Electric field reduced charging energies and two-electron bound excited states of single donors in silicon

TL;DR

This study uses atomistic simulations to show how electric fields reduce charging energies and enable bound excited states of single donors in silicon, aligning well with experimental data.

Contribution

It introduces a large-scale tight-binding simulation approach that accurately models donor charging energies and excited states under applied electric fields in silicon.

Findings

Electric fields significantly lower donor charging energies.

Bound excited states of donors are observed under applied fields.

Simulation results agree with experimental measurements.

Abstract

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 measure- ments. 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 bandstructure of the host, applied fields, and interfaces. An applied field pulls the loosely bound D- electron towards 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 ultra-scaled FinFETs validates the model results and provides physical insights. We also report measured D-data showing for the first time the presence of bound D-excited states under applied fields.