# Optimizing surface defects for atomic-scale electronics: Si dangling bonds

## TL;DR

This paper demonstrates how to engineer silicon surface dangling bonds using first-principles calculations, showing how sample thickness and strain can tune their electronic properties for atomic-scale electronic and quantum devices.

## Contribution

It introduces a method to control dangling bond defect states on silicon surfaces through thickness and strain, unifying various experimental and theoretical findings.

## Key findings

- Ultrathin silicon samples create isolated impurity states in the band gap.
- Strain enhances the isolation of dangling bond states from bulk bands.
- The study provides a unified interpretation of existing literature on silicon dangling bonds.

## Abstract

Surface defects created and probed with scanning tunneling microscopes are a promising platform for atomic-scale electronics and quantum information technology applications. Using first-principles calculations we demonstrate how to engineer dangling bond (DB) defects on hydrogenated Si(100) surfaces, which give rise to isolated impurity states that can be used in atomic-scale devices. In particular we show that sample thickness and biaxial strain can serve as control parameters to design the electronic properties of DB defects. While in thick Si samples the neutral DB state is resonant with bulk valence bands, ultrathin samples (1-2 nm) lead to an isolated impurity state in the gap; similar behavior is seen for DB pairs and DB wires. Strain further isolates the DB from the valence band, with the response to strain heavily dependent on sample thickness. These findings suggest new methods for tuning the properties of defects on surfaces for electronic and quantum information applications. Finally, we present a consistent and unifying interpretation of many results presented in the literature for DB defects on hydrogenated silicon surfaces, rationalizing apparent discrepancies between different experiments and simulations.