M. Grioni

Metal–anion bond strength and room temperature diffusion at metal/GaAs interfaces: Transition versus rare‐earth versus Au metal overlayers

We discuss synchrotron radiation photoemission results for several room temperature transition metal and rare–earth metal GaAs(110) interfaces (Ce, Sm, V, Cr) and Au. Analysis of normalized core intensity attenuation curves shows anion trapping that varies with, but is not entirely controlled by, the ionicity of interface bonds. In particular, very narrow reacted regions were observed for Ce and Sm [3–5 monolayers (ML)]. The reacted region is much wider for the transition metals (9 ML for V, 19 ML for Cr), reflecting a less effective barrier for intermixing. For Au, the amount of As and Ga in the near surface region greatly exceeds that for the transition metals.

Systematics of electronic structure and local bonding for metal/GaAs(110) interfaces

We present high‐resolution synchrotron radiation core level photoemission results which reveal the evolving electronic structures and morphologies of metal/GaAs interfaces for the metals Ce, Sm, Ti, V, Cr, Fe, Co, Cu, and Au. By studying a wide range of overlayer metals we sought to identify common interface characteristics and discriminate between chemical and morphological effects. Quantitative fitting of the Ga and As 3d core level emission provided insight into the stages of interface development. Our results indicate that Ga is found in solution at these interfaces with chemical shifts from −0.40 eV for Au to −1.78 eV for Ce (relative to Ga in GaAs). In contrast, the results for As indicate well‐defined local chemical environments and, in some cases, the possibility of surface segregation. A direct correlation between overlayer electronegativity and core level shifts is observed.

Modeling of interface reaction products with high‐resolution core‐level photoemission

High‐resolution photoemission studies make it possible to distinguish different atomic configurations at evolving interfaces by monitoring chemical shifts. Hence, it is possible to determine the coverage at which reactions are triggered and are effectively completed, the species that outdiffuses into the metal overlayer, and the bonding of surface‐segregated species. Core‐level deconvolutions and plots of the concentration of substrate, reacted, and segregated species as a function of coverage are discussed for Ce/Si(111), Ce/GaAs(110), and Cr/GaAs(110). Our results show that distinct Ce/As and Ce/Si species form but that no distinct Cr/Ga bonding configuration is established at the interface.

Reaction at a refractory metal/semiconductor interface: V/GaAs(110)

Synchrotron radiation photoemission spectroscopy has been used to study the formation of the reactive V/GaAs(110) interface. Valence‐band and core‐level results indicate that metal deposition produces an extended intermixed phase involving the formation of both V–Ga and V–As bonds. In this reacted region the Ga 3d core line exhibits a continuous shift to lower binding energy (total shift 1.55 eV over band bending) indicative of a variable chemical environment, while analysis of the As 3d line shape suggests that As is present in two well‐defined chemical states. Core‐level intensity profiles show preferential outdiffusion of arsenic, with As present at ∼6% of the original level with coverages of 110 A. Comparison to previous results for Cr/GaAs(110) shows similar Ga and As attenuation profiles.