Barrier height inhomogeneities of epitaxial CoSi2 Schottky contacts on n-Si (100) and (111)

The forward current-voltage characteristics of epitaxial CoSi2 contacts grown by Ti-interlayer mediated epitaxy (TIME) scheme on n-type Si substrates of both (100) and (111) orientations are studied in the temperature range from 80 to 300 K. At high temperatures (>220 K), the I-V characteristics obey the ideal thermionic emission model. The Schottky barrier heights stay similar to 0.61 eV and the ideality factors are close to unity. At low temperatures, a change in the characteristics is observed around 10(-4) A/cm(2), which is more significant for the contacts on Si (111) than for those on Si (100). Above this current, the I-V curves can also be fitted by the equation based on the thermionic emission theory, but the apparent barrier heights decrease and the ideality factors increase with decreasing temperature. This abnormal behavior, as well as the curved Richardson plots, are interpreted by the assumption of a Gaussian distribution of barrier heights, which is in agreement with the statistical distribution obtained directly from ballistic electron emission microscopy (BEEM) measurements. The excess current at small bias region is explained by coexistence of some small patches of reduced barrier height with the pinch-off model. The CoSi2 contacts on Si (111) contain more patches with larger parameter values than those on Si (100), which causes a significant difference in the I-V characteristics at low temperature. (C) 2000 Elsevier Science Ltd. All rights reserved.