Stark tuning of the charge states of a two-donor molecule in silicon

TL;DR

This paper investigates gate control of phosphorus donor charge qubits in silicon using a tight-binding model, analyzing molecular states, gate effects, and practical control issues for donor molecules.

Contribution

It provides a detailed analysis of gate control mechanisms and limitations for phosphorus donor molecules in silicon, considering various device configurations and orientations.

Findings

Excited molecular states limit donor separation and gate voltages.

Surface and barrier gates have different roles depending on voltage regimes.

Realistic gate control remains smooth across donor separations, with some orientation-dependent effects.

Abstract

Gate control of phosphorus donor based charge qubits in Si is investigated using a tight-binding approach. Excited molecular states of P2+ are found to impose limits on the allowed donor separations and operating gate voltages. The effects of surface (S) and barrier (B) gates are analyzed in various voltage regimes with respect to the quantum confined states of the whole device. Effects such as interface ionization, saturation of the tunnel coupling, sensitivity to donor and gate placement are also studied. It is found that realistic gate control is smooth for any donor separation, although at certain donor orientations the S and B gates may get switched in functionality. This paper outlines and analyzes the various issues that are of importance in practical control of such donor molecular systems.