STM characterization of the Si-P heterodimer

TL;DR

This study uses STM and Auger spectroscopy to analyze the formation and imaging of Si-P heterodimers on Si(001) surfaces after phosphine exposure and annealing, revealing imaging conditions for atomic-scale doping.

Contribution

It demonstrates the conditions for forming and imaging Si-P heterodimers on Si(001), advancing atomic-scale doping techniques for nanoscale electronics.

Findings

Si-P heterodimers form after annealing at 350°C.

Heterodimers appear as zig-zag features in filled state STM images.

Empty state imaging reliably detects P atoms regardless of H coverage.

Abstract

We use scanning tunneling microscopy (STM) and Auger electron spectroscopy to study the behavior of adsorbed phosphine (PH$_{3}$) on Si(001), as a function of annealing temperature, paying particular attention to the formation of the Si-P heterodimer. Dosing the Si(001) surface with ${\sim}$0.002 Langmuirs of PH$_{3}$ results in the adsorption of PH$_{x}$ (x=2,3) onto the surface and some etching of Si to form individual Si ad-dimers. Annealing to 350$^{\circ}$C results in the incorporation of P into the surface layer to form Si-P heterodimers and the formation of short 1-dimensional Si dimer chains and monohydrides. In filled state STM images, isolated Si-P heterodimers appear as zig-zag features on the surface due to the static dimer buckling induced by the heterodimer. In the presence of a moderate coverage of monohydrides this static buckling is lifted, rending the Si-P heterodimers invisible in filled state images. However, we find that we can image the heterodimer at all H coverages using empty state imaging. The ability to identify single P atoms incorporated into Si(001) will be invaluable in the development of nanoscale electronic devices based on controlled atomic-scale doping of Si.