Quantum electronic devices at the single impurity level demand an
understanding of the physical attributes of dopants at an unprecedented
accuracy. Germanium-based technologies have been developed recently, creating a
necessity to adapt the latest theoretical tools to the unique electronic
structure of this material. We investigate basic properties of donors in Ge
which are not known experimentally, but are indispensable for qubit
implementations. Our approach provides a description of the wavefunction at
multiscale, associating microscopic information from Density Functional Theory
and envelope functions from state of the art multivalley effective mass
calculations, including a central cell correction designed to reproduce the
energetics of all group V donor species (P, As, Sb and Bi). With this
formalism, we predict the binding energies of negatively ionized donors (D-
state). Furthermore, we investigate the signatures of buried donors to be
expected from Scanning Tunneling Microscopy (STM). The naive assumption that
attributes of donor electrons in other semiconductors may be extrapolated to Ge
is shown to fail, similar to earlier attempts to recreate in Si qubits designed
for GaAs. Our results suggest that the mature techniques available for qubit
realizations may be adapted to germanium to some extent, but the peculiarities
of the Ge band structure will demand new ideas for fabrication and control
