The Ag-InP(110) interface: Photoemission studies of interfacial reactions and Schottky-barrier formation

The effects of interfacial reaction at Ag-InP(110) interfaces have been studied with soft-x-ray photoemission spectroscopy of the core levels and valence band. By systematically increasing the Ag coverages, we have been able to identify two coverage ranges with different stages of physical interactions and interface developments from a detailed study of the In $4d$, P $2p$ and Ag $3d$ core levels as well as valence-band structures. At lower Ag coverages [$0<\mathrm{}\Theta <1\mathrm{}$ monolayer (ML)], identified as the "band-bending region," both the In $4d$ and P $2p$ levels shift by the same amount with no measurable changes in the core-level shapes for both $n$ and $p$ type, and a continuous and monotonic shift of the Ag $3d$ core levels toward their metallic positions is observed with increased Ag coverages. At high coverages ($1\le \Theta <72\mathrm{}$ ML), identified as the "intermixed region," the presence of P atoms at the topmost layer and evidence of dissociated In were observed from the core-level variations and relative intensity studies at the interface. In both regions, island growth of the overlayer is observed. The surface-Fermi-level ($E_{\mathrm{Fs}}$) pinning position, determined from core-level movements in this region, can be affected by the intermixing of Ag with dissolved InP constituents. Ag interacts with InP in a way that is essentially different in details as compared with other metals, to the extent that the model identifying Ag as a nonreactive metal on InP may need to be modified.