  Gate-induced wave function manipulation of a single dopant atom is a possible
basis of atomic scale electronics. From this perspective, we analyzed the
effect of a small nearby gate on a single dopant atom in a semiconductor up to
field ionization. The dopant is modelled as a hydrogen-like impurity and the
Schrodinger equation is solved by a variational method. We find that--depending
on the separation of the dopant and the gate--the electron transfer is either
gradual or abrupt, defining two distinctive regimes for the gate-induced
ionization process.
