Half-filled orbital and unconventional geometry of a common dopant in Si(001)

TL;DR

This study reveals that heavy dopants like Bi in Si(001) form pairs with vacancies, retain electrons, and exhibit localized, half-filled orbitals, contrasting with lighter dopants and challenging assumptions based solely on periodic table columns.

Contribution

It demonstrates that heavy dopants exhibit unique electronic structures and bonding behaviors at surfaces, differing from lighter dopants and bulk properties.

Findings

Bi forms pairs with Si vacancies on Si(001)

Bi retains its electrons and has localized, half-filled orbitals

Heavy dopants behave differently from lighter ones at surfaces

Abstract

The determining factor of the bulk properties of doped Si is the column rather than the row in the periodic table from which the dopants are drawn. It is unknown whether the basic properties of dopants at surfaces and interfaces, steadily growing in importance as microelectronic devices shrink, are also solely governed by their column of origin. The common light impurity P replaces individual Si atoms and maintains the integrity of the dimer superstructure of the Si(001) surface, but loses its valence electrons to surface states. Here we report that isolated heavy dopants are entirely different: Bi atoms form pairs with Si vacancies, retain their electrons and have highly localized, half-filled orbitals.