M. W. Ruckman

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.

High‐resolution electron energy loss spectroscopy as a probe of surface morphology and electronic states at metal/semiconductor interfaces

The covering and consumption of sp3 hybridized Si atoms in reactions between a metal and Si(111) are monitored by the use of a chemical probe—atomic hydrogen. The surface vibrational spectrum of H on Cu/Si(111) has been measured at various stages of interface growth. The presence of Si atoms with dangling bonds results in covalent bonding with free H atoms, as seen in the Si–H stretching and bending modes in the HREELS spectrum. As Cu is deposited, the morphology of the surface layer can be deduced by observing the disappearance of Si–H vibrational excitations and correlating with Si 2p photoelectron line shape and attenuation behavior. The picture which emerges from this analysis is that Cu atoms form clusters from 0 to 3 A and that at 3 A the clusters disrupt the surface and trigger outdiffusion of Si. Atomic hydrogen also constitutes a powerful probe of surface electronic states. Previous Auger electron diffraction measurements on the annealed 1 ML Cu/Si(111) interface showed that the surface reconstru...

V/Ge(111): Temperature dependent intermixing studied with high resolution photoemission and quantitative modeling

High resolution, temperature dependent core level photoemission results for the V/Ge(111) interface show the interplay between atomic diffusion and trapping in the boundary layer. Room temperature results show strong intermixing, and core level analysis allows us to identify well‐defined chemical environments for Ge atoms (chemical shifts of −0.5 and −0.95 eV). Through modeling of the interface, we have determined the composition and extent of each reacted species. Studies at higher temperature showed that the extent and composition of the reacted overlayer could be varied. Indeed, by increasing the substrate temperature, we could produce an overlayer which became chemically homogeneous by 475 K. In this range, we find a diffusion activation energy of 5 kcal/mol which controls the width of the reacted layer.

High-Resolution Core Level Study of the Co/Si(111) Interface

There has recently been considerable interest in the reaction between Co and a clean Si surface. This interest stems from the epitaxy of CoSi 2 and NiSi 2 on Si and its potential for the construction of reliable and stable metal-semiconductor structures. In fact, the fabrication of a Si/CoSi 2 /Si transistor has been recently reported.[l] On a more fundamental side, it has been possible to address the problem of the relation between Schottky barrier height and structure at the NiSi 2 /Ni interface, which exhibits both a rotated (B-type) and unrotated (A-type) geometry.[2] For CoSi 2 /Si only the 180° rotated, B-type disilicide is formed. By studying the room temperature interface, we have attempted to describe the nature and physical extent of reaction products; such knowledge is important to understand the formation of interface silicides which ultimately control the nature of the high temperature epitaxial interface.