Reaction and Interdiffusion at III-V Compound Semiconductor-Metal Interfaces
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AND INTERDIFFUSION AT III-V SEMICONDUCTOR-METAL INTERFACES
COMPOUND
L.J. Brillson, Xerox Webster Research Center, 800 Phillips Road 114-41D, Webster, N.Y. 14580. ABSTRACT
The characterization of Il-V compound semiconductor-metal interfaces by surface science techniques has led to new relationships between interfacial chemistry and Schottky barrier formation. These and recent results on ternary alloy Ill-V compounds suggest a greater control of Schottky barrier heights by atomic scale techniques and advanced III-V materials than previously believed. INTRODUCTION
Studies of metal-semiconductor interfaces over the past decade using surface science techniques have revealed that reaction and interdiffusion play a major role in the formation of electrical barriers [1-5]. While such chemical interactions were widely recognized by the materials science community since the early 1970's [6-81, it is only with the advent of surface science techniques that such interface chemistry could be observed near room temperature and with sub-monolayer sensitivity. Moreover, such techniques have proven useful in characterizing the earliest stages of Schottky barrier formation. Among the interfaces receiving the most attention have been metals on the Ill-V compound semiconductors, due in part to their application in high-speed electronic devices. However contacts to III-V compounds have electrical barriers which are generally insensitive to different metals due to a high density of interface charge which "pins" the Fermi level in a relatively narrow energy range [9].
While a number of models involving defects [10-12], interface
dipoles and reacted layers [1-13], effective work functions [14,15] and metal-induced surface states [16-19] have been advanced, the detailed evolution of interface structure is far from understood. Here, I review several aspects of the interface chemistry between metals and Ill-V compound semiconductors as obtained with soft X-ray photoemission spectroscopy (SXPS) and Auger electron spectrocsopy (AES) depth profiling. This includes a brief discussion of the extended metal semiconductor interface as modified by chemical interactions, evidence for such interactions, the systematics of semiconductor outdiffusion and the role of chemical bonding in controlling this process, the observed relation between outdiffusion stoichometry and measured Schottky barrier height, as well as recent measurements on ternary IIl-V compounds which suggest a greater degree of barrier control than hitherto believed. THE EXTENDED METAL-SEMICONDUCTOR INTERFACE Considerable evidence for reaction and interdiffusion at compound semiconductor
interface on a micron scale stems from AES, ion backscattering, and electron microscopy work in the mid 1970's [6-81. For compound semiconductors, the correlation of Schottky barrier heights with the strength of metal-semiconductor bonding was indicative of the influence of chemical interactions on interface electronic structure [13]. In Figure 1, barrier heights measured by internal photoemission
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