Comparative study of the formation of Cr/Ge and Ge/Cr thin-film interfaces

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Abstract
The interface morphologies of Cr/Ge and Ge/Cr thin film junctions have been studied using synchrotron radiation photoemission. Ge 3d and Cr 3p core level results for Ge deposition onto Cr indicate that Ge chemisorbs without disrupting the substrate. With increasing coverage, an amorphous Ge film forms (a-Ge) and buries the abrupt Ge/Cr interface. Examination of the reverse Cr/Ge thin-film interface prepared under identical conditions shows extensive substrate disruption, metal-semiconductor interdiffusion, and a reacted interfacial region. Comparison of this Cr/Ge thin-film interface to Cr/Ge(111) shows analogous Ge outdiffusion and compound formation, demonstrating that disorder in the a-Ge substrate is not the only cause of the enhanced interdiffusion observed for Cr/Ge compared to Ge/Cr. The dissimilar reactivity of Ge/Cr and Cr/Ge is attributed to differing substrate disruption energetics and clustering at the earliest stages of interface formation.