Silicon carbide SiC is a semiconductor with a wide energy gap whose unique properties, such as the high melting point, high thermal conductivity or large critical breakdown electric field, offer a good basis for designing electronic components of important devices and make it be attractive for applications in opto-, high-frequency, high-power, high-voltage, high-temperature and radiation hard microelectronics. It is still difficult to prepare silicon carbide based components on an industrial scale and the related technology is developing slowly. An improvement needs, among others, to overcome the difficulties in fully mastering the processes of defect-free surface preparation as well as the formation of metal based contacts. Controlled formation of the metal/SiC contact with a desired Schottky barrier height is one of primary steps in designing and manufacturing the up-to-date microelectronic devices.
Early stages of Cr contact formation on 6H-SiC(0001) were investigated using the atomic force microscope (AFM) and current-sensing AFM with conducting tip. Cr layers were vapor deposited under ultra high vacuum onto samples cut out of a single crystal of n-type 6H/SiC(0001) that were ex situ hydrogen etched in a tubular flow reactor. Topography of the samples, their local conductance patterns and local current-voltage characteristics of the Cr-SiC contact were examined simultaneously as a function of Cr-layer thickness and annealing temperature.
The growth of Cr follows the Stranski-Krastanov growth mode. The layers of the mean thickness ~4.5 nm have a grainy structure. Differences in quality of the electric contact between the grains and the substrate as well as between the grains themselves enable to obtain a good contrast image of the local conductance of the layer. The contact of the as-deposited at room temperature Cr-layer of the thickness from 1.5 to 10 nm is typical of the rectifying junction. Annealing the Cr-SiC contact at temperatures up to 1800 K leads to coalescence of grains and dissolution of Cr in the substrate. The dissolution essentially disturbs the rectifying character of the electric contact Cr/SiC.
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