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" Ohmic Contacts for High Power and High Temperature Microelectronics. "
Lilyana Kolaklieva
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BL
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| Record Number
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790735
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b610768
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| Main Entry
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Lilyana Kolaklieva
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| Title & Author
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Ohmic Contacts for High Power and High Temperature Microelectronics.\ Lilyana Kolaklieva
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| Publication Statement
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INTECH Open Access Publisher, 2009
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| ISBN
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9533070277
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: 9789533070278
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| Abstract
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The study of ohmic contacts to wide band-gap semiconductors proves that when metal/semiconductor contacts are deposited, they commonly result in rectifying Schottky contacts which barrier height inhibits current flow across the metal/semiconductor interface. There are four primary variables which control the Schottky barrier height at metal/semiconductor interfaces: the work function Ñ"m of the metal; the crystalline or amorphous structure at the metal-semiconductor interface; the diffusion of metal atoms across the interface into the semiconductor; and, the outermost electronic configuration of the metal atoms. Otherwise, there are several constants and properties characterising the wide band-gap semiconductors which postulate the specific approach used for formation of ohmic properties of the metal/semiconductor interface: the high electron affinity, the wide forbidden zone, and low diffusion coefficient of the most metals. Consequently, it is almost impossible to form ohmic properties, relying only to the choice of a metal with suitable work function and metal diffusion into the semiconductor during annealing. Therefore in the case of ohmic contacts to wide band-gap semiconductors metallization schemes have been chosen so as to form intermediate layer at the interface, which could decrease the barrier height and/or narrow the depletion layer at the semiconductor interface. In these cases, heat treatment results interfacial compounds, such as metal/compound/ semiconductor contacts. In these contacts, the metal/semiconductor interface is eliminated and replaced by new interfaces, Đ° metal/compound and Đ° compound/semiconductor interface. The resulting barrier height Ñ"B is not longer dependent on the surface properties of the semiconductor or metal work function. Instead, it depends upon the difference in electron affinity and work function between the metal/compound and compound/ semiconductor. As Đ° result, contacts can be reproducibly formed with Đ° predictable Ñ"B. In the case of Ni-based and Pd-based contacts to SiC such compound is nickel silicide and palladium silicide, respectively. On the basis of XPS data the following mechanism of chemical reactions occurring during the formation of ohmic properties may be proposed. In the case of Ni/SiC the contact formation is initiated by the dissociation of SiC surface, due to the strong reactivity of Ni at 950 0C. The nickel atoms at the interface interact with a part of dissociated Si atoms and Ni2Si is formed. Simultaneously, at the interface nickel atoms diffuse through the mixed Ni2Si+C layer towards the SiC. Thus, the supply of Ni atoms at the SiC interface continues and the above reactions are repeated to the complete consumption of the deposited nickel layer. Carbon accumulates, both at the interface and in the contact layer. The presence of carbon in the contact layer and at the interface could become a potential source of contact.
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Open Access Collection.
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Lilyana Kolaklieva
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Roumen Kakanakov
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