Ab Initio Study of SiC/Metal Polar Interfaces: Relation Between Interface Structure and Schottky-Barrier Height
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Ab Initio Study of SiC/Metal Polar Interfaces: Relation Between Interface Structure and Schottky-Barrier Height Shingo Tanaka (SWING) and Masanori Kohyama Department of Materials Physicis, Osaka National Research Institute, Agency of Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan ABSTRACT Ab initio calculations of the polar interfaces between thin films of titanium and cubic silicon-carbide (SiC) have been performed by using the first-principles molecular dynamics method. Stable configurations, adhesive energies and Schottky-barrier height (SBH) for the Si-terminated and the C-terminated interfaces are obtained. The C-terminated interface has covalent C-Ti bonds, while the Si-terminated interface has shown metallic nature. Adhesive energy/SBH of the C-terminated interface is larger/smaller than that of the Si-terminated one, respectively. In order to examine a conventional SBH model, work functions of SiC slab with Si and with C surface and Ti slab have been calculated and SBHs have been estimated from the difference of work functions. In estimated SBHs between the interfaces, the relationship depend on the crystal orientation as (111) and (001). INTRODUCTION SiC/metal interfaces are very important for the electronic and optoelectronic SiC devices as the structural ceramics. Among them, SiC/Ti interfaces have interested features as strong reactivity and electric properties. Many experiments have been performed using a technique of epitaxial growth developed in the last two decades. Transmission electron microscopy (TEM) observation and an estimation of the Schottky barrier height (SBH) have been done for thin films of Ti deposited on n-type 6H-SiC(0001) [1]. The interface shows very good epitaxy according to the TEM observation. The n-type SBHs estimated from XPS and I-V and C-V measurements are different between as-deposited and after annealed contacts. Under the condition that is careful treatment for SiC surface, a method to control SBH for interfaces between some metals and 6H-SiC(0001) has been proposed [2]. According to the interfaces, SBH is proportional to work functions of metal, which means the Schottky-Mott limit, or unpinning Fermi level, is achieved. TEM observations of Ti thin
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films deposited on the flat (0001) face of the 6H-SiC have been performed [3]. Snap shot of TEM observation indicates that most ideal interface without any defects are formed. It is interesting that the structure of the deposited Ti is face-centered cubic, although no fcc-Ti has been reported in the bulk SiC. On the theoretical point of view, ab initio pseudopotential calculations of 3C-SiC(001)/Ti interface have been done by Kohyama and co-worker [4]. In this interface, the C-terminated interface has strong covalent Ti-C bonds while the Si-terminated interface has shown metallic feature and p-type SBH of the C-terminated interface is smaller than that of the Si-terminated one, similar to 3C-SiC(001)/Al interface [5]. They proposed that it is necessary to take into account the inter
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