Morphology and electric conductance of ultra-thin Cr contacts on 6H-SiC(0001): AFM and current-sensing AFM study

Abstract

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 ultrahigh 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-adlayer thickness and annealing temperature. The growth of Cr follows the Stranski–Krastanov growth mode. The layers of 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.