Two-electron states bound to donors in silicon are important for both two qubit gates and spin readout. We present a full configuration interaction technique in the atomistic tight-binding basis to capture multi-electron exchange and correlation effects taking into account the full bandstructure of silicon and the atomic scale granularity of a nanoscale device. Excited s-like states of A1-symmetry are found to strongly influence the charging energy of a negative donor centre. We apply the technique on sub-surface dopants subjected to gate electric fields, and show that bound triplet states appear in the spectrum as a result of decreased charging energy. The exchange energy, obtained for the two-electron states in various confinement regimes, may enable engineering electrical control of spins in donor-dot hybrid qubits.
@article{arxiv.1703.04175,
title = {Two-electron states of a group V donor in silicon from atomistic full configuration interaction},
author = {Archana Tankasala and Joseph Salfi and Juanita Bocquel and Benoit Voisin and Muhammad Usman and Gerhard Klimeck and Michelle Y. Simmons and Lloyd C. L. Hollenberg and Sven Rogge and Rajib Rahman},
journal= {arXiv preprint arXiv:1703.04175},
year = {2018}
}