STM characterization of the Si-P heterodimer

We use scanning tunneling microscopy (STM) and Auger electron spectroscopy to study the behavior of adsorbed phosphine (PH₃) 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 ∼0.002 langmuirs of PH₃ results in the adsorption of PH_x (x=2,3) onto the surface and etching of Si to form individual Si ad-dimers. Annealing to 350 °C results in the incorporation of P into the surface layer to form Si-P heterodimers and the formation of short one-dimensional Si dimer chains and monohydrides. In filled state STM images, isolated Si-P heterodimers appear as zigzag 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.