Electric Field Reduced Charging Energies and Two-Electron Bound Excited States of Single Donors in Silicon

We present atomistic simulations of the D0 to D? charging energies of a gated donor in silicon as a function of applied fields and donor depths and find good agreement with experimental measurements. A self-consistent field large-scale tight-binding method is used to compute the D? binding energies with a domain of over 1.4 million atoms, taking into account the full band structure of the host, applied fields, and interfaces. An applied field pulls the loosely bound D? electron toward the interface and reduces the charging energy significantly below the bulk values. This enables formation of bound excited D? states in these gated donors, in contrast to bulk donors. A detailed quantitative comparison of the charging energies with transport spectroscopy measurements with multiple samples of arsenic donors in ultrascaled metal-oxide-semiconductor transistors validates the model results and provides physical insights. We also report measured D? data showing the presence of bound D? excited states under applied fields.