Interplay between quantum confinement and dielectric mismatch for ultra-shallow dopants

TL;DR

This study investigates how dielectric mismatch and quantum confinement influence the ionization energy of acceptors near a silicon surface, revealing a delicate balance that affects electronic properties crucial for nano-scale device performance.

Contribution

It provides the first direct measurement of the competing effects of dielectric mismatch and quantum confinement on acceptor ionization energy near a silicon interface.

Findings

Dielectric mismatch increases acceptor binding energy.

Quantum confinement decreases acceptor binding energy.

Ionization energy remains within 5 meV of bulk value for acceptors close to the interface.

Abstract

Understanding the electronic properties of dopants near an interface is a critical challenge for nano-scale devices. We have determined the effect of dielectric mismatch and quantum confinement on the ionization energy of individual acceptors beneath a hydrogen passivated silicon (100) surface. Whilst dielectric mismatch between the vacuum and the silicon at the interface results in an image charge which enhances the binding energy of sub-surface acceptors, quantum confinement is shown to reduce the binding energy. Using scanning tunneling spectroscopy we measure resonant transport through the localized states of individual acceptors. Thermal broadening of the conductance peaks provides a direct measure for the absolute energy scale. Our data unambiguously demonstrates that these two independent effects compete with the result that the ionization energy is less than 5 meV lower than the bulk value for acceptors less than a Bohr radius from the interface.