First-principles dissociation pathways of BCl$_3$ on the Si(100)-2$\times$1 surface

TL;DR

This study uses density functional theory and kinetic modeling to elucidate the dissociation pathways of BCl3 on Si(100), revealing temperature-dependent reaction mechanisms crucial for atomic-precision doping in silicon quantum technologies.

Contribution

It expands the understanding of BCl3 dissociation on silicon by including multi-row reactions, simulating STM images, and integrating pathways into a kinetic model for realistic environmental conditions.

Findings

BCl2 dominates at low temperatures.

High temperatures favor B substitutions and bridging B fragments.

Distinct STM features enable experimental identification.

Abstract

One of the most promising acceptor precursors for atomic-precision $\delta$-doping of silicon is BCl$_3$. The chemical pathway, and the resulting kinetics, through which BCl$_3$ adsorbs and dissociates on silicon, however, has only been partially explained. In this work, we use density functional theory to expand the dissociation reactions of BCl$_3$ to include reactions that take place across multiple silicon dimer rows, and reactions which end in a bare B atom either at the surface, substituted for a surface silicon, or in a subsurface position. We further simulate resulting scanning tunneling microscopy images for each of these BCl$_x$ dissociation fragments, demonstrating that they often display distinct features that may allow for relatively confident experimental identification. Finally, we input the full dissociation pathway for BCl$_3$ into a kinetic Monte Carlo model, which simulates realistic reaction pathways as a function of environmental conditions such as pressure and temperature of dosing. We find that BCl$_2$ is broadly dominant at low temperatures, while high temperatures and ample space on the silicon surface for dissociation encourage the formation of bridging BCl fragments and B substitutions on the surface. This work provides the chemical mechanisms for understanding atomic-precision doping of Si with B, enabling a number of relevant quantum applications such as bipolar nanoelectronics, acceptor-based qubits, and superconducting Si.