Electric-field control and adiabatic evolution of shallow donor impurities in silicon

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 similar to5 nm below the barrier, adiabatic ionization is possible within switching times of the order of one picosecond, while for impurities similar to10 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.