The effect of titanium on Al-Ti contacts to p-type 4H-SiC

The influence of composition on the electrical characteristics of Al-Ti ohmic contacts to p-type 4H-SiC was investigated. On SiC with N-A = 4.8 x 10(18) cm(-3), the lowest specific contact resistance obtained was 2.5 x 10(-4) Omega cm(2). It was found, however, that the titanium concentration had little effect on the electrical properties of the contacts, with specific contact resistance varying by only a factor of four over a range of concentrations from 0 to 50 wt.%,. Additional analytical data were obtained by scanning electron microscope and atomic force microscope observations. It was found that Al-Ti contacts with 31 wt.% Ti resulted in a pit density of approximately 20 pits/100 mum(2) with an average depth of 283 Angstrom and a maximum depth of 477 Angstrom. Pure Al contacts had a lower pit density of approximately 8-10 pits/100 mum(2), but the pits were larger and deeper, with an average depth of 358 A and a maximum depth of 510 Angstrom. Raised areas of unknown composition and origin were also observed. It is likely that both of these types of features contribute to the ohmic behavior of the contact after annealing, but an exact mechanistic description remains to be identified. (C) 2003 Elsevier Science Ltd. All rights reserved.