Morphology and barrier-height development of Bi/InP(110) interfaces.

Abstract

The development of the interface between cleaved n- and p-type InP(110) substrates and overlayers of Bi has been studied in the coverage range of 0.01 to 10 monolayers with use of soft-x-ray photoemission spectroscopy. The attenuation and narrowing of the substrate In 4d and P 2p core-level spectra, as well as the line-shape development of the adatom Bi 5d signal, indicate that the morphology is of the Stranski-Krastanov type, as has been verified previously for Sb and Bi overlayers on GaAs(110). Specifically, the Bi grows in ordered two-dimensional patches that merge at 1 monolayer coverage, and beyond this coverage the deposited adatoms form three-dimensional clusters. The band bending as measured from energy shifts of the In 4d and P 2p spectra approaches midgap near 0.3 monolayer coverage, but between 0.3 and 1.0 monolayer the band bending for both doping types exhibits a reversal. The reduction in band bending in this deposition regime suggests that some of the submonolayer band bending is induced by states originating at the periphery of the two-dimensional Bi patches. The Bi 5d core-level position provides a local measurement of the surface-Fermi-level position directly beneath these Bi patches: specifically, the absence of Bi 5d shifts suggests that these patches are regions of strong local depletion at coverages as low as 0.01 monolayer. As the three-dimensional Bi clusters develop for depositions exceeding 1 monolayer, the n- and p-type-surface Fermi-level positions proceed toward 0.75 eV above the valence-band maximum, a position which has been reported for other unreacted metal-InP interfaces. However, the Sb/InP interface, which exhibits a morphology very similar to Bi/InP, gives a barrier height 0.4 eV higher in the gap. Thus it is observed that the interfacial states at these unreacted and ordered interfaces between such semimetals and InP are strongly dependent on the specific overlayer material.