We investigate theoretically donor-based charge qubit operation driven by
external electric fields. The basic physics of the problem is presented by
considering a single electron bound to a shallow-donor pair in GaAs: This
system is closely related to the homopolar molecular ion H_2^+. In the case of
Si, heteropolar configurations such as PSb^+ pairs are also considered. For
both homopolar and heteropolar pairs, the multivalley conduction band structure
of Si leads to short-period oscillations of the tunnel-coupling strength as a
function of the inter-donor relative position. However, for any fixed donor
configuration, the response of the bound electron to a uniform electric field
in Si is qualitatively very similar to the GaAs case, with no valley quantum
interference-related effects, leading to the conclusion that electric field
driven coherent manipulation of donor-based charge qubits is feasible in
semiconductors