We present a tight-binding study of donor impurities in Si, demonstrating the adequacy of this approach for this problem by comparison with Kohn-Luttinger effective mass theory and experimental results. We consider the response of the system to an applied electric field: donors near a barrier material and in the presence of a uniform electric field may undergo two different ionization regimes according to the distance of the impurity to the Si/barrier interface. We show that for impurities $\sim 5\mathrm{nm}$ below the barrier, adiabatic ionization is possible within switching times of the order of one picosecond, while for impurities $\sim 10\mathrm{nm}$ or more below the barrier, no adiabatic ionization may be carried out by an external uniform electric field. Our results are discussed in connection with proposed Si:P quantum computer architectures.

• Received 27 August 2003

DOI:https://doi.org/10.1103/PhysRevB.69.085320