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

K Iwaya,A M Stoneham,W Wu,V Brázdová,A Ferreira Da Silva,D R Bowler,G Aeppli,Ch Renner,A J Fisher

doi:10.1103/physrevb.88.035440

K Iwaya, A M Stoneham + Show 7 more

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https://doi.org/10.1103/physrevb.88.035440

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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.

Highlights

Semiconductors such as silicon (Si) derive remarkable utility from the ease with which they are converted from insulating to conducting behavior via substitution of dopants from neighboring columns in the periodic table
The bismuth-vacancy feature we describe in this work, referred to as Bi-vacancy pair (Bi-V), is located at the surface; we have found other features which are clearly subsurface features and will be discussed in a future publication; these subsurface donors are considerably less common than the surface Bi-V pairs
The apparent flatness of the surface surrounding the Bi-V feature indicates that the Bi is not charged—strong brightening is seen around charged dopants in Si(001),16 due to band bending

Summary

Introduction

Semiconductors such as silicon (Si) derive remarkable utility from the ease with which they are converted from insulating to conducting behavior via substitution of dopants from neighboring columns in the periodic table. There is growing interest in heavier dopants of conventional semiconductors because of their more tightly bound outer electrons, which increases operating temperatures for applications ranging from THz impurity lasers to quantum computers exploiting their spin.. We report that isolated heavy dopants in the Si(001) surface are entirely different to light dopants: Bi atoms form pairs with Si vacancies, retain their electrons and have highly localized, half-filled orbitals. We have a dopant of silicon with a half-filled orbital at the surface, enabling both new applications in spintronics, as well as Si surface-based quantum many-body physics, hitherto confined to the more complex Si(111) surface

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