Abrupt interfaces with novel structural and electronic properties: Metal-cluster deposition and metal-semiconductor junctions

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Abstract
Abrupt interfaces with no observed substrate disruption are produced by a novel method of metal-semiconductor junction formation. This method involves the condensation of a thin Xe buffer layer on cleaved surfaces to isolate the semiconductor from impinging metal atoms. This Xe buffer layer provides a surface upon which the metal atoms diffuse, nucleate, and grow into metallic clusters. These clusters are then brought into contact with the substrate when the Xe is thermally desorbed. The result is an abrupt, nondisrupted, nearly ideal interface. Photoemission studies of Al, Ag, Au, Ga, Ti, and Co clusters grown on n- and p-type GaAs(110) show unique Fermi-level positions ∼0.3 and 1.0 eV below the conduction-band minimum, respectively, that are nearly metal and coverage independent. We find no evidence that metal-induced gap states or conventional defect levels are important in determining the Fermi-level position in the gap, but photoemission results indicate surface unrelaxation around the clusters. This unrelaxation results in the reappearance of states in the gap. High-resolution electron-microscopy results for Au(clusters)/GaAs(110) show intimate contact with no intermixing at the interface, with sintering of Au clusters to form an interconnected network of metal islands at high coverages. Comparisons of these results with those for interfaces formed by atom deposition at 60 and 300 K emphasize the novel properties of the cluster interface.