Investigation of the structure and stability of the Pt/SiC(001) interface
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I. INTRODUCTION
Silicon carbide is presently considered a potentially useful semiconductor for high-temperature device applications, but development of this technology requires metal contacts having thermally stable electronic characteristics. Recently1 Pt has been shown to form rectifying contacts on n-type cubic j6-SiC which are stable at temperatures as high as 800 °C. Solid state reaction at 900 °C between macroscopic pieces of Pt and /3-SiC has been shown2 to produce periodic structures consisting of alternating layers of Pt3Si and C in the interdiffusion zone. The bonding of Pt (and other metals) to the Si- and C-terminated basal planes of hexagonal aSiC has been studied theoretically.3 Pt is found to bond strongly to both surfaces (although more so to the former) as a result of charge transfer from occupied metal orbitals into unfilled orbitals on surface Si and C atoms. The goal of the present work is an understanding of the microstructure of the Pt/SiC(001) interface and of the source of its unusually high thermal stability. Although we are aware of no previous work (other than Refs. 1-3) on the Pt/SiC interface, the Pt/Si(001) and Pt/Si(lll) systems have been studied in some detail (Refs. 4-11 and work cited) using low energy electron diffraction (LEED), transmission electron microscopy and Raman, Rutherford backscattering (RBS), Auger electron (AES), ultraviolet photoemission (UPS), and x-ray photoemission (XPS) spectroscopies. This work has been extensively reviewed by Rossi.12 In all these studies Pt films were formed by in situ vapor deposition on atomically clean Si substrates prepared and character2882
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ized in ultrahigh vacuum (UHV), i.e., under conditions similar to those of the present work. To the extent that spectroscopic data for the two crystal faces have been compared (Hel valence band UPS and Si LVV AES line shape), no difference has been observed8 with regard to Pt interface formation. Also, no difference was found4 between ordered and Ar+-ion bombarded Si(lll) surfaces with regard to the dependence of the Auger spectrum on Pt coverage. For submonolayer coverages at room temperature on Si(lll), Pt is believed5 to occupy sixfold interstitial sites, leading to long-range effects on the Si surface structure.5'9 The Pt layer is reported to grow uniformly up to about one monolayer4'5 (© = 1) beyond which intermixing occurs, leading to a structurally and chemically inhomogeneous layer the exact nature of which is uncertain.4'10 Most of the Pt appears to remain unreacted,4'8 although evidence for Si-Pt bonding is observed in the Si LVV line shape8 and the Si 2p, Pt 4/ and valence band photoemission,9 and features characteristic of PtSi appear in the Raman spectrum.7 Clustering of the Pt into three-dimensional islands8 may also influence the structure of the interface for coverages of a few monolayers. With increasing Pt coverage beyond © ~ 10 at room temperature, the reaction becomes more extensive, and all the various spectroscopies detect clear evidence of Si-Pt b
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