Bonding of cysteamine on InAs surfaces

Passivation of InAs surfaces in InAs/GaSb type-II strained layer superlattices is important in many applications, and cysteamine has been effectively used for this purpose. However, there is a lack of fundamental understanding of the bonding between cysteamine and InAs. Here, first principles modeling, X-ray photoelectron spectroscopy (XPS), and high temperature XPS were used to characterize the adsorption of cysteamine on InAs surfaces. Our surface modeling results on InAs(1 0 0) showed that the computed adsorption energies were highest for InS and AsS bonds (both approaching 43 kcal/mol), and these values were influenced by the local reconstruction of the InAs(1 0 0) surface and, in some cases, the presence of neighboring cysteamine molecules. XPS results of as-received, control and cysteamine treated InAs(1 0 0) surfaces were consistent with InS and AsS bonding of cysteamine and indicated an indium-rich surface. High temperature XPS results up to 250 °C showed that sulfur persisted at the interface at higher temperatures while carbon and nitrogen were removed, suggesting that the InS and AsS bonds are more stable than the CS bond. Finally, near edge X-ray absorption fine structure (NEXAFS) measurements confirmed that the primary amine group of cysteamine was available for covalent bonding with potential potting materials.