear distance on the electronic spectrum and envelope functions. This approach allows to analyze the valley composition of the wave functions and its dependence on the internuclear distance.