Surface Passivation by Adsorbates and Surfactants

Abstract

Saturation of all dangling bonds on semiconductor surfaces strongly reduces their free energy. This results in a passivation against chemisorption of adsorbates. Hydrogen-coverage, for example, increases the initial sticking coefficient of oxygen, on silicon surfaces by a factor of approximately 10¹³ with respect to what is found on clean silicon surfaces. This behavior is explained by the larger Si-H bond energies in comparison with the Si-Si bond strength. A reduction of the surface free energy may also be used to alter the growth mode of overlayers from island formation to layer-by-layer growth. At the deposition temperature, the solubility of the passivating adatoms has to be small in the bulk of the growing film so that they will segregate on the surface of the growing film. The passivating adatoms then behave as a surface-active species or a surfactant.