Optical investigation of residual doping species in 6H and 4H-SIC layers grown by chemical vapor deposition

We report the results of a series of optical investigations performed on bo th 6H and 4H epitaxial layers grown at low rate (approximate to 1 mu m h(-1 )) in a home-made cold-wall chemical vapor deposition (CVD) reactor. To kee p the level of contamination as low as possible, attempts have been made to investigate the origin of residual dopants. In this way, we have found tha t aluminum comes only from the use of uncoated graphite susceptors. When us ing a SIC coated susceptor, we have found that the protection is only effec tive for about ten runs. (C) 1999 Elsevier Science S.A. All rights reserved .