Interaction of Al overlayers with the InP(110) surface

Abstract

The room-temperature interaction of Al overlayers with the cleaved InP(110) surface has been studied with valence-band and core-level soft-x-ray photoemission spectroscopies. It is shown that for submonolayer coverages, Al interacts weakly with the substrate. In particular, deposition of Al leaves the valence-band spectra devoid of structure other than that characteristic of clean InP(110). The growth mode of the Al overlayer upon sequential deposition of the metal is monitored by changes in the core-level spectra. In particular, Al $2p$ shows peaks with three different binding energies corresponding to three stages of the overlayer growth and reaction with the substrate. These observations are correlated with changes in the In $4d$ spectra, indicating segregation of the metallic In, and behavior of the P $2p$ core line. It is shown that for very low coverages (0.5 \AA{}), the growth of small Al clusters weakly bonded to the substrate atoms dominates the behavior of the interface. The intermediate stage, 0.5 to 2 \AA{}, marks the onset of an Al-In exchange reaction with the segregation of metallic In. For still higher coverages (above \ensuremath{\sim}2 \AA{}), the growth of large Al clusters takes place. These experimental results give strong support to the theoretical model developed recently for the prototype Al/GaAs(110) by Zunger. The Schottky-barrier heights suggested by the core-level shifts are \ensuremath{\sim}0.30 and \ensuremath{\sim}1.10 eV for $n$- and $p$-type InP(110), respectively.